HR: 11:23h
AN: A32B-05    [Abstracts]
TI: Evaluating Snow Surface BRDF Models with MISR
AU: * Wilson, M J
EM: wilson@atmos.uiuc.edu
AF: University of Illinois at Urbana-Champaign, 105 S. Gregory St., Urbana, IL 61802, United States
AU: Di Girolamo, L
EM: larry@atmos.uiuc.edu
AF: University of Illinois at Urbana-Champaign, 105 S. Gregory St., Urbana, IL 61802, United States
AB: Most surface-viewing satellites-to-date have only provided single, near-nadir views of the earth's surface. This has limited our ability to test our understanding of how the earth scatters radiation, because we are solving an underconstrained problem. For example, one can simply match a radiative transfer simulation to the observed radiance by adjusting the albedo of its surface. That type of match does not make the model correct, because a single-view measurement from a satellite is inadequate to describe how that surface scatters radiation in different directions. This is evident through polar imagery from the Multi-angle Imaging SpectroRadiometer (MISR), which offers nine, near-simultaneous views of the same scene with view zenith angles ranging from ±70°. In the nadir camera from MISR, clouds, smooth glaciers, and rough snow may all appear similar. However, the off-nadir cameras of MISR all show significant differences between those three features (Di Girolamo and Wilson, 2003); a testimony that each of these features have different angular scattering properties. Therefore, the MISR observations can provide additional constraints in evaluating radiative transfer calculations. We use MISR to provide constraints on radiative transfer calculations of TOA radiances under clear sky polar conditions. We use MODTRAN4 for our radiative transfer simulation, which we have modified to accept external surface BRDF values. A simple Lambertian model, the Hapke (1981) model, and the Mishchenko (1999) model are all evaluated. We will demonstrate how a Lambertian surface is inadequate to explain angular scattering in ice and snow. We will also show from the MISR observations that surface roughness causes the phase function to shift, as desribed by Hudson et. al, 2006. This shift causes the Hapke and Mishchenko surface models to be mostly appropriate for smooth ice and snow.
DE: 0736 Snow (1827, 1863)
DE: 0738 Ice (1863)
DE: 0798 Modeling
DE: 3359 Radiative processes
DE: 3360 Remote sensing
SC: Atmospheric Sciences [A]
MN: 2007 Fall Meeting