2003 North American interagency intercomparison of ultraviolet spectroradiometers: Scanning and spectrograph instruments

The fifth North American Intercomparison of Ultraviolet Monitoring Spectroradiometers was held June 13 to 21, 2003 at Table Mountain outside of Boulder, Colorado, USA. The main purpose of the Intercomparison was to assess the ability of spectroradiometers to accurately measure solar ultraviolet irradiance, and to compare the results between instruments of different monitoring networks. This Intercomparison was coordinated by NOAA and included participants from six national and international agencies. The UV measuring instruments included scanning spectroradiometers, spectrographs, and multi-filter radiometers. Synchronized spectral scans of the solar irradiance were performed between June 16 and 20, 2003. The spectral responsivities were determined for each instrument using the participants' lamps and calibration procedures and with NOAA/CUCF standard lamps. This paper covers the scanning spectroradiometers and the one spectrograph. The solar irradiance measurements from the different instruments were deconvolved using a high resolution extraterrestrial solar irradiance and reconvolved with a 1-nm triangular band-pass to account for differences in the bandwidths of the instruments. The measured solar irradiance from the spectroradiometers using the rivmSHIC algorithm on a clear-sky day on DOY 172 at 17.0 UTC (SZA = 30^o) had a relative 1-σ standard deviation of +/-2.6 to 3.4% for 300- to 360-nm using the participants' calibration.