Last Updated: September 12, 2008
We wish to acknowledge Kathleen O. Lantz, Cooperative Institute for Research in Environmental Sciences, University of Colorado; and NOAA/SRRB/ARL, Boulder, CO., for her assistance in preparing this section.
The network's UVB-1 Broadband Radiometers are calibrated against a triad of "standard" UVB-1 instruments that are maintained by SRRB's Central UV Calibration Facility (CUCF). The standard instruments are periodically calibrated in the sun by comparing their broadband measurements to the integrated output of UV spectroradiometers. These calibrations are transferred to the field instruments just before they are deployed in the network by operating them side-by-side for a few days. To accomplish this transfer, a scale factor, which is simply a ratio of the test instrument's daily integral to that of the mean of the standards, is computed for each day that the test UVB-1 instrument is run alongside the standards. The mean of the daily scale factors (scale_factor) is used to transfer the standards' well maintained calibrations to the test instruments when they are deployed in the field.
The UVB-1 broadband data are given as erythemal UV irradiance, the total measured surface UV-B flux convoluted with the erythemal action spectrum, i.e., that part of the UV-B spectrum responsible for sunburn on human skin (erythema) and DNA damage. The broadband instruments are calibrated assuming that the total ozone overhead at the site is 300 Dobson units (DU). This assumption can result in significant error if the true ozone value is either much higher or much lower than 300 DU. For example, if total ozone at the site is 200 DU, the erythemally-weighted irradiance at a solar zenith angle of 20 degrees will give erythema too low by approximately 15% unless a correction for the true ozone is applied. You may wish to view plots illustrating the percent error in daily UV dose for a range of ozone levels at two site locations.
The procedure used to convert raw voltage from the UVB-1 broadband instruments to erythemal UV irradiance, as shown on plots and given in data files from this website, is described below.
For data users requiring a higher level of accuracy, calibration files are available for them to compute ozone-corrected erythemal UV irradiances themselves. If you wish to receive these files, you may contact the UVMRP program. Please be aware that these computations will require: a) downloading the raw UVB-1 sensor voltages; b) downloading the total ozone either from TOMS or as calculated by UV-B Monitoring and Research Program from the UV-MFRSR data; and c) obtaining the scale_factor(s) for each broadband instrument involved.
For more information regarding the calibration of UVB-1 broadband radiometers, please refer to Lantz et al., 1999.