基于SCIATRAN模型的二氧化氮DOAS反演敏感性试验

Sensitivity experiment of the DOAS retrieval of nitrogen dioxide based on SCIATRAN mode

气溶胶和地表反照率是影响星载SCIAMACHY仪器观测数据定量遥感NO2大气柱总量的2个主要因子。文中利用高光谱分辨率大气辐射传输模型SCIATRAN,在考虑分子吸收和气溶胶多次散射影响基础上,精确模拟了气溶胶、地表反照率和NO2气体浓度变化对差分处理前后卫星反射光谱的影响,并定义影响因子f,对3个模拟参数进行综合评价。结果表明:(1)通过剔除卫星反射光谱中慢变光谱变化成分,DOAS方法明显降低了气溶胶和地表反照率对卫星反射光谱的影响;(2)差分处理前,3个模拟参数的影响强弱依次为地表反照率、气溶胶和NO2浓度;而差分处理后,3个模拟参数的影响强弱依次为NO2浓度、地表反照率和气溶胶。在影响趋势上,气溶胶和地表反照率很相似,均体现为宽带效应,在440—450nm内有水汽强吸收和多次散射复杂相互作用导致的较大峰值;NO2浓度变化对差分处理前后的光谱都呈现气体吸收结构的影响特性;(3)由于吸收和散射相互作用等因素的影响,在基于卫星观测的差分光谱中仍然残留有气溶胶和地表反照率的误差,地表反照率约占18.6%,气溶胶约占6.2%。因此,当前SCIAMACHY遥感的NO2产品在中国区域浓度偏高,需要对气溶胶和地表反照率进行二次精细化的订正。

Aerosol and surface albedo are two important factors influencing quantitative remote sensing NO2 column with SCIAMACHY observed data.Using high resolution atmosphere radiation transfer model SCIATRAN as well as considering molecules absorption and aerosol multiple scattering,the effects of aerosol,surface albedo and NO2 concentration changes on the satellite reflection spectrum before and after differential processing are accurately simulated,Influence factor f is defined,and the comprehensive evaluation of three simulation parameters performed.The results are：（1） DOAS method has obviously reduced the effect of aerosol and surface albedo on satellite reflection spectrum by eliminating slow changing part of spectrum;（2） Before differential processing,three simulated parameter＇s influence strength is successively surface albedo,aerosol and NO2 concentration;then after processing,the order is NO2 concentration,surface albedo and aerosol.The aerosol and surface albedo are very similar in the influence tendency,and both have a wide band effect.And the big peak value in 440-450 nm is caused by water vapor strong absorption and multiple scattering complex interaction.NO2 concentration change displays its intrinsic absorption structure impact on the satellite reflection spectra before and after processing;（3） Due to the effect of interactions of absorption,scattering and other factors,the differential spectrum based on satellite observed data still contain errors caused by aerosol（about 6.2%） and surface albedo（about 18.6%）.Consequently,the current SCIAMACHY NO2 concentration over China is too higher,and needs to be sophistically corrected for aerosols and surface albedo.