SHDOM: Terminology

The medium properties (extinction, single scattering albedo, Legendre expansion of the phase function, temperature) are input at grid points from a "property file". These fields are defined spatially (X, Y, and Z spacing) by the "property grid", which is defined by the input file and is not the actual spatial grid used for computatations. The internal grid used for computation has two components: the "base grid" is regularly spaced (even in X and Y, even or not in Z) and is defined by input parameters NX, NY, NZ, and GRIDTYPE; the "adaptive grid" is all the grid cells including those defined by subdividing the base grid cells. New cells are made by "cell splitting", which is the process of figuring out which cells need to be subdivided and dividing them in half to create new grid points. The "sequence acceleration" is a method to reduce the number of iterations by extrapolating the source function to where it is hoped the ultimate solution is. The iterations proceed until the "solution criterion" is reached, when the source function is changing by sufficiently small amounts that convergence is declared.

The "spherical harmonic terms" are the series expansion of the angular dependence of the source function. The angular dependence is also represented by "discrete ordinates", which are discrete directions (mu_i, phi_i) at which the source function or radiance is specified. Angles are specified by mu, which is the cosine of the zenith angle, and phi, which is the azimuth angle, counter-clockwise from the X axis. "Delta-M scaling" is a standard method of reducing the forward scattering peak in the phase function, by scaling the phase function, single scattering albedo, and extinction so the solution to the radiative transfer equation is the same. The "independent pixel" approximation is a standard method of solving for horizontal domain averaged radiative properties of an inhomogeneous medium by averaging the results of 1D radiative transfer on separate columns.