Science Service System

Summary of Proposal OCE0085

TitleExploitation of Doppler signatures for ocean current and wind retrievals
Investigator Romeiser, Roland - University of Miami, RSMAS-AMP
Team Members
Dr Romeiser, Roland - University of Miami, Division of Applied Marine Physics
Dr Gurgel, Klaus-Werner - University of Hamburg, Center for Marine and Climate Research, Institute of Oceanography
Dr Horstmann, Jochen - NATO Undersea Research Center (NURC), Applied Research Dept.
Dr Kerbaol, Vincent - CLS (former BOOST), Radar Applications Division
Dr Collard, Fabrice - CLS (former BOOST), Radar Applications Division
Dr. Thompson, Donald R. - Johns Hopkins University, Applied Physics Laboratory
Mouche, Alexis - CLS, Radar Applications Division

Objectives: Main objectives of the project are the demonstration and evaluation of ocean current and wind retrievals from TerraSAR-X data by Doppler residual analysis. As already demonstrated with data from ERS and ENVISAT, one can retrieve (at a reduced spatial resolution) Doppler centroid maps from complex SAR data in various ways. The Doppler centroids are composed of a large contribution of the relative line-of-sight velocity between satellite and rotating earth and a small contribution of additional line-of-sight velocities of moving targets. Since the platform velocity contribution can be calculated quite accurately from available orbit and attitude data, one can extract the Doppler residuals corresponding to target motions and use the SAR as a Doppler radar for ocean current measurements at resolutions on the order of a few km.

A successful demonstration of this technique will stimulate the use of TerraSAR-X for oceanic applications requiring absolute current measurements. The development and use of a low-resolution current data product on the basis of Doppler centroid analysis of conventional SAR data will also stimulate the interest in higher-resolution current data which will be obtained experimentally from the split antenna mode of TerraSAR-X (permitting along-track interferometry) at a later stage.

Method: To demonstrate and evaluate the Doppler residual analysis, the following activities will be performed:

  • Preparation: Existing Doppler residual assessment algorithms will be adapted to TerraSAR-X requirements. The acquisition of TerraSAR-X data and reference data will be planned and initiated. A wind retrieval algorithm for TerraSAR-X imagery will become available through another project.
  • Data acquisition: About 40 TerraSAR-X images and a few ENVISAT ASAR images for comparison will be acquired over two test areas in the German Bight (North Sea), using ascending and descending overpasses, different incidence angles, and covering a variety of tidal phases and wind conditions. Reference data will be acquired by HF radar (WERA), ship radar (WaMoS), acoustic Doppler current profiler (ADCP), and wind sensors, and current fields from numerical circulation models will be ordered from BSH and / or BAW.
  • Data processing: The algorithms for wind and Doppler residual retrievals will be applied, the Doppler residuals will be converted into horizontal velocities and corrected for wind- and wave-induced contributions, and Doppler-based wind retrieval improvements will be tested. Also the reference data will be processed.
  • Evaluation: TerraSAR-X and ASAR-derived currents and winds will be compared with each other and with the reference data, and the measuring accuracy and spatial resolution will be evaluated.
  • Dissemination: All findings will be documented in a comprehensive final report and in online presentations for experts and potential users. Furthermore, results will be presented at international conferences and in publications in peer-reviewed journals.

Data requirements: 40 TerraSAR-X images (stripmap mode, single-look complex), to be acquired over two test areas during Jan-Jun '07. Reference data will be acquired continuously on a routine basis; members of the project team have unlimited access to these data. ENVISAT ASAR data are obtained within other existing projects.

Deliverables: Comprehensive final report and online presentations for experts and potential users, describing the proposed algorithms for current and wind retrievals and all other important findings.

Funding: Most of the scientific work will be financed from internal resources of the participants. Additional funding (including travel, publications, and overhead costs) will be requested from DLR / BMBF.

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