Modeling of atmospheric effects on the angular distribution of a backscattering peak

Atmospheric radiative transfer calculations with extremely high angular resolution of the radiance distribution are used to analyze the effects of atmospheric multiple scattering and absorption on the angular distribution of a narrow retroreflection peak such as the canopy hot spot, or Heiligenschein. Using a realistic aerosol-loaded atmospheric model, the results demonstrate that the angular width of the model hot spot (for half widths between 1 degrees and 4 degrees and various types of vegetative canopies) is, to within about 10%, invariant to atmospheric perturbations for total optical depths of the atmosphere up to 1.0 at 0.55 mu m and up to 0.9 at 0.86 mu m. This result is a consequence of the angular filter effect of the surface bidirectional reflectance distribution function and the comparatively broad angular signature of atmospheric backscattering. However, the contrast ratio of the backscattering peak is strongly influenced by atmospheric extinction. As a consequence for satellite remote sensing, the results indicate that the canopy hot spot can be classified as an angular reflectance signature with an angular width that remains invariant to atmospheric scattering and absorption.<
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