Ocean wind retrieval from polarimetric sar observations

摘要

Coastal wind are strongly influenced by topology, the discontinuity between the land and sea surface, wind assessment from remote sensing in such a complex area remains challenge. Space-borne scatterometer does not provide any information about the coastal wind field, as the coarse spatial resolution hampers the radar backscattering. Synthetic aperture radar (SAR) with a high spatial resolution and all-weather observation abilities has become one of the most important ways of ocean wind retrieval, especially in the coastal area. Conventional ways of wind field retrieval from SAR, however, are always need wind direction as initial information, such as the wind direction from numerical weather prediction models (NWP) which may not match the time of SAR image acquiring. Fortunately, the fully polarimetric observations of SAR make the independent wind retrieval from SAR images become reality. In this paper, a new method of using co-polarization backscattering coefficients from fully polarimetric SAR observations up to polarimetric correlation backscattering coefficients which are acquired from the conjugate product of co-polarization backscatter and cross-polarization backscatter is proposed to obtain the coastal wind field. Co-polarization backscattering coefficients and polarimetric correlation backscattering coefficients are obtained form Radarsat-2 single-look complex (SLC) data, the maximum likelihood estimation is used to gain the initial results followed by the coarse spatial filtering and fine spatial filtering. Wind direction accuracy of the final inversion results ±10.67° with a wind speed accuracy of ±0.32m/s. In comparison to the previous methods, this article based on the SAR data itself to obtain the wind vectors and did not need external wind directional information. High spatial resolution and high accuracy are the most important features of this article since the full use of fully polarimetric observations which contained more information about the objects. This article is a useful attempt to the work of independent SAR wind retrieval. The experimental results show that it is feasible to employ the co-polarimetric backscattering coefficients and the polarimetric correlation backscattering coefficients for coastal wind field retrieval.