Satellite based estimates of solar irradiance at the earth's surface—I. Modelling approaches

Abstract

Various approaches to the calculation of solar radiation at the earth's surface using satellite data are reviewed. The methods range from qualitative and subjective use of hard copy satellite images at low spatial and temporal resolution to the use of high resolution digital data and spectral radiative transfer models. Operational techniques are also described. These can be either statistically or theoretically based with varying degrees of numerical complexity. The nature of the input data requirements also varies. Some methods use widely available hard copy satellite images while others are based on digital data. There is also a wide variation in the requirements for additional environmental data. Some models meet all such requirements by analysis of the satellite data. Other models need such information as precipitable water derived from upper air soundings or empirical calculations. The accuracy of various models is assessed. Accuracy increases dramatically with averaging period (hourly to monthly). Many models, even some of the more easily implemented ones, are able to match the accuracy of the models which use surface based observations of cloud or bright sunshine.