Study on polarisation ratio for X-band using dual-polarisation Terra-SAR X image

In this study, we present the analysis of measurements of normalized radar cross section (NRCS) and the polarisation ratio (PR) in dual-polarisation TerraSAR-X (TS-X) images. Based on two PR functions proposed for C-band SAR (denoted as the Thompson model and Elfouhaily model respectively) and the relationship between NRCS and incidence angle for X-band (it is called X-PR), three PR models are tuned using 45 dual-polarisation TS-X images. The PR is found to be dependent of the incidence angle and VV-polarisation NRCS is larger than HH-polarisation NRCS when the incidence angle is larger than 23°. A total of 20 HH-polarisation TS-X images are analyzed for retrieving the wind field using three PR models and XMOD algorithm together. The results are compared to QuikSCAT data and buoy measurements for validation. The root-mean-square error (RMSE) of wind speed is 2.34m/s, 2.16m/s and 1.99m/s with a correlation of 0.82, 0.87 and 0.88 by using Thompson model, Elfouhaily model and X-PR model respectively for the cases.