Parameterization of a spectral solar irradiance model for the global ocean using multiple satellite sensors

Abstract

Monthly and seasonal means of the spectral solar radiation at the sea surface is determined at global scale (1° × 1° grid) from satellite composite imagery. The transmittance functions of each atmospheric component have been modified from an existing clear-sky radiative model to assimilate data sets from multiple satellite sensors, including the Sea-viewing Wide Field-of-view Sensor (NASA). All satellite-derived parameters and other climatologies were resampled at common scales in time and space, and a cloud correction scheme has been implemented by comparing two different methods based on ultraviolet reflectance from the Total Ozone Mapping Spectrometer (NASA) and cloud fraction from the Special Sensor Microwave Imager (NASA), respectively. The new "PARsat" model relies on a complete computation of the radiative transfer at each grid point, while being less dependent on some meteorological parameters that are often known at local scale only. Although PARsat is a full spectral model providing downwelling irradiance at daily scale and up, the model is applied for 1997 up to present, and only the results for 1998 are shown in this work as monthly global maps of surface photosynthetically active radiation (PAR). A comprehensive evaluation of the model is conducted through comparisons with monthly PAR values obtained globally with other well-referenced models and with a large data set of in situ measurements. An overall uncertainty of 5.2% is obtained when the performance of the model is validated with in situ measurements collected from two array systems of moored buoys.