Along-track interferometric synthetic aperture radar (along-track InSAR) is a new technology for imaging surface current fields from airborne or spaceborne platforms with accuracies of 0.1 m/s or better, spatial resolutions on the order of 10 to 1000 m, and swath widths of up to more than 100 km, depending on platform and instrument parameters. This is particularly attractive for the mapping and monitoring of current fields in coastal areas. The SRTM experiment on a Space Shuttle in early 2000 offered a first chance to demonstrate current measurements by InSAR from space. Although the SRTM configuration was not well suited for current measurements and the coverage of the ocean was very limited, some images of coastal scenes exhibit clear signatures of typical surface current patterns, which have been found to be in good agreement with theoretical predictions and to resolve current variations on spatial scales of about 1 km. The German satellite TerraSAR-X, which will be launched in 2005, will offer similar current measuring capabilities. Concepts for more specific, further optimized InSAR missions for oceanic applications are currently under investigation. We give an overview of these developments.
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