基于两种辐射传输模型的雪粒径与反照率反演

Retrieval of Snow Grain Size and Albedo Using Two Radiative Transfer Models

提出一种渐近辐射传输(ART)理论与离散纵标辐射传输法(DISORT)相结合的方法,用于反演雪光谱反照率。基于雪粒形状的二级科赫分形假设,利用不同卫星数据与ART理论的三种粒径反演方法反演研究区域的雪粒径,反演的雪粒径大小不同,但平均值均在50μm左右。基于雪粒球形假设,根据反演的雪粒径,基于DISORT模型计算波段为0.3~5.0μm的雪光谱反照率,同时基于ART理论计算波段为0.3~1.5μm的雪的黑空与白空光谱反照率。由两种辐射传输模型计算的0.3~1.5μm的雪光谱反照率差异较小,表明雪粒形状假设合理,利用两种辐射传输模型相结合的方法能够计算太阳光谱的雪反照率。考虑到研究区域内黑碳等吸光性杂质的影响,修正了DISORT模型计算的雪光谱反照率。研究区域靠近国境边缘的西伯利亚地区时,吸光性杂质对于雪光谱反照率影响很小;研究区域为东北工业地区时,吸光性杂质会明显降低可见光波段的雪光谱反照率。

A method combining the asymptotic radiative transfer(ART)theory and discrete ordinate radiative transfer(DISORT)method is proposed in this study to retrieve the snow spectral albedo.First,based on the assumption that snow grain shape is the second generation Koch fractals,snow grain size results are retrieved using different satellite data and three methods derived from the ART theory.The average results,although different,are all close to 50μm.Second,assuming the snow grains are spherical,snow spectral albedo is calculated using the DISORT model in the 0.3-5.0-μm region based on the retrieved snow grain size results.Snow black-sky and whitesky spectral albedo are calculated using the ART theory in the 0.3-1.5-μm region.The small difference between the two types of snow spectralt1,recipi albedo calculated through the two radiation transfer models in the 0.3-1.5-μm region reveals that the assumption of different snow grain shapes is reasonable.The method combining the two radiation transfer models can calculate the snow albedo of the solar spectrum.Finally,the snow spectral albedo calculation using DISORT model also considers the light-absorbing impurities such as black carbon.The study area is located in northeast border proximity to Siberia demarks region,where the impurities have a very limited influence on snow spectral albedo.While in the northeast area,which is heavily industrialized,the impurities can markedly decrease snow spectral albedo at visible wavelengths.