Comparison of C-Band Quad-Polarization Synthetic Aperture Radar Wind Retrieval Models

Abstract

This work discusses the accuracy of C-2PO (C-band cross-polarized ocean backscatter) and CMOD4 (C-band model) geophysical model functions (GMF) for sea surface wind speed retrieval from satellite-born Synthetic Aperture Radar (SAR) images over in the Northwest Pacific off the coast of China. In situ observations are used for comparison of the retrieved wind speed using two established wind retrieval models: C-2PO model and CMOD4 GMF. Using 439 samples from 92 RADARSAT-2 fine quad-polarization SAR images and corresponding reference winds, we created two subset wind speed databases: the training and testing subsets. From the training data subset, we retrieve ocean surface wind speeds (OSWSs) from different models at each polarization and compare with reference wind speeds. The RMSEs of SAR-retrieved wind speeds are: 2.5 m/s: 2.11 m/s (VH-polarized), 2.13 m/s (HV-polarized), 1.86 m/s (VV-polarized) and 2.26 m/s (HH-polarized) and the correlation coefficients are 0.86 (VH-polarized), 0.85(HV-polarized), 0.87(VV-polarized) and 0.83 (HH-polarized), which are statistically significant at the 99.9% significance level. Moreover, we found that OSWSs retrieved using C-2PO model at VH-polarized are most suitable for moderate-to-high winds while CMOD4 GMF at VV-polarized tend to be best for low-to-moderate winds. A hybrid wind retrieval model is put forward composed of the two models, C-2PO and CMOD4 and sets of SAR test data are used in order to establish an appropriate wind speed threshold, to differentiate the wind speed range appropriate for one model from that of the other. The results show that the OSWSs retrieved using our hybrid method has RMSE of 1.66 m/s and the correlation coefficient are 0.9, thereby significantly outperforming both the C-2PO and CMOD4 models.

Green Energy Sources Assessment Using Sentinel-1 Satellite Remote Sensing

“…However, the high-spatial-resolution data obtained from the SAR satellite have good accuracy and results in offshore wind analysis (Yang et al, 2011). In recent years, various Geophysical Model Functions (GMFs), particularly the socalled C models (CMOD), tailored to assess wind parameters from SAR satellites have been successfully designed and developed, such as CMOD4 (Fang et al, 2018), CMOD-IFR2 (Jagdish et al, 2018), CMOD5 (Hersbach et al, 2005), CMOD5.n (Soisuvarn et al, 2013, CMOD7 (Stoffelen et al, 2017), and recently a new CMOD model was designed from RADARSAT-2 and S-1 satellite, the so-called C-SARMOD1, and C-SARMOD2 model (Radkani and Zakeri, 2020) for coastal wind speed retrievals (Lu et al, 2018). It should be noted that different types of C-band GMF models have the ability to measure wind speed using data obtained from the different S-1 satellites polarization with a 180 °ambiguous of the wind direction (Diaz et al, 2013).…”

Sea Surface Roughness Observed by High Resolution Radar

“…A hybrid wind retrieval model is proposed by using two models: C-2PO (C-band cross-polarized ocean backscatter) and CMOD4 (C-band model) [7]. Sets of SAR images over the Northwest Pacific off the coast of China are used to establish a wind speed threshold (9.4 m/s).…”

Extensive High-Resolution Synthetic Aperture Radar (SAR) Data Analysis of Tropical Cyclones: Comparisons with SFMR Flights and Best Track

“…In this context, numerous studies already demonstrated the potential to use satellite synthetic aperture radar (SAR) measurements to provide TC surface wind field at very high resolution (Katsaros et al 2000;Li et al 2013). This unique mapping capability, further supported by highly sensitive cross-polarization measurements to increasing winds, has often been highlighted with respect to SFMR (Zhang and Perrie 2012;Horstmann et al 2015;Mouche et al 2019), buoys (Vachon and Wolfe 2011;Zhang et al 2012), L-band passive remote sensing measurements (Mouche et al 2017;Zhao et al 2018), and global models (Fang et al 2018). Still, most of these TC studies were not based on a large number of cases, especially those cases reaching winds higher than 40 m s 21 .…”