Ramon Brcic

Adaptive InSAR Stack Multilooking Exploiting Amplitude Statistics: A Comparison Between Different Techniques and Practical Results

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.

Interferometric Processing of Sentinel-1 TOPS Data

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.

Space-borne high resolution SAR tomography: experiments in urban environment using TS-X Data

Synthetic Aperture Radar (SAR) tomography aims at retrieving the 3-D reflectivity from multi-pass SAR data. It is essentially a spectrum estimation problem. As a consequence, complex values of a specific range cell in a SAR image stack as a function of baseline are closely related to the Fourier transform of the reflectivity function in the elevation direction.

Wide area Persistent Scatterer Interferometry: Current developments, algorithms and examples

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, ESAs upcoming Sentinel-1 mission allows a continuous, repeated without gap and global mapping of the Earths 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.

High precision measurement on the absolute localization accuracy of TerraSAR-X

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.

Ionospheric effects in SAR interferometry: An analysis and comparison of methods for their estimation

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-, L- and 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 P- through X-bands and methods for their estimation which are demonstrated on L-band ALOS-PALSAR acquisitions1.

Interferometric absolute phase determination with TerraSAR-X wideband SAR data

Wideband SAR systems such as TerraSAR-X bring the range resolution down to the order of the carrier wavelength. This opens the possibility to determine not only the fractional phase of SAR interferograms, but also the absolute phase value including the unknown number of integer phase cycles. This possibility enormously helps all interferometric applications such as DEM generation or land surface motion determination. Here we review the basic theory of such processing techniques and show a number of recent results from an ESA study aimed at developing an operational system. Furthermore we show how such techniques can be optimized by the use of customized ‘split-bandwidth’ chirp signals in place of the standard chirps used in contemporary SAR systems.

High resolution geodetic earth observation with TerraSAR-X: Correction schemes and validation

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.

Establishing a Remote Sensing Science Center in Cyprus:First Year of Activities of ATHENA Project

ATHENA H2020 Twinning project is a three-year duration project and its main objective is to strengthen the Cyprus University of Technology (CUT) Remote Sensing Science and Geo-Environment Research Laboratory in the field of “Remote Sensing Archaeology” by creating a unique link between two internationally-leading research institutions: National Research Council of Italy (CNR) and the German Aerospace Centre (DLR). Through the ATHENA project, CUT’s staff research profile and expertise will be raised while S&T capacity of the linked institutions will be enhanced. In this paper the abovementioned objectives are presented through the various activities accomplished in the first year of the project. These activities include both virtual training by experts in topics such as active remote sensing sensors and sophisticated algorithms, as well as scientific workshops dedicated to specific earth observation and cultural heritage aspects. During this first year, outreached activities have been also performed aiming to promote remote sensing and other non-destructive techniques, including geophysics, for monitoring and safeguarding archaeological heritage of Cyprus. The ATHENA center aims to serve the local community of Cyprus, but at the same time to be established in the wider area of eastern Mediterranean.

An advanced co-registration method for TOPSAR interferometry

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.