Radiometry of UVB: comparisons with results of Lowtran 7 and Premar computer codes

A prototype UVMFR instrument (Ultra Violet Multi Filter Radiometer) with 4 different wavelength sensors in the UVB band has been thoroughly tested in Brasimone (44, 11 degrees N; 11.11 degrees E) prior to its installation for long term measurement campaigns of the UVB flux at the ground (890 m. local height), with separation of the direct and diffuse components of radiation. It has also been used for the first validation of a new computer code (PREMAR), developed by ENEA, which solves the radiation transfer equation in the atmosphere by a Montecarlo approach. The new code considers a multilayer geometry, allows for the computation of albedo effects and exploits the rich library and potentialities of the LOWTRAN-7 U.S. computer code. With reference to the best available data, in days with an optimal meteorology to avoid significant cloud effects, an intercomparison of the instrument and code results has been performed at different times (varying solar zenital angles). A good agreement has been obtained between experiment and calculations as to the diffuse/total radiation ratio, and the deduced local albedo has been found to correspond rather well to theoretical estimates