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Characterization Factors

In previous comparisons surface observations made by the Yankee UV-B instrument using the manufacturer's conversion factors produced values with a high bias by as much as 10%.

The NOAA Central Ultraviolet Calibration Facility characterized this instrument and determined conversion factors that varied with both solar zenith angle and total ozone amount(see Figure 3). Once applied, agreement between the Yankee instrument observations and the UV Index forecasts increased tremendously. Therefore, whenever using surface observation data, one must be certain that the correct scaling and calibration factors have been used. Usually, 'readme' files accompany the data sets, but a phone call to the network manager reassures that the data is used properly.

Figure 3

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