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CIMEL sun photometer

JOYCE-TOPHAT ©B. Pospichal
HATPRO-TOPHAT installed at Jülich


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 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)


  • 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 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

Current observations at AERONET data portal

Measurement examples

Time series of Aerosol Optical Depth (left) and Integrated Water Vapor (right) from sun photometer


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
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
cimel.txt · Last modified: 2022/01/19 19:09 by bpospich