Current measurements by SAR along-track interferometry from a Space Shuttle

• Published in: IEEE transactions on geoscience and remote sensing Vol. 43; no. 10; pp. 2315 - 2324
• Main Authors: Romeiser, R., Breit, H., Eineder, M., Runge, H., Flament, P., Karin de Jong, Vogelzang, J.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01-10-2005; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Antennas; Applied geophysics; Current measurement; Current measurements; Earth; Earth sciences; Earth, ocean, space; Exact sciences and technology; Information retrieval; interferometric synthetic aperture radar (InSAR); Internal geophysics; Numerical models; Ocean currents; Oceans; Radar antennas; Retrieval; Separation; Shuttle Radar Topography Mission (SRTM); Space shuttles; Surfaces; Synthetic aperture radar; Synthetic aperture radar interferometry; Time lag; X-band; Wadden Sea; Netherlands; Western Europe; ANE, Wadden Sea; ocean currents; models; Europe; interferometry; Space remote sensing; data processing; exhibits; velocity; space shuttle; Current measurements; interferometric synthetic aperture radar (InSAR); synthetic aperture radar; Shuttle Radar Topography Mission (SRTM); interpretation; separation; circulation; signal-to-noise ratio; prediction; correlation coefficient; errors; high resolution
• ISSN: 0196-2892; 1558-0644
• DOI: 10.1109/TGRS.2005.856116

We present one of the first studies on ocean current retrievals from interferometric synthetic aperture radar (InSAR) data acquired during the Shuttle Radar Topography Mission (SRTM) in February 2000. The InSAR system of SRTM was designed for high-resolution topographic mapping of the Earth's land surfaces, using two SAR antennas on a Space Shuttle with a cross-track separation of 60 m. An additional along-track antenna separation of 7 m resulted in an effective time lag of about 0.5 ms between the two images, which could theoretically be exploited for target velocity retrievals. However, the feasibility of ocean current measurements with SRTM has been questionable, since the time lag was much shorter than the theoretical optimum (about 3 ms at X-band) and the signal-to-noise ratio over water was quite low. Nevertheless, some X-band InSAR images of coastal areas exhibit clear signatures of tidal flow patterns. As an example, we discuss an image of the Dutch Wadden Sea. We convert the InSAR data into a line-of-sight current field, which is then compared with results of the numerical circulation model KUSTWAD. For tidal phases close to the conditions at the time of the SRTM overpass; we obtain correlation coefficients of up to 0.6 and rms differences on the order of 0.2 m/s. Furthermore we find that SRTM resolves current variations down to spatial scales on the order of 1 km. This is consistent with predictions of a numerical InSAR imaging model. Remaining differences between SRTM- and KUSTWAD-derived currents can be attributed mainly to residual motion errors in the SRTM data as well as to a limited representation of the conditions at the time of the SRTM overpass in the available KUSTWAD results.