Total ozone intercomparison measurements made with a scanning filter photometer

The scanning filter photometer, which measures the absorption of solar ultraviolet by atmospheric ozone in the line of sight between the instrument and the Sun is described. Narrow bandwidth interference filters rotate in front of a photomultiplier such that the optical axis of the filters, and their wavelength transmission characteristics, continuously change, which allows the ozone effected solar spectrum to be scanned over a wavelength range of approximately 10 mm for each of the three interference filters. The ozone, wavelength dependent, intensity data are gated into 60 channels and a modified form of the standard double differential absorption technique, where the finite bandwidth of each filter allows a check, by using known features in the absorption spectrum, for wavelength calibration and alignment.