以改进的半分析光谱模型反演近海岸透明度

Estimation of Water Clarity in Offshore Marine Areas Based on Modified Semi-Analysis Spectra Model

针对近海岸混浊水体透明度的分析和半分析算法中吸收系数和散射系数难以获得的难题,试图构建一个不需要计算吸收系数和散射系数且适用于近海透明度的半分析反演模型。基于Preisendorfer(1986)和Tyler(1968)提出的Zsd(Secchi depth)反演理论,综合490nm处垂直漫衰减系数Kd(490)和光束衰减系数c(490)与遥感反射率的关系,建立了以两波段遥感反射率比值和潮汐系数修正的适用于近海岸海水透明度反演的简易半分析光谱模型。将此半分析光谱模型应用于珠江口生态区(2012年10月21日—23日、2012年11月2日)和徐闻珊瑚礁自然保护区(2013年1月13日—14日)的透明度反演。利用同步实测数据验证发现,大潮期间,该模型计算的透明度与实测值整体偏高0.4m左右,小潮期间,该模型计算的透明度比实测值比较吻合。因此对该模型做了潮汐系数修正,潮汐修正后反演的透明度与实测数值的决定系数为0.663,绝对平均误差为0.14m,相对平均误差为19.5%。综合表明,该模型只需要490与560nm两个波段处遥感反射率的比值即可完成透明度的反演,且模型相对简便,透明度反演精度相对较高。

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 ma-rine areas so far .Based on the Zsd（Secchi depth）inversion theory ,a simple semi-analysis spectra model was established for off-shore seawater clarity by analyzing the relationship between vertical diffuse attenuation coefficient Kd （490） and the beam attenu-ation coefficient c（490） with remote sensing reflectance .This semi-analysis spectra model needed two band reflectance ratios on-ly ,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 clari-ty .So the tidal correction coefficient of 0.4 was further applied for the model .After modification ,the coefficient of determina-tion 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 .