水汽吸收和下垫面发射率对晴空大气红外窗区遥感影响的综合分析

从数学上探讨了晴空大气红外窗区通道遥感陆面特性水汽吸收和陆面发射率的综合影响。首先,基于辐射传输方程推导出大气水汽含量和陆面发射率(ε)引起红外窗区通道遥感陆面亮温(Tg)变化的数学表达式,指出红外辐射在传输过程中水汽吸收衰减的影响主要是引起大气透过率的变化;分析了在高温高湿和低温干燥等不同地区,红外窗区通道的大气透过率所受到的不同程度的衰减,以及水汽吸收衰减和陆面发射率对不同的红外窗区通道的影响。此外,还建立了一个红外窗区通道遥感陆面温度与地面亮温差ΔT=(Ts-Tg,imax)与水汽含量变化Δq和陆面发射率ε的二元多项式拟合方程,进一步分析大气水汽含量和陆面发射率对不同的红外窗区通道遥感的影响;指出红外短波窗区通道不但受太阳辐射污染严重,而且受陆面发射率变化的影响激烈,特别是在寒冷干燥的亚北极冬季。最后强调,为了精确地反演陆面温度,最好采用热红外窗区通道;必须考虑大气订正,特别是在高温高湿区;同时应该考虑陆面发射率等因子的作用。

Synthetic Analysis of the Effects of Water Vapor Absorption in Clear Sky and Land Surface Emissivity on IR Window Soundings

In this paper the synthetic effects of water vapor absorption and land surface emissivity(LSE) on IR window soundings of land surface temperature(LST) in clear sky condition are investigated mathematically.The formula of the change of brightness temperature caused by atmospheric water vapor content and LSE is derived from radiative transfer theory at first.Then,the different attenuation of the transmittances for different IR window channels in various regions,such as the regions under high temperature with high humidity and low temperature with dry condition,is analyzed.In addition,a fitting formula of a polynomial with two variables for the LST and surface brightness temperature difference ΔT =(Ts-Tg,i max) changed with water vapor content and LSE is set up.The complex effects of atmospheric water vapor content and LSE in three atmospheric models on the temperature difference ΔT for different IR window channels are further synthetically studied.Finally,the effect of satellite observation angle on the LST remote sensing is briefly discussed.The results emphasize that for retrieval of LST accurately the thermal IR window channels should be used and atmospheric correction must be carried out,especially in hot and humidity regions.And the LSE effects are important and should be considered simultaneously.