pro rayleigh,r,index,wave,ef_sca,ef_ext,ef_bac ;------------------------------------------------------------------ ; ; Purpose: ; ; Routine computes the backscattering, extinction, and ; scattering efficiencies of a spherical particle ; according to Rayleigh theory ; ; input parameters: ; ; r -> particle radius ; index -> particle complex index of refraction ; wave -> wavelength of incident radiation ; ; r and wave must both be in the same units (ie. microns) ; ; output parameters: ; ; ef_sca -> scattering efficiency ; ef_ext -> extinction efficiency ; ef_bac -> backscattering efficiency ; ; source: Mark Hervig ; ;---------------------------------------------------------- pi = 3.141592654 dxr = float(index) dxi = -1.0* abs( imaginary(index) ) index2 = complex(dxr,dxi) chi = pi * r*2./wave eta = (index2^2 -1.)/(index2^2 +2.) kfac = abs(eta) ef_bac = 4.0 * chi^4 * kfac^2 ef_sca = 8.0 * chi^4 * kfac^2 /3.0 ef_abs = 4.0 * chi * imaginary(-1.0*eta) ef_ext = ef_sca + ef_abs return end