However, the amount of data are sparse and scattered, and the too good results may be a cancellation of errors of opposite sign. In conclusion, the CIE-irradiances apparently agree within ±5 percent to the GUV, but a larger data set is required to verify these results.
Table 3.4.3.2.2: Average ratio in CIE-weighted irradiance, relative to GUV#9273.
Time Optronic/GUV Macam/GUV
day 158, 11 UTC 0.98 1.03
day 158, 15 UTC 0.93 1.01
day 158,
average 10.25 UTC to 14.25 UTC 1.02±0.05 1.03±0.02 day 159,
average 10.25 UTC to 17.45 UTC - 0.96±0.11
All the seven GUV 541 and NILU UV-4S at the intercomparison platform
At NRPA, the spectral response of GUV instruments have been measured (not published). By knowing the spectral response data, it is possible to simulate the signal ratios for different source spectra and compare with the real measurements. In Fig 4.1.1 the solar spectra measured by the Brewer at 11 UTC and 15 UTC have been multiplied with the spectral response for the 305nm and 313nm detector channels, and normalized to the same wavelengths. As can be seen by comparing dashed curves (11 UTC) with continuous curves (15 UTC) the product curves become shifted towards longer wavelengths for increasing solar zenith angles. The reason for this asymmetry is the relatively larger attenuation of fluxes towards the shorter wavelengths for higher zenith angles. By comparing ratios of area under curves for respectively the 305-channel and 313-channel, one finds that the areas increase by respectively 4 % (305) and 3 % (313) compared to noon scans, in excellent agreement with the observations in Fig. 3.4.3.1.3 and Table 3.4.2.2a.
It may now be interesting to compare the simulated ratios of 313 to 305 channels for noon and afternoon scans, and compare with the real measurement ratios, as shown in Table 4.1.1 below.
As can be seen, the agreement is within 0.2 %, which provides evidence that the Brewer scans and the spectral response data are quite reliable.
Table 4.1.1 Computed and measured irradiance ratio for 313-channel and 305-channel at noon and afternoon.
11 UTC 15 UTC
S E d
S E d
3 1 3 3 0 5 , ,
λ λ
λ λ
λ λ
∫
∫
8.233 12.785< >
< >
E E
GUV GUV , ,
313 305
, [ / / ]
[ / / ]
µ µ
W cm nm
W cm nm
2
2 4.831 7.486
Simulated measured
12 785 8 233 7 486 4 831
. / .
. / . = 0.998
B re w e r s p e c tra a t 1 1 :0 0 U T C a n d 1 5 :0 0 U T C , n o rm a liz e d a t 3 0 5 n m a n d 3 1 3 n m a n d m u ltip lie d w ith s p e c tra l re s p o n c e c u rve s o f G U V # 9 2 7 3 .
0 .0 0 0 .2 0 0 .4 0 0 .6 0 0 .8 0 1 .0 0 1 .2 0 1 .4 0 1 .6 0 1 .8 0
2 9 0 2 9 2 2 9 4 2 9 6 2 9 8 3 0 0 3 0 2 3 0 4 3 0 6 3 0 8 3 1 0 3 1 2 3 1 4 3 1 6 3 1 8 3 2 0 3 2 2 3 2 4
W a v e le n g th , n m
Relative units
"3 0 5 n m "1 1 :0 0
"3 0 5 n m "1 5 :0 0
"3 1 3 n m "1 1 :0 0
"3 1 3 n m "1 5 :0 0
Fig.4.1.1: Multiplication of noon (dashed curves) and afternoon (whole lines) solar spectrum with the response curves for two channels of the GUV#9273 instrument. The difference between area below curves represents the relative gain in signal for increasing SZA's .
4.2 Intercomparison of network GUV-instruments
The instruments purchased for the Norwegian UV-network are of GUV-type. They have been sun calibrated against a reference spectroradiometer, operating in the United States National Science Foundation (NSF) Ultraviolet Monitoring network. GUV instruments are currently being used in monitoring networks worldwide, in countries such as the United States, Argentina and Chile.
4.2.1 Spectral irradiance, day 156
In Fig.4.2.1.1 the spectral irradiance for each channel of 8 GUV-instruments have been ratioed to the GUV#9273. Scatter from synchronization errors have been reduced by averaging data over 10 minute periods. Except for the lowest channel (305nm), the agreement is better than 1 % all over the day. For the 305nm channel, the agreement is within ±2 % only during noon-time when the signal is strong, but departs quickly for high SZA's. Average ratios for the day aregiven in Table 4.2.1.1, showing agreement of ±0.5 % to ±1 % for the forenoon to afternoon period.
0 . 9 0 0 . 9 2 0 . 9 4 0 . 9 6 0 . 9 8 1 . 0 0 1 . 0 2 1 . 0 4 1 . 0 6 1 . 0 8 1 . 1 0
2 . 2 5 3 . 2 5 4 .2 5 5 .2 5 6 . 2 5 7 . 2 5 8 .2 5 9 .2 5 1 0 . 2 5 1 1 .2 5 1 2 .2 5 1 3 . 2 5 1 4 . 2 5 1 5 . 2 5 1 6 .2 5 1 7 .2 5 1 8 . 2 5 1 9 . 2 5 T i m e ( U T C )
9 2 7 0 / 7 3 9 2 7 1 / 7 3 9 2 7 2 / 7 3 9 2 7 4 / 7 3 9 2 7 5 / 7 3 9 2 7 6 / 7 3
3 0 5 c h a n n e l
0 . 9 6 0 . 9 8 1 . 0 0 1 . 0 2 1 . 0 4
2 . 2 5 3 . 2 5 4 .2 5 5 .2 5 6 . 2 5 7 . 2 5 8 .2 5 9 .2 5 1 0 . 2 5 1 1 .2 5 1 2 .2 5 1 3 . 2 5 1 4 . 2 5 1 5 . 2 5 1 6 .2 5 1 7 .2 5 1 8 . 2 5 1 9 . 2 5 T i m e ( U T C )
9 2 7 0 / 7 3 9 2 7 1 / 7 3 9 2 7 2 / 7 3 9 2 7 4 / 7 3 9 2 7 5 / 7 3 9 2 7 6 / 7 3
3 1 3 c h a n n e l
0 .9 6 0 .9 8 1 .0 0 1 .0 2 1 .0 4
3 .2 2 4 .2 2 5 .2 2 6 .2 2 7 .2 2 8 .2 2 9 .2 2 1 0 .2 2 1 1 .2 2 1 2 .2 2 1 3 .2 2 1 4 .2 2 1 5 .2 2 1 6 .2 2 1 7 .2 2 1 8 .2 2 1 9 .2 2 T im e (U T C )
9 2 7 0 /7 3 9 2 7 1 /7 3 9 2 7 2 /7 3 9 2 7 4 /7 3 9 2 7 5 /7 3 9 2 7 6 /7 3
3 2 0 c h a n n e l
0 .9 6 0 .9 8 1 .0 0 1 .0 2 1 .0 4
3 .2 4 .2 5 .2 6 .2 7 .2 8 .2 9 .2 1 0 .2 1 1 .2 1 2 .2 1 3 .2 1 4 .2 1 5 .2 1 6 .2 1 7 .2 1 8 .2 1 9 .2
T im e ( U T C ) 9 2 7 0 /7 3 9 2 7 1 /7 3 9 2 7 2 /7 3 9 2 7 4 /7 3 9 2 7 5 /7 3 9 2 7 6 /7 3
3 4 0 c h a n n e l
0 . 9 6 0 . 9 8 1 . 0 0 1 . 0 2 1 . 0 4
3 . 2 2 4 .2 2 5 .2 2 6 . 2 2 7 . 2 2 8 .2 2 9 .2 2 1 0 . 2 2 1 1 .2 2 1 2 .2 2 1 3 . 2 2 1 4 . 2 2 1 5 . 2 2 1 6 .2 2 1 7 .2 2 1 8 . 2 2 1 9 . 2 2 T i m e ( U T C )
9 2 7 0 / 7 3 9 2 7 1 / 7 3 9 2 7 2 / 7 3 9 2 7 4 / 7 3 9 2 7 5 / 7 3 9 2 7 6 / 7 3
3 8 0 c h a n n e l
Fig.4.2.1.1 Ratio of spectral irradiance of GUV's, relative to GUV#9273 (day 156).
Table 4.2.1.1: Ratio of spectral irradiance of the GUV-instruments, relative to GUV#9273 (Day 156, averaging interval: 08:00-16:00 UTC). GUV#9222 data is based on lamp calibration, wheras the other are based on solar calibrations.
Instr. ratio 305nm 313nm 320nm 340nm 380nm
#9270 /#9273 0.995±0.009 0.997±0.009 1.000±0.009 1.002±0.011 1.004±0.013
#9271 /#9273 0.993±0.006 1.000±0.004 1.006±0.007 0.999±0.005 1.000±0.006
#9272 /#9273 0.985±0.008 1.000±0.005 1.004±0.006 0.999±0.005 1.001±0.006
#9274 /#9273 0.987±0.021 0.994±0.020 1.003±0.015 0.999±0.024 0.999±0.030
#9275 /#9273 0.995±0.015 0.999±0.015 1.003±0.015 0.994±0.018 0.999±0.022
#9276 /#9273 1.008±0.017 0.998±0.013 0.999±0.013 0.992±0.016 0.994±0.020
#9222 /#9273 0.344±0.016 - 0.811±0.040 0.761±0.042 0.841±0.060 Average of
#9270-76
0.994
(-0.009 to 0.014)
0.998
(-0.004 to 0.002)
1.003
(±0.004) 0.998
(-0.006 to 0.005)
1.000
(-0.006 to 0.004)
4.3 CIE-weighted irradiances
CIE weighted irradiances are derived from the GUV instrument by using a method described by Dahlback (1996). The CIE-irradiances are determined by a linear combination of the irradiances represented by the voltages across the 305, 320, 340 and 380 nm channels with
coefficients derived from a radiative transfer model and comparison with a high wavelength resolution spectroradiometer in San Diego, California, USA, May 1995. The CIE-irradiances are independent of the solar calibration factors used for absolute irradiances for the GUV channels provided by the factory.
The ratios of CIE irradiances for the GUVs to the reference GUV#9273 for 5. and 8. June are displayed in Figs. 4.3.1 and 4.3.2. The agreement (except for the GUV 9222) is better than 2%
for SZA < 70o. The increased deviations for larger SZA may be a result of small differences in the responsivities between the GUV's and decreased signal to noise ratio.
The GUV#9222 diffusor was cleaned 11:47 hr June 6 (day 157). This resulted in an 6%
increase in irradiance. This explains the larger deviation between GUV#9222 compared with the other GUV's in Fig. 4.3.1.
Fig.4.3.1 Ratio of CIE-effective irradiance of GUV-instruments, relative to GUV#9273, for day 156.
Fig.4.3.2 Ratio of CIE-effective irradiance of GUV-instruments, relative to GUV#9273, for day 159.
R atio o f C I E -d o s e rate s f o r G U V s , d ay 1 5 6 (5 /6 -9 5 ), re lative to G U V 9 2 7 3 (running ave rag e o f 1 0 m inute s )
0 .9 0 0 0 .9 2 0 0 .9 4 0 0 .9 6 0 0 .9 8 0 1 .0 0 0 1 .0 2 0 1 .0 4 0 1 .0 6 0 1 .0 8 0 1 .1 0 0
2 .6 2 3 .6 2 4 .6 2 5 .6 2 6 .6 2 7 .6 2 8 .6 2 9 .6 2 1 0 .6 2 1 1 .6 2 1 2 .6 2 1 3 .6 2 1 4 .6 2 1 5 .6 2 1 6 .6 2 1 7 .6 2 1 8 .6 2 1 9 .6 2
T im e (U T C )
Rel. units
" 9 2 7 0 / 7 3
" 9 2 7 1 / 7 3
" 9 2 7 2 / 7 3
" 9 2 7 4 / 7 3
" 9 2 7 5 / 7 3
" 9 2 7 6 / 7 3
" 9 2 2 2 / 7 3
R atio o f C IE -d o s e rate s o f G UV 's , d ay 1 5 9 (8 /6 -9 5 ), re lative to G UV # 9 2 7 3 (running ave rag e o f 1 0 m inute s )
0.900 0.920 0.940 0.960 0.980 1.000 1.020 1.040 1.060 1.080 1.100
2.58 3.58 4.58 5.58 6.58 7.58 8.58 9.58 10.58 11.58 12.58 13.58 14.58 15.58 16.58 17.58 18.58 19.58
T im e (U T C )
Rel. units
"9270/73
"9271/73
"9272/73
"9274/73
"9275/73
"9276/73
"9222/73
Table 4.3.1: Ratio of CIE-effective irradiance of GUV-instruments, relative to GUV#9273 Day no. #9270
/#9273
#9271 /#9273
#9272 /#9273
#9274 /#9273
#9275 /#9273
#9276 /#9273
#9222 /#9273 156 0.995 1.002 0.999 0.998 0.999 1.003 0.923
157 0.994 1.000 - - 1.004 0.995 0.962
158 0.998 - - 0.997 0.992 0.973 0.985
159 1.000 - 1.013 1.009 1.008 1.019 0.968
160 1.006 1.012 1.007 1.008 1.013 - 0.993
163 1.001 1.011 1.004 1.003 - - 0.990
Average of
period 0.999
±0.004 1.006
±0.006 1.006
±0.006 1.003
±0.006 1.003
±0.008 0.998
±0.019 0.97
±0.03
4.4 Intercomparison of measurements based on lamp- and solar calibration factors.
As was shown in Section 4.1, the fairly wide spectral response curve of the GUV-channels (FWHM 10 nm) makes the photocurrent for nominal wavelengths be a function of the source spectrum overlapping with the instrument’s entire passband. The GUV- and PUV-instruments have their individual calibration factors, traceable either to a quartz halogen lamp (GUV#9222, PUV#500, PUV#510) and/or a calibrated solar spectrum (GUV#9270-9276). As the spectral distribution of a lamp and the sun is very different, especially towards the shorter wavelenght range, calibration factors will be increasingly different towards the shorter wavelengths.
In Fig.4.4.1 the lamp-calibrated spectral irradiances obtained by the PUV#500, PUV#510 and GUV#9222 have been ratioed with the sun-calibrated GUV#9273 (day 158). The ratio curves are almost independent of the SZA, but the ratio curves differ by up to 60 % from the normaliser. Averaged ratios are shown in Table 4.4.1, establishing a link between the network reference GUV and the lamp-calibrated radiometers.
R a tio s p e c tr a l irra d ia n c e a t 3 0 5 n m fo r P U V a n d G U V in s tr u m e n ts , d a y 1 5 8 (7 /6 -9 5 ), re la tiv e to G U V # 9 2 7 3
0 .3 0 0 .3 5 0 .4 0 0 .4 5 0 .5 0 0 .5 5 0 .6 0
3 .5 7 4 .5 7 5 .5 7 6 .5 7 7 .5 7 8 .5 7 9 .5 7 1 0 .5 7 1 1 .5 7 1 2 .5 7 1 3 .5 7 1 4 .5 7 1 5 .5 7 1 6 .5 7 1 7 .5 7 1 8 .5 7 1 9 .5 7
T im e (U T C )
rel. units
G U V 9 2 2 2 /G U V # 9 2 7 3 P U V 5 1 0 S /G U V # 9 2 7 3 P U V 5 0 0 U /G U V # 9 2 7 3
R a t io s p e c t r a l ir r a d ia n c e a t 3 2 0 n m f o r P U V a n d G U V in s t r u m e n t s , d a y 1 5 8 ( 7 / 6 - 9 5 ) , r e la t iv e t o G U V # 9 2 7 3
0 .6 0 0 .6 5 0 .7 0 0 .7 5 0 .8 0 0 .8 5 0 .9 0 0 .9 5 1 .0 0 1 .0 5
3 .5 7 4 . 5 7 5 .5 7 6 . 5 7 7 .5 7 8 .5 7 9 .5 7 1 0 . 5 7 1 1 .5 7 1 2 . 5 7 1 3 .5 7 1 4 .5 7 1 5 .5 7 1 6 .5 7 1 7 . 5 7 1 8 .5 7 1 9 . 5 7
T im e (U T C )
rel. units
G U V 9 2 2 2 /G U V # 9 2 7 3 P U V 5 1 0 S /G U V # 9 2 7 3 P U V 5 0 0 U /G U V # 9 2 7 3
R a tio s p e c tr a l ir r a d ia n c e a t 3 4 0 n m fo r P U V a n d G U V in s tr u m e n ts , d a y 1 5 8 (7 /6 - 9 5 ), r e la tiv e to G U V # 9 2 7 3
0 .7 5 0 .8 0 0 .8 5 0 .9 0 0 .9 5 1 .0 0 1 .0 5
3 .5 7 4 .5 7 5 .5 7 6 .5 7 7 .5 7 8 .5 7 9 .5 7 1 0 .5 7 1 1 .5 7 1 2 .5 7 1 3 .5 7 1 4 .5 7 1 5 .5 7 1 6 .5 7 1 7 .5 7 1 8 .5 7 1 9 .5 7
T im e (U T C )
rel. units
G U V 9 2 2 2 /G U V # 9 2 7 3 P U V 5 1 0 S /G U V # 9 2 7 3 P U V 5 0 0 U /G U V # 9 2 7 3
305nm
320 nm
340 nm
R a tio s p e c tr a l irra d ia n c e a t 3 8 0 n m fo r P U V a n d G U V in s tr u m e n ts , d a y 1 5 8 (7 /6 -9 5 ), re la tiv e to G U V # 9 2 7 3
0 .8 0 0 .8 5 0 .9 0 0 .9 5 1 .0 0 1 .0 5 1 .1 0
3 .5 7 4 .5 7 5 .5 7 6 .5 7 7 .5 7 8 .5 7 9 .5 7 1 0 .5 7 1 1 .5 7 1 2 .5 7 1 3 .5 7 1 4 .5 7 1 5 .5 7 1 6 .5 7 1 7 .5 7 1 8 .5 7 1 9 .5 7
T im e (U T C )
rel. units
G U V 9 2 2 2 /G U V # 9 2 7 3 P U V 5 1 0 S /G U V # 9 2 7 3 P U V 5 0 0 U /G U V # 9 2 7 3
Fig.4.4.1 Ratio of spectral irradiance of lamp calibrated instruments, relative to solar calibrated GUV#9273, day 158. The sudden drop in 320-channel output of the PUV510S was due to a hardware/firmware error for this instrument.
Table 4.4.1: Ratio of spectral irradiance of lamp calibrated instruments, relative to solar-calibrated GUV#9273, for day 158. *) Averaged for the forenoon and afternoon periode.
305nm 320nm 340nm 380nm
GUV#9222/ #9273 0.371±0.004 0.865±0.006 0.809±0.006 0.886±0.009 PUV#510 (Surf) /#9273 0.444±0.007 ∼0.94*) 0.914±0.011 0.987±0.013 PUV#500 (Und) /#9273 0.466±0.008 0.981±0.012 0.983±0.008 1.046±0.013
4.5 Lamp measurements of PUV and GUV instruments.
The multichannel instruments (8 GUV’s and 2 PUV) were compared against the SSI-lamp described in Chap. 3.3.2., but only the 150 W no. #3 lamp was tested. The lamp was placed above the filterinstrument in the same way for all instruments. Adjustment of lamp current and stabilization time of the lamp was the same as for the spectroradiometers. The instrument collected 3 minutes averages of samples, logging with the fastest frequency. The mean value for each channel was compared with the mean for the reference (GUV9273) and the deviation is given in figur 4.5.1. A comment should be given in view of the results below: The GUV541 instruments (#9270-76) were using sun-calibration factors for the lamp measurements, whereas the GUV#9222 and the two PUV instruments applied lamp calibration factors. Thus the suncalibrated lamp measurements are not be valid, unless corrections had been made (ref.
discussion in Section 4.4). Reviewing section 3.3.2, where SSI-lamp measurements with the GUV#9273 had been corrected for using sun calibration factors, the agreement with the spectroradiometers was within ±5 % for alle channels.
Continuing the discussion on lamp- and suncalibrated GUVs, relative to suncalibrated GUV#9273: There is a good agreement (±5%) between all the instruments for channels 320 nm, 340 nm and 380 nm, while the 305 nm channel deviate more. All the solar calibrated GUV’s in the nettverk measure more than the reference (up to 20%) for this channel. This difference between the network GUV’s and the reference could not be observed in the solar measuremens at low SZA’s (see Fig. 4.2.1.1).
The lamp calibrated instruments (GUV 9222, PUV 500 and PUV 510) are 50% lower than the reference. For these three instruments the other channels were also too low compared with the
reference. The 340 nm channel deviates more than the 320 nm and 380 nm channels. The deviations were in accordance with the deviations found during solar measurements of different SZA’s (see Table 4.4.1).
These lamp measurements support the need to homogenize the spectral distribution of the standard calibration unit.
-55 % -50 % -45 % -40 % -35 % -30 % -25 % -20 % -15 % -10 % -5 % 0 % 5 % 10 % 15 % 20 %
GUV 9270 GUV 9272 GUV 9274 GUV 9276 PUV 500
Instrumenter
Deviation from GUV 9273
305 nml 320 nm 340 nm 380 nm
Figure 4.5.1 Deviation from the reference for GUV 9273 for the GUV’s 9270, 9271, 9271, 9274, 9275, 9276,
9222 and PUV 500 and 510. Measurements against the SSI-lamp, 150 W.
4.6 NILU UV four channel radiometer (UV-4S)
The instrument measures irradiances in four channels in the UV region of the solar spectrum at 305 nm, 320 nm, 340 nm and 380 nm, all with bandwidths 10 nm FWHM. The center wavelengths are similar to the GUV's. However, the spectral responsivities are somewhat different. The optical part of the instrument consists of a teflon diffusor, interference filters, blocking filters and UV-sensitive photodetectors. One minute averages of the irradiances as well as the detector temperature are sent to an internal data logger. The UV-4S uses power from solar cells/battery and is therefore not temperature regulated. The dark current is determined from the temperature measured close to the detectors.
The instrument arrived late, and for that reason it was compared with the GUVs at the roof of NRPA July 4-5.
As explained in Section 4.3 the GUV's were calibrated against a SUV-100 spectroradiometer in San Diego, California, USA in May 1995. The NILU UV radiometer was calibrated using the same technique, but since a high wavelength resolution spectrum was not available a spectrum calculated with a radiative transfer model was used instead. The spectrum used was
calculated for July 5 at 11:02 hr (clear sky and SZA=37.1) and ozone abundance 352 DU taken from the Dobson instrument at the University of Oslo.
Figs. 4.6.1 and 4.6.2 show CIE irradiances for the UV-4S instrument and GUV #9273 July 4 and 5. July 4 was cloudy whereas July 5 was quite clear except for some clouds in the
afternoon. The ratios of CIE-irradiances from the UV 4S to the GUV #9273 for SZA<75 degrees are displayed in Fig. 4.6.3.
The ratio of CIE irradiances for the UV 4S to the GUV #9273 for different SZA on day 185 and 186 is shown in Table 4.6.1.
The GUV and UV-4S have different spectral responsivities in the 305 channel and therefore the sensitivity to ozone may be different. The ratio 340nm/305nm is not sensitive to clouds and the ratio may therefore be used to study how sensitive the 305 nm channel is to ozone variations.
The ozone abundance changed from 380 DU at noon on July 4 to 352 DU at noon on July 5, a 8% decrease. The 340nm/305nm ratio increased by 14.6% and 26.0% for the GUV and UV-4S, respectively. The UV-4S is therefore more sensitive to ozone changes than the GUV #9273 for this solar elevation (SZA=37 degrees).
C IE -irra d ia n c e o f G U V # 9 2 7 3 a n d N IL U U V -4 S , J u ly 4 'th .
0 2 0 4 0 6 0 8 0 1 0 0 1 2 0
3 .4 0 5 .5 3 6 .5 3 7 .5 3 8 .5 3 9 .5 3 1 0 .5 3 1 1 .5 3 1 2 .5 3 1 3 .5 3 1 4 .5 3 1 5 .5 3 1 6 .5 3 1 7 .5 3 1 8 .5 3 1 9 .6 5
T im e
mW/m2
G U V # 9 2 7 3 N IL U U V -4 S
Fig. 4.6.1: CIE irradances for NILU UV-4S and GUV #9273 at NRPA, July 4 (day 185). Ten minute running mean.
C IE -ir r a d ia n c e o f G U V # 9 2 7 3 a n d N IL U U V -4 S , J u ly 5 'th .
0 2 0 4 0 6 0 8 0 1 0 0 1 2 0
3 .2 3 5 .3 0 6 .3 0 7 .3 0 8 .3 0 9 .3 0 1 0 .3 0 1 1 .3 0 1 2 .3 0 1 3 .3 0 1 4 .3 0 1 5 .3 0 1 6 .2 8 1 7 .3 0 1 8 .3 0 1 9 .3 0 T im e
mW/m2
G U V # 9 2 7 3 N IL U U V -4 s
Fig. 4.6.2: CIE irradiances for NILU UV-4S and GUV #9273 at NRPA, July 5 (day 186). Ten minute running mean.
R a tio in C IE -ir r a d ia n c e o f N IL U U V -2 S , r e la tiv e to G U V # 9 2 7 3 , 4 -5 /7 -1 9 9 5 .
0 .9 0 .9 5 1 1 .0 5 1 .1 1 .1 5 1 .2
3 .9 8 5 .0 3 6 .0 3 7 .0 3 8 .0 3 9 .1 3 1 0 .1 3 1 1 .1 3 1 2 .1 3 1 3 .1 3 1 4 .1 3 1 5 .1 3 1 6 .1 5 1 7 .2 8 1 8 .2 8
T im e
Rel. units
J u ly 4 J u ly 5
Fig. 4.6.3: Ratio of CIE-irradiances for SZA<80 degrees, UV-4S/GUV #9273, july 4 and 5. Ten minute running mean.
Table 4.6.1: Ratio of CIE irradiances, UV-4S/GUV #9273, for different intervals of SZA on 4. and. 5 July.
SZA Day 185 Day 186
Z<50 0.998 ± 0.021 1.009 ± 0.006 Z<60 1.004 ± 0.025 1.009 ± 0.007 Z<70 1.015 ± 0.028 1.016 ± 0.016 Z<75 1.026 ± 0.043 1.023 ± 0.027 Z<80 1.039 ± 0.056 1.035 ± 0.043
5. Single-band filter radiometers