悬浮颗粒物垂直分布对水体光学特性的影响

Effects of Nonuniform Vertical Profile of Suspended Particulate Matter on Water Optical Properties

关键词:  水体垂直分布  遥感反射率  敏感波长  最大影响水深

Key words:  water vertical distribution  remote sensing reflectance  sensitive wave length  maximum influence water depth

摘要:

[目的]研究典型湖泊水体垂直分布对遥感反射率的影响,并了解其主要影响波段和影响水深。[方法]利用实测数据和前向辐射传输模型得到水体垂直分布模拟数据,选取两种典型的湖泊水体垂直分布类型,研究它们对水表面遥感反射率的影响,并分析其敏感波长和最大影响深度。[结果]与均质水体相比,不同类型的水体垂直分布最大会引起遥感反射率100%的高估或者30%的低估且误差随着水深的增大而减小。当表层悬浮颗粒物浓度(SPM₁)较小时,在相同浓度条件下,不同类型水体垂直分布的敏感波长随着水深增大逐渐减小;在同一深度时,敏感波长随着悬浮颗粒物浓度的增大逐渐向长波方向移动;当SPM₁较大时,敏感波长随水深增大没有明显变化。不同类型水体在SPM₁较低时,各波段的最大影响水深各不相同,可达10 m,并随表层悬浮颗粒物浓度的增大而逐渐减小,峰值波长逐渐向长波方向移动;当SPM₁较大时,最大影响水深集中于0.5~2.0 m,随波段递增无明显变化规律。随着表层水体的衰减系数的增大,最大影响水深在不同波段基本呈递减趋势。[结论]研究成果有助于准确的理解表层遥感反射率中所包含的水体垂直结构信息,并为深入研究非均质水体光学特性及其辐射传输过程提供理论依据。

Abstract:

[Objective] The influence exerted by nonuniform vertical profile of suspended particulate matter on remote-sensing reflectance was studied for a typical inland lake.The major sensitive wavelengths and maximum influence water depths were discussed.[Methods] The in situ data and forward radiative transfer model were applied to simulated two typical vertical distributions of water column.The sensitivity of remote sensing reflectance(R_rs) associated with stratified water column showed correlation with suspended particulate matter (SPM),sensitive wavelength and maximum influence water depth.[Results] Compared to vertical uniformed water column,different vertically stratified types could cause more than 100% overestimation or 30% underestimation of R_rs at most and the error decreased with the increase of water depth.When the concentration of surface SPM (SPM₁) was small,the sensitive wavelengths of different water profiles decreased with increasing water depth under the same SPM₁.For the same water depth,the sensitive wavelengths moved towards the longer wavebands with increasing SPM₁.When SPM₁ was large,no obvious correlation between water depth and sensitive wavelength was observed.The maximum influence water depths for different vertical profiles varied and could reach up to 10 m when the water was clear.With the increased SPM₁,the maximum influence water depths decreased and sensitive wavelengths moved towards the longer wavebands.In contrast,the maximum influence water depths centered on 0.5~2.0 m and showed no pronounced tendency when the water was turbid.In addition,the increasing attenuation coefficient of surface water usually led to a decreasing maximum influence water depth.[Conclusion] The results will improve our understanding of the vertical structure information obtained from surface remote sensing reflectance.