Study On Retrieval Algorithms Of Sea Surface Wind Fields And Sea Surface Current Fields From TerraSAR-X Images

Satellite TerraSAR-X launched on June 15, 2007 by Germany is the first operational Satellite, which is quipped with X-Band synthetic aperture radar (SAR) with the following characteristics: multi polarizations, high spatial resolution and along-track interferometric operation mode. So far only the high quality multi operation mode of TerraSAR-X images over earth can be offered but no the retrieved marine environmental parameters such as sea surface wind fields and sea surface current fields. The aim of this thesis is to develop the retrieval algorithms of high resolution satellite sea surface wind fields (SSW) and sea surface current fields (SSC) using the unique properties of TerraSAR-X.So far, the well-rounded retrieval algorithms of SSW from microwave scatterometer and SAR are mainly based on C-, Ku-, and L-band. Generally, the empirical relationship between the normalized radar cross sections (NRCS) and wind vectors is established as the geophysical model function (GMF) to retrieve SSW from SAR images. Masuko proposed an X-band SAR GMF based on airborne experiment. In this thesis, the Masuko model is validated with SIR-C/SAR(X) NRCS and ECMWF ERA-40 data and find that there is an obvious system error. Therefore, a linear X-band VV polarization GMF (XMOD) is developed to describe the relationship between NRCS, 10m height wind speed, wind direction and incidence angle. The global ocean SAR data from SIR-C/SAR(X) missions on April and October 1994 and wind fields From ECMWF ERA-40 are used to tune the linear parameters of XMOD. The correlation and RMS between the simulated NRCS by XMOD and SIR-C/SAR(X) NRCS are 0.91 and 2.68dB respectively. Then the SSW is retrieved from different operation mode of VV polarization TerraSAR-X images. The direct comparison of XMOD results to QuickScat shows that the correlation and the RMS between them are 0.97 and 0.92 m/s respectively. The mean wind speed from TerraSAR-X is 1.10m/s bigger than the results of High Resolution Limited Area Model (HIRLAM). The wind direction used here is extracted from wind streak or model results. XMOD mentioned above can only be applied with VV polarization SAR images, to be use the HH polarization SAR data, a polarization ratio model is needed. On the base study of Thompson and Mouche, two polarization ratio models PR1 and PR2 are developed and used to retrieve SSW. The errors of the retrieved results are 0.56m/s and 0.09m/s respectively, i.e. PR2 model is better than PR1 model. SSW is also retrieved from TerraSAR-X images using PR2 model and the correlation and the RMS against the QuickScat results are 0.96 and 0.86 m/s respectively.The ATI mode of TerraSAR-X enables SSC measurements. Because the ATI data of TerraSAR-X are not disclosed yet, so the X-band airborne ATI data and SRTM data are used to study the retrieval algorithms of SSC with the method proposed by Romeiser in 2002. The airborne ATI data are processed with the following steps: the correction of ATI phase, conversion of ATI phase into first guess current fields, composition of two dimensional SSC, and then correction for contributions of wave motion with the software of SAR imaging model M4S developed by Romeiser in 2000. Then the retrieved SSC is compared to the results of Acoustic Doppler Current Profiler (ADCP) in situ and German Federal Waterways Engineering and Research Institute (BAW), the errors are 0.16 m/s and 0.04 m/s respectively, which are consistent with Romeiser's results. Because there is 7m separation along-track of the cross-track antennas of SRTM, so Romeiser proposed that the SRTM data can be used to study on SSC retrieval. In this thesis, the SRTM data acquired over Lille Baelt in Denmark in 2002 are processed with the following steps: phase correction, phase correction of the effect of flat earth, the non-zero interferometric phase correction and then the corrected phase is converted to SSC. However, the retrieved SSC is needed to be validated.