风云三号传感器红外通道海表比辐射率模拟

Modeling of Sea Surface Emissivity in the Infrared Window Channels of FY-3A Instruments

海表比辐射率(SSE)是从卫星被动遥感数据反演海表温度(SST)的关键参数之一,本文讲述了利用Wu andSmith(1997)发展的SSE模型,对搭载在风云三号(FY-3A)上的红外大气探空仪(IRAS)第8(12.47μm)、9(11.11μm)、19(3.98μm)和20(3.76μm)波段,中分辨率光谱成像仪(MERSI)第5波段(11.54μm),可见光红外扫描辐射计(VIRR)第3(3.65μm)、4(11.00μm)和5(12.13μm)波段的SSE进行模拟计算。模拟结果表明,SSE是观测角度、波长和海表粗糙度(海面风速)的函数。模拟值与IRAS、MERSI和VIRR红外通道波谱响应函数进行卷积计算得到波段SSE。在观测角度小于60°时,波段SSE对海面风速不敏感,使用风速为8m/s的SSE替代其他风速条件下的SSE所引起的误差小于0.5%。另外,使用波段SSE计算卫星观测值所导致的误差不超过0.05K,可以忽略不计。波段SSE随观测角度变化的规律可以用高斯函数进行描述,拟合误差小于0.02%,相关系数为1.000。本文的模拟结果可以用于SST的精确反演。

Sea Surface Emissivity（SSE） is one of the key parameters to retrieve Sea Surface Temperature（SST） from satellite passive remote sensing data.This paper addressed the simulations of SSEs in the InfraRed Atmospheric Sounder（IRAS） channels 8（12.47μm）,9（11.11μm）,19（3.98μm） and 20（3.76μm）,the Visible and InfraRed Radiometer（VIRR） channels 3（3.65μm）,4（11.00μm） and 5（12.13μm）,and the MEdium Resolution Spectral Imager（MERSI） channel 5（11.54μm） aboard the Chinese second generation meteorological satellite FengYun 3A（FY-3A） using the SSE model developed by Wu and Smith in 1997.The results verify that SSE is a function of Viewing Zenith Angle（VZA）,wavelength and wind speed（sea surface roughness）.The channel-averaged SSEs were obtained through the convolution of the modeled SSEs with the spectral response functions of IRAS,VIRR and MERSI imagers.When VZA is less than 60°,the channel-averaged SSEs are not sensitive to wind speed,and the total errors introduced by the SSE modeling and the use of SSEs at 8m/s for any other wind speed are less than 0.5%.Radiative transfer modeling results reveal that the errors in the simulated brightness temperature at top-of-atmosphere introduced by the channel-averaged SSEs is not greater than 0.05 K,which can be neglected completely.The variation of the channel-averaged SSEs with VZA can be accurately described by Gaussian function,and the fitting standard deviations are less than 0.02% and the correlation coefficients are equal to 1.000.The simulated channel-averaged SSEs in this work satisfy the requirement of accurate SST retrieval.