How is solar ultraviolet radiation measured?
The principal setup of an instrument measuring UV radiation is the following: First, radiation enters through fore-optics, which make sure that both radiation coming directly from the sun and also radiation scatted by air molecules is entering the remainder of the system. The next part is a filter, which allows only photons of a specific wavelength range to pass. There are many ways how in practice this filter is implemented. It may be a filter selecting the whole UV range. Or, the transmission of the filter resembles the (wavelength dependent) response of a specific biologic system (for example human skin). In this case, the instrument’s signal is directly proportional to the biological effect that is caused by the incident radiation. A third instrument class are so called “spectroradiometers”. They split up the whole UV range in several “sub-colors”. A typical spectroradiometer used for solar UV measurements would for example measure the whole UV range in steps of 1 nm (see FAQ “What
