The standard instrument of each SKYNET sites 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).
Products and algorithms
SKYNET provides the following optical and microphysical properties of aerosols;
- Aerosol optical thickness (AOT) at the following standard
wavelengths: 340, 380, 400, 500, 675, 870, 1020 nm
- Single scattering albedo (SSA) of aerosols at the same standard
wavelength of AOT
- Volume size distribution of aerosols
- Refractive index
- Phase function and asymmetry factor
These products are retrieved using SKYRAD.pack, a software package
implemented for the POM sky radiometer (e.g., Nakajima et al., 1996,
Hashimoto et al., 2012) that has been previously validated and
compared with other inversion algorithms (Che et al., 2008; Estelles
et al., 2012).
For better quality products, cloud screening is
conducted using a code, the Cloud Screening Sky Radiometer (CSSR)
(Khatri and Takamura, 2009).
Products are made available in semi-real
time for on-line sites and regularly for off-line sites.
Columnar ozone and water vapor estimations, as well as
cloud optical thickness using different wavelengths are under
development in the Regional Sub-Networks.
The sun-sky radiometers are monthly calibrated on site using the
improved Langley method (Nakajima et al., 1996, Campanelli et, 2004,
Inter-calibration of the sun-sky radiometers with a master
instrument calibrated using Langley method at a high mountain (e.g.,
Mt. Mauna Loa) is occasionally performed.
Furthermore, SKYNET has
conducted inter-comparison with AERONET Cimel sun-photometers and
precision filter radiometers (PFRs) at two SKYNET observation sites
(Chiba and Valencia) in recent years (Estelles et al., 2016) and will
continue this inter-comparison observation according to the
possibility of the instruments to remain co-located in these
sites. SKYNET has also the intention to participate to
inter-comparison programs and campaigns.
SKYNET continue updating retrieval and cloud screening codes as well
as calibration methodology as tasks of WGs within the SKYNET
- Campanelli, M., T. Nakajima, B.Olivieri: Determination of the solar
calibration constant for a sun-sky radiometer, Applied Optics, Vol. 43 No. 3, 20 January 2004
- Campanelli, M. V. Estelles, C. Tomasi, T. Nakajima, V. Malvestuto and
J. A. Martinez-Lozan: "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
- Che, H., G. Shi, A. Uchiyama, A. Yamazaki, H. Chen, P. Goloub,
and X. Zhang: Intercomparison between aerosol optical
properties by a PREDE skyradiometer and CIMEL sunphotometer over
Beijing, China, Atmos. Chem. Phys., 8, 3199-3214,
- Estelles, V., M. Campanelli, M. P. Utrillas, F. Exposito, and
J. A. Martinez-Lozano: Comparison of AERONET and SKYRAD4.2
inversion products retrieved from a Cimel CE318
sunphotometer. Atmos. Meas. Tech., 5, 569-579,
- Estelles, V., N. Kouremeti, M. Campanelli, J. Grobner, J.A. Mari
nez-Lozano, S. Kazadzis: Preliminary aerosol optical depth
comparison between ESR/SKYNET, AERONET and GAW international
networks. International SKYNET workshop, Rome (Italy) 2016.
- Hashimoto, M., T. Nakajima, O. Dubovik, M. Campanelli, H. Che,
P. Khatri, T. Takamura, and G. Pandithurai: Development of a new
data-processing method for SKYNET sky radiometer observations,
Atmos. Meas. Tech., 5, 2723-2737, 2012.
- Khatri, P., and T. Takamura: An algorithm to screen cloud
affected data for sky radiometer data analysis,
J. Meteor. Soc. Japan, 87, 189-204, 2009.
- Nakajima, T., G. Tonna, R. Rao, P. Boi, Y. Kaufman, and
B. Holben: Use of sky brightness measurements from ground for
remote sensing of particulate polydispersions, Appl. Opt., 35, 15,