The Performance of Dual-Frequency Polarimetric Scatterometer in Sea Surface Wind Retrieval

Abstract

The wind retrieval performance of HY-2A scanning scatterometer operating at Ku-band in HH and VV polarizations has been well evaluated in the wind speed range of 0–25 ms−1. In order to obtain more accurate ocean wind field, a potential extension of dual-frequency (C-band and Ku-band) polarimetric measurements is investigated for both low and very high wind speeds, from 5 to 45ms−1. Based on the geophysical model functions of C-band and Ku-band, the simulation results show that the polarimetric measurements of Ku-band can improve the wind vector retrieval over the entire scatterometer swath, especially in nadir area, with the wind direction root-mean-square error (RMSE) less than 12° in the wind speed range of 5–25 m s−1. Furthermore, the results also show that C-band cross-polarization plays a very important role in improving the wind speed retrieval, with the wind speed retrieval accuracy better than 2 ms−1 for all wind conditions (0–45 ms−1). For extreme winds, the C-band HH backscatter coefficients modeled by CMOD5.N(H) and the ocean co-polarization ratio model at large incidence are used to retrieve sea surface wind vector. This result reveals that there is a big decrease of wind direction retrieval RMSE for extreme wind fields, and the retrieved result of C-band HH polarization is nearly the same as that of C-band VV polarization for low-to-high wind speed (5–25 ms−1). Thus, to improve the wind retrieval for all wind conditions, the dual-frequency polarimetric scatterometer with C-band and Ku-band horizontal polarization in inner beam, and C-band horizontal and Ku-band vertical polarization in outer beam, can be used to measure ocean winds. This study will contribute to the wind retrieval with merged satellites data and the future spaceborne scatterometer.