Calibration of a Yankee Environmental SystemsUltraViolet Rotating Shadow BandRadiometer at Mauna Loa Hawaii

Presented at the 10th International Pyrheliometer Intercomparisonin Davos, Switzerland September 26 to October 14 2005,

by Fred Denn

Edited by: Jay Madigan

Why is UV important? Health effects Agriculture Energy deposition in the atmosphere

How to measure? Satellites Ground stations

Satellite derived top of atmosphere spectral measurementsare used to determine global and temporal UV surfaceirradiance and atmospheric energy deposition.

Surface measurements are made, to verify the results ofthe atmospheric radiative transport models, requiringwell calibrated surface instrumentation.

A method of calibrating UV-MFRSRs using satellitederived UV spectrum is presented.

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. Langleyanalysis are performed, on the morning data, to determinetop of atmosphere values.

Mauna Loa observatory Hawaii

Langley plots were used to select morning data periods used in later analysis.

To be considered good the standard deviation of the residualsmust be less than 0.006

The daily values were plotted for the entire time period, means and standard deviations were determined. These meanswill be compared to values derived using the MFRSR spectralresponse and the SOlar Radiation and Climate Experiment (SORCE) satellite measured extraterrestrial UV spectrum.

Overview of Method

Use a spectral line lamp to verify functionalityof a monochromator.

Determine the normalized functional responseof the UV-MFRSR head.

Perform a numerical integration using the UV-MFRSRspectral response function and a satellite derived UV spectrum.

Top of Atmosphere MFRSR Measured Values and the ValuesDetermined From the MFRSR Spectral Response Function

and the SORCE Spectrum are Compared.

TOA values are determined, and scale factors used toadjust the MFRSR derived values to more true values.

Normalized to 1 auWavelength, 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

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

Verification of New Values

Conclusion

Manufacturer's calibration can be improvedby applying Langley analysis to the outputvalues supplied by there software.

Acknowledgements

NASA LangleyPMODU.S. Coast Guard