Code system and data base “ATRAD” for precise calculations of atmospheric radiation

The paper contains principles and structure of Computer Code System ATRAD (Atmospheric Radiation) designed for high precision calculations of the radiation transport in the Earth atmosphere for climate studies. System ATRAD uses the Lebesgue averaging method for multiresonance spectra and absorption coefficients of radiation. This method reduces a number of calculations of photon transport equations compared to the “Line-by-Line” method in several orders. Accuracy of results is kept in limits of accuracy of cross sections of atmospheric gases, aerosols and cloud particles.