The Cimel CE318 is a radiometer equipped with a 2-axis robot and a head sensor. The automatic pointing robot follows the observation sequences that have been scheduled and allows two types of basic radiation measurements: direct solar irradiance and sky (radiance) observations . A microprocessor computes the position of the sun based on time, latitude and longitude which directs the sensor head to within approximately one degree of the sun, after which a four quadrant detector tracks the sun precisely prior to a programmed measurement sequence.
The two collimators mounted on the head sensor were designed for straylight rejection for measurements of the aureole 3 degrees from the sun. The field of view (FOV) of the instrument is 1.2°.
The wavelengths in which the measurements are sequentially made by a single detector depend on the interference filters that each version of the radiometer has installed in the filter wheel, which is located inside the sensor head and which is moved by a stepper motor.
The Cimel version installed in the BAQUNIN Super Site mounts the filters for the wavelengths 340, 380, 440, 500, 675, 870, 1020 and 1640 nm. The components of the sensor head are sealed from moisture and desiccated to prevent damage to the electrical components and interference filters.
The intensities of the direct and scattered solar radiations recorded with the photometer are interpreted by standard algorithms at the AERONET processing center.
The algorithm for estimating aerosol parameters from the solar photometer measurements consists in the analysis of spectral attenuation by the atmosphere. The absolute error of the spectral aerosol optical thickness (AOT) is 0.01–0.02 under the conditions of regular photometer calibration (occurring approximately every 300 day). In addition to the AOT, the standard AERONET data interpretation includes the parameterization of the spectral dependence of the AOT (Ångstrom exponent) and spectral single scattering albedo (SSA). The CIMEL measurements allow estimating the total water vapor.
Philippe Goloub, <a href=”mailto:email@example.com” target=”_blank” rel=”noopener noreferrer”>firstname.lastname@example.org</a>
Anna Maria Iannarelli, <a href=”mailto:email@example.com” target=”_blank” rel=”noopener noreferrer”>firstname.lastname@example.org</a>
Monica_Campanelli, <a href=”mailto:email@example.com” target=”_blank” rel=”noopener noreferrer”>firstname.lastname@example.org</a>
<u><a href=”https://aeronet.gsfc.nasa.gov/” target=”_blank” rel=”noopener noreferrer”>https://aeronet.gsfc.nasa.gov/</a></u>