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Summary of Proposal MTH0093

TitleOcean wave and wind vector measured by TerraSAR-X data
Investigator He, Yijun - Institute of Oceanology, Chinese Academy of Sciences, Lab of Ocean circulation and wave studies
Team Members
Mr. Zhang, Biao - Institute of Oceanology, Chinese Academy of Sciences, Lab of Ocean circulation and wave studies
Dr. Lehner, Susanne - German Aerospace Center, MF-GW
Dr. Liu, Yudi - Institute of Oceanology, Chinese Academy of Sciences, Lab of Ocean circulation and wave studies
SummaryAn interesting application of TerraSAR-X is the measurement of high resolution ocean wave field in particular in coastal areas. These measurements are especially important for applications dealing with harbor protection, offshore wind parks, oil drift forecast, as well as wave farming. Apart from the high spatial resolution the relatively low flight altitude of the TerraSAR-X satellite is beneficial for ocean wave measurements, especially because the impact of nonlinear effects will be weaker than known from ERS or ENVISAT. This will make the retrieval of ocean wave information like two-dimensional ocean wave spectrum or the two-dimensional sea surface elevation filed easier. Furthermore, it is known that the availability of polarimetric information will improve the ocean wave measurements, as it gives independent estimation of ocean to SAR transfer function. It is also expected that a statistical analysis of polarimetric TerraSAR-X data will give some new insight into the SAR ocean wave imaging process. For example, the relative role of different scattering. The another application of TerraSAR-X is the measurement of high resolution wind vector. There are three main approaches for extracting winds from SAR images. The first approach estimates wind speed from the degree of azimuth cut-off in the SAR spectrum according to the relationship among wind speed, cut-off wave-length, and wave height. The second approach uses an optimal inversion method to estimate vector winds, combining the SAR data and background numerical weather prediction model data. The third approach is based on an empirical relationship, also denoted the geophysical model function (GMF), between wind vectors and the NRCS (normalized radar cross section) or Sigma zero image, for example CMOD-4. For HH polarization the geophysical model function CMOD is modified by a polarization ratio conversion factor, with this modification, wind vectors are extracted by the same method as used for VV polarization. The main objective is to improve and develop ocean wave and wind vector imaging model of dual-polarization synthetic aperture radar and retrieve and validate ocean wave spectrum and wind vector using high resolution TerraSAR-X data.The innovations are as follows, (1) To develop a theoretic model to measure ocean physical parameter using dual-polarization X band SAR (2) To develop some new methods to remove the ocean wave direction ambiguity. For example, use method of high order spectrum or look cross spectrum to remove direction ambiguity. (3) To implement the retrieved wind vector from dual-polarization X band SAR data. The work plan of the project contains three blocks. The first block treat theoretic problems of ocean wave and wind vector measurement. The second and third blocks are devoted to developing and validating the ocean wave and wind vector retrieval method work, respectively. In the first block a nonlinear mapping between dual-polarization SAR image spectrum and ocean wave spectrum will be derived and A X band Geophysical model function will be obtained using simulation data and C band model function. The second block aims to improve the wind vector retrieval algorithm. New algorithms for the estimation of wind vector will be developed for space born dual-polarization Synthetic aperture radar. The third block of the project is retrieving ocean wave spectrum using the nonlinear mapping. The ocean wave elevation and spectra will be obtained from the Terra SAR dual-polarization data. A validation to ocean wave and wind vector will be implemented using in situ data or model. In order to complete these plans we need the high-resolution dual-polarization data. Expected results: retrieval algorithms for wind vector, ocean wave from Terra SAR data .

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DLR 2004-2016