Establishing the stability of multifilter UV rotating shadow‐band radiometers

Abstract

A modified Langley technique is used in a preliminary evaluation of the stability of ion‐assisted deposition interference filters. The technique uses lamp‐calibrated direct‐normal irradiance measurements to return estimates of the extraterrestrial solar irradiance over the passband of the filter. Results from prototype and production UV‐multifilter rotating shadow‐band radiometers deployed in the U.S. Department of Agriculture UV Radiation Monitoring program indicate a 1%/yr drift in filter measurements. Measurements are reported to be within 8% of the SUSIM Atlas‐3 extraterrestrial solar irradiance.