参数化计算海洋上空大气漫射透过率

A Parameterization of the Atmospheric Diffuse Transmittance over Ocean

精确计算大气漫射透过率和下列面反射率是任何一种卫星反演气溶胶特性的方法的关键所在.相关文献已经给出了计算海洋上空的大气漫射透过率经验公式,利用该公式计算MODIS第一波段到第七波段的海洋上空的大气漫射透过率,发现无论是在瑞利———气溶胶双层大气还是在纯瑞利大气下其精度都是有限的;在观测角00到400范围内,气溶胶为无吸收或弱吸收性且光学厚度最大0.4的情况下,其误差是3%-4%;误差随着气溶胶吸收性、气溶胶光学厚度和观测角度的增大而增大,随着波长的减小而减小.为了提高计算精度和适用范围,用一个简单的数学方法来改写该公式.在观测角θ≤60°、多种成份气溶胶且光学厚度τa≤0.6时,改写后的公式计算的MODIS第一波段到第七波段的海洋上空的大气漫射透过率,其误差小于1%.该参数公式的确立,对精确反演海岸带的气溶胶光学特性和水色有重要意义.

To account for surface reflection and atmospheric diffuse trasmittance is a major and most complex issue of any satellite aerosol retrieval algorithm. According to the literature by Wang [Appl. Opt. 38,451 -455 （1999） ] to using the reciprocal equation derived by Yang and Gordon [ Appl. Opt. 36, 7887- 7897（1997） ] for atmospheric diffuse transmittance of the ocean-atmosphere system, I examined the accuracy of an analytical equation proposed by Gordon et al. [ Appl. Opt. 22, 20- 35 （1983）] in computing the atmospheric diffuse transmittance for wavelengths from MODIS band 1 to MODIS band 7 for both a pure Rayleigh and a two-layer Rayleigh-aerosol atmosphere overlying a rough ocean surface. It was found that for viewing angles up to approximately 400, the analytical formula produces errors between 3% and 4% for nonabsorbing and weakly absorbing aerosols and for aerosol optical thicknesses. The error increases with an increase in aerosol absorption, aerosol optical thicknesses, and viewing angle, and with the decrease of wavelength. By a simple numerical fit to modify the analytical formula, the atmospheric diffuse transmittance can be accurately computed usually to within 1% for a variety of aerosol models, aerosol optical thicknesses, viewing angles, different aerosol vertical structure distribution, and for wavelengths from MODIS band 1 to MODIS band 7.