Ground-based multitemporal measurements of global solar spectral irradiance and estimation of atmospheric transmittance

Multitemporal measurements in ten discrete spectral bands in the range from 0.4 to 1.0 micron have been carried out with the help of the indigenously developed spectro-polarimeter. The measurements have been carried out under minimum haze sky conditions twice a week in a period of about 100 days. In-band exoatmospheric solar spectral irradiance values for the corresponding sun angles have been computed from the standard available data. The values have been corrected for sun-earth distance and the atmospheric transmittances from space to ground have been estimated. This estimation has been compared with the AFGL LOWTRAN 6 atmospheric model. This exercise would be useful to support/verify existing theoretical models and practical measurements. Additionally, it could be useful to interpolate global ground irradiance with maximum radiometric uncertainties of 11%. This paper describes the experimental details and some of the results obtained.