Monitoring coastal areas: a brief history of measuring instruments for solar radiation

The beginning of the development of instruments for the measurement of solar radiation is quite recent even though this quantity is the main engine of environmental physics and marine and terrestrial biology and their primary connection element as it was highlighted by environmental physics studies since second half of the 19th century. Although already in the classical era there were some mentions to the concept of solar radiation, in terms of heat and light, discussions on the role of the Sun remained on a philosophical level until the scientific revolution when the first studies were made, in the astronomical field, about solar radiation. Only in the first half of the 19th century the first specific instruments were made for measuring solar radiation for meteorological purposes such as the Pouillet pyrheliometer.The birth of the Organization Météorologique Internationale, OMI, (1879) started the process that will lead to the standardization of instruments and observation methodologies for solarimetry. In 1896 OMI established the Solar Radiation Commission. In 1905, Third Conference of Directors of National Meteorological Services decided to take the Ångström pyrheliometer as a standard instrument. In the following decades, other types of radiometers were development to measure the other components of solar radiation (such as the Robitzsch pyranograph in 1932) from which began the realization of instruments whose signal could be recorded analogically on the acquisition data system. Other pyranometers were realized to measure the intensity of the radiation using the Moll-Gorczynki thermopile; other versions were built using a photocell as a sensitive element.In the last decades of the 20th century, digital recording instruments for radiometry were also realized. Furthermore, instruments have been developed that drastically reduce maintenance operations, an essential aspect for quantities measures, such as sunshine duration and diffuse radiation, performed in remote and difficult to reach sites. In the 2000s, for studies concerning physical and biological marine-oceanic quantities, apparatuses were developed for measuring solar radiation in the water column in the global blue, green and red ranges.