Assessments of Ocean Wind Retrieval Schemes Used for Chinese Gaofen-3 Synthetic Aperture Radar Co-Polarized Data
Date of Issue:2022-04-12
Reading:1733
This paper assesses different retrieval schemes used for the Chinese Gaofen-3 Synthetic Aperture Radar (GF-3 SAR) co-polarized data. The data consist of 4186 GF-3 data points and collocated wind information from sources including the ASCAT scatterometer, HY2A-SCAT scatterometer, and National Data Buoy Center (NDBC) buoy wind data set. The VV-polarized geophysical model function (GMF) is a CMOD7 model while the HH-polarized GMF is a hybrid of the CMOD7 and PR model. Assessments involve comparisons between SAR-derived and collocated winds in terms of the root-mean-square difference (RMSD) and bias. First, a comparison between the two retrieval schemes for the VV-polarized data clearly shows that the optimal scheme performs better than the classical scheme for wind speed retrieval. Comparisons for HH-polarized data show similar results. These experiments indicate that the wind speed RMSDs for the GF-3 co-polarized data are within 2 m/s when using the optimal scheme. Moreover, the wind direction RMSDs from the two schemes have no significant difference, with values near 20 ◦ . Overall, these assessments indicate that the GF-3 co-polarized data are sufficient for operational wind speed retrieval using the optimal scheme. However, wind direction retrieval requires further improvement.
Figure 1. Retrieved wind vectors and several wind speed differences. (a) Wind vectors retrieved from the VV-polarized data using the classical scheme, (b) wind speed differences between the HH- and VV-polarized data using the classical scheme, (c) wind speed differences between the optimal and classical scheme for the VV-polarized data, and (d) wind speed differences between the HH- and VV-polarized data using the optimal scheme. Red dot represents the location of the collocated NDBC buoy 46069. Both the background color and the arrow length represent the wind speed magnitude and arrow direction represents the wind direction.
Figure 2. Scatterplots of winds retrieved from the GF-3 VV-polarized data using the optimal scheme and CMOD7 against the collocated (a) ASCAT scatterometer wind speed, (b) ASCAT scatterometer wind direction, (c) HY2A-SCAT scatterometer wind speed, (d) HY2A-SCAT scatterometer wind direction, (e) NDBC buoy wind speed, and (f) NDBC buoy wind direction.
