Analysis of the Influence of Input Conditions on the Diffuse Attenuation Coefficient for Downwelling Irradiance Based on the Radiative Transfer Model

The diffuse attenuation coefficient for downwelling irradiance (K d ) represents the exponential decrease of light with depth due to scattering and absorption in seawater, and is one of the key products for describing ocean optical properties.To estimate K d over broad oceanic regions, semi-analytical models utilizing remote-sensing reflectance (R rs ) and inherent optical properties (IOPs) derived from satellite observations are commonly employed.Among these, K d models based on radiative transfer simulations often consider only the solar zenith angle (SZA) among various atmospheric and water quality variables, which can lead to discrepancies between estimated and actual values.In this study, we investigate the effects of four atmospheric variables-SZA, wind speed, aerosol type, and aerosol optical depth (AOD)-on K d using radiative transfer simulations.To reflect varying water quality, simulations were conducted for three water types: clear, intermediate, and turbid.By analyzing the change in K d values as each environmental variable was changed from its minimum to maximum condition, we found that SZA had the greatest impact, followed by AOD.In contrast, wind speed and aerosol type showed minimal influence and may be excluded from future algorithm improvement considerations.When analyzing K d estimated from the semi-analytical model, SZA-induced errors reached up to 28.17% in turbid waters, and AOD-related errors were as high as 17.93%.Although the semi-analytical model theoretically accounts for SZA, significant discrepancies were still observed, especially under turbid conditions.Therefore, to improve the accuracy of K d estimation, the influence of SZA should be prioritized, and additional corrections for AOD and turbidity should also be incorporated into the K d model development.This study identifies key environmental variables affecting K d retrieval and suggests directions for improving the model, contributing to the development of more accurate K d algorithms applicable under diverse marine conditions.