====== CIMEL sun photometer ======

{{:wiki:instruments:cimel01.jpg?direct&600|JOYCE-TOPHAT ©B. Pospichal}} \\
//HATPRO-TOPHAT installed at Jülich//

===== Principle =====

The CIMEL sun photometer performs measurements of spectral sun irradiance and sky radiances. It is part of the Aerosol Robotic Network (AERONET).
It measures spectral aerosol optical Depth (AOD), inversion products, and precipitable water in diverse aerosol regimes. Aerosol optical depth data are computed for three data quality levels: Level 1.0 (unscreened), Level 1.5 (cloud-screened), and Level 2.0 (cloud screened and quality-assured). Inversions, precipitable water, and other AOD-dependent products are derived from these levels and may implement additional quality checks. 
More information can be found on the [[https://aeronet.gsfc.nasa.gov/|Aeronet website]]


===== Measurement modes =====

  * Direct sun measurements in eight spectral bands (340, 380, 440, 500, 670, 870, 940 and 1020 nm)
  * Extinction is calculated from these measurements in each channel and Aerosol optical depth determined.
  * Temporal resolution 15 minutes
  * Sky radiance observations along the solar principal plane and almucantar observations are performed up to 9 and 6 times per day, respectively. From these data, aerosol size distribution and phase function can be derived.

 

===== JOYCE-CF Standard Operation Procedures =====
  * Operations according to AERONET standards (see above)

===== Calibrations =====
  * Absolute calibration 1x/year

===== Data quality assurance procedures =====
  * Data screening according to AERONET standards 

===== Data availability =====

All data are available via the AERONET data portal [[https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3?site=FZJ-JOYCE&nachal=2&level=2&place_code=10|AERONET data portal]]. 

 
^ Dataset     ^ Temporal resolution       ^ File size          ^ Filename   ^ Retrieval / Remarks   ^ 
| Aerosol optical depth (8 spectral bands)   | ~15 minutes   |      |   |   |
| Precipitable water   | ~15 minutes   |      |   |   |
| Ångström exponent   | ~15 minutes   |      |   |   |



===== Link to current observations =====

Current observations at [[https://aeronet.gsfc.nasa.gov/cgi-bin/data_display_aod_v3?site=FZJ-JOYCE&nachal=2&level=2&place_code=10|AERONET data portal]]



===== Measurement examples =====

{{wiki:examples:aod_20171017.gif?direct&450|AERONET-AOD}}
{{wiki:examples:pw_20200804.gif?direct&450|AERONET-IWV}} \\
//Time series of Aerosol Optical Depth (left) and Integrated Water Vapor (right) from sun photometer//






===== Specifications =====
^  Parameter                    ^  Specification                                  ^ 
| Spectral channels  | 340, 380, 440, 500, 675, 870, 937, 1020, 1640 nm  |
| Azimuth range  | 0° – 360°  |
| Zenith range  | 0° – 180°  |
| Tracking resolution  | 0.003°   |
| Sun / Moon tracking accuracy (automatic active tracking)  | 0.01°   |
| Full scale digital count precision  | < 0.1%   |
| Half field of view  | 0.63°  |
| Smallest scattering angle (from the sun) for sky measurements  | 2°  |
| Spectral range  | Si detector: from 340 to 1020 nm \\ InGaAs detector: from 1020 to 1640 nm  |
| Long term drift of single band filters’ transmission rate  | < 1% / year   |