121
Pyrheliometer Direct radiation Circum 1 Circum 2 “Measured”
CRO3 770 2.92 7.74 780.7
ABS 770 3.05 8.04 781.1
KIPP 770 3.11 8.65 781.8
NIP 770 3.11 10.92 784.0
Table C 2.2b. Pyrheliometer irradiances in W m
-2
CRO3 is the absolute pyrheliometer designed by D. Crommelynck. ABS is a group of absolute
pyrheliometers (HF, PMO5, etc), KIPP and NIP are thermoelectric station pyrheliometers
Instrument Deficit
percent
Deficit
norm alized to HunIII
Austria 6.1 2.54
Germany I 5.4 2.25
Germany III 1.0 0.42
Hungary II 1.3 0.54
Hungary III 2.4 1.00
USA 1.0 0,42
Table C 2.3. Comparison to the standard group.
There exists a group of diffusometers, the 4 members of the group give same diffuse radiation value
according to the calculations, therefore it is suggested that this group could be regarded as geometrical
standard of diffusom etry.
C 2.3.1 Intercalibration of pyranometers
Kipp & Zonen CM5 pyranometers were used. Their intercalibration were made for each month. In overcast
conditions the three diffusometers should provide the same value, since then the circumsolar effect
is quite negligible. The ratio of HunI/HunII and of HunI/HunIII have different standard deviation, namely
0.011 and 0.006. This m eans that the “m iddle” pyranom eter is m ore uncertain than the other two. This
was recognized during the data processing, so the change of the uncertain pyranometer could not
be made. It is lucky, that not the other pyranometers were problematic.
C 2.3.2 Dependence of ratios of measured diffuse radiation values on other parameters
For the whole data series the HunI/HunII and HunI/HunIII ratios had been calculated and their connection
to other radiation measurements were looked for. A special “demonstration sample” of
50 observations has been selected to present here the relations. In this sample the cases of high direct
radiation are over-represented.
Figure C 2.4 shows the connection between the ratio and the diffuse radiation itself. The upgoing part
of the plot is the clear weather part. Figure C 2.5 shows the connections with the direct radiation. The
highest ratios belong to the clearest atmospheric situations. The dependence on the diffuse per global
ratio is seen in Figure C 2.6.
To estimate the deviation from the standard, the following type of equation is suggested:
Hu nIII
RATIO = a + b/(X-c)
Where a, b,c = regression parameters,
X = either the direct radiation or the diffuse/global ratio.
For the direct radiation a = 0.98621
b = - 14.9824
c = 1086.5
For the diffuse/global ratio a = 0.99419
b = 0.00537
c = -0.07553.
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