Calibration of a Yankee Environmental Systems

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Calibration of a Yankee Environmental
Systems UltraViolet Rotating Shadow
Band Radiometer at Mauna Loa Hawaii Presented at
the 10th International Pyrheliometer
Intercomparison in Davos, Switzerland September
26 to October 14 2005, by Fred Denn
Edited by Jay Madigan
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Why is UV important? Health effects
Agriculture Energy deposition in the
atmosphere How to measure? Satellites
Ground stations
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Satellite derived top of atmosphere spectral
measurements are used to determine global and
temporal UV surface irradiance and atmospheric
energy deposition. Surface measurements are
made, to verify the results of the atmospheric
radiative transport models, requiring well
calibrated surface instrumentation. A method of
calibrating UV-MFRSRs using satellite derived UV
spectrum is presented.
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The UV-MFRSR is located at the Mauna Loa
Observatory, Hawaii for a period of time each
year because of the exceptionally clear and
stable atmosphere. Langley analysis are
performed, on the morning data, to determine top
of atmosphere values.
Mauna Loa observatory Hawaii
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Langley plots were used to select morning data
periods used in later analysis. To be
considered good the standard deviation of the
residuals must be less than 0.006
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The daily values were plotted for the entire time
period, means and standard deviations were
determined. These means will be compared to
values derived using the MFRSR spectral response
and the SOlar Radiation and Climate Experiment
(SORCE) satellite measured extraterrestrial UV
spectrum.
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Overview of Method
Use a spectral line lamp to verify
functionality of a monochromator. Determine the
normalized functional response of the UV-MFRSR
head. Perform a numerical integration using the
UV-MFRSR spectral response function and a
satellite derived UV spectrum.
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Top of Atmosphere MFRSR Measured Values and the
Values Determined From the MFRSR Spectral
Response Function and the SORCE Spectrum are
Compared.
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TOA values are determined, and scale factors used
to adjust the MFRSR derived values to more true
values.

Normalized to 1 au Wavelength, nm Scale
factor U95 TOA, W/m2 U95
300.2 1.11 23.7
0.405 16.8 305.6
0.94 9.62 0.547
6.8 311.7 1.04
7.92 0.641 5.6
317.8 1.11 8.63
0.677 6.1
325.4 1.09 7.21
0.824 5.1 332.5
1.26 8.49 0.947
6.0 368.1 1.05
7.21 1.169
5.1
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Verification of New Values

Corrected Wavelength SIM
derived TOA UVMFR-7 TOA Difference
nm W/m2
W/m2 W/m2
------- -------
------- -------
300.2 0.408
0.405 0.003 305.6
0.547 0.547
0.000 311.8
0.642 0.641
0.001 317.8 0.678
0.677 0.001
325.4 0.825
0.824 0.001 332.5
0.948 0.947
0.001 368.1
1.171 1.169
0.002
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Conclusion
Manufacturer's calibration can be improved by
applying Langley analysis to the output values
supplied by there software.
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Acknowledgements NASA Langley PMOD U.S. Coast
Guard