观测路径和光谱分辨率对吸收性气溶胶指数的影响

Sensitivity Study of Viewing Path and Spectral Resolution on Absorbing Aerosol Index

吸收性气溶胶指数(AAI)在监测污染物方面有较好的应用,其反演结果受边界层高度、云高、相对湿度以及仪器指标和观测几何路径等因素影响.利用大气辐射传输模型MODTRAN,对辐射传输方程中多次散射计算的不同近似方法和不同观测几何角度下的AAI进行模拟,研究这些因素对AAI结果的作用,并分析仪器光谱分辨率对AAI探测结果的影响.结果表明,折衷考虑计算效率与精度的情况下,应选择8流近似的离散坐标法进行带有多次散射计算的辐射方程解析.AAI在不同浓度和不同类型气溶胶下随观测角度变化的趋势相同:相对方位角<120°时,AAI误差在太阳天顶角和卫星方位角均为40°～60°时最大;相对方位角在120°～180°时误差均较小;光谱分辨率对AAI反演结果无明显影响.

Absorbing Aerosol Index(AAI) has a broad application in pollution monitoring. AAI is influenced by many factors in atmosphere, such as altitude of boundary layer, height of cloud,relative humidity, as well as factors from instrumental properties and geometric observation view angles. The atmospheric radiance transfer model MODTRAN was used to simulate the effects of the streams used in the DISORT multiple scattering calculation in radiance transfer equation and view angle of instrument on the biases of AAI derivation. The results indicate that 8 Streams is the best choice in radiative transfer simulation of aerosol scattering, both in accuracy and computational efficiency. AAI varies similarly with the view angle for different aerosol thickness and types: When Relative Azimuth Angle < 120°, the bias of AAI is largest when both the Solar Zenith Angle and Satellite Viewing Angle are between 40° and 60°;When Relative Azimuth Angle <180° and > 120°,the bias of AAI is relatively small. Besides, spectral resolution has no significant influence on AAI retrieval results.