THE 1995 NORTH-AMERICAN INTERAGENCY INTERCOMPARISON OF ULTRAVIOLET MONITORING SPECTRORADIOMETERS

Concern over stratospheric ozone depletion has prompted several govern ment agencies in North America to establish networks of spectroradiome ters for monitoring solar ultraviolet irradiance at the surface of the Earth. To assess the ability of spectroradiometers to accurately meas ure solar ultraviolet irradiance, and to compare the results between i nstruments of different monitoring networks, the second North American Intercomparison of Ultraviolet Monitoring Spectroradiometers was held June 12 to 23, 1995 at Table Mountain outside Boulder, Colorado, USA. This Intercomparison was coordinated by the National Institute of Sta ndards and Technology (NIST) and the National Oceanic and Atmospheric Administration (NOAA). Participating agencies were the Environmental P rotection Agency; the National Science Foundation; the Smithsonian Env ironmental Research Center; the Department of Agriculture; and the Atm ospheric Environment Service, Canada. Instruments were characterized f or wavelength uncertainty, bandwidth, stray-light rejection, and spect ral irradiance responsivity, the latter with a NIST standard lamp oper ating in a specially designed field calibration unit. The spectral irr adiance responsivity, determined once indoors and twice outdoors, demo nstrated that while the responsivities changed upon moving the instrum ents, they were relatively stable when the instruments remained outdoo rs. Synchronized spectral scans of the solar irradiance were performed over several days. Using the spectral irradiance responsivities deter mined with the NIST standard lamp and three different convolution func tions to account for the different bandwidths of the instruments, the measured solar irradiances generally agreed to within 3 %.