Solar Radiation Measurement and Solar Radiometers

An instrument able to measure electromagnetic radiation, in its different forms and spectral ranges, is called a radiometer. This chapter focuses on the radiometers used for sensing solar radiation and on the measurements of different components and types of solar irradiance. As a simple classification, we will distinguish between broadband and spectral (narrowband) sensors. First, the fundamentals of physical sensors used to measure solar radiation are briefly described. Then, importance about calibration methods and uncertainty, as well as the structure of the traceability chain in the magnitude of solar irradiance, are presented. Next, solar radiometers and measurement techniques are described, starting from direct radiation in Earth’s surface, global irradiance in horizontal and tilted surfaces, diffuse irradiance, and finally another kind of radiation sensor. This structure is not casual but follows a path similar to that of the traceability chain, starting from the more accurate to the less accurate instruments. There are two additional sections devoted to the measurement of the spectral distribution of irradiance and to the measurement of aerosol contents in the atmosphere by using filter radiometers.