咸水湖泊固有光学-偏振-介电特性研究

Saline Lakes in the endoheic regions are especially sensitive to climate change. Due to the remote and harsh environmental settings, and inconvenient accessibility, optical and microwave remote sensing technology provides the only practical approach for monitoring the aquatic environment change for saline lakes. Till to now, there lack a systematic research on dielectric constant and bio-optical properties of saline waters, which hinders the saline water quality monitoring with remotely sensed data. In this proposal, the inherent optical properties (IOPs), apparent optical properties (AOPs), polarized light properties, and dielectric constant of saline waters and the relationships with respect to optically active constituent (OACs), and salinity will be systematically investigated. Data set for this research will be collected, measured or simulated through field campaigns, laboratory analysis, and simulation based on tank experimentation concerning optical, polarized light and dielectric properties, combined with radiative transfer modeling based on the coupling of Hydrolight and RayXP for examining the relationship between IOPs and AOPs, and IOPs and polarized light properties of saline waters. Efforts will be devoted to: 1) examine the optical properties of CDOM, its components and source of saline waters based on fluorescence spectroscopy; 2) the IOPs influences on AOPs and polarized light properties will be systematically investigated in this research, and sensitivity analysis will be carried out to find out the dominant controlling IOP parameters for AOPs and polarized light properties; 2) the relationship between salinity and dielectric constant with respect to saline categories of waters; 3) the relationship between salinity and dielectric constant, as well as salinity and polarized degrees, with respect to saline categories of waters. At last, remote sensing models will be established for different water quality parameters and IOPs in these saline lakes, and salinity inversion models will be established based on scalar water leaving radiance, dielectric and polarized light properties. The potential results from this project will broaden our knowledge on bio-optical and dielectric properties for saline waters, and remote estimate models for water quality of saline waters will be established or improved through implementation of this project. Further, the proposed findings from this project will greatly advance remote sensing for water quality monitoring of saline waters residing in harsh and remote regions for systemic assessing aquatic environmental change of these waters.

咸水湖泊对全球变化尤为敏感，光学与微波遥感为系统监测咸水湖泊环境变化提供了最为可行的技术手段。目前国内外缺乏对咸水湖泊盐度介电特性与水质参数光学特性的系统研究，阻碍了咸水湖泊水质遥感的发展。本项目以咸水湖泊固有（IOPs）-表观（AOPs）-偏振-介电特性的关系为主线，通过野外实验、室内分析与模拟实验等主要技术手段获得相关数据。重点关注高剂量太阳辐射作用下咸水湖泊CDOM光学特性、组分变化的时空特征与主控因子；光学活性物质IOPs-AOPs及IOPs-偏振特性的相互作用机制；耦合生物光学与矢量辐射传输模型，阐明水体与水表偏振特性的关系；基于标量与偏振特性反演水体IOPs与水质参数；研究不同离子类型盐湖的介电特性，并构建盐度反演模型。本研究对系统认识咸水湖泊光学与介电特性，改进咸水湖泊水质遥感反演方法，提升遥感技术在咸水湖泊环境变化监测中的作用具有重要的理论与应用价值。

咸水湖泊地处干旱或者半干旱的闭流区，对全球变化尤为敏感，光学与微波遥感为大面积监测咸水湖泊环境变化提供了可行的技术手段。本项目基于样带理念，通过多次野外实验采集了200多个咸水与淡水湖泊，并结合室内分析与模拟实验等技术手段，系统揭示了咸水湖泊固有（IOPs）-表观（AOPs）-偏振-介电特性，并以淡水湖泊进行了对比研究。由于咸水湖泊处于相对封闭的汇流区，换水周期长且溶解性物质不断富集。在高剂量太阳辐射作用下，咸水湖CDOM吸收系数和荧光组分强度都显著高于淡水湖，同时由于CDOM含量的增加会导致水体偏振度变大，CDOM-DOC的相关性会随着湖水盐度的增加而增强；此外研究表明咸水湖泊CDOM吸收曲线斜率显著高于淡水湖泊，并且以小分子的碳组分为主，这主要是长期光化学作用的结果。水体颗粒物浓度的增加会导致不同波长下的颗粒物吸收系数呈现显著上升的趋势，但该吸收系数与颗粒物粒径、质地密切相关。本研究结合多角度偏振信息与矢量辐射传输模型、生物光学模型，阐明了水体吸收增加会使水下偏振度变大。由于盐度变化导致水体折射吸收发生变化，因此可以利用水体偏振遥感信息实现水体盐度的反演，并且通过透射偏振信息与水质参数之间的关系，实现了咸水湖CDOM和叶绿素浓度的反演。本研究基于水体固有-表观光学特性，实现了中国咸水湖CDOM、TSM、SDD和叶绿素浓度的遥感反演，结果表明由于水文、气候和湖泊形态学特征的差异，加之汇水区的景观格局和植被覆盖特征的变化，导致咸水湖泊水质参数的时空特征与淡水湖泊有显著差异。对不同类型咸水湖泊盐度的介电特性及盐度反演模型进行了研究，发现湖水介电常数随盐度变化而有规律地变化，并构建了咸水湖微波介电模型，为监测湖水盐度奠定了技术基础。本研究对系统认识咸水湖泊光学与介电特性，改进咸水湖泊水质遥感反演方法，提升遥感技术在咸水湖泊环境变化监测中的作用具有重要的理论与应用价值。