Photometrical invariants in the radiative transfer theory

It is shown that the basic classical problem of radiative transfer theory possesses the fundamental property of photometrical invariance both for the free atmosphere and when there exists a reflecting bottom to its lower boundary. The use of the new notation-photometrical invariants-allows one to represent more rationally the analytical spatial and angle structures of the radiation fields of a uniform slab. Simultaneously the algorithms of numerical modelling of radiation fields are simplified.<>