Single-pass Interferometric SAR satellite configurations offer unique opportunities for observing dynamic features of ice masses. Future cross-track interferometry constellations of satellite missions will produce interferometric DEMs over virtually all glaciers globally and will offer significant advancements for regular monitoring their surface elevation. In the present contribution we want to address some of the main issues encountered when mapping the topographic changes with multitemporal TanDEM-X InSAR DEMs over glaciers. We illustrate open questions for InSAR DEM data acquisition when targeting height change rate calculation for mountain and outlet glaciers at large scale.

The TanDEM-X mission acquires data used for the generation of Digital Elevation Models (DEMs) since 2010. From this data two global DEMs are already generated or in generation. The DEM acquisitions used for new TanDEM-X DEM 2020 are also used to generate TanDEM-X DEM Change Maps. Furthermore, the DEM Change Maps can be combined with the additional TanDEM-X DEM datasets and used for the generation of TanDEM-X DEM Change Map Stacks. This paper presents these new products on the basis of an example of an open-pit mining area in Australia. Additionally, the potentials and challenges of the DEM Change Map stacks are presented.

The Venus Interferometric Synthetic Aperture Radar (VISAR) is one of two instruments carried by the VERITAS Discovery Mission to Venus that was selected by NASA in 2021 [1] , [2] . VERITAS (Venus Emissivity, Radio Science, Insar, Topography And Spectroscopy) is a partnership between scientists and engineers at NASA/JPL in an international cooperation with the Germany Aerospace Center (DLR), the Italian Space Agency (ASI) and the French Space Agency (CNES). VISAR aims to be the first to image Venus at 30 m resolution on a global scale and deliver a digital elevation model at 6 m height accuracy in addition to proving interferometric deformation maps of activity on another planet. The VISAR instrument has several interesting features and challenging aspects. The focus is put on SAR performance and the options for the radar operation and imaging mode parameters given the constraints inherent to a planetary mission.

Differential SAR interferometry for deformation measurement and coherent change detection has revolutionized our understanding of many geophysical processes on the Earth since its first demonstration in the 1980’s. The recently selected NASA Discovery mission VERITAS aims to be the first planetary mission to use differential radar interferometric techniques for measuring surface deformation and for coherent change detection measurements. These measurements provide the most sensitive means for detecting and measuring present day geologic activity on Venus. Differential SAR interferometric measurements at Venus by the VERITAS mission has several interesting and unique features including the atmosphere and orbit considerations that are described in this paper.

The Earth is a very dynamic system and the topographic height of its landmass changes over time, especially in forested areas, glaciers, permafrost regions or where human activities take place. After the TanDEM-X mission provided a first global DEM of unprecedented quality in 2016, a new complete coverage of the Earth's landmass was acquired mainly between 2017 and 2020. This data is used to create another global DEM. In addition to providing more up-to-date elevation information, these new acquisitions also provide a great dataset to show the changes that have occurred in the few years between the two global datasets. The new product - the TanDEM-X DEM Change Maps - will be produced in 30m and 90m postings and will focus on showing these changes between the first global TanDEM-X DEM and the newly acquired time-tagged DEM scenes. It will also include the in-house automatically edited TanDEM-X DEM.

The TanDEM-X mission has acquired multiple global coverages of data over the last years in order to create digital elevation models (DEMs). The data between 2017 and 2020 is processed to Change RawDEMs (CRaw DEMs). These scenes are successfully pre-calibrated individually during the processing. However, in order to determine and quantify terrain changes between the new data and the former global TanDEM-X DEM, the calibration can be improved even further. In the case of large-scale terrain changes like glaciers or forestation areas CRaw DEMs might be calibrated on the change instead of the smaller stable regions. A comparison of to the calibration of neighboring scenes gives information on which scene has to be corrected. This paper summarizes the pre-calibration during the processing of the CRaw DEMs and analyzes the results of the calibration and corresponding change detection. Furthermore, a method for a post-calibration of the CRaw DEMs is presented. This method will be used to create TanDEM-X DEM Change Maps in the future.

In 2017, the TanDEM-X Mission decided to generate a second - more recent - global DEM. The acquisitions took place from 2017 till mid 2020 and represent a new global coverage of the whole Earth's landmass. This global dataset is well separated in time from the data used for the first global TanDEM-X DEM. Recent terrain height information can be delivered globally again with similar accuracy and consequently, terrain changes can be monitored. Currently, this data is being processed by the Integrated TanDEM-X Processor (ITP) into pre-calibrated single scenes. A reference DEM is a pre-requisite to enable a correct interferometric processing.

Over the last years the TanDEM-X mission acquired data for a second global digital elevation model (DEM) the TanDEM-X Change DEM. This new DEM is temporally independent of the former global TanDEM-X DEM and therefore yields the possibility of change detection. In order to decrease the phase noise level the interferometric processing for the Change DEM has been upgraded. This also allows a more accurate change detection. Currently, the processing of the global data is performed operationally. It includes the detection of terrain changes and first examples of detected terrain changes can be presented.

The “TanDEM-X Change DEM” will be a new DEM consisting of the data globally acquired by the TanDEM-X mission from 2017 until 2020. This new DEM aims to characterize terrain changes which occurred between the acquisition of the TanDEM-X global DEM, acquired between 2010 and 2015, and the new temporally independent and up-to-date data set. The new data will mostly contain only one global coverage. Therefore, necessary improvements in the acquisition planning process as well as in the interferometric processing were made. Specifically, a new adaptive filtering approach is presented in this paper as well as its influence on the interferometric phase and the DEM for test sites over Germany and Chile.

With the global TanDEM-X DEM generation being finished in 2016, the mission is now acquiring a new dataset to provide an independent DEM, the so-called "TanDEM-X Change DEM". It is based on a completely new dataset acquired from 2017 - 2019 in contrast to the acquisitions for the global DEM between 2010 and 2015 in the aim to characterise terrain changes. It benefits from improvements in the acquisition planning process and in the data processing which enable to achieve reliable DEM data of high accuracy with fewer acquisitions. For this goal, the use of an edited TanDEM-X DEM as "starting point" for the processing is mandatory. Detectable 3d elevation changes are presented exemplarily in Indonesian forest and on an outlet glacier in Antarctica.

Tandem-L is a proposal for an innovative L-band SAR mission for the systematic observation of dynamic processes on the Earth's surface. The mission concept is based on two SAR satellites flying in close formation featuring latest digital beamforming techniques in combination with a large deployable reflector for increasing the swath width and imaging resolution. This enables innovative operation modes such as polarimetric SAR tomography for determining the vertical structure of vegetation and ice. With novel imaging and processing techniques and the vast recording capacity of up to 8 Terabyte/day, it will provide vital information for solving pressing scientific questions in the biosphere, geosphere, cryosphere, and hydrosphere and will make an essential contribution for a better understanding of the Earth system and its dynamics. This paper gives an overview of the Tandem-L mission project which has successfully passed the intermediate system requirements review of Phase B1.

This paper presents a nonlocal interferometric synthetic aperture radar (InSAR) filter with the goal of generating digital elevation models (DEMs) of higher resolution and accuracy from bistatic TanDEM-X strip map interferograms than with the processing chain used in production. The currently employed boxcar multilooking filter naturally decreases the resolution and has inherent limitations on what level of noise reduction can be achieved. The proposed filter is specifically designed to account for the inherent diversity of natural terrain by setting several filtering parameters adaptively. In particular, it considers the local fringe frequency and scene heterogeneity, ensuring proper denoising of interferograms with considerable underlying topography as well as urban areas. A comparison using synthetic and TanDEM-X bistatic strip map data sets with existing InSAR filters shows the effectiveness of the proposed techniques, most of which could readily be integrated into existing nonlocal filters. The resulting DEMs outclass the ones produced with the existing global TanDEM-X DEM processing chain by effectively increasing the resolution from 12 to 6 m and lowering the noise level by roughly a factor of two.

The TanDEM-X mission is the first free flying bistatic SAR mission. It has the primary objective to generate within a short time frame a global digital elevation model (DEM) of 10-m absolute vertical accuracy and 2-m relative height accuracy. For that, the whole land mass has been mapped at least twice with different baselines. The success of the mission depends on the accuracy of the final DEM and therefore on the reliability of the phase unwrapping (PU) algorithm. Hence, a robust and versatile PU method, which is in accordance with the acquisition concept, is necessary. This paper presents a new method that combines bistatic high-resolution interferometric data in order to perform an accurate PU on a huge amount of data. The dual-baseline PU correction (DB-PUC) framework addresses this challenge by correcting errors that occurred during the single-baseline PU procedure. It benefits from the additional information available through the differential interferogram and the stereo-radargrammetric phase, which are used to correct region-wise the ambiguity bands of the misestimated unwrapped phases to be less sensitive to noise and possible temporal changes. The multilevel of the DB-PUC approach makes it flexible, computationally efficient, and well adapted to deal with the various PU error scenarios. This framework is used operationally for the processing of the data of the TanDEM-X mission.

We investigate the feasibility of generating highly accurate digital elevation models (DEM) from TanDEM-X interferograms by using nonlocal filters for phase denoising. Some of the shortcomings of existing nonlocal filters that render them not applicable to our goal are briefly described and a new filter is proposed that alleviates these problems. The most significant new properties are addressing the slope dependent denoising performance of existing nonlocal InSAR filters and several measures to bolster denoising near edgelike features. We evaluate the proposed filter using synthetic interferograms and by visual inspection of a DEM generated from a TanDEM-X interferogram.

The next milestone in the TanDEM-X mission is the generation of high-resolution DEMs for selected areas. New scenes with lower heights of ambiguity are being acquired to fulfill the goal on the relative height accuracy of 0.8 m. To enable a reliable phase unwrapping in a finite time, a processing concept based on the usage of the final global TanDEM-X DEM has been developed. Since the global DEM provides an up-to-date measurement of the terrain height with an unprecedented high accuracy, it is of great help for the phase unwrapping procedure. This paper proposes an adaption of the Integrated TanDEM-X Processor, which is used operationally for the generation of the global DEM data, so that it can process DEMs of higher resolution from interferometric bistatic data with very low height of ambiguity and better resolution by making good use of the finalized global DEM. The final paper will focus more particularly on the assessment of the unwrapping results.

This paper reports on the current status and recent extensions of the TerraSAR-X ground segment in its ninth year of operation.

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.

InSAR Processing and especially phase unwrapping is a crucial step in the realization of the global TanDEM-X DEM. After three years of operation, the InSAR chain has delivered more than 350,000 RawDEMs, which mostly fulfill already the high accuracy requirements. At the same time, it has been also optimized and improved to cope with input data of various quality. Special efforts have been made in the dual-baseline interferometric chain to deal with CoSSCs with larger ranges of height of ambiguity and time spans. This paper presents the key elements of the InSAR chain and analyses the dual-baseline phase unwrapping results.

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.

This paper presents the processing results of the dual-baseline phase unwrapping correction chain of the Integrated TanDEM-X Processor. Second year data are operationally processed since August 2012 with the help of supporting CoSSCs. They are shifted of half a swath width with respect to the first year data. Supporting CoSSCs are the first year scenes. The first and second year scenes have different height of ambiguity but are taken from the same look angle. The chain has to deal with huge amount of data of different quality and from every part of the world landmass. A success rate of more than 97% is achieved overall.

The german TerraSAR-X and TanDEM-X satellites are able to acquire images operationally in ScanSAR mode and experimentally in TOPS mode, the future Sentinel-1 Interferometric Widesath and Extra Wideswath modes. This paper gives an overview of the interferometric processing steps of burst-mode acquisitions and present the current status in preparation for future algorithm development towards PSI. Interferometric results of TerraSAR-X repeat-pass images in ScanSAR and TOPS mode are shown.

Started in June 2010, the TanDEM-X satellite joined the TerraSAR-X satellite in space to perform the conjoint interferometric TanDEM-X mission to acquire a truly global Digital Elevation Model (DEM) of unprecedented accuracy [1]. Since the very first interferometric acquisitions, the Integrated TanDEM-X Processor (ITP) delivered operationally “Raw”-DEMs and complex products of mono- and bistatic data. The RawDEMs are scenes of about 50 km × 30 km, generated for a dedicated DEM Mosaicking and Calibration Processor (MCP) which produces the final DEM. The so-called Coregistered Single-look Slant-range Complex (CoSSC) products are provided for each of these scenes in different flavors for production internal purposes and system performance monitoring as well as for scientific use. The capabilities of the ITP go far beyond the primary mission objective of DEM generation alone: it also provides the operationally available end-user products from different experimental modes as e.g. pursuit monostatic, dual polarization bistatic data, alternating bistatic in single and dual polarization and different bistatic and alternating bistatic spotlight modes. This paper focuses on the accuracy of the generated products, the ITPs contribution to the achieved accuracy of the data and the direct effect of it on the use and interpretation of RawDEM heights for temporal change detection. Also the basic characteristics of the operational experimental products are introduced..

During the second operational year of the TanDEM-X mission, a second coverage of the whole land mass is acquired in order to produce a high accurate and high resolution DEM from a combination of both data sets. This paper presents the dual-baseline interferometric processing chain. Its main steps consist of coregistering the different interferograms (having different baselines), of unwrapping the phases and of comparing them to eliminate the possible unwrapping errors.

Since July 2010, TerraSAR-X and TanDEM-X jointly acquire interferometric data. Starting their common commissioning phase with a so called pursuit monostatic configuration with 3 seconds time lag between the two passes, they were later put in a close formation in October 2010, acting since then as the first freely configurable bistatic SAR interferometer in space. All operational acquisitions were processed from instrument raw data to DEMs from day one of the data taking on by one single processing system: the Integrated TanDEM-X Processor (ITP) (see [1],[2]). Data take analysis, common parameter calculation, synchronization, bistatic focusing, filtering, co-registration, phase unwrapping and geocoding are all performed in one sequence inside this processor. This approach allows a high precision processing by passing all applied corrections and determined parameters from one step to the next. Specifically the geometric & phase accuracy and stability of the instruments, the processor and the auxiliary data (i.e. the millimetric precision of the baseline products) provide an unprecedented level of relative and absolute geometric accuracy in the bistatic operation. While many challenges of bistatic processing of the TanDEM-X data are encountered, the benefits of this single pass acquisition mode can be used to derive additional information from the data itself for further processing and calibration. In this paper, we will outline the bistatic interferometric processing steps of the ITP and focus on the aspects of geometric accuracy in DEM generation.

The TanDEM-X Mission has as primary objective to generate a high resolution global Digital Elevation Model. This paper proposes a new method for multibaseline Phase Unwrapping which is the critical point of this generation. We propose to combine both Minimum Cost Flow (MCF) and Maximum a Posteriori (MAP) estimation. The latter is used to solve phase gradient ambiguities. The problem is posed as an energy minimization one and solved using Belief Propagation (BP) which is an iterative process. Nevertheless, although very good results are obtained on loopy graphs, it is not guaranteed to converge. Thus, phase unwrapping of the most accurate interferogram is finally performed with the MCF algorithm and takes as input the unwrapped gradients.

The purpose of this paper is to provide an algorithmic overview of the interferometric processing embedded in the Integrated TanDEM-X Processor (ITP), settled to the generation of the raw digital elevation model (DEM). The main processing blocks are described, with a focus on the spectral matching of the azimuth spectra, the high-precision coregistration, the dual-baseline phase unwrapping and the geocoding of the products. The robustness of the algorithms is demonstrated through a dual-pass TerraSAR-X scenario.

The TerraSAR-X mission was launched in June 2007. After successful completion of the commissioning phase, the mission entered its operational phase in January 2008. Since that time, TerraSAR-X provides the scientific remote sensing community and commercial customers with high-quality spaceborne synthetic aperture radar (SAR) data products. The intention of this paper is to present the SAR data processing concept and the comprehensive portfolio of products reflecting the instrument's diverse imaging capabilities together with options of processing and achieved product quality as well as the essentials of SAR processing. Furthermore, it shall also provide details on how to fully exploit the precision of the TerraSAR-X products.

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.

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.