Zhengqiang Li, Luc Blarel, Thierry Podvin, Philippe Goloub, Jean-Pierre Buis, and Jean-Philippe Morel, "Transferring the calibration of direct solar irradiance to diffuse-sky radiance measurements for CIMEL Sun-sky radiometers," Appl. Opt. 47, 1368-1377 (2008)
Two types of sunphotometric measurement are considered in this study: direct-Sun irradiance and diffuse-sky radiance. Based on CIMEL CE318 Sun–sky radiometer characteristics, we introduce a gain-corrected solid angle that allows interconverting calibration coefficients of these two types of measurement, thus realizing a “vicarious” radiance calibration. The accuracy of the gain-corrected solid angle depends on the number of available historical calibration records. The method is easy to use, provided that at least one laboratory calibration has been made previously. Examples coming from three distinct CE318 versions belonging to the AERONET/PHOTONS network are presented to provide details on the vicarious calibration method and protocols. From the error propagation analysis and the comparison with laboratory results, the uncertainty of the vicarious radiance calibration is shown to be comparable with the laboratory one, e.g., 3%–5%.
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Instrument Characteristics with Respect to CE318 Functions and Versionsa
Function
Application
Collimator
Detector
Internal Gain
User Gain
User Gain Parameter
Scanning Angle Range
s
Direct-Sun irradiance
Sun
Sun
a
Aureole radiance
Sun
Sun
k
Dark-sky radiance
Sun (NE, DP)
Sun (NE, DP)
max
Sky (1, 2, N)
Sky (1, 2, N)
Versions 1, 2, N, NE and DP in parenthesis. Among different CE318 versions, N, NE and DP are equipped with new electronic compo nents providing better accuracy than versions 1 and 2. More information can be found in the CE318 user manual ( in this table is written as in the user manual) and the AERONET Web (http://aeronet.gsfc.nasa.gov/new_web/system_descriptions_instrument.html)
Table 2
Typical Uncertainties (%) in the Calibration Parameters for CIMEL Radiometers Belonging to AERONET/PHOTONS Networka
UV
Visible and Near-IR
MIR
Ave
340
380
440
500
675
870
1020
1640
733
FWHM ()
2
2
10
10
10
10
10
25
10
3.0
1.0
3.6
1.6
0.3
3.0
1.1
4.0
2.2
(master)
2.0
1.0
0.5
0.5
0.5
0.5
0.5
0.5
0.75
(field)
3.0
2.0
1.5
1.5
1.5
1.5
1.5
1.5
1.75
(lab)
(master)
(field)
Case A: vicarious calibration usingderived from 3 wavelengths (440, 675, and)
(field)
(field)
Case B: vicarious calibration usingderived from 4 wavelengths (440, 500, 675, and)
(field)
(field)
Master and field instruments are presented separately.
Table 3
Modeled CIMEL Band Extraterrestrial Solar Irradiance
Using () derived from nine years of calibration records, and comparison with laboratory results (2 February 2007). units,
Units,
Dif., difference between vicarious and laboratory calibration coefficients.
Table 5
Vicarious Radiance Calibration for Radiometer no. 140 (CE318-NE Version) and Comparison with Laboratory Resultsa
λ (nm)
(DN)
vica
lab
vica
lab
Dif. (%)
Dif. (%)
1020
69.97
14178.16
0.0625
0.01815
0.01835
64.02
16
0.004536
0.004588
870
95.61
21680.13
0.0625
0.01563
0.01523
64.02
16
0.003907
0.003808
2.7
2.6
675
149.58
23531.63
0.0625
0.02253
0.02208
64.02
16
0.005632
0.005520
2.1
2.0
440
188.47
16362.70
0.0625
0.04083
0.03993
64.02
16
0.01021
0.009969
2.3
2.4
500
196.32
20722.76
0.0625
0.03358
0.03380
64.02
16
0.008394
0.008449
Vicarious calibration 15 June 2007; laboratory results 22 June 2007; units and abbreviations as in Table 4.
Table 6
Verifying Laboratory Radiance Calibration versus the Vicarious Method for Radiometer no. 350 (CE318-DP Version).a
λ (nm)
(DN)
vica
lab
Dif. (%)
1020
69.81
9330.75
0.125
0.01842
0.01857
870
96.01
18129.04
0.125
0.01266
0.01283
675
148.56
21303.95
0.125
0.01667
0.01626
2.5
440
191.26
13516.38
0.125
0.03382
0.03354
0.8
500
196.69
18774.12
0.125
0.02504
0.02552
380
116.77
33369.94
4
0.26763
0.26784
340
100.67
20258.84
4
0.38005
0.40114
Laboratory calibration 2 August 2006; units as in Table 4.
Tables (6)
Table 1
Instrument Characteristics with Respect to CE318 Functions and Versionsa
Function
Application
Collimator
Detector
Internal Gain
User Gain
User Gain Parameter
Scanning Angle Range
s
Direct-Sun irradiance
Sun
Sun
a
Aureole radiance
Sun
Sun
k
Dark-sky radiance
Sun (NE, DP)
Sun (NE, DP)
max
Sky (1, 2, N)
Sky (1, 2, N)
Versions 1, 2, N, NE and DP in parenthesis. Among different CE318 versions, N, NE and DP are equipped with new electronic compo nents providing better accuracy than versions 1 and 2. More information can be found in the CE318 user manual ( in this table is written as in the user manual) and the AERONET Web (http://aeronet.gsfc.nasa.gov/new_web/system_descriptions_instrument.html)
Table 2
Typical Uncertainties (%) in the Calibration Parameters for CIMEL Radiometers Belonging to AERONET/PHOTONS Networka
UV
Visible and Near-IR
MIR
Ave
340
380
440
500
675
870
1020
1640
733
FWHM ()
2
2
10
10
10
10
10
25
10
3.0
1.0
3.6
1.6
0.3
3.0
1.1
4.0
2.2
(master)
2.0
1.0
0.5
0.5
0.5
0.5
0.5
0.5
0.75
(field)
3.0
2.0
1.5
1.5
1.5
1.5
1.5
1.5
1.75
(lab)
(master)
(field)
Case A: vicarious calibration usingderived from 3 wavelengths (440, 675, and)
(field)
(field)
Case B: vicarious calibration usingderived from 4 wavelengths (440, 500, 675, and)
(field)
(field)
Master and field instruments are presented separately.
Table 3
Modeled CIMEL Band Extraterrestrial Solar Irradiance
Using () derived from nine years of calibration records, and comparison with laboratory results (2 February 2007). units,
Units,
Dif., difference between vicarious and laboratory calibration coefficients.
Table 5
Vicarious Radiance Calibration for Radiometer no. 140 (CE318-NE Version) and Comparison with Laboratory Resultsa
λ (nm)
(DN)
vica
lab
vica
lab
Dif. (%)
Dif. (%)
1020
69.97
14178.16
0.0625
0.01815
0.01835
64.02
16
0.004536
0.004588
870
95.61
21680.13
0.0625
0.01563
0.01523
64.02
16
0.003907
0.003808
2.7
2.6
675
149.58
23531.63
0.0625
0.02253
0.02208
64.02
16
0.005632
0.005520
2.1
2.0
440
188.47
16362.70
0.0625
0.04083
0.03993
64.02
16
0.01021
0.009969
2.3
2.4
500
196.32
20722.76
0.0625
0.03358
0.03380
64.02
16
0.008394
0.008449
Vicarious calibration 15 June 2007; laboratory results 22 June 2007; units and abbreviations as in Table 4.
Table 6
Verifying Laboratory Radiance Calibration versus the Vicarious Method for Radiometer no. 350 (CE318-DP Version).a
λ (nm)
(DN)
vica
lab
Dif. (%)
1020
69.81
9330.75
0.125
0.01842
0.01857
870
96.01
18129.04
0.125
0.01266
0.01283
675
148.56
21303.95
0.125
0.01667
0.01626
2.5
440
191.26
13516.38
0.125
0.03382
0.03354
0.8
500
196.69
18774.12
0.125
0.02504
0.02552
380
116.77
33369.94
4
0.26763
0.26784
340
100.67
20258.84
4
0.38005
0.40114
Laboratory calibration 2 August 2006; units as in Table 4.