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Comparison of Geophysical Model Functions for SAR Wind Speed Retrieval in Japanese Coastal Waters
National Institute of Advanced Industrial Science and Technology, 1-1-1 Umezono, Tsukuba, Ibaraki 305-8568, Japan
Graduate School of Maritime Science, Kobe University, 5-1-1 Fukaeminamimachi, Higashinadaku, Kobe, Hyogo 658-0022, Japan
Department of Wind Energy, Technical University of Denmark, Frederiksborgvej 399, 4000 Roskilde, Denmark
* Author to whom correspondence should be addressed.
Received: 13 February 2013; in revised form: 18 March 2013 / Accepted: 16 April 2013 / Published: 19 April 2013
Abstract: This work discusses the accuracies of geophysical model functions (GMFs) for retrieval of sea surface wind speed from satellite-borne Synthetic Aperture Radar (SAR) images in Japanese coastal waters characterized by short fetches and variable atmospheric stability conditions. In situ observations from two validation sites, Hiratsuka and Shirahama, are used for comparison of the retrieved sea surface wind speeds using CMOD (C-band model)4, CMOD_IFR2, CMOD5 and CMOD5.N. Of all the geophysical model functions (GMFs), the latest C-band GMF, CMOD5.N, has the smallest bias and root mean square error at both sites. All of the GMFs exhibit a negative bias in the retrieved wind speed. In order to understand the reason for this bias, all SAR-retrieved wind speeds are separated into two categories: onshore wind (blowing from sea to land) and offshore wind (blowing from land to sea). Only offshore winds were found to exhibit the large negative bias, and short fetches from the coastline may be a possible reason for this. Moreover, it is clarified that in both the unstable and stable conditions, CMOD5.N has atmospheric stability effectiveness, and can keep the same accuracy with CMOD5 in the neutral condition. In short, at the moment, CMOD5.N is thought to be the most promising GMF for the SAR wind speed retrieval with the atmospheric stability correction in Japanese coastal waters, although there is ample room for future improvement for the effect from short fetch.
Keywords: satellite-borne SAR; geophysical model function; sea surface wind speed retrieval
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MDPI and ACS Style
Takeyama, Y.; Ohsawa, T.; Kozai, K.; Hasager, C.B.; Badger, M. Comparison of Geophysical Model Functions for SAR Wind Speed Retrieval in Japanese Coastal Waters. Remote Sens. 2013, 5, 1956-1973.
Takeyama Y, Ohsawa T, Kozai K, Hasager CB, Badger M. Comparison of Geophysical Model Functions for SAR Wind Speed Retrieval in Japanese Coastal Waters. Remote Sensing. 2013; 5(4):1956-1973.
Takeyama, Yuko; Ohsawa, Teruo; Kozai, Katsutoshi; Hasager, Charlotte B.; Badger, Merete. 2013. "Comparison of Geophysical Model Functions for SAR Wind Speed Retrieval in Japanese Coastal Waters." Remote Sens. 5, no. 4: 1956-1973.