Characteristics of spectral absorption, fluorescence and remote sensing algorithms of chromophoric dissolved organic matter in winter, Lake Taihu

Abstract

基于2006年和2007年1月两次太湖采样,对50个点位的有色可溶性有机物(CDOM)光谱吸收、荧光、溶解性有机碳(DOC)浓度及遥感反射率进行测定与分析,探讨冬季太湖CDOM的吸收荧光特性及空间分布,建立CDOM吸收系数的遥感反演算法.结果表明,太湖冬季CDOM在355nm处吸收系数a(355)变化范围和均值分别为1.83-7.34 m^-1、3.37±1.01 m^-1,相应的荧光及DOC浓度变化范围、均值分别为9.79-29.18N.FL.U、13.4±3.37N.FL.U;4.61-10.45mg/L、6.37±1.24mg/L.CDOM吸收系数、CDOM荧光值、DOC浓度三者呈显著正相关.空间分布上,两次调查均显示CDOM吸收系数、CDOM荧光值、DOC浓度呈现出明显的南低北高,最大值都出现在太湖北部的藻型湖区梅梁湾内,最小值则在东太湖和贡湖湾2个草型湖区.通过单波段、一阶微分和BP神经网络模型3种不同CDOM反演方法精度的分析、比较发现,BP神经网络模型反演结果最好,模型验证的相对均方根误差和平均相对误差分别为14.9%、11.7%,可以用于冬季太湖CDOM吸收系数a(355)的遥感估算.;Based on two investigations with 100 sampling sites in Lake Taihu in January, 2006 and 2007, the eharactedsfies of spectral absorption and fluorescence, spatial distribution, and the retrieval model of ehromophofie dissolved organic matter (CDOM) were studied.The ranges and mean values of CDOM absorption coefficient at 355 nm a(355), fluorescence nomudized F_n(355) and dissolved organic earn(DOC) concentration were 1.83-7.34, 3.37±1.01 m^-1;9.79-29.18, 13.4±3.37 N. FL. U;and 4.61-10.45, 6.37±1.24 mg/L, respectively.Significant positive correlations between a(355) and DOC, a(355) and F_n(355) were found.Spatially, two surveys have shown that the higher values of a(355), F_n(355), DOC concentration were follnd in Meiliang Bay and lower values were found in East Lake Taihu and Gonghu Bay.Overall, a(355), F_n(355), and DOC concentration were significantly higher in two transects in northern lake regions than those in other transects in southern lake regions.The results showed that BP neural network model wag superior to a single band model and the first order differential model for CDOM absorption estimation.The relative root ineall square error(RRMSE) and mean relative error(MRE) of BP neural network model were 14.9% and 11.7%, respectively, based on an independent validation dataset including 25 samples. Thus, BP neural network model could be better used to estimate CDOM absorption in Lake Taihu.