The universal radiative transport equation
SIO Reference 59-21. The various radiative transport equations used in general radiative transfer theory (for astrophysical and geophysical applications) over the past fifty-four years can be unified by a single transport equation— the universal transport equation. The 34 types of transport equations discussed in this work range from the transfer equation for radiance to the time-dependent transport equation for n-ary scattered radiant energy. Besides serving as a mathematical focal point of unification of the various transport equations, the universal transport equation supplies several new practical results which are beyond the capabilities of the individual standard transport equations for the radiometric concepts; for example, the proofs of the asymptotic theorems about the light field in deep optical media, and the basis for the equilibrium principle.