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First TOPSAR interferometry results with TerraSAR-X

Adriano Meta(1), Pau Prats(1), Ulrich Steinbrecher(1), Josef Mittermayer(1) and Rolf Scheiber(1)

(1) DLR, Oberpfaffenhofen, 82234 Wessling, Germany

Abstract

TerraSAR-X is a versatile SAR satellite which is able to perform SAR acquisitions in different modes: stripmap, sliding spotlight, ScanSAR and the new proposed TOPSAR. TOPSAR is an alternative acquisition mode to ScanSAR. It is based on the fast steering of the azimuth antenna pattern in an opposite fashion as in spotlight. The main characteristic of TOPSAR data is the removed presence of scalloping effects and of the azimuth dependency of the signal to noise ratio. Sentinel-1, the European Space Agency SAR satellite to be launched in the coming future, has a main operation mode, the wide swath interferometry. It is foreseen to use TOPSAR for this main mode. TerraSAR-X is demonstrating the TOPSAR mode on space under an ESA contract.

First TerraSAR-X TOPSAR images have been successfully acquired and processed at DLR. Results are very impressive. As predicted from theory, scalloping effects are removed in TOPSAR images when compared with respect to ScanSAR images acquired over the same areas and with the same system and geometric configuration. Next step is the generation of TOPSAR interferometric results.

Differently from ScanSAR, TOPSAR interferometry poses greater constraints on the required coregistration and unwrapping steps. The reason is the Doppler centroid variation during the burst acquisition due to the azimuth steering of the antenna pattern. Typical Doppler variations within one burst of a TerraSAR-X acquisition are around 8000 Hz. When producing interferometric data with such a big variation of the Doppler centroid, small misregistration errors will cause the presence of unwanted phase differences in the interferograms. This effect is less problematic in ScanSAR data, because data are usually acquired with an azimuth broadside configuration. Coregistration requirements will be discussed in the final version of the paper.

Pairs of data takes over a high coherent area (a salt lake in Bolivia which has already shown good phase stability with 11 days repeat pass TerraSAR-X acquisitions) are currently being acquired by TerraSAR-X with the TOPSAR acquisition mode. First TerraSAR-X TOPSAR interferometry results will be presented in the final version of the paper.

Suggestions for Sentinel-1 TOPSAR interferometry will be given.

The work in this paper is being partially founded by ESA contract C20679/07/NL/BC.

 

Workshop presentation

Keywords: ESA European Space Agency - Agence spatiale europeenne, observation de la terre, earth observation, satellite remote sensing, teledetection, geophysique, altimetrie, radar, chimique atmospherique, geophysics, altimetry, radar, atmospheric chemistry