Broadband Spectral Response

Figure 2 illustrates three successive spectral response characterizations of a single Yankee Environmental Systems UVB-1 Broadband Pyranometer. A legend in the upper right corner of the plot indicates the serial number of the meter being displayed, its characterization date and the agency that performed the characterization. The black line of the plot represents the original spectral characterization of the instrument by NIST. Differences in the dynamic range of subsequent overlays reflect differences in laboratory capabilities. Most characterization facilities are not able to achieve the 10E-5 measurement thresholds that have been achieved at NIST.

This plot also illustrates the differences in spectral response that will be noted when differing materials are used for the meter's transparent dome. The red line (the plus symboled plot and highest line in the shorter wavelengths) represents a dome constructed with UV-grade fused silica whereas the blue line (triangle symbol and line with the shortest spectra), one with Schott 280 glass.

Initial characterizations of the USDA meters at NIST (black line and open circle symbol) indicate that the meters were constructed with Schott 280 glass. It should be noted that all instruments currently used by the network have UV-grade fused silica domes.

Figure 2: Sample Spectral Response of a YES UVB-1 Broadband Pyranometer

NIST characterization of the initial broadband instruments deployed by the USDA network indicated that 8 of 13 instruments exhibited peak spectral responses at 298 nm while 3 instruments had a peak response at 296 nm. Two instruments peaked at 300 nm.