A Linear Relationship Between Temporal Multiband MODIS BRDF and Aerodynamic Roughness in HiWATER Wind Gradient Data

Aerodynamic roughness (AR) is an important parameter affecting land-atmosphere interactions. Previous studies on inversions based on bidirectional reflectance distribution functions (BRDFs) have focused on spatial analysis over desert and gobi, which are vegetation-free areas, due to the lack of wind gradient data for continuous time periods over vegetated surfaces. This study uses meteorological gradient data from a new long-term site that is supported by the Heihe Watershed Allied Telemetry Experimental Research project and is located in an irrigated farmland area in the Heihe River Basin of northwestern China. These data are used to calculate a field AR time series over maize using an iterative computation method based on Monin-Obukhov similarity theory. A linear relationship is demonstrated between the field AR and the BRDF parameters derived from multiband Moderate Resolution Imaging Spectroradiometer data. The correlation analysis for the near-infrared and shortwave bands reveals R² values of 0.8739 and 0.8833, respectively; however, R² is only 0.0146 for the visible band. Various band combinations do not improve the outcome. Thus, the near-infrared and shortwave parameters have the potential to be used to infer AR and its related evapotranspiration at more extensive temporal and spatial scales.