基于热红外波段遥感观测的沙尘定量反演研究

Mineral dust is an important factor in earth system energy budget, global climate, and biogeochemical cycles. It also affects air quality and human health. Satellite radiometer measurements in thermal infrared channels are advantageous in monitoring the spatial and temporal variations of dust events during both the daytime and the nighttime. However, the satellite measurements provide the mixed signal of both the atmosphere and land surface. Since the properties of underlying surface and atmospheric profiles have complicated effects on the observed top of atmosphere (TOA) brightness temperature (BT), it is challenging to retrieval dust optical properties from satellite measurements. In this proposal, a novel method for compositing land surface references in thermal infrared channels is developed. The atmospheric transfer model is used to simulate the quantitative relationships between aerosol optical depth and TOA BTs in thermal infrared bands in various atmospheric profiles, underlying surface properties and viewing geometry. Based on these simulations, the relationships among land surface references, dust optical properties and satellite thermal infrared measurements are established and used to retrieve the dust optical properties from MODIS thermal infrared measurements. The results are evaluated by comparing to OMI, MODIS aerosol products, CALIPSO lidar observations and field measurements.

沙尘是地球系统能量平衡、全球气候系统和生物地球化学循环的重要影响因子，并对空气质量和人类健康有着显著影响。卫星热红外波段观测可同时获得白天和夜间的沙尘信息。但是，热红外传感器所捕获的是地表及大气的混合信息，地表和大气状况对大气顶层亮温的影响非常复杂且相互叠加，导致从热红外波段定量提取沙尘信息变得很困难。本申请将提出一种独立于温度的热红外地表背景合成方法，并基于大气辐射传输模型，全面模拟在不同大气剖面、地表特性和卫星观测角度状况下，沙尘气溶胶光学厚度和热红外波段大气顶层亮温的关系，并进一步建立热红外地表背景参数、沙尘特性与卫星热红外波段观测值的定量关系。在此基础上，以MODIS数据为数据源，实现沙尘气溶胶光学厚度的定量反演，并利用OMI、MODIS气溶胶产品、CALIPSO激光雷达和地面观测对反演结果进行验证。

沙尘作为一种重要的气溶胶类型，影响空气质量、地球系统能量平衡、全球气候系统和生物地球化学循环。卫星热红外波段的亮温差常用于沙尘检测，但会受到地表状况特别是地表温度的干扰，这也是沙尘检测中需要解决的关键问题。本项目设计了新的沙尘气溶胶反演方法，基于大气辐射传输模拟和多年遥感观测合成了独立于温度的动态地表背景，解决了地表温度对于沙尘反演的干扰问题。项目研究主要取得了以下成果：.(1) 构建了日夜适用的沙尘反演算法：利用大气辐射传输模型SBDART模拟了不同地表和大气温度、水汽等状况下沙尘气溶胶光学厚度和大气顶层亮温的定量关系；选择沙尘重要源地和分布区域中国北方和蒙古为研究区域，基于2000-2008年MODIS热红外观测合成了独立于温度的地表背景分布图；在此基础上，基于MODIS 热红外波段观测设计了沙尘气溶胶指数DRBTDI，并建立了其与沙尘气溶胶光学厚度的定量关系，从而构建了日夜适用、亮地表适用的沙尘气溶胶反演算法。.(2) 中国北方和蒙古沙尘日夜时空分布监测：基于2002-2013年MODIS观测，利用上述算法进行了中国北方和蒙古沙尘白天和夜间时空分布的研究。白天和夜间沙尘的空间分布、季节和年际变化相似，夜间沙尘频率低于白天。沙尘主要源地为中国北方和西北的沙漠及干旱区域，塔里木盆地沙尘最为频发。沙尘呈现出显著的年际和季节变化，3-5月特别是4月频率最高。