1Physikalisch-Meteorologisches Observatorium Davos, World Radiation Center (PMOD/WRC), Dorfstrasse 33, CH-7260 Davos Dorf, Switzerland (julian.groebner@pmodwrc.ch)
A new cavity for pyrgeometer characterizations has been built at the Infrared Radiometry Section of the World Radiation Center (WRC-IRS) at PMOD/WRC. The calculated effective emissivity of was obtained from Monte Carlo simulations taking into account the geometry and the measured temperature distributions of the cavity. The cavity is operated in a temperature range of to and is initially flushed with nitrogen to reduce the relative humidity in the cavity. The estimated uncertainties of retrieved pyrgeometer parameters , , and are , , and , respectively. The relative uncertainty of pyrgeometer sensitivity C is 0.8%. The comparison with the cavity used since 1995 at PMOD/WRC gave average differences of 0.005, 0.00026, and 0.08 for , , and , respectively. The pyrgeometer sensitivity retrieved with the new cavity is on average 1.0% higher than with the original cavity.
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Results of Monte Carlo Simulations Yielding Effective Emissivity , Cavity Exitance E, and Radiation Temperature a
E
[K]
[K]
[]
[]
[]
288.06
288.03
0.999578
390.28
390.40
283.20
283.19
0.999801
364.69
364.72
273.42
273.42
0.999956
316.91
316.89
263.68
263.68
1.000012
274.09
274.09
0.00
254.03
254.05
1.000230
236.20
236.11
244.39
244.39
1.000000
202.29
202.26
For the six prescribed temperature distributions shown in Fig. 3. Background radiation was taken into account but had negligible influence on the results. The standard deviation of random error for is , for less than and for E less than . The cavity exitance is shown in the fifth column and the difference between and E in the sixth.
Table 2
Uncertainty Estimate of Pyrgeometer Sensitivity Ca
Parameter
Relative
Type
Uncertainty
Uncertainty in C [%]
U
0.06
E
0.5
0.024
0.4
0.0008
0.3
0.03
0.0
0.2
0.1
Residuals
0.3
Total
0.8
Based on the uncertainty propagation of the individual components of Eq. (2). The total uncertainty is calculated from the square root of the sum of squares of the components.
Table 3
Pyrgeometer Characterizations wth BB1995 and BB2007a
Pyrgeometer ID
Cavity
PIR 31463F3
3.62
0.047
0.9956
3.14
BB1995
3.48
0.007
0.9943
3.34
BB2007
0.9
PIR 31464F3
3.81
0.015
0.9956
2.72
BB1995
3.66
0.9943
2.81
BB2007
0.6
PIR 3055xF3
4.22
0.9988
2.48
BB1995
4.34
0.011
0.9990
2.71
BB2007
1.3
PIR 3119xF3
4.14
0.054
1.0024
2.54
BB1995
4.23
0.063
1.0027
2.62
BB2007
1.4
PIR 3400xF3
3.68
0.061
0.9989
3.34
BB1995
3.71
0.064
0.9998
3.22
BB2007
0.4
PIR 3400yF3
3.67
0.011
1.0012
2.85
BB1995
3.76
0.030
1.0015
2.84
BB2007
0.3
CG4 FT004
11.5
0.9970
-
BB1995
11.9
0.9977
-
BB2007
1.0
CG4 010535
8.87
0.9978
-
BB1995
8.93
0.9984
-
BB2007
0.7
CG4 FT006
11.7
0.088
0.9996
-
BB1995
11.8
0.096
1.0003
-
BB2007
0.6
CG4 0105x
9.41
1.0003
-
BB1995
9.91
0.016
1.0012
-
BB2007
1.6
CG4 0508x
10.6
0.043
0.9958
-
BB1995
11.0
0.063
0.9966
-
BB2007
2.3
Min Difference
-0.12
0.3
Max Difference
0.035
0.0009
0.23
2.3
Mean Difference
0.005
0.00026
0.08
1.0
The last column contains the relative difference between sensitivities C derived from BB2007 with the coefficients of BB1995 and BB1995. The values shown in the last three rows are calculated from the differences between the BB2007 and BB1995 retrievals.
Tables (3)
Table 1
Results of Monte Carlo Simulations Yielding Effective Emissivity , Cavity Exitance E, and Radiation Temperature a
E
[K]
[K]
[]
[]
[]
288.06
288.03
0.999578
390.28
390.40
283.20
283.19
0.999801
364.69
364.72
273.42
273.42
0.999956
316.91
316.89
263.68
263.68
1.000012
274.09
274.09
0.00
254.03
254.05
1.000230
236.20
236.11
244.39
244.39
1.000000
202.29
202.26
For the six prescribed temperature distributions shown in Fig. 3. Background radiation was taken into account but had negligible influence on the results. The standard deviation of random error for is , for less than and for E less than . The cavity exitance is shown in the fifth column and the difference between and E in the sixth.
Table 2
Uncertainty Estimate of Pyrgeometer Sensitivity Ca
Parameter
Relative
Type
Uncertainty
Uncertainty in C [%]
U
0.06
E
0.5
0.024
0.4
0.0008
0.3
0.03
0.0
0.2
0.1
Residuals
0.3
Total
0.8
Based on the uncertainty propagation of the individual components of Eq. (2). The total uncertainty is calculated from the square root of the sum of squares of the components.
Table 3
Pyrgeometer Characterizations wth BB1995 and BB2007a
Pyrgeometer ID
Cavity
PIR 31463F3
3.62
0.047
0.9956
3.14
BB1995
3.48
0.007
0.9943
3.34
BB2007
0.9
PIR 31464F3
3.81
0.015
0.9956
2.72
BB1995
3.66
0.9943
2.81
BB2007
0.6
PIR 3055xF3
4.22
0.9988
2.48
BB1995
4.34
0.011
0.9990
2.71
BB2007
1.3
PIR 3119xF3
4.14
0.054
1.0024
2.54
BB1995
4.23
0.063
1.0027
2.62
BB2007
1.4
PIR 3400xF3
3.68
0.061
0.9989
3.34
BB1995
3.71
0.064
0.9998
3.22
BB2007
0.4
PIR 3400yF3
3.67
0.011
1.0012
2.85
BB1995
3.76
0.030
1.0015
2.84
BB2007
0.3
CG4 FT004
11.5
0.9970
-
BB1995
11.9
0.9977
-
BB2007
1.0
CG4 010535
8.87
0.9978
-
BB1995
8.93
0.9984
-
BB2007
0.7
CG4 FT006
11.7
0.088
0.9996
-
BB1995
11.8
0.096
1.0003
-
BB2007
0.6
CG4 0105x
9.41
1.0003
-
BB1995
9.91
0.016
1.0012
-
BB2007
1.6
CG4 0508x
10.6
0.043
0.9958
-
BB1995
11.0
0.063
0.9966
-
BB2007
2.3
Min Difference
-0.12
0.3
Max Difference
0.035
0.0009
0.23
2.3
Mean Difference
0.005
0.00026
0.08
1.0
The last column contains the relative difference between sensitivities C derived from BB2007 with the coefficients of BB1995 and BB1995. The values shown in the last three rows are calculated from the differences between the BB2007 and BB1995 retrievals.