  We present a general solution for the radiation intensity in front of a
purely absorbing slab moving toward an observer at constant speed and with a
constant temperature. The solution is obtained by integrating the lab-frame
radiation transport equation through the slab to the observer. We present
comparisons between our benchmark and results from the Kull simulation code for
an aluminum slab moving toward the observer at 2% the speed-of-light. We
demonstrate that ignoring certain material motion correction terms in the
transport equation can lead to 20-80% errors with the error magnitude growing
as the frequency resolution is improved. Our results also indicate that our
benchmark can identify potential errors in the implementation of material
motion corrections.
