**31st Annual Meeting of the DPS, October 1999**

*Session 4. Asteroids: Spanning the Spectrum*

Contributed Oral Parallel Session, Monday, October 11, 1999, 10:30am-12:00noon, Sala Plenaria
[Previous] |
[Session 4] |
[Next]

## [4.06] Light Scattering from Particulate Surfaces: Radiative Transfer Models

*A. F. Cheng (Applied Phys Lab Johns Hopkins Univ)*

New, accurate numerical solutions of the radiative transfer
equation are compared with the Hapke (1981) analytic
approximation which is widely used to analyze planetary
observations. The numerical solutions use the Ambartsumian
invariance principle as do the well-known Chandrasekhar
H-function solutions, but the invariance principle has been
re-expressed in a form which allows high order-accurate
numerical integrations without any required interpolations.
The new numerical solutions reproduce the Chandrasekhar
H-function solutions for Legendre phase functions to within
O(10^{-4}), but the new solutions allow single scattering
phase functions of arbitrary form. For example, the
numerical solution and the Hapke solution are compared for
the Henyey-Greenstein phase function with albedo 0.4, width
parameter b = 0.2, and forward scattering parameter c = 0.7.
In this case, the error of the Hapke solution generally
increases as incidence angles increase, i.e., lowest errors
occur near normal incidence. This contrasts with the
dependence on emission angles, where the greatest errors
occur at intermediate emission angle. The Hapke solution for
bidirectional reflectance I/F is systematically as much as 4
errors in the Hapke solution depend in general on the form
of the scattering phase function, and are typically greater
for backscattering phase functions where the errors can
exceed 20% Results from an extensive survey will be
reported.

[Previous] |
[Session 4] |
[Next]