Several techniques for calculating photoelectron fluxes at a single energy level (with inelastic collisions included as the only loss mechanism) are compared in detail, especially with respect to the various approximations of pitch angle effects. The methods compared include the modified diffusion formulation, the Monte Carlo simulation of electron trajectories, a probabilistic distribution approach, the two-stream approximation, and a complete analytic solution valid for the case of isotropic scattering. Differences are generally less than 10% but are systematic when fixed pitch angle distributions are applied to the fluxes rather than to the collisional scattering. The statistical fluctuations of the Monte Carlo method for comparative computer resource expenditures are generally somewhat greater than the systematic differences resulting from other methods. The ability of each method to handle departures from isotropic scattering for ionospheric applications is briefly discussed. Several suggestions are given for numerical implementations of each method. |