Estimation of Azimuth Phase Undulations with Multisquint Processing in Airborne Interferometric SAR Images

This letter presents a technique to detect and correct phase errors appearing in interferometric airborne synthetic aperture radar (SAR) systems due to the lack of precision in the navigation system. The technique is based on a multisquint processing approach, i.e., by processing the same image pairs with different squint angles we can combine the information of different interferograms to obtain the desired phase correction. Airborne single-pass interferometric data from the Deutsches Zentrum für Luft- und Raumfahrt (DLR) Experimental airborne SAR is used to validate the metho

Topography dependent motion compensation for repeat-pass interferometric SAR systems

This letter presents a new motion compensation algorithm to process airborne interferometric repeat-pass synthetic aperture radar (SAR) data. It accommodates topography variations during SAR data processing, using an external digital elevation model. The proposed approach avoids phase artifacts, azimuth coregistration errors, and impulse response degradation, which usually appear due to the assumption of a constant reference height during motion compensation. It accurately modifies phase history of all targets before azimuth compression, resulting in an enhanced image quality. Airborne L-band repeat-pass interferometric data of the German Aerospace Center experimental airborne SAR (E-SAR) is used to validate the algorithm.Peer Reviewe

Refined estimation of time-varying baseline errors in airborne SAR interferometry

The processing of airborne synthetic aperture radar (SAR) data requires a precise compensation of the deviations of the platform movement from a straight line. This is usually carried out by recording the trajectory with a high-precision navigation system and correcting them during SAR focusing. However, due to the lack of accuracy in current navigation systems, residual motion errors persist in the images. Such residual motion errors are mainly noticeable in repeat-pass systems, where they are causing time-varying baseline errors, visible as artefacts in the derived phase maps. In this letter, a refined method for the estimation of time-varying baseline errors is presented. An improved multisquint processing approach is used for obtaining robust estimates of higher order baseline errors over the entire scene, even if parts of the scene are heavily decorrelated. In a subsequent step, the proposed method incorporates an external digital elevation model for detection of linear and constant components of the baseline error along azimuth. Calibration targets in the scene are not necessary.Peer Reviewe

Interpolation-free Coregistration and Phase-Correction of Airborne SAR Interferograms

This letter discusses the detection and correction of residual motion errors that appear in airborne synthetic aperture radar (SAR) interferograms due to the lack of precision in the navigation system. As it is shown, the effect of this lack of precision is twofold: azimuth registration errors and phase azimuth undulations. Up to now, the correction of the former was carried out by estimating the registration error and interpolating, while the latter was based on the estimation of the phase azimuth undulations to compensate the phase of the computed interferogram. In this letter, a new correction method is proposed, which avoids the interpolation step and corrects at the same time the azimuth phase undulations. Additionally, the spectral diversity technique, used to estimate registration errors, is critically analyzed. Airborne L-band repeat-pass interferometric data of the German Aerospace Center (DLR) experimental airborne SAR is used to validate the metho

Secondary Fault Activity of the North Anatolian Fault near Avcilar, Southwest of Istanbul: Evidence from SAR Interferometry Observations

Strike-slip faults may be traced along thousands of kilometers, e.g., the San Andreas Fault (USA) or the North Anatolian Fault (Turkey). A closer look at such continental-scale strike faults reveals localized complexities in fault geometry, associated with fault segmentation, secondary faults and a change of related hazards. The North Anatolian Fault displays such complexities nearby the mega city Istanbul, which is a place where earthquake risks are high, but secondary processes are not well understood. In this paper, long-term persistent scatterer interferometry (PSI) analysis of synthetic aperture radar (SAR) data time series was used to precisely identify the surface deformation pattern associated with the faulting complexity at the prominent bend of the North Anatolian Fault near Istanbul city. We elaborate the relevance of local faulting activity and estimate the fault status (slip rate and locking depth) for the first time using satellite SAR interferometry (InSAR) technology. The studied NW-SE-oriented fault on land is subject to strike-slip movement at a mean slip rate of ~5.0 mm/year and a shallow locking depth of <1.0 km and thought to be directly interacting with the main fault branch, with important implications for tectonic coupling. Our results provide the first geodetic evidence on the segmentation of a major crustal fault with a structural complexity and associated multi-hazards near the inhabited regions of Istanbul, with similarities also to other major strike-slip faults that display changes in fault traces and mechanisms

Harmony: Die ESA Earth Explorer Mission zur Dynamik von Ozeanen, Eis- und Landflächen

Im Fokus der Erdbeobachtungsmission Harmony steht die Beobachtung und Auswertung von kleinsten Bewegungen der Erdoberfläche, sei es an der Luft-Meer-Grenzfläche, wie Wind, Wellen, Oberflächenströmungen, auf der festen Erde wie bei tektonischen Deformationen und Höhenänderungen an Vulkanen, oder in der Kryosphäre, in Form von Gletscherströmen und Höhenänderungen. Die Harmony-Mission wird zwei Satelliten einsetzen, die einem der Copernicus Sentinel-1-Satelliten folgen. Sie fliegen in zwei verschiedenen Formationen. Bei der Stereo-Formation wird ein Harmony-Satellit jeweils im Abstand von 350 km vor und hinter dem Sentinel-1-Satelliten platziert. In der engen Flugformation werden beide Harmony-Satelliten relativ nahe zueinander – etwa 200-500 Meter – und im Abstand von 350 Kilometern zum Sentinel-1 fliegen. Jeder Harmony-Satellit trägt als Hauptnutzlast ein passives Radar mit synthetischer Apertur (SAR). Dieses erfasst die von Sentinel-1 zur Erde gesendeten reflektierten Signale. Eine thermische Infrarotkamera mit mehreren Blickrichtungen ist ebenfalls an Bord, damit werden die Wolkenhöhe und die Bewegungsvektoren der Wolken gemessen. Durch das Zusammenspiel der drei Satelliten gewinnt man eine Deformationsmessung der Erdoberfläche in drei Dimensionen sowie eine Geschwindigkeitsmessung der Meeresströmungen mit bisher unerreichter Genauigkeit

Suppression of Additional Azimuth Ambiguities under Multi-Channel and Multi-Waveform SAR

Future spaceborne SAR satellites are going to handle multiple receivers to take both high resolution and wide observation swath. In addition, they will transmit multiple chirp patterns to reduce the effect of the range ambiguity. Such a multi-channel and multi-waveform system raises additional azimuth ambiguities caused by the phase distortion of the received pulse. The phase distortion is a nonlinear effect and, the number of the channels and waveforms directly affect the processing results as if the pulse repetition frequency (PRF) is lower than it should be. In order to solve this problem, we propose to detect the aliased signal analytically in the Doppler frequency domain. Simulation results showed the suppression of the peak for 5 to 17 dB

Accurate Azimuth Ground Deformation Estimation From Sentinel-1 Time Series

This letter proposes the exploitation of the overlapping areas between bursts of Sentinel-1 interferometric wide (IW) swath data for the estimation of ground azimuth deformation velocities from time series, which provides high sensitivity to the North–South direction. The availability of two separated Doppler spectral looks over these areas allows one to obtain high accurate estimates, overcoming the limited performance of classical correlation techniques with coarse resolution modes. Since the estimation is restricted to the (sparsely distributed) burst overlaps, its applicability is limited to geophysical phenomena characterized by a slow spatial variability, e.g., seismic scenarios. We demonstrate the suitability of this approach to time series over a region in Pakistan affected by post-seismic deformation. The estimated mean azimuth velocity performance from real data indicates an accuracy better than 7 mm/year over high long-term coherent areas for a three-year data stack