Estimating hemispherical reflectance and selected biophysical parameters for boreal forest canopies using spectral bidirectional reflectance data acquired by ASAS

Advanced Solidstate Array Spectroradiometer (ASAS) hyperspectral, multiangle data were obtained over BOREAS sites in Saskatchewan and Manitoba, Canada during four field campaigns in 1994. Flown aboard the NASA C-130B at an altitude of approximately 5000 m above ground level, ASAS acquired off-nadir data from 70 degrees forward to 55 degrees aft along-track, in 62 contiguous spectral bands ranging from 400-1025 nm. These measurements were collected to develop linkages between optical remote sensing data and biophysical parameters at the canopy level, and to provide an intermediate level in the process of scaling local ground conditions to satellite observations. ASAS at-sensor radiances over various canopies were atmospherically corrected using the Second Simulation of the Satellite Signal in the Solar Spectrum (6S) and at-surface reflectance factors were derived. Using the multiangle spectral reflectance factors, spectral hemispherical reflectance (PAR, red, and near-IR) was estimated, and spectral vegetation indices, including hemispherical measures, were calculated. The values of the SVIs varied widely depending on the particular angular inputs to the calculation.