ScanSAR InSAR Processing of ASAR Wide Swath SLC (WSS) Products

David Small(1) , Erich Meier(1) , Sigurjon Jonsson(2) , and Daniel NĂ¼esch(1)

(1) University of Zurich, Winterthurerstrasse 190, CH-8057 Zurich, Switzerland
(2) Swiss Federal Institute of Technology, Schafmattstrasse 30, CH-8093 , Switzerland

Abstract

The relatively new single look complex level one product from ASAR's wide swath mode, known as wide swath SLC (or WSS) presents new possibilities for SAR interferometry due to the mode's wider swath coverage, but also challenges in adapting InSAR processors to deal with changes to long-held assumptions concerning what constitutes an SLC product. Backscatter measurements are organised by each burst of ASAR's WS ScanSAR mode, rather than as a simple function of monotonically increasing zero Doppler azimuth time, as in conventional (e.g. ERS SLC) products.

We first validate the WSS product's geometry, using sample products generated from WS acquisitions of the ASAR transponders in the Netherlands to estimate the accuracy of the WSS product timing annotations. We compare the transponder's location retrieved via prediction (using the product timing annotations and precise DORIS orbits) to measurements made from the image content.

Modifications necessary to a conventional InSAR processing chain to enable WSS-based processing are described. These include subswath separation as well as adapting co-registration methods based on image-to-image correlation to be organised on a burst-by-burst basis, and implementing a new co-registration model determined by Zero-Doppler azimuth time rather than range line azimuth index.

The interferogram generation process itself must make the same adaptations, then following generation of initial interferograms that are still organised by burst, a "debursting" step must be added to produce an interferogram in a more conventional image geometry with monotonically increasing azimuth time. In WSS products, the sampling interval in the azimuth direction is coarser than in range. For ERS SLC or ASAR IMS/APS products, the opposite is true. This difference implies that in order to create relatively "square" image samples on the ground from WSS products, multilooking must be performed in the range direction. In conventional image mode SLC products it is the opposing azimuth dimension that must be subjected to multilooking. In cross-track interferometry by necessity a phase-flattening step must be applied before range multilooking, to avoid loss of coherence. Synthetic interferograms based on either ellipsoid or DEM models are subtracted from the raw interferogram before debursting, and "square pixel" multilooking steps are applied.

Finally, after interferograms for each subswath have been generated in geometries with conventional monotonically increasing azimuth time, the results may be merged into a full swath interferogram showing the full extent of the data coverage.

We demonstrate application of WSS-based interferogram generation using sample products covering the area of Bam (Iran). Differential interferograms are generated, providing a further estimate of displacement caused by the earthquake of Dec. 26, 2003. We showcase new parameter extraction methodologies made possible with the new product.

 

Workshop presentation

 

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