Analysis of the regional spectral properties in northwestern South China Sea based on an empirical orthogonal function
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Analysis of the regional spectral properties in northwestern South China Sea based on an empirical orthogonal function Dongyang Fu1, Yuye Huang2, 3*, Dazhao Liu1, Shan Liao1, Guo Yu1, Xiaolong Zhang1 1 College of Electronic and Information Engineering, Guangdong Ocean University, Zhanjiang 524088, China 2 State Key Laboratory of Tropical Oceanography, South China Sea Institute of Oceanology, Chinese Academy of
Sciences, Guangzhou 510301, China 3 University of Chinese Academy of Sciences, Beijing 100049, China
Received 30 August 2019; accepted 8 October 2019 © Chinese Society for Oceanography and Springer-Verlag GmbH Germany, part of Springer Nature 2020
Abstract
This study presents an analysis of the spectral characteristics of remote sensing reflectance (Rrs) in northwestern South China Sea based on the in situ optical and water quality data for August 2 018. Rrs was initially divided into four classes, classes A to D, using the max-classification algorithm, and the spectral properties of whole Rrs were characterized using the empirical orthogonal function (EOF) analysis. Subsequently, the dominant factors in each EOF mode were determined.The results indicated that more than 95% of the variances of Rrs are partly driven by the back-scattering characteristics of the suspended matter. The initial two EOF modes were well correlated with the total suspended matter and back–scattering coefficient. Furthermore, the first EOF modes of the four classes of Rrs (A–D Rrs–EOF1) significantly contributed to the total variances of each Rrs class. In addition, the correlation coefficients between the amplitude factors of class A–D Rrs–EOF1 and the variances of the relevant water quality and optical parameters were better than those of the unclassified ones. The spectral shape of class A Rrs–EOF1 was governed by the absorption characteristic of chlorophyll a and colored dissolved organic matter (CDOM). The spectral shape of class B Rrs–EOF1 was governed by the absorption characteristic of CDOM since it exhibited a high correlation with the absorption coefficient of CDOM (ag (λ)), whereas the spectral shape of class C Rrs–EOF1 was governed by the back-scattering characteristics but not affected by the suspended matter. The spectral shape of class D Rrs–EOF1 exhibited a relatively good correlation with all the water quality parameters, which played a significant role in deciding its spectral shape. Key words: northwestern South China Sea, remote sensing reflectance, empirical orthogonal function analysis, ocean color control factors Citation: Fu Dongyang, Huang Yuye, Liu Dazhao, Liao Shan, Yu Guo, Zhang Xiaolong. 2020. Analysis of the regional spectral properties in northwestern South China Sea based on an empirical orthogonal function. Acta Oceanologica Sinica, 39(7): 107–114, doi: 10.1007/s13131020-1625-x
1 Introduction One of the foundations of ocean color remote sensing research is the spectral properties of water such as the inherent optical properties (IOPs) and apparent optical properties (AOPs). IOPs depend only on the
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