Development of a UV Index Estimation Model Using Global Horizontal Irradiance from the GK-2A Satellite

 Ultraviolet(UV; 100–400 nm) radiation represents the short-wavelength portion of the solar spectrum and poses significant risks to human health, including skin aging, erythema, and skin cancer. Because excessive UV exposure induces erythemal responses of the skin, the UV Index(UVI), derived from erythemally weighted UV irradiance(EUV), is widely used as a public health indicator to communicate UV-related risk levels. Accurate estimation of UVI is therefore essential for both environmental monitoring and public health applications. In this study, we develop an empirical model to estimate UVI over South Korea using global horizontal irradiance(GHI) observations from the GK-2A geostationary satellite. The model incorporates key radiative and atmospheric parameters, including the clearness index derived from GK-2A GHI data, total ozone column, and solar zenith angle, in order to account for atmospheric attenuation processes and solar geometric effects governing surface UV radiation. The GK-2A GHI–based UVI estimates are evaluated against satellite-derived UVI products from the Geostationary Environment Monitoring Spectrometer(GEMS) onboard the GK-2B satellite. The comparison reveals a strong agreement between the two datasets, with a correlation coefficient(R) of 0.95, demonstrating that the proposed UVI estimation algorithm based on GK-2A GHI is physically consistent with spectrally resolved UV observations from GEMS. This high level of consistency indicates that broadband solar radiation measurements can be effectively utilized to reproduce biologically relevant UV metrics. These results highlight the potential of GHI-based UVI estimation as a robust complementary approach to conventional UV retrieval methods, particularly in regions with limited ground-based UV monitoring networks. Furthermore, the proposed framework enables high-resolution and continuous UVI monitoring, supporting applications in public health risk communication, climate studies, and operational UV exposure assessment. This study demonstrates that satellite-based GHI products can play a critical role in expanding the practical use of geostationary satellite observations for UV-related environmental and societal applications.