Exploring the Applicability of the Semi-Empirical BRDF Models at Different Scales Using Airborne Multi-Angular Observations
Juan Cheng, Jianguang Wen, Qing Xiao, Dalei Hao, Xingwen Lin, Qinhuo Liu
Abstract
Semi-empirical bidirectional reflectance distribution function (BRDF) models are developed based on various spatial-resolution pixels. Because of its simplicity and physical significance, it is widely used in medium- and low-spatial-resolution quantitative remote sensing. With the emergence of high-spatial-resolution remote sensing data and the lack of high-spatial-resolution BRDF models, semi-empirical BRDF models have also been directly applied to high-spatial-resolution qualitative and quantitative remote sensing research. However, whether semi-empirical BRDF models can be directly applied to pixels with high resolution remains unclear. To answer this question, this letter quantitatively evaluates the applicability of semi-empirical BRDF models for remote sensing data with 0.5–30 m spatial resolution based on the WIDAS multi-angular observation dataset obtained during the HiWATER experiment in 2012. The results demonstrate that the semi-empirical BRDF models are not applicable at the 0.5 m pixel scale but are applicable at the 10 m pixel scale. There is a transitional pixel scale from not applicable to applicable between 0.5 and 10 m. We define this scale as the optimal minimum pixel scale (OMS) of semi-empirical BRDF models. The OMS is related to the spatial structure of the vegetation scene, and it is highly consistent with the canopy characteristic scale calculated based on the semivariogram method ( <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"> <tex-math notation="LaTeX">$R^{2}=0.901$ </tex-math></inline-formula> ). Therefore, the range of the semivariogram can be used to estimate the OMS to answer the question of which scale semi-empirical BRDF models are applicable to high-spatial-resolution images.