Study Of Lunar Surface Reflectance And Albedo Models Based On Macroscopic Topographic Correction

Lunar reflectance, albedo and mineral abundance are important sources for lunar surface material characteristics, compositions and landform. Due to the impact of the small bodies, the lunar surface has a large terrain variation. When lunar surface is observed by the sensors, it is always seen as a plain. So the data obtained from the sensors can not represent the real condition of lunar surface. Therefore, it is necessary to consider the topographic influence when studying the reflectance, albedo and mineral abundance.According to the researches of reflectance and albedo, the radiative transfer model with parameters which have specific physical meanings is chosen to infer the reflectance and albedo models considering the macroscopic topographic influence. And then the models are applied to lunar surface. It is known that the radiance is divided into three parts: direct solar radiance, sky diffuse radiance and adjacent terrain-reflected radiance. The directional-directional reflectance and the hemispherical-directional reflectance are used to establish the relationship between the irradiance and the radiance. Then the reflectance model is obtained. There is almost no atmosphere on the Moon, so the diffuse irradiance can be ignored. The reflectance model is simplified.According to Hapke’s BRDF model, the narrowband albedo model has been inferred. Because the model proposed by Hapke does not take the macroscopic topographic influence into account, in this paper, this factor is taken into Hapke model. There are two approaches to get the narrowband albedo model. The first one is based on the single-scattering albedo after topographic correction, the other is based on the macroscopic topographic function which is a ratio between the reflectance before and after topographic function. But the results are just narrowband albedos, the object is to get the broadband albedo. According to the definition of albedo, the proportional coefficient is the ratio of the irradiance from a single band and the solar total irradiance. So the narrowband albedo model is converted to the broadband albedo model.The M3 data obtained by Chandrayaan-1 satellite is selected and the Apollo16 landing area is chosen as the study area. Combining with the model, the parameters, including the altitude, the slope and aspect, the incident angle and emergence angle, the sky-view factor and the terrain-view factor, the solar direct irradiance and the total irradiance on a horizontal surface, the binary coefficient, are calculated. The reflectance and albedo are derived by the reflectance and albedo models. The reflectance and broadband albedo results show that the models can remove the topographic variations in some degree. Combining the reflectance and albedo results, the mixed spectral decomposition method is used to derive the lunar surface mineral abundance. According to the definition of the single-scattering albedo, a linear relationship between the mixed mineral single-scattering albedo and the endmember mineral single-scattering albedo is established using the mineral abundance. The results show that the mixed spectral decomposition considering topography is more accurate, and is more suitable to the ilmenite. The result of plagioclase is close to the summary of the plagioclase and glass measured by the laboratory. The results of other mineral are less accurate.