基于查找表的塔基平台O2-A波段大气校正方法研究

塔基光谱观测是连接通量站点与卫星遥感数据间的重要桥梁,而水平地表与塔基平台之间大气吸收、散射的作用对O2-A等大气吸收波段的影响难以忽略。首先,分析了大气辐射传输对塔基平台上下行辐射的影响,建立了基于上下行透过率的大气校正方法,即通过直射光透光率和总的透过率校正上下行辐射的影响。其次,利用中分辨率大气传输模型的模拟数据,定量分析了550nm气溶胶光学厚度(Aerosol Optical Depth at 550nm,AOD550)、辐射传输路径长度对大气透过率的影响,并建立了基于近红外与红光波段下行辐照度比值和太阳天顶角的AOD550查找表(Look-up Table,LUT),以及基于AOD550和辐射传输路径长度的上下行大气透过率LUT。最后,利用塔基平台观测的不同生育期玉米冠层光谱数据,分析了大气校正前后O2-A波段吸收线内外表观反射率的差异。结果表明:基于AOD550和辐射传输路径长度的LUT大气校正方法,可以较好地校正塔基平台O2-A吸收波段大气上下行辐射传输的影响,为塔基平台的日光诱导叶绿素荧光观测等应用提供了重要方法支持。

An O2-A Band Atmospheric Correction Algorithm for Tower-based Platform based on Look-up Table

Tower-based spectral observation is an important connecting bridge between flux sites and satellite remote sensing data，and the effect of atmospheric absorption and scattering between horizontal surface and tower-based platform on the atmospheric absorption band such as O2-A is difficult to ignore.Firstly，the influence of atmospheric radiation transfer on the up-welling radiance and down-welling irradiance of the tower-based platform is analyzed，and the atmospheric correction method of based on upward and downward transmittance is established，that is，the influence of the upwelling radiance and down-welling irradiance is corrected by the direct transmittance and the total transmittance.Secondly，using the simulation data of MODTRAN model，the influence of AOD550 and radiative transfer path length on atmospheric transmittance is quantitatively analyzed，and the LUT of AOD550 is established based on the ratio of down-welling irradiance of near-infrared and red bands and solar zenith angle，as well as the upward and downward atmospheric transmittance LUT based on the AOD550 and the radiative transfer path length.Finally，using the canopy spectral data of different growth stages observed by the tower-based platform，the difference of the apparent reflectance between the inside and outside of the O₂-A band absorption line before and after atmospheric correction was analyzed.The results show that the atmospheric correction method based on LUT of AOD550 and radiative transfer path length proposed in this paper can better correct the influence of upwelling radiance and down-welling on the O₂-A absorption band of the tower-based platform，and provides important method support for applications such as SIF observation on the tower platform.