Ground-based and Satellite Measurements of Solar Spectral Irradiances at 305 nm and 380 nm at a Tropical Site.

The solar radiation has been monitored through ground-based and satellite instruments all over the world for decades. This is also important for both checking and validation of satellite probing. In this work, we compare spectral irradiances at 305 nm (UV-B) and 380 nm (UV-A) from a ground-based radiometer and the Ozone monitoring instrument (OMI) for a tropical site in 2019-2020. Measurements had the auxiliary support of a ground-based imager to identify cloud cover. The presence of clouds introduces the largest differences between satellite and ground-based measurements. In fact, on average, for all-sky (AS, only cloudy skies) conditions such differences (satellite - ground-based) were 46% and 30% at 305 nm and 380 nm, respectively, while for cloud-free-sky (CFS) conditions, the differences dropped to 17% and 8%. In addition, the linear fitting between ground-based and satellite measurements yielded a coefficient of determination (r ) of 0.857 (for AS) and 0.984 (for CFS) at 305 nm and 0.774 (for AS) and 0.950 (for CFS) at 380 nm. The differences between these AS and CFS values of r were 95% statistically significant. Such results imply the hindrance clouds (and also aerosols based on the results for CFS) still set to obtain UV-B and UV-A surface irradiance from satellite probing.