Field calibration unit for ultraviolet spectroradiometers.

Horizontal standard lamps calibrate the spectral irradiance responsivity of spectroradiometers that measure solar ultraviolet irradiance. A field calibration unit and power supply developed to meet the requirements for using these standards in the field are described and their operation and associated uncertainties are detailed. Results from assessments obtained at two field instrument intercomparisons indicate that the horizontal standard, field calibration unit, and power supply operate within the design tolerances, making them suitable for performing routine calibrations in the field on most ultraviolet spectroradiometers.