Extraction of spectral hemispherical reflectance (albedo) of surfaces from nadir and directional reflectance data

Abstract

A radiative transfer model was used to explore how the error in inferring spectral hemispherical reflectance (p_λ) from nadir reflectance values varies as a function of wavelength, solar zenith angle, leaf area index and leaf orientation distribution. Secondly, a technique using multiple spectral nadir reflectance values to infer p_λ for a single wavelength was tested using field data. In addition, several techniques that use multiple off-nadir view angles taken in azimuth planes (called strings of data) were tested using field data. These latter techniques were very accurate (with errors less than 4 percent of the true value)and are ideally suited to present and future sensor systems that scan in a known azimuth plane (e.g. Advanced Very High Resolution Radiometer (AVHRR) and other scanning radiometers) or view fore and aft in a known azimuth plane (e.g. Advanced Solid-State Array Sensor (ASAS)Moderate Resolution Imaging Spectrometer (MODIS)High Resolution Imaging Spectrometer (HIRIS)), a brief analysis was performed to explore the effects of errors in hemispherical reflectance on terrestrial energy budget and productivity calculations.