UV-B Robertson-Berger meter characterization and field calibration

The New Zealand Meteorological Service has used a Robertson-Berger meter (RB meter) to monitor solar UV-B radiation for the past decade. The radiometric properties of the instrument have been analyzed and agree with the standard values published by Berger. A detailed theoretical treatment of the RB meter response that fully accounts for its cosine response is presented. Field measurements made with the RB meter and with a double monochromator spectral radiometer were used to validate the theoretical model and to derive a calibration for the RB meter. Only cloud-free data were considered so that the downward radiation field at the surface could be modeled as the sum of direct solar and isotropic diffuse components. The imperfect cosine responses of both instruments were modeled. A RB meter count was found to equate to 0.25 +/- 0.02 Jm(-2) referenced to 300-nm radiation at vertical incidence.