  We outline a general procedure for simulating the surface brightness of
astrophysical jets (and other astronomical objects) by post-processing gas
dynamical simulations of densities and temperatures using spectral line
emission data from the astrophysical spectral synthesis package {\em Cloudy}.
Then we validate the procedure by comparing the simulated surface brightness of
the HH~30 astrophysical jet in the forbidden [O~I], [N~II], and [S~II] doublets
with {\em Hubble Space Telescope}\/ observations of Hartigan and Morse and
multiple-ion magnetohydrodynamic simulations of Tesileanu et al. The general
trend of our simulated surface brightness in each doublet using the gas
dynamical/{\em Cloudy}\/ approach is in excellent agreement with the
observational data.
