The thermal radiation transfer equation is considered for the case of observing the horizon under condition of the axial symmetry of the sky radiation. The equation is solved using model representations of the brightness field and scattering phase functions. It is shown that formation of the sky brightness field on the horizon mainly depends on the magnitude of the upward and downward radiation (34% variations), while the asymmetry of the scattering phase function is of minor importance (less than 3% variations). The algorithm is proposed for determining the single scattering albedo based on the measurements of the following parameters: angular distribution (from zenith to nadir) of the incident radiation, sky brightness on the horizon and the blackbody brightness at the temperature of the near-ground atmosphere. The atmospheric conditions preferable for realization of the method, as well as the reasons for the difference between radiative temperatures of the sky on the horizon and near-ground atmosphere are considered.