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.