CyCLOPS is the only Tier-1 permanent GNSS station network in Cyprus and it is currently comprised of GNSS CORS, co-located with precise weather stations, tilt meters and calibration-grade InSAR corner reflectors. The main objective of this strategic research infrastructure unit was to precisely monitor geohazards in Cyprus and the broader EMMENA region and to render Cyprus a dedicated SAR calibration and validation site. To date, CyCLOPS has successfully estimated very precise positions and velocities of national CORS stations, highlighted the geodynamic regime of the area, and monitored very dynamic landslides occurring throughout the island. CyCLOPS+ is the expansion phase, which will form the Cyprus Ground Motion Service (CyGMS), a continuously updated national velocity model, aiming to deliver precise and reliable ground displacement metrics, and densify the European Ground Motion System, thereby improving the country's resilience to seismic and geological threats.

The Cyprus Continuously Operating Natural Hazards Monitoring and Prevention System (CyCLOPS) is a national, strategic research infrastructure focusing on geohazard monitoring in Cyprus, and EMMENA region. CyCLOPS comprises six permanent sites, each equipped with a Tier-1 GNSS reference station and two calibration-grade corner reflectors (CRs), oriented to the ascending and descending tracks of ESA's Sentinel-1 satellite mission. As of June 2021, CyCLOPS has reached full operational capacity and plays a crucial role in monitoring the geodynamic regime and tracking landslides in Cyprus. Furthermore, it supports the radiometric calibration and geometric validation of C- and X- band SAR imagery. This paper presents initial validation results from analyzing Sentinel-1 products using CyCLOPS CRs, showing consistent performance with a high-quality CR network. Radiometric parameters remained constant, and geolocation measurements were precise in range and azimuth. These results, based on two years of operational data, enhance understanding of SAR product quality and CyCLOPS infrastructure's effectiveness.

This work introduces a dataset for automated earthquake-damaged building detection from post-event satellite imagery. Using very high-resolution Synthetic Aperture Radar (SAR) and optical data from the 2023 Turkey-Syria earthquakes, the dataset includes over four thousand co-registered building footprints and patches. The task is framed as a binary image classification problem, serving as a reference for researchers to expedite algorithm development for rapid damaged building detection in future events. The dataset and codes together with detailed explanations will be made publicly available at https://github.com/ya0-sun/PostEQ-SARopt-BuildingDamage.

Quick and automated earthquake-damaged building detection from post-event satellite imagery is crucial, yet it is challenging due to the scarcity of training data required for developing robust algorithms. This letter presents the first dataset dedicated to detecting earthquake-damaged buildings from post-event very high resolution (VHR) Synthetic Aperture Radar (SAR) and optical imagery. Utilizing open satellite imagery and annotations acquired after the 2023 Turkey–Syria earthquakes, we deliver a dataset of co-registered building footprints and satellite image patches of both SAR and optical data, encompassing more than four thousand buildings. The task of damaged building detection is formulated as a binary image classification problem, that can also be treated as an anomaly detection problem due to extreme class imbalance. We provide baseline methods and results to serve as references for comparison. Researchers can utilize this dataset to expedite algorithm development, facilitating the rapid detection of damaged buildings in response to future events. The dataset and codes together with detailed explanations and visualization will be made publicly available at https://github.com/ya0-sun/PostEQ-SARopt-BuildingDamage.

Satellite interferometric SAR (InSAR) has demonstrated to be a powerful technology to perform millimeter-scale precision measurements of ground motions typically caused by landslides, subsidence, earthquakes or volcanic activity, and to monitor the stability of slopes, mining areas, buildings, infrastructures, etc. This work presents the European Ground Motion Service (EGMS), funded by the European Commission as an essential element of the Copernicus Land Monitoring Service (CLMS). EGMS constitutes the first application of the interferometric SAR (InSAR) technology to high-resolution monitoring of ground deformations over an entire continent, based on full-resolution processing of all Sentinel-1 (S1) satellite images over most of Europe. EGMS employs advanced persistent scatterer (PS) and distributed scatterer (DS) InSAR processing techniques. Moreover, a global navigation satellite system (GNSS) model is realized to calibrate the InSAR ground motion products. To foster as wide usage as possible, EGMS also provide tools for visualization, exploration, analysis and download of the ground deformation products, as well as elements to promote best practice applications and user uptake.

We report on first results of the European Ground Motion Service from the perspective of GAF AG and DLR who are responsible for specific tasks and areas of the overall project. The EGMS products and processing chain are shortly described and first results on point density and data quality are presented.

This paper introduces the extended timing annotation dataset (ETAD) product for Sentinel-1 (S-1) which was developed in a joint effort of German Aerospace Center (DLR) and the European Space Agency (ESA). It allows to correct range and azimuth timing of S-1 images for geophysical effects as well as for inaccuracies in synthetic aperture radar (SAR) image focusing. In combination with the precise orbit solution, these effects determine the absolute geolocation accuracy of S-1 SAR images and the relative collocation accuracy of repeat pass image stacks. ETAD contains the gridded timing corrections for the tropospheric and ionospheric path delays, the tidal-based surface displacements, and the SAR processing effects, all of which are computed for each data take using standard models from geodesy and auxiliary atmospheric data. The ETAD product helps S-1 users to significantly improve the geolocation accuracy of the S-1 SAR products to better than 0.2 m and offers a potential solution for correcting large scale interferometric phase variations. The product layout and the product generation are described schematically. The paper also reports first results for different SAR techniques: first, the improvement in geolocation accuracy down to a few centimeters by verification of accurately surveyed corner reflector positions in the range-azimuth plane; second, the well-established offset-tracking technique, that is used for systematic ice velocity monitoring of ice sheets and glaciers, where ETAD can reduce velocity biases down to sub-centimetric values; and third, the correction of atmospheric phase contributions in wide-area interferograms used for national and European ground motion services. These early results proof the added value of the ETAD corrections and that the product design is well suited to be integrated into the processing flows of established SAR applications such as absolute ranging of targets, speckle/feature tracking and interferometry.

Interferometric processing of a time series of acquisitions from synthetic aperture radar (SAR) satellites makes it possible to detect and measure ground motion phenomena, typically caused by landslides, subsidence, earthquakes or volcanic activity, with millimeter-scale precision. This enables, for example, monitoring of the stability of slopes, mining areas, buildings and infrastructures. This work presents the European Ground Motion Service (EGMS), funded by the European Commission as an essential element of the Copernicus Land Monitoring Service (CLMS). The EGMS constitutes the first application of the interferometric SAR (InSAR) technology to high-resolution monitoring of ground deformations over an entire continent, based on full-resolution processing of all Sentinel-1 (S1) satellite acquisitions over most of Europe (Copernicus Participating States). Upscaling from existing national precursor services to pan-European scale is challenging. The EGMS will employ the most advanced persistent scatterer (PS) and distributed scatterer (DS) InSAR processing techniques in combination with a high-quality Global Navigation Satellite System (GNSS) model to calibrate the ground motion products. To foster as wide usage as possible, the EGMS will also provide tools for visualization, exploration, analysis and download of the ground deformation products, as well as elements to promote best practice applications and user uptake.

This article shows how the array of corner reflectors (CRs) in Queensland, Australia, together with highly accurate geodetic synthetic aperture radar (SAR) techniques-also called imaging geodesy-can be used to measure the absolute and relative geometric fidelity of SAR missions. We describe, in detail, the end-to-end methodology and apply it to TerraSAR-X Stripmap (SM) and ScanSAR (SC) data and to Sentinel-1 interferometric wide swath (IW) data. Geometric distortions within images that are caused by commonly used SAR processor approximations are explained, and we show how to correct them during postprocessing. Our results, supported by the analysis of 140 images across the different SAR modes and using the 40 reflectors of the array, confirm our methodology and achieve the limits predicted by theory for both Sentinel-1 and TerraSAR-X. After our corrections, the Sentinel-1 residual errors are 6 cm in range and 26 cm in azimuth, including all error sources. The findings are confirmed by the mutual independent processing carried out at University of Zurich (UZH) and German Aerospace Center (DLR). This represents an improvement of the geolocation accuracy by approximately a factor of four in range and a factor of two in azimuth compared with the standard Sentinel-1 products. The TerraSAR-X results are even better. The achieved geolocation accuracy now approaches that of the global navigation satellite system (GNSS)-based survey of the CRs positions, which highlights the potential of the end-to-end SAR methodology for imaging geodesy.

A recent publication claims that closure phases in SAR interferometry bear no relationship to physical changes of the scatterer, but only to the statistical properties of the averaged pixels. We disprove this claim with a simple counterexample and remind the reader of cases in which closure phases indicate a clear physical content, including the exploitation of closure phases in other fields.

We report our first results with Sentinel-1 Interferometric Wide Swath (IW) data using novel off-the-shelf electronic corner reflectors (ECRs) for geometric measurements with C-band Synthetic Aperture Radar (SAR). At the German Aerospace Center (DLR) campus in Oberpfaffenhofen, we set up an arrangement consisting of two trihedral corner reflector and two active ECRs. We describe the practical aspects of such ECRs as well as first radiometric characteristics. Moreover, we present geometric accuracy as derived from imaging geodesy, i.e. absolute radargrammetric positioning in 2D and 3D, as well as interferometric phase measurements.

We describe a new method for precise, geometrically high-resolution and large-scale measurement of plate tectonics with the aid of radar remote sensing and show first results. For the derivation of the 3D vectors of tectonic displacements two measurement intervals, separated by at least one year are necessary. At each interval several satellite images from different radar viewing angles are obtained, and the 3D-coordinates of ground control points (GCPs) are calculated. By correcting the influence of the ionosphere, atmosphere and earth tides, it is possible to measure the absolute coordinates of ground control points with high accuracy. By comparing the absolute positions of the GCPs of the two acquisition periods, the displacements that have occurred in the meantime can be determined in X, Y and Z. The applications are in the measurement of continental drift, of elevations and subsidence by the melting of very large glacier areas, as well as of tectonic shifts after earthquakes. Furthermore, the continuity of continental drift in earthquake-prone areas can be checked with the help of long-term recording series.

The capacity of SAR interferometry to measure surface deformation with accuracy of 1 mm/year or better are well known. However this is typically limited to relative motion at short distance. Thanks to several advances in SAR sensor quality, data availability, orbit determination, processing, and calibration of atmospheric delays it is now possible to achieve that accuracy even across large distances of hundreds of kilometers.In this paper we revise the main contributions to the large scale error, considering available mitigation techniques. We provide a first validation for a processing based on Sentinel-1 data, by comparing our results with GNSS stations.For future SAR's operating at lower frequencies, it is vital to consider ionospheric corrections and likely also the influence of moisture variations in natural scatterers. The choice of processing algorithms, though typically not discussed, can also have a significant effect on the quality of the result.

Synthetic Aperture Radar (SAR) satellites observe range and azimuth geometric accuracies at the low centimeter level. The accuracy of geolocation is driven by several aspects, e.g. orbit determination, SAR image processing, or atmospheric error correction. Our paper concentrates on the Sentinel-1 mission and the compensation of the platform motion effects in the geolocation, which were found to limit the best possible geolocation capabilities of Sentinel-1. The key to advance the geolocation results is the rigorous compensation of the bistatic effect in azimuth, and the correction of the Doppler-induced shifts in range. First results for Sentinel-1 at the Australian reflector array consisting of 40 Corner Reflector (CR) show consistent improvement in the geolocation$(1\sigma)$to 6 cm in range and 28 cm in azimuth for both spacecrafts when using the Interferometric Wide swath (IW) product.

Geodetic stereo synthetic aperture radar (SAR) is capable of absolute 3-D localization of natural persistent scatterers, which allows for ground control point (GCP) generation using only SAR data. The prerequisite for the method to achieve high-precision results is the correct detection of common scatterers in SAR images acquired from different viewing geometries. In this contribution, we describe three strategies for automatic detection of identical targets in SAR images of urban areas taken from different orbit tracks. Moreover, a complete workflow for automatic generation of large number of GCPs using SAR data is presented and its applicability is shown by exploiting TerraSAR-X high-resolution spotlight images over the city of Oulu, Finland, and a test site in Berlin, Germany.

Geodetic stereo SAR is capable of absolute 3-D localization of natural persistent scatterers (PS)s which allows for Ground Control Point (GCP) generation using only SAR data. The prerequisite for the method to achieve high precision results is the correct detection of common scatterers in SAR images acquired from different viewing geometries. In this contribution, we describe three strategies for automatic detection of identical point targets in SAR images of urban areas taken from different orbit tracks. Moreover, a complete work-flow for automatic generation of large number of GCPs using SAR data is presented and its applicability is shown by exploiting TerraSAR-X high resolution spotlight images over the city of Oulu, Finland and a test site in Berlin, Germany.

Range accuracy of synthetic aperture radar using modern satellites has been proven in centimeter-range after consideration of geodynamic, atmospheric effects and systematic errors; it is so-called Imaging Geodesy technique. Based on this technique, we have proposed the next-generation of Synthetic Aperture Radar (SAR) products and developed operational software SAR Geodesy Processor in the previous paper. In this paper, we are concentrated on validation of processor and accuracy analysis on a global-scale. Two datasets with different spatial resolutions generated from European Centre for Medium-Range Weather Forecast are used to compensate atmospheric refraction effect in range. At the end, we apply corrections on a Sentinel interferogram by using both datasets.

This paper presents a novel approach to determine 3D absolute geolocation of point targets using just two long-aperture SAR acquisitions. Moreover, the Zenith Path Delay of both acquisitions is obtained. First results presented here show that the absolute positioning accuracy reaches the sub-meter level.

Determining the frontal position of a calving glacier at different moments of time is a prerequisite for the estimation of the calving rate and flux. Therefore, we developed an automatic detection algorithm of glacier fronts which should be applied to large time series of SAR data and replace the manually mapping. The methodology is based on the analysis of the SAR backscattering amplitude value distribution along defined longitudinal profiles which cover the glacier terminus and traverse the transition zone between the glacier ice and the water at its front. The technique reduces the 2D amplitude image to 1D amplitude profiles and is therefore called profile method.

Tandem-L is a highly innovative SAR satellite mission for the global observation of dynamic processes on the Earth's surface with hitherto unknown quality and resolution. Thanks to its novel imaging techniques and its unprecedented acquisition capacity, Tandem-L will deliver urgently needed information for the solution of pressing scientific questions in the areas of the biosphere, geosphere, cryosphere and hydrosphere. The feasibility of Tandem-L has been analyzed and confirmed in the scope of a phase A study, which has been conducted in close cooperation between the German Aerospace Center (DLR) and the German space industry. This paper provides an overview of the Tandem-L mission concept and summarizes the actual development status.

Only until recently, it has been demonstrated that absolute localization with centimeter accuracy can be achieved for manually matched Persistent Scatterer (PS)s from TerraSAR-X images acquired from cross-heading geometries [1]. This paper describes an automatic algorithm for absolute localization of natural PSs in SAR images, where the detection of potential PSs is aided by high resolution optical data. As the focus of the study is on urban area, the target detection part relies on identification of lamp posts using template matching. These targets are, most probably, the only ones visible in SAR images acquired from both ascending and descending orbits. Thus, the methodology includes identification of lamp posts from high resolution optical data and retrieves the precise absolute three-dimensional coordinates of the points from corrected TerraSAR-X timing measurements using the stereo SAR method [1]. Preliminary results for a test site in the city of Berlin acquired from TerraSAR-X high resolution spotlight mode are shown.

This paper evaluates the applicability and achievable SAR accuracy for octahedrons - a combination of eight corner reflectors with a common phase centre. In an experiment at the observatory in Wettzell from July to November 2015 these cost-efficient and mobile radar targets were measured with TerraSAR-X Staring Spotlight and High-Resolution Spotlight. Applying the geodetic stereo SAR concept, octahedrons are very robust for absolute 3D positioning through their backscattering in multiple directions. Using octahedrons with as size of 47 cm, we achieve 3σ standard deviations of about 3 cm for east, north and height components. For individual measurements in Staring Spotlight the standard deviation shows 1.4 cm in range and 3.2 cm in azimuth.

A conventional interferometric synthetic aperture radar (SAR) system provides 1-D line-of-sight motion measurements from repeat-pass observations. Two-dimensional motions may be measured by combining two observations from ascending and descending geometries. The third motion component may be retrieved by adding a third geometry and/or by integrating along-track measurements although with much reduced precision compared to the other two components. Several options exist to improve the accuracy of retrieving the third motion component, such as combining left- and right-looking observations or exploiting recently proposed innovative SAR acquisition modes (BiDiSAR and SuperSAR). These options are, however, challenging for future SAR systems based on large reflector antennae, due to lack of capability to electronic beam steering or frequent toggle between left- and right-looking modes. Therefore, in this letter, we assess and compare the realistic acquisition scenarios for a reflector-based SAR in an attempt to optimize the achievable 3-D precision. Investigating the squinted SAR geometry as one of the feasible scenarios, we show that a squint of 13.5° will yield comparable performance to the left-looking acquisition, while further squinting outperforms this or other feasible configurations. As an optimum configuration for 3-D retrieval, the squinted acquisition is further elaborated: the different acquisition plans considering a constellation of two satellites as well as the challenges for data processing are addressed.

The differential ionospheric path delay is a major error source in L-band interferograms. It is superimposed to topography and ground deformation signals, hindering the measurement of geophysical processes. In this paper, we proceed toward the realization of an operational processor to compensate the ionospheric effects in interferograms. The processor should be robust and accurate to meet the scientific requirements for the measurement of geophysical processes, and it should be applicable on a global scale. An implementation of the split-spectrum method, which will be one element of the processor, is presented in detail, and its performance is analyzed. The method is based on the dispersive nature of the ionosphere and separates the ionospheric component of the interferometric phase from the nondispersive component related to topography, ground motion, and tropospheric path delay. We tested the method using various Advanced Land Observing Satellite Phased-Array type L-band synthetic aperture radar interferometric pairs with different characteristics: high to low coherence, moving and nonmoving terrains, with and without topography, and different ionosphere states. Ionospheric errors of almost 1 m have been corrected to a centimeter or a millimeter level. The results show how the method is able to systematically compensate the ionospheric phase in interferograms, with the expected accuracy, and can therefore be a valid element of the operational processor.

Differential synthetic aperture radar tomography (D-TomoSAR), similar to its conventional counterparts such as differential interferometric SAR and persistent scatterer interferometry, is only capable of capturing 1-D deformation along the satellite's line of sight. In this paper, we propose a method based on L1-norm minimization within local spatial cubes to reconstruct 3-D displacement vectors from TomoSAR point clouds available from at least three different viewing geometries. The methodology is applied on two pairs of cross-heading-combination of ascending and descending-TerraSAR-X (TS-X) spotlight image stacks over the city of Berlin. The linear deformation rate and the amplitude of seasonal deformation are decomposed, and the results from two test sites with remarkable deformation pattern are discussed in detail. The results, to our knowledge, demonstrate the first attempt for motion decomposition using TomoSAR data from multiple viewing geometries.

Sentinel-1 (S-1) has an unparalleled mapping capacity. In interferometric wide swath (IW) mode, three subswaths imaged in the novel Terrain Observation by Progressive Scans (TOPS) SAR mode result in a total swath width of 250 km. S-1 has become the European workhorse for large area mapping and interferometric monitoring at medium resolution. The interferometric processing of TOPS data however requires special consideration of the signal properties, resulting from the ScanSAR-type burst imaging and the antenna beam steering in azimuth. The high Doppler rate in azimuth sets very stringent coregistration requirements, making the use of enhanced spectral diversity (ESD) necessary to obtain the required fine azimuth coregistration accuracy. Other unique aspects of processing IW data, such as azimuth spectral filtering, image resampling, and data deramping and reramping, are reviewed, giving a recipe-like description that enables the user community to use S-1 IW mode repeat-pass SAR data. Interferometric results from S-1A are provided, demonstrating the mapping capacity of the S-1 system and its interferometric suitability for geophysical applications. An interferometric evaluation of a coherent interferometric pair over Salar de Uyuni, Bolivia, is provided, where several aspects related to coregistration, deramping, and synchronization are analyzed. Additionally, a spatiotemporal evaluation of the along-track shifts, which are directly related to the orbital/instrument timing error, measured from the SAR data is shown, which justifies the necessity to refine the azimuth shifts with ESD. The spatial evaluation indicates high stability of the azimuth shifts for several slices of a datatake.

Interferometric synthetic aperture radar (InSAR) measurements are merely sensitive to the deformation along the Line of Sight (LOS) direction of the sensor. To improve the geometrical sensitivity and retrieve the three-dimensional deformation, the integration of InSAR from non-coplanar acquisitions as well as fusion with resolution-scale SAR image shift measurements has become a standard approach. Using different statistical measures, we assess and compare the influence of different image acquisition strategies as well as data fusion on the performance of InSAR in 3D deformation retrieval. Integrating nominal InSAR acquisitions, i.e. a set of measurements from ascending and descending tracks acquired from right-looking geometry, a strong correlation between the retrieved 3D parameters in the local vertical-north plane is observable. This correlation is sought to be decreased by non-nominal acquisitions; i.e. left-looking or squinted observations. These acquisition strategies are discussed for consideration in the future L-band mission Tandem-L.

In this paper we propose a new SAR data product that shall allow for geometric corrections down to millimeter level. We propose methods to generate and architecture to represent a new type of geodetic SAR product. The product concept can easily be applied to different type of sensors as a kind geometric correction layer.

The TanDEM-X satellite mission through its bistatic formation provides high horizontal and vertical resolution topographic data. Multi temporal TanDEM-X acquisitions allow short term analysis of variations of the earth surface elevation which in turn can be converted to volume changes. We are investigating the capabilities of the TanDEM-X data to detect and map short term changes at glacier surfaces in two different situations. One study case is Jorge Montt outlet glacier of the South Patagonia Icefield known for its accelerated mass depletion and front retreat. The second example is located on the Vatnajökull Ice Cap in Iceland and is related to the activity of the Bárǒarbunga volcanic system in summer 2014 as a consequence of climate driven depletion as well as due to volcanic activities below the ice surface.

The paper describes the direct retrieval of global coordinates of persistent scatterers (PS) including their secular displacement by plate tectonics from Synthetic Aperture Radar (SAR). For this purpose we combine stereo SAR methods, least squares parameter estimation, and geodetic observation corrections. The procedure is based on our previous research with TerraSAR-X and now applied for PS situated on the facade of a building of Technische Universität München (TUM). In order to verify the PS-based solution, we have created an accurate building model with global coordinates suitable for SAR simulations, and we use the results of permanent Global Navigation Satellite Systems (GNSS) to validate the displacement rates. Our preliminary results for the simulated phase centers and stereo SAR already indicate similar phase centers on the building facade, and the displacement rates could be retrieved with mm/year accuracy.

The differential atmospheric path delay is a major error source in L-band interferograms. Refractivity index variations with respect to the nominal value, in the troposphere and in the ionosphere, delay the propagation of radio waves changing the slant range distance. This additional delay is superimposed to topography and ground deformation signals, hindering the measure of geophysical processes. Therefore, it needs to be corrected. In this work we present the correction results for two test cases. We mitigate the impact of height-dependent tropospheric effects (stratified delay) with a method based on the direct integration using numerical weather prediction data. We compensate the ionospheric delay using the split-spectrum method, which is based on the dispersive nature of the ionosphere and estimates the delay from the SAR data itself. Errors are reduced from almost one meter to a centimeter level.

ALOS-Next/Tandem-L is a proposal for a highly innovative L-band SAR satellite mission for the global observation of dynamic processes on the Earth's surface with hitherto unparalleled quality and resolution. It is based on a collaboration between DLR and JAXA which started with a pre-phase A study in 2013 and is currently undergoing a phase A study. Thanks to the novel imaging techniques and the vast recording capacity with up to 8 Tbytes/day, it will provide vital information for solving pressing scientific questions in the biosphere, geosphere, cryosphere, and hydrosphere. By this, the new L-band SAR mission will make an essential contribution for a better understanding of the Earth system and its dynamics. ALOS-Next/Tandem-L will, moreover, open new opportunities for risk analysis, disaster management and environmental monitoring by employing especially designed acquisition modes and techniques in combination with a reconfigurable tandem satellite configuration and an L-band SAR instrument with advanced digital beamforming techniques.

SAR interferometry is a well-known technique to produce digital surface models (DSM). In the global scale, the quality of these models significantly increased with the use of bistatic systems as for the TanDEM-X mission. DSM uncertainty can be measured in two scales: a global and a local one. A global scale analysis involves measures for the complete take, characterizing the whole correctness with a single parameter. A local scale analysis enters instead in the single elevation model cell, evaluating the quality obtained by different terrains and media present in the take. A coherence analysis is a typical measure for InSAR models. Globally, a simple average gives an overall quality measure hint. Locally, it provides a measure of the DSM pixel height error. Unfortunately, this measure lacks in several aspects as not considering unwrapping errors and not being valid for certain types of scattering. In this paper, various strategies for assessing elevation accuracy methods and demonstrate the different capabilities of the bistatic TanDEM-X system are proposed for variegated terrain types.

This paper reports on the absolute 3-D localization of radar corner reflectors and persistent scatterers (PSs) by stereo synthetic aperture radar (SAR) carried out with TerraSAR-X and TanDEM-X. The novel combination of rigorously linearized range-Doppler equations with thorough sensor modeling, consideration of atmospheric delays, geodynamic signals, satellite dynamics, and geometrical calibration allows a direct target localization at the centimeter level. Therefore, there is no need for the application of geocoding since our approach delivers 3-D positions directly in the International Terrestrial Reference Frame (ITRF) 2008. Four radar corner reflectors located at the Wettzell Geodetic Observatory, Metsähovi Geodetic Observatory, and German Antarctic Receiving Station O'Higgins were localized in 3-D with a precision better than 4 cm. By introducing an updated geometrical calibration of TerraSAR-X and TanDEM-X, the absolute accuracy of the same level becomes possible, which was demonstrated by externally validating the reflector positions at Metsähovi and Wettzell against results of terrestrial geodetic surveying. Furthermore, PSs located in Berlin were retrieved with a precision of 10 cm, making the method a suitable tool for radar “positioning” in urban environments. Potential fields of application for our approach are the joint analysis with phase-based methods, geometrical calibration of radar satellites, and direct integration of SAR observations into Global Navigation Satellite System networks.

Layover affects the quality of urban interferometric synthetic aperture radar (InSAR) digital elevation models. Moreover, it is generally difficult to interpret because of the superposition of several contributions in a single SAR pixel. In this paper, a novel technique for the extraction of building layovers is first presented. It makes use of the geocoding stage embedded in the InSAR processor. It is shown that building layovers create a regular pattern in the mapping counter, a map describing the number of occurrences of a SAR pixel in the elevation model. Its exploitation yields a generation of a layover map without the use of external supports. The integration in the processor with a limited additional computational load and the capability to isolate layover signatures are additional benefits. Layover patches are then individually analyzed toward a better understanding of the complex urban signal return. A spectral estimation framework is employed to assess the slopes superimposed in the patches. Fringe-frequency estimation is involved. A set of simulations made for a nonparametric (fast Fourier transform) and a parametric (multiple signal classification) technique is performed prior to testing on real data. It is demonstrated that in X-band, for a single interferogram, just one layover contributor, when it dominates over the others, can be extracted with a sufficient accuracy. The algorithms are tested on a TanDEM-X spotlight acquisition over Berlin (Germany).

Due to the indirect measurement principle of radar on base of signal travel time, a very precise calibration of the sensor's internal clock with regard to clock rate and potential time offsets relative to the Coordinated Universal Time is an essential prerequisite for accurate pixel localization in Synthetic Aperture Radar. Giving special considerations on this aspect, we developed two algorithms that improve the already high localization accuracy of TerraSAR-X: The either one very precisely determines the true oscillator clock rate, while the other one effectively refines the accuracy of time annotation. Experimental analyses evaluate the obtained improvements in localization accuracy from both techniques.

This paper deals with the fusion of TanDEM-X raw DEMs in ascending and descending pass over Mumbai test area and enhance its quality. Before applying fusion method, a robust layover and shadow map has been calculated in ITP using TanDEM-X DEM and the corresponding slant range image. The selection of optimum weights for fusion has been based on height error map calculated from interferometric coherence. Results show a substantial reduction in number of invalid pixels after fusion. In the fused DEM, invalid is only 1.2%, while ascending and descending pass DEMs have 6.7% and 5.7% respectively. The improvement in accuracy of the DEM is very slight in this case which is due to the coarse resolution of the SRTM DEM used as reference.

We propose a new method to determine the level of remote water bodies with centimeter accuracy. The method is based on accurately determining the distance between the SAR antenna and the virtual phase center of a device that produces a double or triple bounce reflection with a well-known phase center. In the paper we describe a special mechanical arrangement to produce such a reflection and we report about results of first experiments.

The German satellites TerraSAR-X/TanDEM-X are high resolution imaging SARs with a resolution in the meter and even sub-meter range. The original product specification document stated an absolute geometric pixel localization accuracy in the same order of magnitude i.e. 1 meter. It was shown by several teams that this accuracy requirement is easily met and even surpassed [1] by the operational products. During the last years the remaining residual error sources could be further studied and attributed mainly to tropospheric delay variations [2] geodynamic effects such as solid earth tides [3] and plate tectonics to refraction in the ionosphere and to technical limitations in the satellite [4]. Our team investigated all these contributions developed correction and calibration methods and validated them in experiments with corner reflectors at different locations. Furthermore we explore novel applications of this high geolocation accuracy that range from classical earth surface displacement measurements to the localization of scatterers in 3D space with a precision comparable to GNSS. This paper provides a summary of latest measurement results of our globally distributed corner reflectors which show consistently a high accuracy better than 2 cm in range and azimuth. Furthermore we report on new developments concerning tropospheric correction using ECMWF and numerical weather models (WRF). Using the best available compensation techniques we can demonstrate accurate 3D localization of corner reflectors and of other objects. Current investigations aim to further improve the orbital accuracy to sub-centimeter level by improved modelling of air-drag and solar radiation pressure on the spacecraft.

Ionosphere irregularities along the synthetic aperture generate shifts and blurring that cause decorrelation. In this paper it is shown how, by partially focusing SAR images to the height of the ionosphere, it is possible to reduce the ionospheric azimuth effects and increase the coherence. This permits, even in case of turbulent ionosphere, to obtain better accuracies when separating the deformations phase from the ionospheric phase using the delta-k split-band interferometry method.

Spectral estimation is considered in the paper as an additional instrument towards a better understanding of the physical phenomena behind the layover scattering decomposition. A super-resolution technique is employed to derive the fringe frequencies characterizing the layover portion. Due to the limited estimation support, only the dominant frequency is found to be reliable information. The non-linear relationship with slopes is employed to derive a principal slope map. A bistatic interferometric scenario is tested. It is found that for the majority of the detections the facade contribution is the prevailing one due to the presence of targets with a high backscattered signal return at the vertical slope. The number of layover contributors is assessed prior to the spectral estimation. It has been estimated that the signal return is dominated by a single contribution for the majority of the layovers.

This paper addresses the November 2013 Balochistan Earthquake. A co-seismic TerraSAR-X pair acquired in wide-swath ScanSAR mode has been used to derive two-dimensional deformation measurements (radar line-of-sight and azimuth direction) of the eastern part of the main M7.7 earthquake and the large M6.8 aftershock by correlating SAR amplitude images. Atmospheric and solid Earth tide corrections have been considered to achieve accuracy in the order of several centimeters. Correlation measurements from Landsat-8 images have been additionally estimated. The intention is to isolate vertical and horizontal components in order to obtain three-dimensional deformation measurements. Interferometric processing issues of ScanSAR data for non-stationary scenarios, specifically co-registration, are additionally discussed.

The standard TanDEM-X product meats HRTI-3 DEM specification and comes with a sample spacing of 12 m. We apply non-local means (NL) interferogram filtering to the TanDEM-X data. In this paper, we present modifications of the original NL filter which render it more appropriate and efficient for massive processing of TanDEM-X data. Further, we investigate the noise reduction properties as well as the resolution and the coherence estimation accuracy of the new NL filter. Simulations and tests with TanDEM-X data hint that the improved DEMs possess a quality close to the HRTI-4 standard. Also future global InSAR missions like Tandem-L will greatly benefit from this type of filters.

Previous studies have shown the unprecedented absolute pixel localization accuracy of the German SAR (Synthetic Aperture Radar) satellites TerraSAR-X and TanDEM-X. Now, by thoroughly correcting all signal path delays and geodynamic effects like tides, loadings and plate movements, range accuracies of about 1 centimeter are demonstrated to be attainable. While Global Navigation Satellite System (GNSS) data provide local correction values for the atmospheric delays, correction values for the geodynamic effects are based on the IERS (International Earth Rotation and Reference Systems Service) conventions. Our recent measurements are based on a corner reflector with very precisely known ground position which we installed at Wettzell, Germany, close to the local GNSS reference stations. Further comparable high precision test sites in the world are in progress and shall prove the worldwide reproducibility of the achieved results.

A procedure to simulate the effects of the ionosphere on Synthetic Aperture Radar (SAR) images is presented. The propagation delay errors induced by the ionosphere have to be compensated to millimeter level in order to meet the scientific requirements for an L-band mission dedicated to deformation measurements, which are summarized in [1]. The simulator presented in this paper can be used to study the effects of an arbitrary ionospheric state on SAR images and to generate disrupted raw and focused images starting from ionospherefree real SAR images and use them to validate ionosphere estimation methods.

We compare ice elevation from TanDEM-X DEMs of 2011/2012 and SRTM DEM of 2000 over the Southern Patagonia Icefield (SPI) in order to quantify the volume loss of the icefield over the last decade. The map of elevation change rate is discussed. Detailed results are shown for two glaciers: Jorge Montt and Pio XI, exhibiting opposite trends in elevation and front position.

The German SAR (synthetic aperture radar) satellites TerraSAR-X (TSX-1) and TanDEM-X (TDX-1), launched in June 2007 and June 2010 respectively, provide an unprecedented geometric accuracy. Previous studies showed an absolute pixel localization for both sensors at the centimeter level [4] [5] [6]. However, recent measurements show that in range, under extraordinary good conditions, a location accuracy of even a few millimeters seems to be attainable. While on a long-term scale, we observed a slow variation of subsequent measurements; on a short-term scale, they coincided to within a few millimeters. The measurement series will be continued. The cause of the long-term variation is the subject of current investigation.

In order to obtain the accurate ground deformation from SAR interferograms on volcanic areas, the signal propagation delay through the atmosphere needs to be considered. In this paper numerical weather model data are used to compensate the stratified atmospheric delay in test site El Hierro (Canary Islands). Three GPS stations, installed on the nearby Island, are selected for validating and evaluating the weather model data. Atmospheric phase screen from PS-estimation shows a good agreement with turbulence induced atmospheric effect.

With the enhancing availability and variety of space borne Synthetic Aperture Radar (SAR) data and a growing number of analysis algorithms the need for a vital user community is increasing. Therefore the German Aerospace Center (DLR) together with the Friedrich-Schiller-University Jena (FSU) and the Technical University Munich (TUM) launched the education initiative SAR-EDU. The aim of the project is to facilitate access to expert knowledge in the scientific field of radar remote sensing. Within this effort a web portal will be created to provide seminar material on SAR basics, methods and applications to support both, lecturers and students.

Our paper reports about temporal changes of the Earth's topography found in first samples of TanDEM-X data when compared to SRTM Digital Elevation Models collected ten years earlier. We give an accuracy prediction and explain the methods to avoid systematic errors from biases and phase unwrapping ambiguities. Our paper provides examples from different Earth surface domains such as glaciers, volcanoes, mining activity and urban areas. We demonstrate and conclude that the higher the resolution of a DEM gets, the more frequent updates are required to keep the DEM valid with time.

The paper explains the mechanisms implemented by DLR to support the GEO Supersite initiative by providing TerraSAR-X data with simplified access procedures. It reports on the usage of the supported sites and shows exemplary results.

The operational dual-baseline phase unwrapping algorithm for the TanDEM-X mission is based on a combination of separate single-baseline phase unwrapping and a correction procedure of different levels of complexity. It benefits from all the information available from the two TanDEM-X acquisitions by computing a differential interferogram to obtain a more reliable unwrapped phase. This may still be prone to phase unwrapping errors, but these can be mitigated using a stereo-radargrammetric measurement. Hence, the resulting dual-baseline phase unwrapping algorithm outperforms a single-baseline one.

Observations of ice flow velocity with TerraSAR-X were carried out over main outlet glaciers of the Southern Patagonia Icefield (SPI) since 2008 by means of amplitude correlation technique. Velocity data are required to estimate the ice export due to calving. Furthermore we compare ice elevation from a TanDEM-X DEM of 2011 and from an SRTM DEM of 2000 in order to quantify the volume loss of these glaciers over the last decade. Results are shown for three glaciers of the central section of SPI, exhibiting distinct differences in the observed trends for surface topography and ice velocity.

It is a matter of fact that atmosphere causes a significant effect in interferometric measurements. A stack of acquisitions is needed to reduce this nuisance influence. Another approach is to use numerical weather predictions (NWP) [1]. However, it is not straight forward to choose parameters of a NWP-system to get the best possible result. Also, different input data can be used. Ensemble methods are well established to get a most reasonable forecast which is a mixture of differently initialized forecasts. Based on these weather predictions (NWPs), a collection of possible atmospheric phase screens (APSs) is computed and a most reasonable atmospheric phase screen (APS) is estimated. The idea behind this ensemble is, that the difference between every two pixels in an interferogram should match the difference of the corresponding pixels of a restricted linear combination of different estimated APS which results from different NWPs. This paper describes the technique in detail and provides an example demonstration using real data.

In this letter, we report on two major improvements with respect to the results presented in our recent paper on imaging geodesy: the atmospheric delay estimation using numerical weather model data and the continental drift adjustment from different geodetic coordinate systems. First, we demonstrate that the GPS-based zenith delay estimates used in our recent paper to correct synthetic aperture radar (SAR) data can be replaced by estimates calculated from numerical weather model data. This leads to a much wider applicability of our approach and even improves the accuracy from 3.8 cm to 3.2 cm. Second, for measuring the absolute position within the SAR image, the coordinate system used has to be carefully chosen, otherwise continental drift affects the results. We show that correct consideration of the reference frames eliminates residual offsets by up to 3.1 cm.

Recent radar satellites like TerraSAR-X and COSMO-SkyMed deliver very high resolution synthetic aperture radar images at a spatial resolution of less than 1 m. Persistent scatterer (PS) positions obtained from stacks of high-resolution spotlight data show very much details of buildings and other structures in 3-D due to the enormous amount of PS obtainable from data of this resolution class. As soon as more than one stack covering the same area is available, a combination of the results is eligible. However, geocoded PSs cannot be simply united due to residual offsets in their absolute positions which stem from unknown absolute height values of the different reference points chosen when processing the individual stacks independently. In this letter, two different methods for a geometrical fusion of geocoded PSs from stacks acquired at different aspect and incidence angles are presented. The algorithms are applied to PS interferometry results of both urban and nonurban areas.

Japan was struck by an M9.0 megathrust earthquake on March 11, 2011. Synthetic aperture radar (SAR) images from the TerraSAR-X satellite have been used to generate a ground motion map by means of correlation techniques. Geophysical corrections due to solid Earth tide and atmospheric path delay effects have been applied. These corrections can reach up to 20 cm in the radar line of sight. Using this approach, absolute displacements in the radar line of sight and in the satellite flight direction are determined. This letter shows the potential of correlation techniques for ground motion monitoring and a comparison with the interferometric technique. Using multiple scenes, a wide area displacement map is generated and quantitatively compared with GPS data, showing a divergence of about 15 cm.

The German SAR (synthetic aperture radar) satellites TSX-1 and TDX-1 outperform former civilian space-borne radar sensors in terms of geometric accuracy. Recently, both satellites constitute the first bistatic SAR system in space: TanDEM-X. With the high geometric accuracy of both satellites, the geolocation of ground targets has to accurately consider signal propagation effects and geodynamic effects which formerly were negligible. The prediction of expected radar positions is additionally complicated by the bistatic acquisition geometry of TanDEM-X. Here, we present our approach to cope with these demanding requirements. With the application of these techniques, measurements of the geometric accuracy of TSX-1 and TDX-1 reveal that their pixel localization accuracy is significantly better than in previous studies.

For spaceborne SAR (Synthetic Aperture Radar) systems, the dispersive effects of the ionosphere on the propagation of the SAR signal can be a significant source of phase error. While at X-band frequencies the effects are small, current and future P-, Land C-band systems would benefit from ionospheric compensation to avoid errors in topographic retrieval. In this paper the focus is on the effects of the ionosphere on repeat-pass SAR interferometry from Pthrough X-bands and methods for their estimation which are demonstrated on L-band ALOS-PALSAR acquisitions.

The German TanDEM-X mission flies the two satellites TerraSAR-X (TSX) and TanDEM-X (TDX) in a close orbit formation establishing a bistatic interferometer in space. A major challenge in bistatic SAR data processing is the synchronization of the satellites' oscillators. The paper at hand summarizes the synchronization concept, provides in-orbit verification and performance figures, describes the compensation approach within the SAR processing workflow and finally quantifies the synchronization performance in terms of achieved DEM accuracy.

We report on results from spaceborne velocity and topography measurements of the Drygalski glacier, Antarctic Peninsula. For our analysis we use a time series of TerraSAR-X data acquired between 2007 and 2010 which enables us to perform an error analysis and to determine higher order velocity parameters such as acceleration. Our estimated accuracy for velocity estimation is on the order of 2 cm/day and we find a weak slow down at the terminus of the glacier. Very first TanDEM-X single pass interferometric data sets acquired in 2010 allow us to reconstruct the 3D-glacier topography with unprecedented accuracy, delivering both, surface topography and roughness.

On the 12thof January 2010, Haiti was struck by a M7.0 earthquake; the hypocenter (18.443°N, 72.57ΓW, Depth 13 km) was located very close to the capital Port-au-Prince, causing considerable damage to buildings and infrastructure in the city and its conurbation and a high number of human fatalities. For evaluation of the co-seismic surface shift caused by this earthquake, especially at the Enriquillo Plantain Garden fault zone (EPGF), TerraSAR-X Stripmap data from ascending and descending orbits were acquired and processed using InSAR and incoherent cross-correlation techniques. The results, azimuth and range offset maps, were then geocoded and corrected for Solid Earth Tides (SET) and atmospheric propagation delays, as described in Eineder et al [1] . Each data-set indicated strong surface deformations. By combining the different viewing geometries and performing a 3D-Inversion (ascending & descending crossing directions), 3D-motion vectors, describing the surface displacements caused by the earthquake could be generated. As a reference, pre-seismic and post-seismic interferometric pairs were processed accordingly. The results showed no indications for strong deformations and thus validated the results.

Tandem-L is a mission proposal for an innovative interferometric L-band radar instrument that enables the systematic monitoring of dynamic Earth processes using advanced techniques and technologies. The mission is science driven aiming to provide a unique data set for climate and environmental research, geodynamics, hydrology and oceanography. Important application examples are global forest height and biomass inventories, measurements of Earth deformation due to tectonic processes and/or anthropogenic factors, observations of ice/glacier velocity field and 3-D structure changes, and the monitoring of soil moisture and ocean surface currents. The Tandem-L mission concept consists of two cooperating satellites flying in close formation. The Pol-InSAR and repeat-pass acquisition modes provide a unique data source to observe, analyse and quantify a wide range of mutually interacting processes in the bio-, litho-, hydroand cryosphere. The systematic observation of these processes benefits from the high data acquisition capacity and the novel high-resolution wide-swath SAR imaging modes that combine digital beamforming with a large reflector antenna. This paper provides an overview of the Tandem-L mission concept and its main application areas. It is planned to realise the Tandem-L mission in cooperation with NASA/JPL. The mission concept was developed in detail in a joint two-year pre-phase A study and it will be further studied in the next 18 months. This will allow a cost-effective implementation, whereby each partner contributes its predevelopments and experience. According to current planning, the Tandem-L satellites could be launched in 2019.

Ice velocities mapped by means of TerraSAR-X images in combination with surface elevation profiles measured by the altimeter system of ICESat are used to estimate glacier thinning and the increased calving flux after collapse of northern Larsen Ice Shelf on the Antarctic Peninsula in 1995 and 2002. InSAR analysis of one-day repeat pass SAR images from the ERS-l/ERS-2 tandem mission of 1995 and 1999 are these basis for retrieving the mass fluxes in the pre- collapse state. Applications of the various satellite data are shown for analysing the mass deficit and ice flow properties of Crane Glacier after disintegration of Larsen-B Ice Shelf. The ice flow acceleration shows a similar pattern for all calving glaciers on Larsen_B. The highest acceleration is observed at the front, decreasing upstream. Due to dynamic thinning at the frontal sections all main glaciers are now floating. This condition and the ongoing mass depletion will cause further frontal retreat in the coming years.

In this paper, we report on experiments to measure large-scale Earth surface displacements, such as those caused by solid Earth tides, with centimeter-level accuracy using TerraSAR-X radar images. With two totally different approaches, corner reflectors and image correlation techniques, we show the clear interrelation between the radar range measurements and the projection of the solid Earth tide motion vector onto the radar line of sight. Pixel location accuracies of up to 2.6-cm standard deviation can be achieved after a single calibration. We further demonstrate that solid Earth tides and tropospheric water vapor variations are the largest sources of ranging error if not compensated for. Alternatively, tropospheric water vapor can be estimated with centimeter accuracy using our proposed technique of synthetic aperture radar (SAR) image correlation and solid Earth motion compensation by the existing models. We also consider ionospheric delays which improve the results marginally in the X-band. Our results show the best ranging accuracies so far reported for spaceborne radar amplitude images and make TerraSAR-X-together with our simple compensation methodology-suitable for the imaging of centimeter-level Earth displacements. Absolute measurements of volcanoes or glaciers are possible without the use of ground equipment and without the use of SAR interferometry, thus avoiding the associated problems of phase ambiguity, phase unwrapping, and reference points.

The persistent scatterer interferometry (PSI) is a powerful technique to monitor the line of sight (LOS) deformation with Millimeter accuracy in urban areas. Nowadays, this technique is well established for the sensors ERS and Envisat/ASAR. Nevertheless, the availability of high resolution SAR sensors enables new applications which require new estimation principles. Application test cases for the sensor TerraSAR-X were demonstrated already. However, the high resolution data are not really fully exploited at the moment. This paper describes a newly developed PSI estimation principle which improves the spatial resolution by the support of distributed scatterers and increases the temporal sampling by the joined estimation of different beams. The prototyped technique needs to cope with the different projections of the horizontal and vertical deformation components onto the line of sight (LOS). Basically, this allows the inversion of the beam's observation equation and finally retrieves the vertical and horizontal deformation components.

For spaceborne SAR (Synthetic Aperture Radar) systems, the dispersive effects of the ionosphere on the propagation of the SAR signal can be a significant source of phase error. While at X-band frequencies the effects are small, current and future L-band systems would benefit from ionospheric compensation. We consider two ways to estimate the ionospheric delay in SAR signals and evaluate them on L-band ALOS-PALSAR acquisitions.

On June 21st, 2010, the German radar satellite TanDEM-X was launched and successfully placed in an orbit approaching the TerraSAR-X satellite until both systems will fly in close formation and will establish the only available bi-static interferometer in space. The primary TanDEM-X mission goal is to generate a global Digital Elevation Model (DEM) with a relative point-to-point height accuracy of 2 meters for moderate terrain at 12 m posting. For that purpose interferometric SAR data will be acquired over a period of 3 years in parallel to the operational running TerraSAR-X mission. Systematic processing of SAR raw data to so-called Raw-DEMs is performed by one single processing system, the Integrated TanDEM Processor (ITP). The final global DEM is then calibrated and mosaicked by a second system, the Calibration and Mosaicking Processor (MCP). The scope of this paper is to present an overview of ITP functionalities and to summarize the first processing results.

In this paper, different methods for the detection of the deformation signal with SAR data based on persistent scatterer interferomety (PSI) are described. Two test sites have been selected. For experimental purposes, two corner reflectors (CRs) were installed in the Fogo volcano. The location, phase as well as intensity of corner reflectors were analyzed with 11 TerraSAR-X stripmap (TSX-SM) data. For algorithmic development and validation, four stacks of TerraSAR-X high resolution spotlight (TSX-HSL) data from the Stromboli volcano have been acquired and used for PSI processing. The PSI results of deformation and topography update are fused by using point matching method with Iterative Closest Point (ICP). This research is a part of the German volcano monitoring project Exupèry, Work Package 2: `Space based observation techniques'.

We report on a method and experiments to achieve about 3 centimeters pixel location accuracy of TerraSAR-X SAR images. The method is based on atmospheric refraction corrections, Earth tide compensation and image correlation or the use of corner reflectors. Our method does not exploit the SAR phase and is therefore not subject to phase unwrapping problems or unknown phase offsets.

An incoherent correlation approach is used to derive ice motion fields for outlet glaciers through the Transantarctic Mountains, Antarctica. High-resolution repeat-pass, left-looking-mode TerraSAR-X data from 2009 were analyzed. Detailed ice velocity patterns on the Nimrod glacier basin and Starshot glacier are presented.

Tandem-L is a proposal for an innovative interferometric and polarimetric radar mission that enables the systematic monitoring of dynamic processes on the Earth surface. Important mission objectives are global forest height and biomass inventories, large scale measurements of millimetric displacements due to tectonic shifts, and systematic observations of glacier movements. The innovative mission concept and the high data acquisition capacity of Tandem-L provide a unique data source to observe, analyze and quantify the dynamics of a wide range of mutually interacting processes in the bio-, litho-, hydro- and cryosphere. By this, Tandem-L will be an essential step to advance our understanding of the Earth system and its intricate dynamics.

In this paper, an integrated approach is presented to determine the suitable parameters of a magma-filled dyke, which causes observable deformation at the ground surface. By this approach, the finite element method (FEM) and metamodel techniques are combined. FEM is used to establish the numerical model of the dyke and to produce the data required to identify metamodel parameters. Parameter identification problems are also known as parameter estimation or inverse problems. The metamodel technique is employed to make the whole procedure efficient in the identification phase. The identification approach is carried out by a systematic routine based on particle swarm optimization (PSO) algorithm. The approach is tested with synthetic data generated by analytic models. Moreover, it has been also applied to Stromboli Volcano (Italy) as an example, and the ground deformation data is acquired by using interferometry SAR technique. With the approach, the parameters can be successfully estimated with acceptable degree of accuracy. The results also indicate that only one kind of geophysical data are not sufficient for solving such a complex problem.

The German radar satellite TerraSAR-X was launched in June 2007. Since then, it is continuously providing high resolution space-borne radar data which are perfectly suitable for sophisticated interferometric applications. I.e. the mission concept and the SAR sensor support the coherent stacking of radar scenes which is the basis for advanced processing techniques e.g. Persistent Scatterer Interferometry (PSI) and SAR tomography. In particular, the short repeat cycle of eleven days and the highly reproducible scene repetition of the spotlight acquisitions support the stacking and consequently the time series analysis of the radar data. Furthermore, the sensor's orbital tube is precisely controlled to be in the order of 200 m which basically allows to utilize the baseline spread of the stacked acquisitions. However, this small spread is actually limiting the resolution in the SAR tomography. Interferometric applications could be demonstrated already in a very early stage of the TerraSAR-X mission. Because the resolution is 0.6 m in slant range and 1.1 m in azimuth in the high resolution spotlight mode the PSI and the SAR tomography processing results were impressive. Urban areas and single buildings could be mapped from space in three dimensions. Even the structural stress of single buildings caused by thermal dilation could be demonstrated. However, extended layover areas are caused by typical buildings and as a consequence complicated scattering situations need to be resolved. DLR's operational In-SAR processing system GENESIS had already been adapted to cope with the new sensor modes of TerraSAR-X and their new specific spectral characteristics. Now, the new image characteristics e.g. the extended layover areas and the long time coherent distributed scatterer need better to be supported. Subject is to optimally exploit the available information e.g. the radar reflectivity. Several algorithms of the processing system can take advantage of this, e.g. the scatterer configuration detection. As a matter of fact, the scatterer configuration has now become a very important characteristic for each resolution cell. It influences e.g. the estimation data extraction, the estimation of the 3D location and basically the estimation precision. A typical resolution cell can be composed of a single dominant point scatterer surrounded by clutter, two or more dominant point scatterers in clutter and of distributed scatterers with a specific phase stability over time. The paper provides technical details and a processing example of a newly developed algorithm to retrieve the 3D location of point scatterers from the scene's intensity which finally also provides the information on the scatterer configuration in a resolution cell.

In 2009, the German radar satellite TerraSAR-X will be supplemented with the TanDEM-X satellite to form the first bi-static single pass interferometer in space. TanDEM-X will fly close to TerraSAR-X in a controlled helix configuration for 3 years to jointly acquire interferometric SAR data in bistatic mode. The primary TanDEM-X mission goal is to generate a global Digital Elevation Model (DEM) with a relative point-to-point height accuracy of 2 meters for moderate terrain at 12 m posting. This paper outlines the SAR data workflow from quality check screening through to bistatic focusing and interferometric processing to raw DEM generation.

DLR is currently studying a space borne mission based on two L-band satellites to map Earth surface deformation and vegetation structure from space. In this study the scientific requirements for deformation measurements are collected, traded off versus technical feasibility and a mission concept is investigated that provides a global monitoring capability of geo-tectonic threats.

An incoherent amplitude correlation approach is used to derive ice motion fields of three major outlet glaciers of the Patagonia Icefields. High resolution repeat pass TerraSAR-X data of 2008 and 2009 were analyzed. The strong gradients in ice velocity of the terminus of San Rafael glacier, ranging from 2 to 16 m d-1, were captured well. Significant acceleration of the ice flow and losses in mass were observed for Upsala glacier.

We present a comparison of 1997 RADARSAT Antarctic Mapping Project (RAMP) SAR data with 2008-09 TerraSAR-X observations of a tributary glacier that is part of the Recovery Glacier drainage network in Coates Land Antarctica. The Recovery Glacier system is of scientific interest because of its role in discharging East Antarctic ice to the sea and because it has been subsequently learned that the flow of the glacier is likely controlled by the presence of subglacial lakes near the onset of faster glacier flow.

Recently, synthetic aperture radar (SAR) data with 1-m resolution acquired by satellites in spotlight mode became available to the public. In this paper, we elucidate the differences between interferometric processing of strip map and of spotlight SAR data, and we outline adequate algorithms for key processing steps such as azimuth Doppler filtering. We further present first TerraSAR-X spotlight interferograms, together with an evaluation of the paraeters that are critical for interferometry. Our results indicate a very good geometric accuracy, stability, and phase fidelity of the TerraSAR-X sensor and its products. From the interferograms, we are able to determine the heights of larger buildings and millimeter-scale structural deformation in several examples. The high detail level of imaged buildings and the good temporal phase coherence of urban areas in X-band make spotlight interferometry an exciting processing technique that enables new applications such as surveying individual buildings.

Since the launch of TerraSAR-X on June 15, 2007, the required precise orbit products have been provided by the German Space Operations Center to support operational spaceborne synthetic aperture radar (SAR) and interferometric SAR image processing. The TerraSAR-X precise trajectory is reconstructed solely based on the Global Positioning System (GPS) measurements from a geodetic-grade dual-frequency Integrated Geodetic and Occultation Receiver (IGOR) onboard the spacecraft. The GPS-based precise orbit determination (POD) strategy used in the estimation of the precise TerraSAR-X orbit and its performance will be fully described in this paper. Five-month statistics from the internal and external orbit assessment indicate a root-mean-squared 3-D orbit accuracy of better than 10 and 20 cm for the precise science orbit and precise rapid orbit (PRO) products, respectively. The POD performance of the backup single-frequency MosaicGNSS receiver to support operational PRO product generation in case of IGOR tracking failure or interruptions is described as well.

The German radar satellite TerraSAR-X was launched in June 2007. Radar interferometry (InSAR) is supposed to be one of the major applications of this sensor. It allows the three-dimensional mapping of the Earth's surface (InSAR) or even its displacement effects using differential interferometry (D-InSAR) or the more advanced persistent scatterer interferometry (PSI). All InSAR-applications are well-supported by the sensor, the SAR-processor and the mission design. DLRs operational interferometric system PSI-GENESIS has been adapted to cope with the new sensor and the innovative acquisition modes. Interferometric example applications could be shown already in the early stage of the six months commissioning phase. In this paper, recent processing examples and an update on the interferometric characteristic are presented.

TerraSAR-X data are operationally available to the public since January 2008. This paper shows selected TerraSAR-X interferometric examples with an emphasis on challenges introduced by the high resolution in spotlight mode and with 300 MHz.

The capabilities of TerraSAR-X data for feature tracking by amplitude correlation over glacier surfaces are investigated. Methodical aspects of the amplitude correlation approach are described. The TerraSAR-X based velocity fields are compared with former InSAR derived velocities and field measurements on three outlet glaciers on the South Patagonia ice field.

Multiple scattering may render synthetic aperture radar (SAR) image interpretation difficult, particularly when it comes to imaging of man-made structures. In medium-resolution SAR images, contributions from different scattering mechanisms can only be distinguished for large objects and under favorable conditions, like bridges over calm water. Since the launches of TerraSAR-X and COSMO-SkyMed, high-resolution SAR imagery is readily available from every spot on the Earth, and multiple scattering image features will be increasingly found in many of these data. Some of the first TerraSAR-X images show the pyramids of Gizeh in a seemingly unexpected geometry. Instead of being geometrically distorted, the near-range faces of the pyramids look like ground projected. This letter explains this image puzzle by a mixture of two scattering effects. The theory is confirmed by an interferometric evaluation. The discussed image artifact can be seen as representative for many other multiple-scattering SAR imaging scenarios in high-resolution images. This letter also demonstrates once again that the interpretation of complex scattering configurations benefits from interferometric information.

The German radar sensor TerraSAR-X will be launched by the middle of the year 2007 and will provide high-resolution data with also high radiometric and geometric accuracy. First interferometric results can be reported at the time of the conference. Various interferometric tests and a prediction on the performance of the monostatic interferometry will be described in the course of the presentation. Unfortunately, no data are available at the moment.

In February 2007 the German TerraSAR-X satellite will be launched and the TerraSAR-X mission will enter its approximately 5 months commissioning phase. At that time, the challenging developments on both sides, the advanced high- resolution multi-mode SAR instrument on the one hand and the corresponding sophisticated TerraSAR-X ground segment on the other hand will prove correct interaction and functioning. Screening and processing of the SAR data is the task of the DLR developed TerraSAR Multi Mode SAR Processor TMSP. Preceded by data reception, transcription including decryption and followed by archiving, cataloguing and product delivery, processing of the data by the TMSP is the central part of the SAR data workflow implemented in the Payload Ground Segment PGS. Space and ground segment have been subject to intense complete system testing on ground. Here, the compatibility of SAR instrument commanding, SAR instrument operations and subsequent SAR data processing has been successfully proven for the various acquisition modes of the sensor. Compliance of specified and measured product performance has been investigated as far as possible utilizing simulated point target SAR data. However, the real challenge will be the screening and SAR processing of TerraSAR-X data acquired in orbit and linked down to the receiving station. Therefore, the complete reception and processing chain will be properly tuned and adjusted to the properties of the received TerraSAR-X payload data. The TMSP algorithms have to be configured, e.g. thresholds for calibration pulse analysis, estimation window sizes for SAR data analysis, parameterization of estimation algorithms. Also the configuration of product variants with respect to resolution and radiometric quality will be checked and refined. This paper presents the very first experiences in reception, transcription, screening and processing of TerraSAR-X data with respect to performance, throughput and quality. During the TMSP checkout phase the compatibility of instrument commanding and SAR processing have to be verified and the accordance of SAR performance prediction and the obtained product performance and quality have to be investigated. First characteristics of the SAR data with respect to raw data statistics, calibration pulse analysis and Doppler centroid measurements will be shown. As far as available examples of SAR image products featuring the different image modes, Stripmap, ScanSAR and Spotlight at different incidence angles and polarizations will be displayed and a first estimate of product performance parameters will be given.

The TanDEM-X (TerraSAR-X add-on for Digital Elevation Measurement) mission will start in 2009 with the aim of generating a global Digital Elevation Model with high accuracy corresponding to HRTI-3 specifications (12 m posting, 2 m relative point-to-point height accuracy for flat terrain). To achieve this goal, a second satellite similar to TerraSAR-X will fly close to TerraSAR-X in a controlled Helix configuration for 3 years to jointly acquire interferometric SAR data in bistatic mode. According to the current mission concept, there will be at least two complete coverages of the global land surface, each one running one year. The different coverages will have different heights of ambiguity to allow multi-baseline phase unwrapping. For the sake of a homogenous data quality the second acquisition will be shifted by half the swath width with respect to the first coverage. Finally difficult terrain will be covered two more times with different acquisition geometries (i.e. different look direction and/or incidence angles). This paper presents first study results of phase unwrapping algorithms foreseen to process SAR data from the bistatic TanDEM-X configuration.

Space borne radar systems are capable of providing wind field information over the ocean. Radar instruments are of high value for operational applications because of their all weather and daylight capabilities. Synthetic aperture radar (SAR) instruments as flown on the European satellites ERS-2, ENVISAT or the Canadian platform RADARSAT are of particular interest for applications where high resolution two- dimensional information on the near surface wind field is needed. All these operate in C-band. The respective wind field algorithm CMOD was tuned to this wavelength. New research focussed on high speed cases to be able to measure wind speeds above 20 m/sec and on the VV to HH polarisation ratio. For future missions like TerraSAR-X, to be launched in May 2007 new wind field algorithms tuned to X-band are needed. The TerraSAR-X instrument has a spatial resolution of up to 1 m and additional features like multi polarisation which make it a very interesting tool for oceanographic applications. In this paper a new X band wind field algorithm, XMOD1.0 is introduced. The algorithm is based on the detection of wind streaks in the SAR images and scatterometer measurements of [1]. Data from the SRTM mission flown on the shuttle in February 2000 and SIR C/X SAR in 1994 are used to test the algorithm. Results are validated against in situ data and model data from ECMWF. The potential of SAR measurements to support the optimal siting, the design, as well as the operation of offshore wind parks is shown. Applications for offshore wind farming of the TerraSAR-X mission will be discussed. The platform FINO 1 was chosen as a primary test site to calibrate and validate wind fields for X band satellite images. For the development, optimisation and validation of the retrieval algorithms comparisons with in situ data, e.g., acquired at the FINO platform will be carried out. The respective calibration and validations strategies will be summarized.

Summary form only given. The advanced high-resolution German SAR satellite TerraSAR-X is scheduled to be launched at the end of May 2007. Due to its daylight and weather independent applicability in combination with a large spatial coverage and a short acquisition time, SAR has become a promising tool for traffic monitoring in recent years. Ground moving target indication (GMTI) techniques shall be applied to TerraSAR-X data in order to demonstrate the capability of a space borne SAR sensor to monitor traffic flows on highways. A series of GMTI experiments were to be carried out during the commissioning phase of the TerraSAR-X satellite. In first trials, cars, which are equipped with special radar reflectors and GPS receivers, were to be used as moving target references that are imaged in TerraSAR-X data takes. In a follow on experiment, arbitrary cars on motorways were to be imaged simultaneously by TerraSAR-X and by an airborne high-resolution camera. Car tracks extracted from the series of the optical images shall serve as a reference for the evaluation of the TerraSAR-X moving target data in this case. The paper presents first results of the data evaluation. An experimental GMTI processing system is used to detect and measure moving targets in both single-channel and dual-channeldata. The dual-channel data, which enable the application of well established GMTI methods like the along-track interferometry (ATI) or displaced phase centre array (DPCA) techniques, are acquired either in the so-called "aperture switching" mode with virtual multiple receiving channels or in the dual-receive antenna (DRA) mode with physically separated receiving channels. The paper reports on the analysis of the first experimental GMTI data by using different detection and measurement strategies. This includes the adapted processing of the SAR raw data with respect to the moving target signals, the incorporation of GIS data in the detection and measurement process and the application of different detectors for across- and along-track velocity components of the moving cars. The quality of the data is thoroughly analyzed and conclusions are drawn for the development and the performance of a fully automatic GMTI processing system for TerraSAR-X. Furthermore, an outlook on the planned experiments is given.

TerraSAR-X is a German satellite to be launched towards end of the year 2006. The SAR instrument built by EADS/Astrium has a multipolarized active phased array antenna and is programmable in wide ranges. This allows to operate imaging modes such as e.g. stripmap, spotlight, ScanSAR and dual-polarization modes. By further dividing the antenna in halves with different position or different polarization, experimental modes for ground moving target detection (GMT) or Quad-Polarization are possible. As a consequence of the various sensor capabilities the tree of SAR products offered by the DLR Ground Segment contains many different variants of polarization, resolution and scene size. Even more product variants are caused by different processing parameters selectable by the user. Some product performance parameters, such as the radiometric accuracy as a function of geometric resolution or the image resolution as a function of incidence angle depend on both, sensor settings (PRF, pulse duration) and on processing parameters (bandwidth, weighting, multi-looking). The processing parameters for the products have been designed by DLR in a way so that valuable products with maximum information content are offered to the user. In order to generate the specified products, the TerraSAR Multi Mode SAR Processor TMSP has been designed by DLR. This processor will be operated at the DLR payload ground segment in Neustrelitz for commercial and scientific customers. The processor will also be operated at additional direct access partner stations of Infoterra GmbH, who will serve private and public customers.

The Shuttle Radar Topography Mission flown in the year 2000 was the first approach to generate a global DEM from interferometric SAR. The C-band and X-band data acquired in 11 days have been processed with great success at NASA/JPL and at the German Aerospace Center DLR, respectively. Both data sets however show problems that should be taken care of in the design of future InSAR DEM missions: \n-\tphase unwrapping turned out to be unreliable in rugged mountain areas with very steep slopes \n-\tradar shadow and layover rendered significant areas in rugged mountain unusable \n-\tthe vertical accuracy was limited by the signal to noise ratio (SNR), by the baseline length and by the baseline knowledge \nThe SNR is expensive to improve and future missions like, e.g. the TanDEM-X mission currently studied at DLR, tend to use larger baselines therefore. This, however, will further complicate phase unwrapping. \n \nThe key to improve phase unwrapping stability while simultaneously increasing height accuracy is a multi channel InSAR system. Multiple channels can be achieved by different frequencies, delta-k processing, multiple simultaneous baselines or multiple observations with different baselines. \n \nThis paper summarizes the SRTM difficulties and sketches the strategies that could overcome them in future multi satellite missions. A baseline selection and acquisition strategy together with accompanying processing techniques are proposed in order to generate a global high precision DEM of the Earth in a reasonable time with available technologies.

The measurement of river currents can essentially contribute to determine river run-offs, whose knowledge is of great importance, e.g. in climate research. Remote sensing would be a convenient way to regularly monitor river currents on a large scale. The paper presents results from an airborne flight campaign in which SAR techniques were used to map and estimate river surface currents. As the radar backscatter of rivers is usually very low due to the lack of a rough surface, the test sites must be chosen carefully. From a radar point of view the surface patterns behave like moving objects. These cause several effects in SAR images such as azimuth displacements that complicate measurements. It is shown that by taking them into account the estimation of river currents with SAR techniques is possible.

Estimation of differential shift of image elements between two synthetic aperture radar (SAR) images is the basis for many applications, like digital elevation model generation or ground motion mapping. The shift measurement can be done nonambiguously on the macro scale at an accuracy depending on the range resolution of the system or on the micro scale by employing interferometric methods. The latter suffers from phase cycle ambiguities and requires phase unwrapping. Modern wideband high-resolution SAR systems boast resolutions as small as a few tens of a wavelength. If sufficiently many samples are used for macro-scale shift estimation, the accuracy can be increased to a small fraction of a resolution cell and even in the order of a wavelength. Then, accurate absolute ranging becomes precise enough to support phase unwrapping or even make it obsolete. This letter establishes a few fundamental equations on the accuracy bounds of shift estimation accuracy for several algorithms: coherent speckle correlation, incoherent speckle correlation, split-band interferometry, a multifrequency approach, and correlation of point scatterers in clutter. It is shown that the performance of split-band interferometry is close to the Crame/spl acute/r-Rao bound for a broad variety of bandwidth ratios. Based on these findings, Delta-k systems are proposed to best take advantage of the available radar bandwidth.

This paper presents theory, algorithm, and results of a maximum-likelihood algorithm that is capable to fuse a number of heterogeneous synthetic aperture radar interferograms into a single digital elevation model (DEM) without the need for the critical phase-unwrapping step. The fusion process takes place in the object space, i.e., the map geometry, and considers the periodic likelihood function of each individual interferometric phase sample. The interferograms may vary regarding their radar wavelength, their baseline, their heading angle (ascending or descending), and their incidence angle. Geometric baseline error estimates and a priori knowledge from other estimates like existing DEMs are incorporated seamlessly into the estimation process. The presented approach significantly differs from the standard DEM generation method where each interferogram is first phase-unwrapped individually, then geocoded into a common map geometry, and finally averaged with DEMs generated from other interferograms. By avoiding the phase-unwrapping step, the proposed algorithm does not depend on gradients between samples and is therefore capable to reconstruct the arbitrary height of each single scatterer. Because the height of each DEM sample is determined individually, spatial propagation of phase-unwrapping errors is avoided. The algorithm is targeted to fuse an ensemble of interferometric multiangle or multibaseline observations in areas of rugged terrain or highly ambiguous data where algorithms based on phase unwrapping may fail. The algorithm is explained, and examples with real data from the Shuttle Radar Topography Mission are given. Conditions of future missions are simulated, and optimization criteria for the viewing geometry are discussed.

We present one of the first studies on ocean current retrievals from interferometric synthetic aperture radar (InSAR) data acquired during the Shuttle Radar Topography Mission (SRTM) in February 2000. The InSAR system of SRTM was designed for high-resolution topographic mapping of the Earth's land surfaces, using two SAR antennas on a Space Shuttle with a cross-track separation of 60 m. An additional along-track antenna separation of 7 m resulted in an effective time lag of about 0.5 ms between the two images, which could theoretically be exploited for target velocity retrievals. However, the feasibility of ocean current measurements with SRTM has been questionable, since the time lag was much shorter than the theoretical optimum (about 3 ms at X-band) and the signal-to-noise ratio over water was quite low. Nevertheless, some X-band InSAR images of coastal areas exhibit clear signatures of tidal flow patterns. As an example, we discuss an image of the Dutch Wadden Sea. We convert the InSAR data into a line-of-sight current field, which is then compared with results of the numerical circulation model KUSTWAD. For tidal phases close to the conditions at the time of the SRTM overpass; we obtain correlation coefficients of up to 0.6 and rms differences on the order of 0.2 m/s. Furthermore we find that SRTM resolves current variations down to spatial scales on the order of 1 km. This is consistent with predictions of a numerical InSAR imaging model. Remaining differences between SRTM- and KUSTWAD-derived currents can be attributed mainly to residual motion errors in the SRTM data as well as to a limited representation of the conditions at the time of the SRTM overpass in the available KUSTWAD results.

Estimation of differential shift of image elements between two SAR images is the basis for many applications, like DEM generation or ground motion mapping. The shift measurement can be done nonambiguously on the macro scale at the accuracy of the range resolution of the system or on the micro scale by employing interferometric methods. The latter suffers from phase cycle ambiguities and requires phase unwrapping. Modern wideband high resolution SAR systems boast resolutions as small as a few tens of a wavelength. If sufficiently many samples are used for shift estimation, the accuracy can be increased to a small fraction of a resolution cell and even in the order of a wavelength. Then accurate absolute ranging becomes precise enough to support phase unwrapping or even make it obsolete. The paper gives equations and simulation results for the achievable shift estimation accuracy for several algorithms: coherent speckle correlation, incoherent speckle correlation, split band interferometry, and correlation of point scatterers in clutter. It is shown that the performance of split band interferometry is close to the one of optimum MLE. Special /spl Delta/k systems are proposed to best take advantage of the available bandwidth.

This paper describes the simulation of Staring Spotlight as well as Sliding Spotlight distributed target raw data sets from Stripmap raw data, using a time variant bandpass filter. Examples of simulated raw data generated from X-SAR/SRTM Stripmap raw data, are shown for both, Staring as well as Sliding Spotlight modes. The simulated raw data are processed using the TerraSAR-X Spotlight processor. The focused data are compared to the results of the operational X-SAR/SRTM Stripmap processor. Quality analyses of a point target contained within the data, demonstrate the applicability of both, the simulation approach and the TerraSAR-X Spotlight processor

This paper presents an approach to fuse an ensemble of interferograms of different wavelengths and viewing geometries to one common digital elevation model (DEM). Phase unwrapping and geocoding are performed "on the fly" and the different interferograms support each other. Propagation of phase unwrapping errors to large areas can no more occur which makes this method especially suitable for rugged mountains. The method is explained and a fusion of SRTM ascending and descending data with data with different wavelengths is demonstrated. The limits and possibilities are demonstrated by varying the number of interferograms and the viewing conditions. Furthermore a performance measure is given and compared with reference data

In February 2000, the Shuttle Radar Topography Mission (SRTM) successfully mapped the entire landmass between 60deg N and 54deg S using an Interferometric Synthetic Aperture Radar (InSAR). The data were acquired in Cand X-band and were independently processed to Digital Elevation Models (DEM) by NASA-JPL (C-band) and DLR (X-band). A commonly used source was the Position and Attitude Determination Record (PADR) generated by the Attitude Orbit Determination Avionics (AODA) system. The PADR file provides the orbit and baseline information. All C- and X-band data were systematically processed to 1 arc-second resolution DEMs. The X-band DEMs are globally available at DLRs German Remote Sensing Data Center (DFD). USGS provides the C-band derived elevation data in 1 arc-second for the US and globally a reduced version with 3 arc-second spacing. The presentation compares the X- and C-band derived elevation models. Starting from the individual verification results the correspondence of the SRTM DEMs with respect to height and location accuracy is investigated. Potential global and local discrepancies are discussed. Both datasets are compared to the Altimetry Corrected Elevations global DEM (ACE)

An update of the status of SAR Along Track Interferometry (ATI) is given and examples from X-SAR/SRTM for the waters around the Orkney Islands are provided. A special InSAR "Ocean-Processor" is described. The derived SRTM "velocity maps" demonstrate how valuable this method can be for a world-wide mapping of tidal ocean currents and for the detection of promising sites for hydropower installations

The TerraSAR-L system, currently being designed in a Phase B definition study, provides ESA with its most powerful radar-imaging programme to date. The platform is optimized for and built around the 11 mtimes2.9 m active phased array antenna of the L-band Synthetic Aperture Radar (L-SAR). The L-SAR features, on top of standard Stripmap and ScanSAR operations, full polarimetric capabilities, repeat-pass ScanSAR interferometry and a Wave Mode. Specification of the L-SAR has been guided by a careful analysis of the product requirements resulting in a robust baseline design with considerable margins. Besides, a major contribution to applications in areas of climate change and oceanography, the TerraSAR-L design responds specifically to requirements from interferometric applications. One key element of the TerraSAR-L operations strategy is a long-term systematic and repetitive acquisition scenario to ensure consistent data archives and to maximize the scientific and commercial exploitation of this SAR system. The other important factor is a systematic processing of all acquired data to Single-look Slant-range Complex (SSC) products to facilitate higher level product generation and services based on these products. This paper describes the TerraSAR-L basic product tree and explains the rationale behind. The nominal TerraSAR-L imaging modes are introduced and their performance characteristics are described. The generation concept of multi-look detected products based consistently on complex products - generated either at an intermediate stage during ground segment processing or serving as input product into a stand-alone tool - is introduced. A modular SAR processor design using the same complex product generation algorithms as far as possible independent of the underlying imaging mode is addressed

For ten years, a long history of data was acquired by the SAR sensors on the satellite ERS-1 and ERS-2 offering a wide range of interferometric applications. In 2002, the more advanced satellite ENVISAT was launched. The SAR on board on ENVISAT (ASAR) can continue the success of the remote sensing mission of the ERS satellites and preserve or even increase the value of the archived ERS data. The subject of this study is to demonstrate the continuity of the interferometric measurements by the combination of the SAR scene of the different sensors to interferograms (cross interferometry).

In February 2000, the shuttle radar topography mission SRTM was flown as the first single-pass SAR interferometer in space. The goal was to obtain a global digital elevation model. Therefore, a secondary receive-only antenna on the top of a 60 m long deployable mast supplemented the primary transmit and receive antenna mounted in the shuttle cargo bay. Due to mechanical constraints, the interferometric baseline did not only consist of the terrain height sensitive across track component but also contained an along track component of 7 m. The resulting time lag between the data acquisitions by the two antennas causes phase differences, which are proportional to the line-of-sight velocity of moving targets. Since this system ability has been expected prior to the SRTM launch, a traffic monitoring experiment has been carried out during the mission, which showed a surprisingly good agreement between the GPS velocity measurements on ground and the measurement from space. A strategy to exploit the along track interferometric (ATI) phase and the coherence together with the azimuth displacement of moving vehicles in focused SAR images has been developed and applied on sample test sides for traffic monitoring on highways.

Bistatic interferometric SAR systems like e.g. the Interferometric Cartwheel are characterized by spatially separated transmitters and receivers. Such systems pose much higher requirements on the stability of the local oscillator used for demodulation than SAR systems that are used for imaging only. Apart from the higher cost of such an oscillator it is questionable whether oscillators with sufficient accuracy are technically feasible in space at all. The paper establishes some strong interferometric requirements on the oscillator clock stability in bistatic SAR configurations from the consequences of oscillator phase errors in the SAR interferograms. A new method for the compensation of oscillator phase errors is presented that allows the use of standard

Latest concepts for the TerraSAR-X hardware design include the availability of a split antenna mode, in which the fore and aft halves of the SAR antenna array with a total length of 4.8 m can act as separate receiving antennas for along-track interferometry (ATI). The effective ATI time lag is 0.17 ms. We discuss in this paper whether the split antenna mode is suitable for ocean current measurements. Typical (tidal) currents in coastal areas are on the order of 1 to 2 m/s. To measure them, the ATI time lag should ideally be 20 times longer than the time lag of TerraSAR-X. Furthermore, the backscattered power from the ocean at low wind speeds can be below the noise floor of the instrument. However, the high resolution of TerraSAR-X permits averaging over many pixels to reduce noise. Simulated data products suggest that TerraSAR-X is capable of measuring currents with satisfactory accuracy at a spatial resolution of about 1 km, which is sufficient for many applications.

The feasibility of exploiting the along-track separation of 7 m between the two X band antennas of SRTM for ocean current measurements was already demonstrated by us at IGARSS 2002. We presented an SRTM image of the Dutch Waddenzee with clear phase variations in water-covered areas, which could be converted into line-of-sight current variations by about 1.3 m/s. A comparison with a current map from a tidal atlas showed good qualitative agreement, but digital reference data for a quantitative validation of the SRTM results were not available. In this work we present a detailed comparison of the SRTM data with simulated current fields from the numerical circulation model KUSTWAD. We obtain an overall correlation of 0.558, a regression coefficient of 1.011, and an rms difference between SRTM and KUSTWAD currents of 0.24 m/s. Furthermore, we analyze the correlation of spatial variations in the measured and simulated current fields on different length scales. We find that SRTM can resolve the current variations which are relevant to KUSTWAD down to scales on the order of 1 km.

With the Shuttle Radar Topography Mission (SRTM) flown in February 2000, the most comprehensive interferometric SAR data of the Earth's land mass so far were acquired. At the German Aerospace Center the X-SAR data are processed to a precise and homogeneous Digital Elevation Model (DEM). One of the most critical processing steps is phase unwrapping (PU). We are using an implementation of the Minimum Cost Flow (MCF) algorithm. Now that a total of 16,000 interferograms between /spl plusmn/60/spl deg/ latitude have been processed, this offers the unique opportunity to study the behavior of the MCF algorithm using a very large data pool. In this paper we report on the practical experiences with MCF gained during operational SRTM/X-SAR data processing. We present the results of a throughput analysis. Further, the problems experienced with MCF PU of the X-SAR data are discussed. It is shown how specific adoptions of the MCF cost functions can help to overcome them. The paper also presents the methods of PU quality assessment used in our operational processing.

Interferometric synthetic aperture radar (InSAR) techniques are today applied in many areas of remote sensing, ranging from digital elevation model (DEM) generation to surface motion mapping and InSAR tomography. To enhance the understanding of the InSAR mapping process and to test new algorithms, accurate tools for the simulation of the topographic InSAR phase are necessary. Whereas the equations for the interferometric phase of a given DEM are well known, the actual implementation is tedious. Furthermore, a straightforward implementation would take far more computation time than all the other InSAR processing steps put together. This paper presents a novel algorithm for the efficient simulation of the InSAR phase, taking into account the special problems in mountainous terrain. Simulation results are compared to and illustrated with real data from the European Remote Sensing satellite (ERS-1/2) tandem mission and the Shuttle Radar Topography Mission (SRTM). Accuracy estimates for the phase simulation are given for different terrain types. The algorithm is described in enough detail that it can be implemented as a general-purpose tool for the accurate simulation of interferograms with virtually unlimited size, taking no more processing time than other InSAR processing steps. The algorithm in the presented form is used operationally within the interferometry software GENESIS to support the processing of SRTM/X-SAR data at the German Aerospace Center (DLR).

This letter presents a new approach to actively use radar shadow in order to unwrap and geocode objects that cannot be reconstructed by synthetic aperture radar interferometry alone. This new algorithm may significantly improve phase unwrapping and digital elevation model reconstruction in mountainous topography or in urban areas. The algorithm is explained and examples are given with data from the Shuttle Radar Topography Mission, where shadow is a serious problem in Alpine terrain.

In February 2000, the Shuttle Radar Topography Mission acquired a global digital elevation model (DEM) within only 11 days. During the years 2000 and 2001 extensive testing and calibration activities primarily based on ocean surface data took place at DLR. The calibration phase is now finished and the quality of the products analyzed so far met all specifications. The routine processing of the German X-band data at DLR began in November 2001, starting with Europe. Now, that hundreds of image frames over Europe are being processed and mosaicked to a continent-wide DEM, the largescale system stability becomes visible. Our paper reports the experiences from mosaicking based on self-consistency tests and on comparison with independent reference data. While the overall quality is promising, there are still some outliers to be investigated and compensated. The calibration concept based on the use of ocean data will be presented and discussed. Adaptations and improvements based on self-consistency will be presented, that allow a more robust and automated processing.

In February 2000, the Shuttle Radar Topography Mission acquired a global digital elevation model (DEM) within only 11 days. During the years 2000 and 2001, extensive testing and calibration activities followed at DLR. One of the questions during that phase was, which kind of interferogram filtering should be performed. We analyzed different types of filters from the perspective of an operational DEM processing chain. Our paper describes the filters investigated and the arguments that finally led us to the decision to implement a relatively simple Gaussian smoothing in the time domain. This filter performed best in many disciplines and produced the smallest artifacts.

We present one of the first studies in which interferometric synthetic aperture radar (InSAR) data from the Shuttle Radar Topography Mission (SRTM) are analyzed with regard to the detectability of ocean surface current variations. The InSAR system of SRTM was designed for high-resolution topographic mapping, using two SAR antennas on a Space Shuttle with a cross-track separation of 60 m. For technical reasons, there was an additional along-track antenna separation of 7 m, which results in a time lag of about 0.5 ms between the acquisitions of images by the two antennas. In theory, this time lag causes additional phase differences, which are proportional to the line-of-sight velocity of moving targets and can thus be exploited, to some extent, for measuring oceanic currents. Indeed, some SRTM images acquired over water exhibit clear signatures of typical flow patterns. We show an example of an X-band phase image of the Dutch Waddenzee and discuss the plausibility of interpreting it in terms of sea surface height or current variations or the effect of waves. We find that only currents can be responsible for phase variations of the observed magnitude on spatial scales of a few 100 meters. We convert the data into a surface current field, which is found to be consistent with the theoretical current field at the time of the SRTM overflight according to a current atlas. Based on this encouraging result and theoretical findings, we discuss the general potential of SAR interferometry from space for oceanic applications.

Processing ScanSAR or burst-mode SAR data by standard high precision algorithms (e.g., range/Doppler, wavenumber domain, or chirp scaling) is shown to be an interesting alternative to the normally used SPECAN (or deramp) algorithm. Long burst trains with zeroes inserted into the interburst intervals can be processed coherently. This kind of processing preserves the phase information of the data-an important aspect for ScanSAR interferometry. Due to the interference of the burst images the impulse response shows a periodic modulation that can be eliminated by a subsequent low-pass filtering of the detected image. This strategy allows an easy and safe adaptation of existing SAR processors to ScanSAR data if throughput is not an issue. The images are automatically consistent with regular SAR mode images both with respect to geometry and radiometry. The amount and diversity of the software for a multimode SAR processor are reduced. The impulse response and transfer functions of a burst-mode end-to-end system are derived. Special attention is drawn to the achievable image quality, the radiometric accuracy, and the effective number of looks. The scalloping effect known from burst-mode systems can be controlled by the spectral weighting of the processor transfer function. It is shown that the fact that the burst cycle period is in general not an integer multiple of the sampling grid distance does not complicate the algorithm. An image example using X-SAR data for simulation of a burst system is presented.

Repeat-pass interferometry data were acquired during the first and second SIR-C/X-SAR missions in April and October 1994. This paper presents the first results from X-SAR interferometry at four different sites. The temporal separations were one day and six months. At two sites the coherence requirements were met, resulting in high quality interferograms. A digital elevation model in ground range geometry has been derived. The limitations of the X-SAR interferometry are discussed.>