The 1994 North American interagency intercomparison of ultraviolet monitoring spectroradiometers

Abstract

Concern over stratospheric ozone depletion has prompted several government agencies in North America to establish networks of spectroradiometers for monitoring solar ultraviolet irradiance at the surface of the Earth. To assess the ability of spectroradiometers to accurately measure solar ultraviolet irradiance, and to compare the results between instruments of different monitoring networks, the first North American Intercomparison of Ultraviolet Monitoring Spectroradiometers was held September 19–29, 1994 at Table Mountain outside Boulder, Colorado, USA. This Intercomparison was coordinated by the National Institute of Standards and Technology and the National Oceanic and Atmospheric Administration (NOAA). Participating agencies were the Environmental Protection Agency, National Science Foundation, Smithsonian Environmental Research Center, and Atmospheric Environment Service, Canada. Instruments were characterized for wavelength accuracy, bandwidth, stray-light rejection, and spectral irradiance responsivity, the latter with a NIST standard lamp calibrated to operate in the horizontal position. The spectral irradiance responsivity was determined once indoors and twice outdoors, and demonstrated that, while the responsivities changed upon moving the instruments, they were relatively stable when the instruments remained outdoors. Synchronized spectral scans of the solar irradiance were performed over several days. Using the spectral irradiance responsivities determined with the NIST standard lamp, and a simple convolution technique to account for the different bandwidths of the instruments, the measured solar irradiances agreed within 5 %.

Development and Intercalibration of Ultraviolet Solar Actinometers

“…Frequent sampling, in conjunction with measurement of two dark channels per rotation, makes this instrument ideal for determination of time-integrated UV-B irradiances. Further details of the instrument are available, including extensive intercalibration with numerous spectroradiometers (17,41).…”

“…When spectral scans are performed, irradiance data can be integrated to yield the photon exposure, which is defined by the International Union of Pure and Applied Chemistry as the irradiance integrated over the time of irradiation (16). However, measurement of the photon exposure in the UV-B (290-320 nm) is often inaccurate because of rapid temporal variations in UV-B on a time-scale that is faster than a spectral scan, and because low levels of UV-B can provide a signal near the background dark current of the instrument (7,15,17). Recent development of a rapidly scanning UV-B radiometer (17) allows for better measurement of the irradiance and photon exposure in the UV-B, while still providing some spectral resolution.…”

“…However, measurement of the photon exposure in the UV-B (290-320 nm) is often inaccurate because of rapid temporal variations in UV-B on a time-scale that is faster than a spectral scan, and because low levels of UV-B can provide a signal near the background dark current of the instrument (7,15,17). Recent development of a rapidly scanning UV-B radiometer (17) allows for better measurement of the irradiance and photon exposure in the UV-B, while still providing some spectral resolution. Disadvantages of spectral instruments are that they are expensive, often temperature dependent and typically have a slow response time (ca 1 scan per 10 min).…”

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

“…In this paper, the results are presented for five scanning spectroradiometers and one spectrograph. The Brewer spectrophotometer, the USDA U111 spectroradiometer, and earlier versions of the BSI spectroradiometer and RSS Spectrograph have been described in previous Intercomparison papers [2,3,4,5]. Several of the instruments have been described in other intercomparison campaigns or cited references [13,14,15,16,17].…”

“…The main reason is that most instruments have been fully characterized in previous studies and/or have participated previously in North American Intercomparisons where instrument characterization occurred (i.e. ASRC_RSS, EPA_BRW, USDA_U11) [2,3,4,5]. Instruments that have not participated in previous North American Intercomparisons (NSF_SUV, IMUK_BEN, NOAA_NIWA) have been characterized fully elsewhere.…”