Phase inconsistencies and water effects in SAR interferometric stacks

SAR Interferometry with stacks has already shown its potential in identifying permanent scatterers, in processing decorrelating targets, mitigating atmospheric delays, etc., but we believe that there is still potential for retrieving information on the scattering environment which has not been extensively studied yet. In particular interferometric stacks can reveal systematic phase inconsistencies which are not detectable in single interferograms, challenging any simple interpretation of the interferometric phase and associated coherence. The explanation of such inconsistencies requires more complex propagation models than the one based on a simple delay

MirrorSAR: An HRWS Add-On for Single-Pass Multi-Baseline SAR Interferometry

This paper reports the Phase A study results of the interferometric extension of the High-Resolution Wide-Swath (HRWS) mission with three MirrorSAR satellites. According to the MirrorSAR concept, small, low cost, transponder-like receive-only satellites without radar signal demodulation, digitization, memory storage, downlink, and synchronization are added to the planned German X-band HRWS mission. The MirrorSAR satellites fly a triple helix orbit in close formation around the HRWS orbit and span multiple single-pass interferometric baselines. A comprehensive system engineering and performance analysis is provided that includes orbit formation, MirrorLink, Doppler steering, antenna pattern and swath design, multi-static echo window timing, SAR performance, height performance and coverage analysis. The overall interferometric system design analysis of Phase A is presented. The predicted performance of the global Digital Elevation Model (DEM) is improved by one order of magnitude compared to presently available global DEM products like the TanDEM-X DEM

Lack of triangularity in SAR Interferometric phases

If three SAR images are available, it is possible to form three interferograms. In some cases the phases of the three averaged interferograms will not agree among each other and indicate a sort of phase excess or deficit (which we call "lack of triangularity"). In this paper we illustrate theoretically which models can explain such phenomenon and show some real-data examples. The observation of lack of triangularity might be useful to derive information on the target and also as a warning that the scatterer presents a temporal covariance matrix which is not intrinsically real

Phase inconsistencies and multiple scattering in SAR interferometry

With three coherent synthetic aperture radar images, it is possible to form three interferograms. In some cases, the phases of the three averaged interferograms will be significantly inconsistent and indicate a sort of phase excess or deficit (which we call lack of triangularity or inconsistency). In this paper, we illustrate theoretically which models can explain such phenomenon and provide some real-data examples. It is also shown that two or more independent scattering mechanisms are necessary to explain phase inconsistencies. The observation of lack of consistency might be useful to derive information on the target and as a warning that the scatterer presents a temporal covariance matrix which is not intrinsically real, with consequences for the processing of interferometric stacks

On the exploitation of polarimetric ratio for oil spill detection

Oil spills in sea water represent one of the most conspicuous forms of damage to the marine environment. They can be detected in SAR images by the exploitation of the normalized cross section (NRCS) and the co-polarization ratio (PR) and by the use of a combined detector. In this paper we describe the simulation of sea surface SAR data by means of the statistical compound model and we use these data for testing the proposed NRCS and PR-based oil spill detection approach. It shows good performance compared to detectors based on the single PR or NRCS information

Persistent Point Scatterers in multibaseline SAR interferometry

This paper addresses the problem of selecting Persistent Point Scatterers (PPS) in a stack of interferometric Synthetic Aperture Radar images suitable for accurate SAR parameters estimation. PPS are a subset of the well known Persistent Scatterers: besides the usual PS properties, they are characterized by an impulsive trend and a good degree of isolation from neighbor targets. Using their specific features, a simple and efficient algorithm for the PPS selection has been developed; a statistical model for PPS is also provided and experimentally validated. Results are illustrated using real X-band Cosmo SkyMed data

Statistical Analysis of Ambiguity to Signal Ratio Levels based on Global Backscattering Maps

Ambiguities are one of the limiting factors of SAR product quality and are thus important subject to every mission performance analysis. Since target NRCS is highly heterogeneous, the resulting ambiguities affect different areas at very different levels. Therefore using global average ambiguity levels for product performance assess-ment is of limited use. In this paper we present a statistical analysis of signal to ambiguity levels taking into account the spatial variability of the NRCS by exploiting global backscattering maps