Quality Assessment of Surface Current Fields From TerraSAR-X and TanDEM-X Along-Track Interferometry and Doppler Centroid Analysis

• Published in: IEEE transactions on geoscience and remote sensing Vol. 52; no. 5; pp. 2759 - 2772
• Main Authors: Romeiser, Roland, Runge, Hartmut, Suchandt, Steffen, Kahle, Ralph, Rossi, Cristian, Bell, Paul S.
• Format: Journal Article
• Language: English
• Published: New York, NY IEEE 01.05.2014; Institute of Electrical and Electronics Engineers; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Accuracy; Applied geophysics; Centroids; Current measurement; Data integrity; Doppler; Doppler effect; Earth sciences; Earth, ocean, space; Exact sciences and technology; Interferometry; Internal geophysics; Noise levels; radar velocity measurement; remote sensing; Satellites; Spaceborne radar; Synthetic aperture radar; synthetic aperture radar (SAR); X-band; United Kingdom; Scotland; Great Britain; Europe; Western Europe; British Isles, Scotland, Highland, Caithness, Pentland Firth; British Isles, Scotland; remote sensing; radar velocity measurement; synthetic aperture radar (SAR); Interferometry; antenna; ocean currents; interferometry; Space remote sensing; satellite measurements; accuracy; baseline; velocity; tides; quality; noise; radar methods; Synthetic aperture radar
• ISSN: 0196-2892; 1558-0644
• DOI: 10.1109/TGRS.2013.2265659

All existing examples of current measurements by spaceborne synthetic aperture radar (SAR) along-track (AT) interferometry (ATI) have suffered from short baselines and corresponding low sensitivities. Theoretically, the best data quality at X-band is expected at effective baselines on the order of 30 m, i.e., 30 times as long as the baselines of the divided-antenna modes of TerraSAR-X. In early 2012, we had a first opportunity to obtain data at near-optimum baselines from the TanDEM-X satellite formation. In this paper, we analyze two TanDEM-X interferograms acquired over the Pentland Firth (Scotland) with effective AT baselines of 25 and 40 m. For comparison, we consider a TerraSAR-X dual-receive-antenna (DRA)-mode interferogram with an effective baseline of 1.15 m, as well as velocity fields obtained by Doppler centroid analysis (DCA) of single-antenna data from the same three scenes. We show that currents derived from the TanDEM-X interferograms have a residual noise level of 0.1 m/s at an effective resolution of about 33 m × 33 m, while DRA-mode data must be averaged over 1000 m × 1000 m to reach the same level of accuracy. A comparison with reference currents from a 1-km resolution numerical tide computation system shows good agreement in all three cases. The DCA-based currents are found to be less accurate than the ATI-based ones but close to short-baseline ATI results in quality. We conclude that DCA is a considerable alternative to divided-antenna mode ATI, while our TanDEM-X results demonstrate the true potential of the ATI technique at near-optimum baselines.