The Cimel CE-318 is a multi-wavelength automatic sun-photometer that measures direct solar irradiance and sky radiance at seven bands centered at 340 nm, 380 nm, 440 nm, 500 nm, 675 nm, 870 nm, 939 nm, and 1020 nm (10 nm FWHM), with a field of view of 1.2░.
The photometer is programmed to perform either direct sun or sky radiance measurements several times during the day, for airmass values below 7.
The direct sun measurements are made at all seven wavelength bands. The aerosol optical depth is derived at 340 nm, 380 nm, 440 nm, 500 nm, 675 nm, 870 nm, and 1020 nm using the Beer-Bouguer law, after removing the extinction due to Rayleigh scattering, ozone and other gas absorption. The 939 nm channel is used to estimate the column water vapor.
Additionally, the instrument measures sky radiance in four bands (440, 675, 870, and 1020 nm) along the solar principle plane (at fixed azimuth angle equal to the sun azimuth and changing the scattering angle) and along the solar almucantar (at fixed elevation angle and changing the azimuth angle). Using the inversion of Dubovik and King [A flexible inversion algorithm for the retrieval of aerosol optical properties from sun and sky radiance measurements, JGR, 105, 20673-20696, 2000], the aerosol size distribution in the size range 0.1-15 Ám, the phase function and refractive indices are derived.
The Cimel installed at the ENEA laboratory is part of the Aerosol Robotic Network (AERONET) and is identified with the #172. The instrument was first operated by the University of Modena and Reggio Emilia from 2000 to 2005. Since March 2010 the instrument is operated on the roof of one of the ENEA buildings jointly by ENEA and the University of Modena and Reggio Emilia.
The instrument was calibrated in 2009 and 2011 at the NASA GSFC facility, and in 2013 at the GOA facility under ACTRIS.
Picture of the Cimel #172 installed at Lampedusa