Wind Speed Retrieval From Hybrid-Pol Compact Polarization Synthetic Aperture Radar Images

This paper presents an attempt to retrieve wind speed from hybrid-pol compact polarization (CP) synthetic aperture radar (SAR) data. Cross-polarization (cross-pol, denoted by HV or VH) facilitates wind speed retrieval and improves the accuracy of the results, especially with respect to high wind speeds. Although the cross-pol data cannot be obtained from CP SAR data directly, these data can be reconstructed from CP SAR data. However, the existing reconstruction algorithms cannot satisfy the quantitative wind-speed retrieval requirements for specifying the critical parameter, denoted “N” in reconstruction algorithms, either as a constant, or as a variable with limited range. Here, N is defined in terms of the ratio between cross- and co-polarization channels and the coherence coefficient between co-polarization (denoted by HH and VV) channels. Thus, we have improved the empirical reconstruction algorithm for the modified N based on a data set of more than 2000 RADASAT-2 (RS-2) quad-polarization images and collocated buoy observations. The algorithm improves the accuracy for the reconstruction of cross-pol data and, ultimately, gives improved wind speed retrievals from the hybrid-pol CP SAR data. With the new algorithm, results show that the wind speed retrievals from reconstructed cross-pol data can approximate the accuracy of VH observations collected by RS-2.