On the effect of stratification of atmospheric optical characteristics on the sky radiance in the solar principal plane

Resumo

The detailed information on the “in situ” vertical distribution of optical characteristics of atmospheric aerosol is frequently absent because of the complexity and high cost of environmental monitoring from aircraft. This paper presents estimates of the atmospheric optical characteristic stratification effects on downward scattered radiation measured by a sun photometer at the Earth’s surface for two basic viewing geometries: in the solar almucantar and in the solar principal plane. We obtained estimates on the basis of numerical experiments, key parameters of which imitate both background (areas with low anthropogenic load) and extreme atmospheric situations (urban smog, dust haze over land, and dust outflow over water surface). In the visible spectral region, outside the oxygen, ozone, water vapor, and nitrogen dioxide absorption bands, the stratification of the atmospheric optical characteristics is shown to have no significant effect on the sky radiance in solar almucantar, however becoming important in the solar principal plane. The main factor is the vertical behavior of the aerosol extinction coefficient. The radiance calculation errors can be substantially reduced by using the simplest vertical profiles and, in particular, the exponential distribution of the extinction coefficient over height.