Estimation of Water Clarity in Offshore Marine Areas Based on Modified Semi-Analysis Spectra Model
HAN Liu-sheng1，2, CHEN Shui-sen2*, CHEN Xiu-zhi1, 2, LI Dan1, LI Yong1, SUN Lin3, LU Chu-qian4, CHEN Wei-qi2
1. Guangzhou Institute of Geochemistry, Chinese Academy of Sciences, Guangzhou 510640, China 2. Guangzhou Institute of Geography, Guangzhou 510070, China 3. Geomatics College，Shandong University of Science and Technology，Qingdao 266510，China 4. South China Sea Environment Monitoring Center, State Oceanic Administration, Guangzhou 510300, China
Abstract：The main objectives of the research described in the present paper are to develop a semi-analysis model of water clarity for case 2 waters without inputting the absorption and scattering coefficient, which are not easy to be obtained for offshore marine areas so far. Based on the Zsd(Secchi depth)inversion theory, a simple semi-analysis spectra model was established for offshore seawater clarity by analyzing the relationship between vertical diffuse attenuation coefficient Kd (490) and the beam attenuation coefficient c(490) with remote sensing reflectance. This semi-analysis spectra model needed two band reflectance ratios only, while tidal correction was produced for this model to improve the precision of the retrieving results. The semi-analysis spectra model was applied to ASD hyperspectral reflectance data measured in the Pearl River Estuary Ecological Zone (October 21, 23, 2012, November 2, 2012; N=20) and the Xuwen Coral Reef Protection Zone (January 13, 14, 2013, N=25) which covered different water body of tidal times and different pollution sources. The results indicated that the changing tendency of predicted values was consistent with the synchronous measurement values after comparing them. However, water clarity calculated by the ASD hyperspectral reflectance measured in spring tidal time, generated 0.4 m deviation compared with in-situ water clarity, while water clarity calculated by the ASD hyperspectral reflectance measured in neap tidal time is close to the in-situ water clarity. So the tidal correction coefficient of 0.4 was further applied for the model. After modification, the coefficient of determination between the inversed and measured water clarity was 0.663, the average absolute error was 0.14 m and the average relative error was 19.5%. Research demonstrated that this semi-analysis inversion algorithm just needs two band reflectance ratio to complete the inversion of water clarity, which is simple and works relatively well for lower clarity (less than 2 meters) waters compared to He’(2004) and Doron’(2011) algorithms.
韩留生1, 2，陈水森2*，陈修治1, 2，李 丹1，李 勇1，孙 林3，卢楚谦4，陈玮琦2 . 以改进的半分析光谱模型反演近海岸透明度 [J]. 光谱学与光谱分析, 2014, 34(02): 477-482.
HAN Liu-sheng1，2, CHEN Shui-sen2*, CHEN Xiu-zhi1, 2, LI Dan1, LI Yong1, SUN Lin3, LU Chu-qian4, CHEN Wei-qi2 . Estimation of Water Clarity in Offshore Marine Areas Based on Modified Semi-Analysis Spectra Model . SPECTROSCOPY AND SPECTRAL ANALYSIS, 2014, 34(02): 477-482.
[1] HE Xian-qiang, PAN De-lu, HUANG Er-hui, et al(何贤强，潘德炉，黄二辉, 等). Engineering Sciences(中国工程科学), 2004, 6(9): 33. [2] Nutchanart Sriwongsitanon, Kritsanat Surakit, Sansarith Thianpopirug. Journal of Hydrology，2011, 405: 203. [3] Maéva Doron, Marcel Babin, Odile Hembise, et al. Remote Sensing of Environment，2011, 115: 2986. [4] Maritorena S, Siegel D A，Peterson A. Applied Optics，2002, 41(15): 2705. [5] Lee Z P，Carder K，Amone R. Applied Optics，2002，41(27): 5755. [6] Maritorena S, Siegel D A, Peterson A R. Applied Optics, 2002, 41: 2705. [7] Mueller J L. NASA Technical Memorandum 2000-206892, Greenbelt, Maryland: NASA-GSFC. 2000, 11: 24. [8] Berthon J F, Zibordi G, Doyle J P, et al. NASA Technical Memorandum 2002-206892, Greenbelt, Maryland: NASA-GSFC. 2002, 20: 1. [9] Gordon H R, Brown O B, Evans R H, et al. Journal of Geophysical Research, 1988, 93: 10909. [10] SONG Chao-jing，ZHAO Huan-ting, WANG Li-rong(宋朝景，赵焕庭，王丽荣). Tropical Geography(热带地理)，2007, 27(4): 294. [11] TANG Jun-wu, TIAN Guo-liang, WANG Xiao-yong, et al(唐军武，田国良，汪小勇，等). Journal of Remote Sensing(遥感学报)，2004, 8(1)：37. [12] Preisendorfer R W. Limnology and Oceanography, 1986, 31(5): 909. [13] Tyler J E. The Secchi Disc. Limnology and Oceanography，1968，8(1): 1. [14] Doron M，Babin M，Mangin A，et al. Journal of Geophysical Research，2007, 112: C06003. [15] Albert A，Mobley C D. Optics Express, 2003，11(22): 2873.
