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.

The European Ground Motion Service (EGMS) is the newest addition to the Copernicus Land Monitoring Service, managed by the European Environmental Agency (EEA). EGMS provides continental-scale, homogeneous maps of ground motion based on Copernicus Sentinel-1 mission data. The service delivers the InSAR based ground motion products with millimetre-per-year precision with full time-series included. Notably, part of the EGMS product portfolio is referenced with respect to a GNSS based model. This paper reports on the argumentation of how and why to use GNSS in the context of EGMS.

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.

InSAR Norway, a public national ground motion service, based on Copernicus Sentinel-1 data, was launched in November 2018. The service provides regularly updated ground motion time series on over two billion locations in Norway. The service provides this data freely and openly to all interested users, through a web browser interface. Within the government, this data in instrumental for landslide hazard and risk assessment as well as monitoring. Other applications include evaluation of urban subsidence and infrastructure monitoring. Many scientific applications also benefit, such as in the fields of geomorphology and geodesy. InSAR Norway is operated by the Geological Survey of Norway, with cofunding from the Norwegian Space Centre and the Norwegian Water and Energy Directorate. Processing is done on a high-performance computing cluster (HPCC) using software developed by the KSAT-GMS partnership (NORCE - formerly NORUT, PPO.labs and Kongsberg Satellite Services).

The two-satellite Copernicus Sentinel-1 (S1) constellation became operational in Sep 2016, with the successful in-orbit commissioning of the S1B unit. During, the commissioning phase and early operational phase it has been confirmed that the interferometric performance of the constellation is excellent, with no observed phase anomalies. In this work, we show an analysis of selected performance parameters for the S1 constellation, as well as initial results based on the available data from the first months of operations.

The subaperture cross-correlation magnitude (SCM) has previously been proposed as a statistic that improves the contrast between small ship targets and the surrounding sea in synthetic-aperture-radar images. This preprocessing technique utilizes the fast decorrelation of open-water surface ripples on the scale of the SAR wavelength relative to coherent targets such as a ship. However, optimization of the bandwidth splitting in the subband extraction has not received any attention. The aim of this letter is twofold: 1) to describe the technical details of the algorithm, including modifications that are necessary to allow overlapping subapertures; and 2) to study the effect of splitting the bandwidth into two azimuth subapertures with respect to varying bandwidths and subaperture overlap. The impact on the SCM is investigated in terms of measures of speckle reduction and target-to-clutter contrast. Experiments are performed on real single-look complex SAR data containing repeated acquisitions of a vessel in open sea. The results indicate that the subband extraction strategy has a clear impact on performance.

This paper investigates the impact of terrain correction on change detection results. We firstly assess the effects of topography on radar brightness and show how we can produce the radiometrically terrain corrected multilook complex (MLC) covariance data. Next, changes on radar cross section as a function of polarization states due to azimuth slope variations will be studied. Finally experimental results on glacier dataset are shown by focusing on change detection results before and after terrain corrections.

The objective of the paper is to compare and combine Synthetic Aperture Radar (SAR) C- and L-band data for tropical forest monitoring over a study area located in the west of Democratic Republic of Congo (DRC) in the Congo Basin. For C-band ERS-2 SAR data as well as ASAR Alternating Polarization (AP) and Wide-Swath (WS) mode images were available. For L-band PALSAR Fine Beam Single (FBS) and Fine Beam Dual (FBD) polarization scenes were used. SAR data from 1995 to 2011 were analyzed. The overall aim is to improve forest and sub-forest classification by using time series with the given challenge of working with data from different sensors, acquisition modes and dates. This statistical pre-study of backscatter signals of three specific land cover types, forest, swamp forest and non-forest areas, has therefore been carried out. The data is examined on a yearly, seasonal and diurnal basis with a major focus on backscatter differences between the dry and the wet season.

In Norway, deformation monitoring of dams is regulated by law; traditionally it is done by geodetic measurements [1]. To ensure early recognition of problem areas at the dam and/or at the slopes around the reservoir, frequent deformation measurements are necessary. Here, we investigate the feasibility of applying satellite based SAR interferometry to monitor deformations at dams and reservoir slopes. We present results of an InSAR study at Svartevatn dam in south west Norway, an earth-rockfill dam. Two ERS image stacks have been acquired in ascending and descending mode, respectively. Each image stack has been processed with the Small Baseline Subset (SBAS) to generate deformation maps. The results show that historic SAR data can be used to monitor deformations at the dam with a resolution comparable to geodetic measurements.

We have used the repeat pass Synthetic Aperture Radar (SAR) intensity tracking for two dimensional (2-D) glacier surface motion estimation using X-band data. It has been observed that the viability of SAR interferometry (InSAR) often is limited by coherence loss over glaciers in land locked regions using SAR data pairs of more than one-day temporal baseline. An alternative to InSAR is the intensity tracking approach, which relies on intensity cross-correlation for estimation of subpixel surface motion in range and azimuth directions. In this work we have applied this approach for two-dimensional glacier surface motion estimation in northwestern (NW) Himalayas, using TerraSAR-X (TS-X) spotlight mode high-resolution data pairs of 11 day, 22 day and 33 day temporal separation of August- September, 2008. Gangotri glacier motion in NW Himalayas are studied and analyzed over short period and it has been observed that its motion was 10 cm/day. The technique is found to be highly appropriate for monitoring the flow rate of glaciers in Himalayas and can be used to routine monitoring of glacier characteristics and dynamics.

The main operational mode of the European Space Agency's upcoming Sentinel-1 operational satellite will be the Terrain Observation by Progressive Scans (TOPS) imaging mode. This paper presents a very efficient wavenumber domain processor for the processing of TOPS mode data. In particular, a novel signal transform, called a moving band chirpZ-transform, is introduced in order to allow the entire azimuth aperture to be focused simultaneously without any need for temporary unaliasing, which requires upsampling, or subaperture processing.

Satellite synthetic aperture radar interferometry (InSAR) is an invaluable tool for land displacement monitoring. Improved access to time series of satellite data has led to the development of several innovative multitemporal algorithms. Small baseline (SB) is one such time-series InSAR method, based on combining and inverting a set of unwrapped interferograms for surface displacement. Two-dimensional unwrapping of sparse data sets is a challenging task, and unwrapping errors can lead to incorrectly estimated deformation time series. It is well known that L1-norm is more robust than L2-norm cost function minimization if the data set has a large number of outlying points. In this paper, we present an L1-norm-based SB method using an iteratively reweighted least squares algorithm. We show that the displacement phase of both synthetic data, as well as a real data set that covers the San Francisco Bay area, is recovered more accurately than with L2-norm solutions.

The repeat pass interferometric phase change between a summer reference and a dry snow SAR image is proportional to the snow water equivalence. The technique is, however, com- plicated due to rapid de-correlation and low coherence. Phase wrapping is also a problem, and occurs at typically 20 cm dry snow. Phase unwrapping can be remedied by using a delta-K processing technique. By taking into account refined masks for land cover and folding, averages at catchment level may be per- formed to retrieve SWE and finally a field value for the total water content in a catchment. A carefully controlled experiment was performed at our test site at Altevatn, in northern Norway (N68o42', E18o50') the winter 2004. A total of 63 ASAR SLC scenes with high incidence angle (IS1 and IS2) were collected during winter and summer (refer- ence-scenes) following 10 repeated geometries. Two corner reflec- tors were deployed to provide calibration. Three field campaigns were carried out during the winter to validate the SWE results.

We present a definition of a dual-frequency dual-wavenumber cross-spectrum of two nonstationary and inhomogeneous harmonizable random fields, which is in fact a generalization of the Loeve (dual-frequency) cross-spectrum of two random processes. Furthermore, a geometric argument shows that a proper normalization yields a natural measure of cross-coherence, and application of Cauchy-Schwarz's inequality results in a necessary and sufficient condition for full cross-coherence. Finally, estimators of the cross-spectrum and the cross-coherence based on the multitaper approach are suggested, and tested on simulated data.

Frequency-selective channels can be converted to a set of flat-fading subchannels by employing orthogonal frequency-division multiplexing (OFDM). Conventional differential encoding on each subchannel, however, suffers from loss of multipath diversity, and a very high peak-to-average power ratio (PAPR), which causes undesirable nonlinear effects. To mitigate these effects, we design a block differential encoding scheme over the subchannels that preserves multipath diversity, and in addition, results in constant modulus transmitted symbols. This property is shown to ensure that the PAPR of the continuous-time transmitted waveform is reduced by a large factor. The maximum-likelihood decoder for the proposed scheme, conditioned on the current and previous received block, is shown to have linear complexity in the number of subcarriers. The constant modulus scheme will yield good bit-error rate performance with full rate only if short blocks are used. However, one may mitigate this problem by relaxing the constant modulus requirement. We show that in a practical OFDM system, we can group the subcarriers into shorter subblocks in a certain manner, and apply the constant modulus technique to each subblock. Thus, we improve diversity at a very low decoder complexity, and at the same time, we introduce an upper bound on the discrete-time PAPR, which, in turn, may lead to appreciable reduction in continuous-time PAPR, depending on the system parameters. Finally, in situations where we can sacrifice rate, additional complex field coding may be used to exploit the multipath diversity provided by channels longer than those the simple scheme can handle.

We present a definition of wavelet bicoherence based on wavelet polyspectra. We propose a simple estimator for wavelet bicoherence, and discuss its statistical properties. In particular it is shown that wavelet bicoherence estimation has a larger number of effective degrees of freedom than traditional Fourier-based bicoherence estimation. The proposed estimator is applied to detection of coherent couplings in rocket measurements from the ionospheric E-region. It is concluded that wavelet bicoherence is a tool well-suited for analysis of non-stationary mode coupling.