Abstract
Topography complicates the modeling and retrieval of land surface albedo due to shadow effects and the redistribution of incident radiation. Neglecting topographic effects may lead to a significant bias when estimating land surface albedo over a single slope. However, for rugged terrain, a comprehensive and systematic investigation of topographic effects on land surface albedo is currently ongoing. Accurately estimating topographic effects on land surface albedo over a rugged terrain presents a challenge in remote sensing modeling and applications. In this paper, we focused on the development of a simplified estimation method for snow-free albedo over a rugged terrain at a 1-km scale based on a 30-m fine-scale digital elevation model (DEM). The proposed method was compared with the radiosity approach based on simulated and real DEMs. The results of the comparison showed that the proposed method provided adequate computational efficiency and satisfactory accuracy simultaneously. Then, the topographic effects on snow-free albedo were quantitatively investigated and interpreted by considering the mean slope, subpixel aspect distribution, solar zenith angle, and solar azimuth angle. The results showed that the more rugged the terrain and the larger the solar illumination angle, the more intense the topographic effects were on black-sky albedo (BSA). The maximum absolute deviation (MAD) and the maximum relative deviation (MRD) of the BSA over a rugged terrain reached 0.28 and 85%, respectively, when the SZA was 60° for different terrains. Topographic effects varied with the mean slope, subpixel aspect distribution, SZA and SAA, which should not be neglected when modeling albedo.
Highlights
Land surface albedo, defined as the fraction of incident solar radiation (0.3–3 μm) reflected by land surfaces [1,2], is one of the most significant geophysical variables affecting the Earth’s climate and controlling the surface radiation budget
Land surface albedo remote sensing estimation algorithms have been developed, demonstrating that a bihemispherical integration method using the bidirectional reflectance distribution function (BRDF) [7,8,9] has a robust performance and is widely used in albedo estimation. This method for estimating albedo generally assumes that the land surface terrain is flat and homogeneous [10,11], and albedo products have been created with this method using different satellite datasets, such as the Moderate Resolution Imaging Spectroradiometer (MODIS) [12], the polarization and directionality of Earth reflectances (POLDER) [13], the multi-angle imaging spectroradiometer (MISR) [14], and the Clouds and the Earth’s Radiant Energy System (CERES) [15]
The validation results showed that the modeled black-sky albedo (BSA) were consistent with the reference BSA, with an root mean square errors (RMSE) smaller than 0.01, which confirmed the ability of the proposed method to estimate BSA
Summary
Land surface albedo, defined as the fraction of incident solar radiation (0.3–3 μm) reflected by land surfaces [1,2], is one of the most significant geophysical variables affecting the Earth’s climate and controlling the surface radiation budget. The topographic effects on albedo over a rugged terrain are related to the spatial distribution characteristics of the subpixel topography, the solar zenith angle (SZA), and the solar azimuth angle (SAA) [17,19,25]. Considering that the analysis of topographic effects on land surface albedo required huge amounts of typical albedo data over the rugged terrain to ensure the reliability of the analysis results, this method was inconvenient for the large-scale simulation of surface albedo because the rugged terrain reflectances under the entire hemispheric view space were required during each albedo calculation under different SZAs and SAAs. we dedicated ourselves to developing a simplified method to estimate the albedo over a rugged terrain directly by the subpixel albedo in this paper based on the same idea in Wen et al [19]. WherethEesareaproefstehnetpsrtohjeectdeidrehcotriszoolnatralirpriaxdeli,anacj edienndoetepsetnhdeesnlotpoefotfotphoegsruabpphixye,l slocpoes,ajddAAtj tjdreenporteessents the artehae oinfctrheempenrotajel cstuerdfacheoarrizeaonoftathl episxueblp, iaxjedl selnopoeteasntdhtehselosupbescorfiptht etjsuibs pthixeejtlhslsoupbep,ixdeAl stljodpeen. otes the incremental surface area of the subpixel slope and the subscript tj is the jth subpixel slope
Sign-in/Register to view highlights & summary Sign-in/Register to access full text options 
Free) 
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Schedule a call
