The improvements done in an Optronic OL-752 spectroradiometer to measure direct solar radiation and compute the aerosol optical depth are presented. The features of the collimating tube and the optical fiber bundle that connects it to the monocromator are shown The equipment was installed at the Izana GAW (Global Atmospheric Watch) station to calculate the extraterrestrial signal to 630 nm (Langley's method). Finally, the instrument was placed at Nautical School (at sea level) in Santa Cruz. A correlation about 85% between the Optronic and the NOAA satellites data was obtained. Our implementation of the King's method to retrieval the aerosol size distribution, considering a Maritime distribution for a set of wavelength was checked: the best agree was in the region between 0.1 and 5 ^tm.