Long-term stability of UV multifilter rotating shadowband radiometers

Abstract

This is a continuation of work begun by Dave Bigelow and James Slusser in their study of the same name published in 2000 in J. Geophys. Res., 105, 4833-4840. This continuation study began in January 2002, when the entire database for the UV Multifilter Rotating Shadowband Radiometers (UV-MFRSR) was analyzed using the Langley regression technique, as described in "Langley Method of Calibrating UV Filter Radiometers," Slusser et. al., 2000, J. Geophys. Res., 105, 4841-4849. In conjunction with scientists at ASRC, SUNY, Albany (New York), the UVMRP has refined the air mass range versus wavelength that is used in the Langley analysis methodology to conform to the greater optical depths in the UV (290)-380 nm) compared with the visible (400-965 nm). A time series of direct Sun voltage intercepts (Vo's) from Langley plots is an indication of stability, which augments the traditional periodic standard lamp calibrations. Overall, 129 cases representing 28 sites and 39 instruments, with 21 sites and 30 instruments having multiple cases, were studied. The results presented herein show the mean annual drift in sensitivity for the seven nominal wavelengths of the UV-MFRSR instrument are: 300 nm - 1.2%, 305 nm - 4.8%, 311 nm - 2.6%, 317 nm - 3.0%, 325 nm - 4.8%, 332 nm - 4.9%, 368 nm - 3.7%.