The radiation balance of slopes

The radiation balance problenl, at present, has rather a poor and one-sided solution. Only the inflow of direct solar radiation to differently oriented slopes has been closely studied. The precise theoretical formula has been derived for determining the flux of direct solar radiation to slopes of different exposure; numerous calculations, tables, and nomograms for defining the irradiation of slopes with direct solar radiation are being carried out by various workers. The nature of the flux of scattered and reflected radiation to the slopes and the effective long-wave radiation of the slopes have scarcely been investigated; such studies have been reviewed (1, 2, 3). The computation of scattered and reflected radiation fluxes to the slopes as well as the effective radiation of the slopes is rather complicated owing to the fluxes being considerably non-isotropic. As a rule, the radiation is assumed to be isotropic in all cases where practical calculations of the scattered and reflected radiation to the slopes are involved, simple formulae expressing the components of the slope radiation balance being derived with the help of the corresponding components of the radiation balance of a horizontal surface. However, it is not ascertained in what cases and with what accuracy the "isotropic" approximation can be valid. The fluxes of scattered and reflected radiation to the slopes and the effective radiation of the slopes can be exactly determined either by measuring them for each specific slope, or by calculating the radiation influx to the slopes according to the given angular distribution of the radiation intensity. If the angular distribution of the scattered radiation to the slope is known, the flux of this scattered radiation can be estimated from the following exact formula: