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.

The Extended Timing Annotation Dataset (ETAD) product provides timing corrections for Sentinel-1 (S-1) single-look complex (SLC) data for improved geometric accuracy. Given the close relationship between path delay and radar signal phase, it also has the potential to serve as the basis for phase corrections in SAR interferometry (InSAR) applications with Sentinel-1. The provided timing corrections may be converted to phase offsets, which can be used to derive interferometric phase screens between pairs of repeat-pass acquisitions. In this work we explore the capabilities and limitations of ETAD to provide accurate interferometric phase corrections and introduce new features currently under investigation in the context of S1-ETAD scientific evolution study.

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.

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 paper deals with the analysis of InSAR performance for large-scale deformation measurement. The study evaluates the use of models, especially numerical weather prediction reanalysis, to mitigate disturbances in SAR interferograms. The impact of such corrections is evaluated and, using GNSS measurements, the predicted error bars are validated on a large Sentinel-1 dataset.

This article deals with the analysis of InSAR performance for large-scale deformation measurement. The study evaluates the use of models, especially numerical weather prediction reanalysis, to mitigate disturbances in SAR interferograms. The impact of such corrections is evaluated by analyzing short-time baseline phase variograms in order to derive a lower bound for the interferometric accuracy, especially at large distances. The variance is then propagated from single interferograms to deformation rates. Finally, using GNSS measurements, the predicted error bars are validated on a large Sentinel-1 data set.

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.

The presence of stochastic and systematic inconsistencies is a concern for the precision and interpretability of Interferometric Synthetic Aperture Radar (InSAR) when distributed scatterers are exploited for SAR time series analysis [1]. Multitemporal phase estimators aim at retrieving a consistent common-master interferometric time series, thereby reducing the effect of stochastic inconsistencies. Exploiting data redundancy the latter estimators are theoretically expected to decrease the susceptibility to systematic inconsistencies as well. In this contribution we seek a computationally efficient quality measure to show the effectiveness of multitemporal phase estimation in the reduction of inconsistencies. Choosing the ensemble coherence as a candidate, we firstly seek a constant false alarm rate detector for initial detection of signal-bearing areas. Furthermore the impact of phase inconsistencies on the ensemble coherence will be brought into attention.

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.

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.

This paper presents a robust mis-registration estimator based on ESD method for TOPSAR interferometry. For the in-terferometric applications of TOPSAR mode data, a master and slave SLC pair requires a co-registration accuracy in the milli-pixel order due to the large Doppler centroid frequency variation. Although ESD method estimates the mis-registration with the required sensitivity, a prior fine co-registration step is a prerequisite. This paper presents an advanced co-registration method that relaxes the fine co-registration requirement of the ESD and improves the estimation sensitivity. Experimental results with Sentinel-1A data are shown to validate the proposed method.

Constraining the deformation analysis to scatterers with high phase coherence, known as persistent scatterers (PS), in the InSAR time series plays a major role in advanced coherent approaches such as Persistent Scatterer Interferometry (PSI). Although crucial in overcoming the shortcomings of conventional InSAR in retrieving the deformation signals, this constraint appears to be too strict and lead to information loss in cases where the scatterers are coherent in merely a short period of the time series. Exploiting such scatterers, referred to as temporal coherent scatterers (TCS), is a necessity in PSI analysis in order to enhance the density of the resulted point clouds and consequently the quality of PSI. In here, statistical properties of the SAR calibrated amplitude time series are exploited to propose a new method for detection of the TCSs and estimation of the coherent intervals. The proposed methodology also allows for estimation of signal to clutter ratio (SCR) as an indication of the phase coherence. The method is evaluated using the simulated SAR stack as well as TerraSAR-X high resolution complex images.

In recent years, Persistent Scatterer Interferometry (PSI) [1], [2] has been widely used for scientific applications and has developed into an operational and commercially rewarding remote sensing technology. Now, ESA's upcoming Sentinel-1 mission allows a continuous, repeated without gap and global mapping of the Earth's surface based on Terrain Observation by Progressive Scans (TOPS). The idea at ESA is to also extend PSI processing to such large coverages, mapping countries and continents. This will support users in subsidence monitoring of volcanic and seismogenic areas, of costal lowland, of landslides in mountainous areas and of mining and ground water regulation on a small scale. For this reason, a wide area product (WAP) for PSI monitoring has been developed at DLR. The paper has three specific objectives. The first objective is to list and describe the updated algorithms. In this context, we illustrate the improvement with respective processing examples. Our second objective is to explain the characteristics of the WAP. The last objective is to provide WAP processing results for seismogenic areas. The test cases of Greece and of Turkey demonstrate WAPs potential, its applicability and use.

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.

In PSI (Persistent Scatterer Interferometry) the PSs are implicitly assumed to have a stable phase throughout a stack of images so that all images can be used for estimation. However, PSs can fade due to changes in acquisition geometry where the elevation or azimuth response of the PS for different baselines or zero Doppler frequencies is imprinted on the return. Physical changes caused by construction or seasonal changes due to snow cover can also cause the sudden appearance or disappearance of a PS. Here, several parametric change point estimators are assessed for their suitability in detecting such events both through simulation and their application to an ERS stack over Hamburg.

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.

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.

Efficient estimation of the interferometric phase and complex correlation is fundamental for the full exploitation of SAR Interferometry capabilities [1]. Particularly when combining interferometric measures arising both from distributed and concentrated point targets, the interferometric phase has to be correctly extracted in order to preserve its physical meaning and respect the homogeneity hypothesis that we assume when performing a coherent averaging [2]. Recently, an amplitude-based algorithm for the adaptive multilooking of InSAR stacks was proposed [3], [4] where it was shown that a comparison of the backscatter amplitude statistics is a suitable way to adaptively group and average the pixels in order to preserve the phase signatures of natural structures in the observed area.

Efficient estimation of the interferometric phase and complex correlation is fundamental for the full exploitation of interferometric synthetic aperture radar (InSAR) capabilities. Particularly, when combining interferometric measures arising both from distributed and concentrated targets, the interferometric phase has to be correctly extracted in order to preserve its physical meaning. Recently, an amplitude-based algorithm for the adaptive multilooking of InSAR stacks was proposed where it was shown that a comparison of the backscatter amplitude statistics is a suitable way to adaptively group and average the pixels in order to preserve the phase signatures of natural structures in the observed area. In this letter, different methods to compare amplitude statistics will be presented, compared through simulation and applied to real data. Based on these, recommendations are made concerning which method to use in practice.

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.

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.

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.

We propose a sequential M-estimation algorithm as an alternative to sequential least squares. Being an approximation of the exact M-estimator, the proposed technique is robust to nonGaussian processes and outperforms sequential least squares. Simulation results demonstrate the power of the proposed sequential M-estimator.