Abstract
Abstract. In this paper, we examine the effect of terrain on terrestrial albedo estimation. Terrestrial albedo is one of the most important parameters for understanding the global heat balance. The existing approach for estimating terrestrial albedo involves the estimation of model parameters of the bidirectional reflectance distribution function (BRDF) based on measurements obtained at different geometries. Then, narrowband albedos are estimated from the BRDF model parameters and the broadband albedo is finally estimated by narrowband-tobroadband conversion. Previous studies have not considered the terrain effect for generating the terrestrial albedo. Experiments using in situ measurements showed that the BRDF model, which transforms the geocoordinate of the reflectance of the shadowed terrain, generates the best accuracy. The improvement in the accuracy by the terrain effect correction is limited, and therefore further investigations using more in situ and simulated data are necessary for operational products.
Highlights
Terrestrial albedo is one of the most important physical parameters for understanding the global circulation of water and heat
Among many proposed bidirectional reflectance distribution function (BRDF) models, kernel-driven models are regarded as robust semiempirical BRDF models that are applicable to any land cover type (Lucht et al, 2000)
We examined five approaches to geometric kernels in the kernel-driven BRDF model using in situ measurements in a forest
Summary
Terrestrial albedo is one of the most important physical parameters for understanding the global circulation of water and heat. A common estimation approach for multispectral satellite observations involves a series of processing steps, typically including atmospheric correction for estimating land-surface directional reflectance, angular modeling for calculating spectral albedos, and narrowband-to-broadband albedo conversion (Liang, 2000; Liang, 2004). Such albedo products are acceptably accurate when applied to paddy fields (Susaki et al, 2007). MODIS operational BRDF/albedo products use at least seven good-quality reflectance observations within a 16-day window This requirement is challenging for tropical and subtropical climate regions, for which optical images are very often contaminated by clouds.
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