ESR is a research and development network providing the following products:
1. The Standard inversion
from Skyrad.pack processes both the direct and diffuse measured irradiances from POMs instruments.
Products are: aerosol optical depth at all the available wavelengths, Angström exponent using all the
available wavelengths from 400 to 1020 nm, single scattering albedo, phase function,complex refractive index and
aerosol size distribution.
Products are provided at 4 different levels:
Level 0: daily analysis are performed using the last available calibration constants. Burden of absorbent gases (O3 and NO2) are chosen from nominal values or previous climatologies. Daily plots of Level O output, when available, are shown in the main page of each site, together with the Level O data previously processed within the same month.They can be daily downloaded from the ARCHIVE link.
Level 1: data are re-processed at the end of each month after the calculation
of the last solar calibration constants, and, when possible, updating the measured gases contents.
They can be monthly downloaded from the ARCHIVE link.
Level 2: the following screening criteria are applied to Level 1 data
- Reject result if retrieval error is greater than 0.07
- Reject result for irregular volume size distribution
Level 3: the following screening criteria are applied to Level 1 data
- Reject result if AOT(500nm) is less than 0.4
- Reject result if retrieval error is greater than 0.07
- Reject result for irregular volume size distribution
The Cloud screening is performed using the method described by Khatri and Takamura (2009).
Two types of products are possible:
Cloud screening 1: is performed when measurements of global irradiance are not available.
Cloud screening 2: is performed using simulataneous and co-located measurements of global irradiance.
2. The Custom inversion
(ESR.pack) is an open source code, developed in two modules:
Sunrad module:
This module processes only the direct sun measurements.
Products are: aerosol optical depth and Angström exponent using all the wavelenghts from 400 to 1020 nm.
This module is implemented in two different modes:
Level 0:
daily analysis are performed using the last available
calibration constants. Burden of absorbent gases (O3 and NO2) are chosen from nominal values
or previous climatologies.
Daily plots of Level O processing, when available, are shown in the main page of each site, together with the Level O
data previously processed within the same month. They can be daily downloaded from the ARCHIVE link.
Level 1:
data are re-processed at the end of each month after the
calculation of the last solar calibration constants, and, when possible, updating the measured gases contents.
They can be monthly downloaded from the ARCHIVE link.
The Cloud screening is performed using a procedure based on the methodology developed by Smirnov et al. (2000).
Data from CIMEL CE 318 are cloud screened using the method explained by Holben et al. (1998).
In the solar aureole technique, two different calibrations are needed:
The solar calibration constant (F0):
it is the signal corresponding to the solar irradiance incident at
the top of the atmosphere. All the instruments in ESR and SKYNET are calibrated
using an in situ procedure called Improved Langley (Campanelli et al 2004; Campanelli et al. 2007), a modified version of the standard Langley plot technique.
In the Improved Langley, F0 is retrieved by fitting the natural logarithm of the direct solar irradiance versus
the product of the relative optical air mass and the total extinction optical thickness (retrieved by the inversion)
instead of the air mass alone, as done with the standard Langley plot. This in situ calibration
procedure allows the operators to track and evaluate the calibration status on a continuous basis, keeping the revision of the
instrument mostly for maintenance reasons and offering the advantage of reducing the number of instrument expeditions. In this way, the
data gaps incurred by the periodical shipments are considerably reduced, and the likelihood of instrumental damages attributable to
transport also decreases.
ESR calibrates its instruments on a monthly base.
In order to observe the requirements from WMO, ESR and SKYNET instruments are periodically calibrated at the WRCC in
Davos and at the MAUNA LOA laboratory, respectively. Some ESR instruments attended the
QUATRAM campaign for in 2017-2019 treacebility studies
and validation of the Improved Langley technique.
The Solid view angle:
it corresponds to the field of view of the instrument. Its value can be approached by the geometric solid
viewing angle of the telescope. However, several factors contribute to this value: color aberration of the lens,
diffraction at the edges, misalignment of the optical axis, and surface nonuniformity of filters and sensor.
As a consequence, an in situ method is made available for determining the actual solid view angle (only
for PREDE sun-sky radiometers) from optical data. This in situ method consists on performing a scanning of the
irradiance field around the Sun, centered at the origin of a local system of rectangular coordinates
(Boi et al. 1999).
ESR mostly assumes this value as privided by the company using the above method.
T. Nakajima, M. Tanaka and T. Yamauchi, Retrieval of the optical properties of aerosols from the aureole and extinction data. App. Opt. No.22, pp.2951-2959, 1983.
T. Nakajima, G. Tonna, R. Rao, P. Boi, Y. Kaufman and B. Holben, Use of sky brightness measurements from ground for remote sensing of particulate polydispersions. App. Opt. vol.35,No.15, pp.2672-2686, 1996.
M. Hashimoto, T. Nakajima, O.Dubovik, M. Campanelli, H. Che, P. Khatri, T. Takamura, G. Pandithurai, Development of a new data-processing method for SKYNET sky radiometer observations, Atmos. Meas. Tech., 5 (11), pp. 2723-2737, 2012.
Kudo, R., Nishizawa, T., and Aoyagi, T.: Vertical profiles of aerosol optical properties and the solar heating rate estimated by combining sky radiometer and lidar measurements, Atmos. Meas. Tech., 9, 3223–3243, https://doi.org/10.5194/amt-9-3223-2016, 2016.
Kudo, R., 2019.2.13, Developement of aerosol and cloud retrieval methods using the sky radiometer, 5th International SKYNET workshop, New Delhi, India
V. Estellés, M. Campanelli, T. J. Smyth, M. P. Utrillas, and J. A. Martínez-Lozano. "AERONET and ESR sun direct products comparison performed on Cimel CE318 and Prede POM01 solar radiometers". Atmos. Chem. Physics Discuss. 12, 4341-4371, 2012, doi:10.5194/acpd-12-4341-2012.
V. Estellés, M. Campanelli, T.J. Smyth, M.P. Utrillas and J.A. Martinez-Lozano, Comparison of AERONET and SKYRAD4.2 inversion products retrieved from a Cimel CE318 sunphotometer, Atmos. Meas. Tech., 5, 1-11, 2012.
M. Campanelli, T. Nakajima, B.Olivieri, "Determination of the solar calibration constant for a sun sky radiometer. Proposal of an in situ procedure". Applied Optics, Vol 43 n. 3, 20 January 2004
M. Campanelli, V. Estellés, C. Tomasi, T. Nakajima, V. Malvestuto and J. A. Martínez-Lozano. "Application of the SKYRAD improved Langley plot method for the in situ calibration of CIMEL sun-skphotometers" Vol. 46, No. 14 May, 2007, Applied Optics.
Paolo Boi, Glauco Tonna, Giuseppe Dalu, Teruyuki Nakajima, Bruno Olivieri, Alberto Pompei, Monica Campanelli, and R. Rao, "Calibration and data elaboration procedure for sky irradiance measurements," Appl. Opt. 38, 896-907 (1999).
Khatri, P. and T. Takamura. "An algorithm to screen cloud-affected data for sky radiometer data anlaysis". J. Meteorol Soc. Jpn., 87, 189-204,2009.