Toward a Broadband Parameterization Scheme for Estimating Surface Solar Irradiance: Development and Preliminary Results on MODIS Products

Abstract

A broadband parameterization scheme for estimating surface solar irradiance (SSI, ~ 0.3–4.0 μm) is developed based on extensive radiative transfer simulations on a diversity of atmospheric conditions. In the new scheme, the accumulated SSI arriving at the surface is considered as a whole, but the different radiative attenuations, such as the ozone absorption, permanent gas absorption, water vapor absorption, Rayleigh scattering, aerosol absorption and scattering, and cloud absorption and scattering, are accounted for separately. In particular, for the cloud radiative attenuations, the single scattering and multiple scattering of clouds are parameterized respectively to improve the accuracy. Compared with the complicated spectral radiative transfer model of LibRadtran (Emde et al., 2016, https://doi.org/10.5194/gmd-9-1647-2016), more than 90% of the SSI discrepancies are within ±5%, which means in theory the new parameterization scheme is very accurate. When the broadband parameterization scheme is practically applied to Moderate Resolution Imaging Spectroradiometer (MODIS) products, the validation results indicate that the high-quality instantaneous SSI can be thus acquired. At eight sites over China, R2 ranges from 0.86 to 0.96 and all RMSEs lie within 100 W/m2, while at seven sites over the United States, R2 fluctuates within the range of 0.82–0.94 and the RMSEs at most sites are <90 W/m2, with the exception of Table Mountain. The performance of the new parameterization scheme is comparable to those of more complicated methods such as the look-up-table methods and the δ-two-stream approximation methods. But it is more attractive due to its simplicity and efficiency.