基于紫外偏振被动遥感的气溶胶层高度与吸收特性联合反演研究

The lidar CALIOP on board the satellite CALIPSO is currently the only instrument that provides aerosol vertical information on a global scale. The main limitation of CALIPSO measurements is their sparse spacial and temporal resolution, which could be overcome by deriving aerosol altitude directly from passive imaging instruments. But it is very difficult to get vertical distribution of aerosol properties from passive sensors. The advanced spectral multi-angle polarimetric satellite observations make the extract of the aerosol layer height possible. As the upwelling radiance at the top of the atmosphere in the UV region is sensitive to the absorbing aerosol layer and its vertical distribution, we propose to develop an algorithm to retrieve the aerosol height and the UV single-scattering albedo (SSA) simultaneously. At first, we will study the sensitivity of both intensity and polarization signals to the aerosol absorption and layer height, as well as the interacted impactions from them. Then the aerosol height and UV SSA will be derived assuming that the aerosol optical depth (AOD) and aerosol model are estimated from the visible and near-infrared polarized radiances, while the total and polarized radiances in UV bands deconvolve the relative influences of height and absorption. At last, the retrieval algorithm will be tested by numerical experiments and application to the airborne multi-angle polarimetric measurements, which are validated by the ground-based observations. This work will not only achieve passive remote sensing of aerosol layer height, but also retrieve the UV SSA with higher precision simultaneously.

星载激光雷达是目前获取全球气溶胶垂直分布信息的最主要手段，但其具有点线扫描、时空分辨率低的缺点。遥感获取面覆盖的气溶胶垂直分布一直是气溶胶遥感领域的难题。新一代多光谱、多角度偏振卫星传感器的发展为气溶胶层高度被动遥感提供了可能。为实现面覆盖的气溶胶层高度监测，本研究提出利用紫外波段大气反射辐射对气溶胶吸收（单次散射反照率，SSA）和高度（Height）的敏感特性，开展二者联合被动反演算法研究。首先通过敏感性分析，研究矢量大气反射函数中气溶胶吸收与垂直分布作用的耦合机理；然后建立气溶胶Height和紫外SSA及AOD等参数的联合退耦合方案，通过可见-近红外波段偏振测量确定AOD和气溶胶类型，紫外标量和偏振测量同时反演气溶胶Height和SSA；最后通过数值模拟、实测反演与地基验证，评估算法精度和可靠性。本研究创新性地实现气溶胶Height紫外偏振被动遥感反演，同时可提高紫外SSA的反演精度。

多光谱、多角度和偏振同步探测技术，可提供最全面的大气辐射测量，进而最大化获取大气中粒子特性信息。其中，偏振探测为大气遥感提供独立的信息维度，对大气中粒子的尺度、形状等微物理特性及垂直分布等信息更敏感，被认为是最有潜力提高大气气溶胶参数探测精度的观测手段。国际上已成功发射和应用POLDER系列偏振卫星传感器。我国于2018年5月成功发射了首颗气溶胶偏振传感器DPC/GF05。国内外一系列的偏振卫星传感器也在规划中。本项目针对国际和国内已发射或规划中的气溶胶偏振卫星载荷设计，如波段覆盖范围、观测角度数和角度覆盖范围，开展了大气顶反射辐射对气溶胶Height和SSA等参数的敏感性研究，并分析了其与气溶胶AOD、谱分布等其它参数的相互耦合关系，从定性和定量两种方式分析Height反演的可行性。在敏感性分析的基础上，建立气溶胶AOD、Height、SSA等多参数联合退耦合方案，并通过数值模拟反演，验证了算法可行性和可靠性。利用国际上已有的偏振卫星POLDER历史观测数据和我国首颗DPC/GF05传感器实测数据，开展了气溶胶AOD、Height、SSA等多参数的反演和初步验证。该研究经进一步完善，可应用于我国后续偏振载荷的气溶胶垂直分布遥感监测，为大气环境监测和气候评估提供数据支撑。