The 1996 North American Interagency Intercomparison of Ultraviolet Monitoring Spectroradiometers

Area of Science:

• Earth and Atmospheric Sciences
• Environmental Monitoring
• Spectroradiometry

Background:

• Stratospheric ozone depletion concerns have led North American agencies to establish spectroradiometer networks for monitoring surface ultraviolet (UV) irradiance.
• Accurate UV irradiance measurements are crucial for understanding ozone depletion effects and for public health advisance.

Purpose of the Study:

• To evaluate the accuracy of spectroradiometers used in UV monitoring networks.
• To compare the performance of instruments from different North American agencies.
• To identify potential sources of error in UV irradiance measurements.

Main Methods:

• The third North American Interagency Intercomparison of Ultraviolet Monitoring Spectroradiometers was conducted in June 1996.
• Participants' calibrated standard lamps were measured against the National Institute of Standards and Technology (NIST) scale.
• Instruments underwent characterization for wavelength uncertainty, bandwidth, stray-light rejection, and spectral irradiance responsivity.

Main Results:

• Spectral irradiance scales agreed within uncertainties, but horizontal lamp irradiance was lower than vertical.
• Spectral irradiance responsivity showed instabilities in some instruments.
• Synchronized solar scans revealed unexplained systematic differences in measured solar irradiances between instruments, even after calibration.

Conclusions:

• While initial lamp calibrations showed good agreement, instrument performance and solar measurements revealed inconsistencies.
• Further investigation is needed to understand and resolve the systematic differences in solar irradiance measurements.
• Ensuring the accuracy and comparability of UV monitoring networks is essential for reliable environmental and health assessments.