Product & Method


The standard instrument of each SKYNET site is the sun-sky radiometer Prede Co. Ltd. model POM. The sun-sky radiometer is a scanning spectral radiometer able to perform routine and long-term automated measurements of direct and scattered solar radiations at seven wavelengths from 315 to 1020 nm (model POM-01) or eleven wavelengths from 315 to 2200 nm (model POM-02).


Objective and
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ISDC implements two data analysis flows (SR-CEReS & ESR-MRI) and provides two types of standard products by the above two data analysis flows. The following are typical products provided by the two analysis flows(*1). Related information can be found here.

You can download or view the products from here.

(*1) The wavlengths and products differ slightly depending on the instruments used, analysis flow, and measurement defects. Columnar ozone and water vapor estimations, as well as cloud optical thickness using different wavelengths are under development in the Regional Sub-Networks.
(*2) The wavelengths used for AE calculation are the same wavelength of AOT for SR-CEReS; those are wavelengths of 400, 500, 675, 870, and 1020 nm for ESR-MRI.

--- Release of Standard Products---

< SR-CEReS flow >
  ISDC releases the near-real time data as Level 2 (L2).

< ESR-MRI flow >
  ISDC releases the following levels of data:

(*3) The calibration constants are available for the Principal Investigators (PIs) of the instruments and anyone who explicitly requests them to ISDC.

Method & Calibration

In the above two analysis flows, the products are retrieved mainly using SKYRAD.pack, a software package implemented for the POM sky radiometer (e.g., Nakajima et al., 1996) that has been previously validated and compared with other inversion algorithms (Che et al., 2008; Estelles et al., 2012a). The SKYRAD.pack and calibration methods used for each analysis flow are as follows. Related information can be found here.

< SR-CEReS flow >

< ESR-MRI flow >

Other calibration activities


Campanelli M. et al., Determination of the solar calibration constant for a sun-sky radiometer, Applied Optics, Vol. 43 No. 3, 20 January 2004

Campanelli M. et al., Application of the SKYRAD improved Langley plot method for the in situ calibration of CIMEL sun-sky photometers, Applied Optics. Vol. 46, No. 14 May, 2007

Campanelli M. et al., The SKYNET radiometer Network: Aerosol Optical Depth retrieval performance at the ERC-IV campaign and long-term comparison against GAW-PFR and AERONET standard instruments, WMO Technical Conference on Meteorological and Environmental Instruments and Methods of Observation (CIMO TECO 2016), 2016

Che H. et al., Intercomparison between aerosol optical properties by a PREDE skyradiometer and CIMEL sunphotometer over Beijing, China, Atmos. Chem. Phys., 8, 3199-3214, doi:10.5194/acp-8-3199-2008, 2008

Estelles V., et al., Comparison of AERONET and SKYRAD4.2 inversion products retrieved from a Cimel CE318 sunphotometer. Atmos. Meas. Tech., 5, 569-579, doi:10.5194/amt-5-569-2012, 2012a

Estelles V., et al., AERONET and ESR sun direct products comparison performed on Cimel CE318 and Prede POM01 solar radiometers, Atmos. Chem. Physics Discuss. 12, 4341-4371, doi:10.5194/acpd-12-4341-2012, 2012b

Estelles V., et al., Preliminary aerosol optical depth comparison between ESR/SKYNET, AERONET and GAW international networks. International SKYNET workshop, Rome (Italy) 2016.

Kaufman YJ. et al., Aerosol climatology using a tunable spectral variability cloud screening of AERONET data, Geophys. Res. Lett., 33,, 2006

Kudo R. et al., Optimal use of the Prede POM sky radiometer for aerosol, water vapor, and ozone retrieavls, Atmos. Meas. Tech., 14, 3395-3426, 2021

Smirnov et al. Cloud screening and quality control algorithms for the AERONET database, Remote Sens. Environ, 73, 337-349, 2000

Khatri P., and Takamura T., An algorithm to screen cloud affected data for sky radiometer data analysis, J. Meteor. Soc. Japan, 87, 189-204, 2009.

Momoi M. et al., Development of on-site self-calibration and retrieval methods for sky-radiometer observations of precipitable water vapor, Atmos. Meas. Tech., 13, 2635-2658,, 2020.

Nakajima T.,et al., Use of sky brightness measurements from ground for remote sensing of particulate polydispersions, Appl. Opt., 35, 15, 2672-2686, 1996.

Nakajima T. et al., An overview of and issues with sky radiometer technology and SKYNET, AMT, 13, 4195-4218, 2020.

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