Abstract
Gaofen-3 (GF-3), the first Chinese civil C-band synthetic aperture radar (SAR), was successfully launched by the China Academy of Space Technology on 10 August 2016. Among its 12 imaging modes, wave mode is designed to monitor the ocean surface waves over the open ocean. An empirical retrieval algorithm of significant wave height (SWH), termed Quad-Polarized C-band WAVE algorithm for GF-3 wave mode (QPCWAVE_GF3), is developed for quad-polarized SAR measurements from GF-3 in wave mode. QPCWAVE_GF3 model is built using six SAR image and spectrum related parameters. Based on a total of 2576 WaveWatch III (WW3) and GF-3 wave mode match-ups, 12 empirical coefficients of the model are determined for 6 incidence angle modes. The validation of the QPCWAVE_GF3 model is performed through comparisons against independent WW3 modelling hindcasts, and observations from altimeters and buoys from January to October in 2017. The assessment shows a good agreement with root mean square error from 0.5 m to 0.6 m, and scatter index around 20%. In particular, applications of the QPCWAVE_GF3 model in SWH estimation for two storm cases from GF-3 data in wave mode and Quad-Polarization Strip I mode are presented respectively. Results indicate that the proposed algorithm is suitable for SWH estimation from GF-3 wave mode and is promising for other similar data.
Highlights
Ocean surface wave measurements are valuable for various areas
These include the C-band WAVE algorithm for ERS-2 wave mode (CWAVE_ERS) [19], C-band WAVE algorithm for Envisat wave mode (CWAVE_ENV) [20] and X-band WAVE algorithm (XWAVE) [21,22] developed by German Aerospace Center (DLR), C-band WAVE algorithm for Sentinel-1A wave mode (CWAVE_S1A) and CWAVE_Fnn [23] proposed by Institut Français de Recherche pour l’Exploitation de la Mer (IFREMER), and other empirical Significant wave height (SWH) retrieval attempts for synthetic aperture radar (SAR) data provided by Envisat ASAR (Advanced Synthetic Aperture Radar) [24], Sentinel-1A [25,26], Radarsat-2 [27,28], and TerraSAR-X [29]
The normalized variance which is used for the imagette inhomogeneity rejection is found to contain the longer wave information caused by the swell modulation [19,20,23]
Summary
Ocean surface wave measurements are valuable for various areas. Significant wave height (SWH) is one of the most important parameters for ocean wave observations. Similar to the Geophysical Model Functions (GMFs) used for SAR ocean wind measurements i.e., [16,17,18], the SAR SWH empirical models could estimate SWH directly from inputs computed from SAR images and/or SAR spectra These include the C-band WAVE algorithm for ERS-2 wave mode (CWAVE_ERS) [19], C-band WAVE algorithm for Envisat wave mode (CWAVE_ENV) [20] and X-band WAVE algorithm (XWAVE) [21,22] developed by German Aerospace Center (DLR), C-band WAVE algorithm for Sentinel-1A wave mode (CWAVE_S1A) and CWAVE_Fnn [23] proposed by Institut Français de Recherche pour l’Exploitation de la Mer (IFREMER), and other empirical SWH retrieval attempts for SAR data provided by Envisat ASAR (Advanced Synthetic Aperture Radar) [24], Sentinel-1A [25,26], Radarsat-2 [27,28], and TerraSAR-X [29].
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