Calculation of albedo on complex terrain using MODIS data: a case study in Taihang Mountain of China

Albedo is one of the import parameters for the routine applications of various remote sensing models, and most methods for estimating albedo are only applicable in plain areas with relatively flat topography. Due to the existence of the undulant terrain in mountain areas, the incoming radiance can be decomposed into beam, diffuse, and terrain radiance, which are affected by atmospheric transmittance, solar zenith and azimuth angles, terrain slope and aspect, etc. The existence of partial shadow in low-resolution pixel makes the calculation of albedo more complicated in the mountain areas. This paper presents a rapid and operational method for estimating albedo on complex terrain using high-resolution Digital Elevation Model (DEM) and MODerate-resolution Imaging Spectroradiometer (MODIS) data with sensor view angles less than 20. Shadow coverage ratio of the low-resolution map was retrieved from high-resolution shadow map, and was used for the correction of beam radiance. The parameters used for the atmospheric correction of narrowband beam radiance and weighting coefficients for the calculation of broadband albedo using MODIS with and without band 5 were developed based on the SMARTS2 simulation under different atmospheric conditions. Taken the Taihang Mountain in the North China as the study area, the calculated reflectance and albedo were compared with the MODIS reflectance and albedo products. The maximum deviations between estimated and blue-sky albedos were 0.0155 and +0.0151 in plain areas, and 0.00667 and 0.01747 in the mountain areas, respectively. Good agreements indicate that the procedure presented in this paper is applicable for the albedo calculation in the mountain areas using MODIS images and high-resolution DEM.