The Cimel CE318 sunphotometer measures the radiation received from the sun at 15 wavelengths in the wavelength range 340 nm to 1640 nm. It uses these measurements to deduce the aerosol optical thickness (AOT) of the atmosphere at these wavelengths. It order to do this reliably, there must be no cloud present in the direction of the sun for the duration of the measurements. If the sky is clear enough it can also derive other quantities such as particle size, real and imaginary components of refractive index and phase function at various wavelengths.
Many other sensors at Chilbolton, such as the lidars and the Grimm Optical Particle Counter, are sensitive to aerosols. As well as being useful in their own right, the sunphotometer measurements can be used to better quantify the remote aerosol measurements from the lidars.
The sunphotometer operates continuously, but needs the sun to be at a sufficient elevation and to not be partially nor totally obscured by cloud in order to operate. It contributes measurements to the worldwide AERONET (link opens in a new window) network.