Validation of OMI satellite erythemal daily dose retrievals using ground-based measurements from fourteen stations

The satellite Ozone Monitoring Instrument (OMI) erythemal daily dose (EDD) product is validated through an inter-comparison with ground-based measurements at 14 ground-based stations distributed worldwide between 43°N and 64°S in 5 different countries of both hemispheres: Argentina, Australia, Italy, Israel, and Spain. The results show that OMI data overestimate ground-based EDD measurements except in stations with high surface albedo (e.g., covered by snow), in agreement with the results reported by previous studies. The average differences between satellite and ground-based data reached a maximum of ~25% for all-sky cases. When cloudless conditions are selected, removing intra-daily changes in cloudiness, the agreement improves; although average differences between 10 and 20% still appear for seven low-albedo stations. The influences of ozone and aerosol on the observed differences show opposite trends: viz., high ozone column values result in a decrease whereas high turbidity conditions produce an increase in the differences. A correction factor based on the aerosol absorbing optical thickness was applied to correct for this effect, which is not considered in the OMI algorithm. After applying this correction, the agreement between OMI and ground-based EDD measurements improves and the difference between them falls below 20% for more than 90% of the cases at 8 stations. A dependence on station altitude is also noted for both all-sky and clear-sky cases.