A comparative study of the UV index between OMI and ground-based measurements in Nepal

Abstract The study on solar ultraviolet radiation (UVR) is essential for understanding the solar status of any location, which enables the determination of the level of exposure to solar UV radiation and the necessary precautions to be taken at that location. The measurement of solar UV radiation and its validation are increasingly prevalent worldwide, using various ground-based observations and satellite estimates. This paper compares the Ozone Monitoring Instrument (OMI)/Aura satellite solar ultraviolet index (UVI) with the ground-based UVI measurements at Biratnagar, Pokhara, Kathmandu, and Lukla in Nepal using data from 2009 to 2012. Trend analysis of UVI using moving averages, a box plot of overpass UVI and Total Ozone Column (TOC) to analyze their trends, and a scatter plot for comparison of OMI overpass UVI with ground-based UVI. Statistical tools were used to compare the datasets for UVI in all-sky conditions. The results show that satellite estimates tended to overestimate ground-based UVI levels, with a mean bias, relative bias, MAPE, RMSE, correlation coefficient, and standard deviation of error corresponding to 0.92, 1.9, 28.44, 1.6, 0.69, and 1.44 for UVI, respectively. The result also shows that the altitude effect is found to be (6.5-8.8) %/km approximately.