Estimating albedo from limited spectral and angular data
A database of synthetic albedo and directional reflectance values for vegetated surfaces was constructed utilizing mathematical models. This database enables the comparison of albedo with reflectances measured in narrow spectral bands in particular viewing directions for specified vegetation canopy and solar conditions. The analysis reported here is for spectral bands and angular regimes corresponding to the Along-Track Scanning Radiometer (ATSR-2) sensor on ERS-2. In the analysis multiple linear regression is used to calculate the best fit between modelled reflectance and modelled albedo. A primary estimate of albedo is calculated using reflectance data from the nadir direction only. Data from the forward view of the ATSR sensor are then used to provide additional information to correct the nadir estimate. The relationship between the regressed coefficients and the illumination conditions was investigated in order to provide a universal albedo estimation. Preliminary results for representative solar zenith and azimuth angles show an extremely good fit between modelled albedo and that estimated using the modelled ATSR-2 reflectance.
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