Surface albedo from bidirectional reflectance

Abstract

Total hemispherical shortwave reflectance (albedo) is a major parameter of interest for studies of land surface climatology and global change. Efforts to estimate albedo from remote sensing data have been constrained by the available instrumentation that typically provide observations of reflected radiance from a single view direction in narrow spectral bands. However, the capability to obtain multiple angle observations over the shortwave region is planned for Earth Observing System sensors. In this paper, methods for estimating albedo from multiple angle, discrete wavelength band radiometer measurements are examined. The methods include a numerical integration technique and the integration of an empirically derived equation for bidirectional reflectance. The validity of the described techniques is examined by comparing albedo computed from multiband radiometer data with simultaneously acquired pyranometer data from vegetated and bare soil surfaces. Shortwave albedo estimated from both techniques agree favorably with the independent pyranometer measurements. Absolute root mean square errors were 0.5% or less for both grass sod and bare soil surfaces.