A newly developed ocean significant wave height retrieval method from Envisat ASAR wave mode imagery
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A newly developed ocean significant wave height retrieval method from Envisat ASAR wave mode imagery Chenqing Fan1, Xiaochen Wang2, 3*, Xudong Zhang1, 4, Dong Gao1 1 First Institute of Oceanography, Ministry of Natural Resources, Qingdao 266061, China 2 Aerospace Information Research Institute, Chinese Academy of Sciences, Beijing 100190, China 3 Laboratory of Target Microwave Properties, Deqing Academy of Satellite Applications, Deqing 313200, China 4 College of information and engineering, Ocean University of China, Qingdao 266071, China
Received 19 January 2018; accepted 1 May 2018 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2019
Abstract
The main objective of this paper is to propose a newly developed ocean Significant Wave Height (SWH) retrieval method from Envisat Advanced Synthetic Aperture Radar (ASAR) imagery. A series of wave mode imagery from January, April and May of 2011 are collocated with ERA-Interim reanalysis SWH data. Based on the matched datasets, a simplified empirical relationship between 22 types of SAR imagery parameters and SWH products is developed with the Genetic Algorithms Partial Least-Squares (GA-PLS) model. Two major features of the backscattering coefficient σ0 and the frequency parameter S10 are chosen as the optimal training feature subset of SWH retrieval by using cross validation. In addition, we also present a comparison of the retrieval results of the simplified empirical relationship with the collocated ERA-Interim data. The results show that the assessment index of the correlation coefficient, the bias, the root-mean-square error of cross validation (RMSECV) and the scattering index (SI) are 0.78, 0.07 m, 0.76 m and 0.5, respectively. In addition, the comparison of the retrieved SWH data between our simplifying model and the Jason-2 radar altimeter data is proposed in our study. Moreover, we also make a comparison of the retrieval of SWH data between our developed model and the wellknown CWAVE_ENV model. The results show that satisfying retrieval results are acquired in the low-moderate sea state, but major bias appears in the high sea state, especially for SWH>5 m. Key words: significant wave height, Envisat ASAR, GA-PLS, optimal feature subset Citation: Fan Chenqing, Wang Xiaochen, Zhang Xudong, Gao Dong. 2019. A newly developed ocean significant wave height retrieval method from Envisat ASAR wave mode imagery. Acta Oceanologica Sinica, 38(9): 120–127, doi: 10.1007/s13131-019-1480-2
1 Introduction The Significant Wave Height (SWH) is a noteworthy ocean surface parameter and is shown to be of great importance to ocean dynamics monitoring, disaster forecasting and off-shore engineering. With the advantage of high spatial resolution, a relatively large spatial coverage and the capability of imaging under almost all weather, day-and-night conditions, the Synthetic Aperture Radar (SAR) has great potential in ocean surface monitoring, especially for SWH (Gonzalez et al., 1979; Longuet-Higgins et al., 1963). Generally, there are
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