INCORPORATION OF PHYSICAL OPTICS EFFECTS AND COMPUTATION OF THE LEGENDRE EXPANSION FOR RAY-TRACING PHASE FUNCTIONS INVOLVING DELTA-FUNCTIONTRANSMISSION
M. Mishchenko et A. Macke, INCORPORATION OF PHYSICAL OPTICS EFFECTS AND COMPUTATION OF THE LEGENDRE EXPANSION FOR RAY-TRACING PHASE FUNCTIONS INVOLVING DELTA-FUNCTIONTRANSMISSION, J GEO RES-A, 103(D2), 1998, pp. 1799-1805
The standard geometric optics (GO) technique predicts that the phase f
unction for large nonspherical particles with parallel plane facets (e
.g., hexagonal ice crystals) should have an infinitesimally narrow del
ta-function transmission peak caused by rays twice transmitted(refract
ed) in exactly the forward scattering direction. However, exact T-matr
ix computations and physical considerations based on the Kirchhoff app
roximation suggest that this peak is an artifact of GO completely igno
ring physical optics effects and must be convolved with the Fraunhofer
pattern, thereby producing a phase function component with an angular
profile similar to the standard diffraction component. This convoluti
on can be performed with a simple procedure which supplements the stan
dard ray-tracing code and makes the computation of the phase function
and its Legendre expansion both more physically realistic and more acc
urate.