忽略1.6μm偏振计算对二氧化碳反演精度的影响  

CO_2 column-retrieval errors arising from neglecting polarization in forward modeling of 1.6 μm band measurements

作　　者：白文广[1,2] 张鹏[2] 张文建[2] 马刚[2] 漆成莉[2] 刘辉[2] Wenguang Bai1,2, Peng Zhang2., Wenjian Zhang2, Gang Ma2, Chengli Qi2 , Hui Liu2(1 School of Atmosphere Physics, Nanjing University of Information Science ＆ Technology, Nanjing 210044, China; 2 National Satellite Meteorology Center, Beijing 100081, Chin)

机构地区：[1]南京信息工程大学大气物理学院,南京210044 [2]国家卫星气象中心,北京100081

出　　处：《科学通报》2018年第8期766-776,共11页Chinese Science Bulletin

基　　金：国家高技术研究发展计划(2015AA123704;2011AA12A104);国家自然科学基金(41475031);公益性行业(气象)科研专项(GYHY201506074;GYHY201506002)资助

摘　　要：散射引起的偏振效应会对卫星遥感二氧化碳精度产生较大的影响.本文利用逐线积分方法和累加法精确模拟了星载仪器近红外1.6μm波段的大气层顶偏振辐射特征,计算了分子散射和气溶胶散射引入的偏振效应,分析了偏振效应对大气二氧化碳反演精度的影响.研究表明:1.6μm波段散射引入的偏振效应明显,并随太阳高度角、观测天顶角、气溶胶光学厚度、地表反射率而变化.除个别大角度观测天顶角外,偏振效应随太阳天顶角升高、气溶胶光学厚度增加、地表反射率的减小而变大,并且在吸收线位置的影响要高于窗区.忽略偏振效应导致的大气二氧化碳反演误差随太阳天顶角的升高、气溶胶光学厚度的增加以及地表反照率减小而增大,并且该误差与仪器观测角度有关.模拟结果显示在高太阳天顶角、高气溶胶光学厚度以及低反照率场景下,忽略偏振计算可能引入高于10 ppmv(1 ppmv=10^(-6) L/L)反演误差,远高于1~2 ppmv观测需求.为减小误差,基于该波段的二氧化碳反演需要考虑大气辐射偏振的影响.Carbon dioxide （CO2） is a major anthropogenic greenhouse gas. Atmospheric CO2 has increased from a preindustrial value of about 280 ppmv to more than 400 ppmv, mainly due to the fossil-fuel combustion and changes in land use. Un- derstanding the CO2 distribution and variability of sources and sinks is essential for predicting changes in future CO2 concentration. However, in-situ measurements collected at a network of surface stations are sparse to allow the CO2 sources and sinks to be inferred. Satellite remote sensing is one of the best ways to obtain such global observations. The radiances reflected or transmitted by the atmosphere contain information about the atmospheric gases through their ab- sorption signatures. High spectral radiance in the near-infrared 1.6 μm band, observed by OCO and Chinese TanSat, can be used to derive the CO2 column densities in the atmosphere. Surface reflection and atmospheric scattering processes act to reduce the intensity of radiation polarized in the direction parallel to the principal plane, as defined by the incoming solar beam and the beam entering the instrument. Both the OCO and TanSat instruments are typical polarizing instruments that are designed to measure only the radiation perpendicular to the principal plane; this will create a disparity between the simulation and measurements if polarization effects are neglected in forward modeling. In this paper, the US standard atmospheric profile with multiple layer aerosol loading is used to evaluate the for- ward-modeling error made by scalar approximations in the near-infrared 1.6 μm band. Numerical computations were performed using the line-by-line and doubling-adding methods. The atmosphere is assumed to be plane parallel and the surface is set to offer Lambert reflection. The polarizations introduced by molecular Rayleigh scattering and aerosol Mie scattering are calculated respectively. Solar zenith angle, view zenith angle, surface-reflectance, and aerosol optical depth are varied one at a time to evaluate the i

关 键 词：矢量辐射传输计算 卫星近红外1.6μm观测 二氧化碳反演误差 

分 类 号：P407[天文地球—大气科学及气象学]