Intercomparison of New Zealand filter ozonometer and Dobson spectrophotometer total ozone measurements

A commercial version of the prototype New Zealand narrowband interference filter instrument has been run at Garmisch-Partenkirchen since autumn 1977. The vicinity of the Dobson stations Hohenpeissenberg and Arosa permitted a check of the filter instrument's utility, reliability and long-term stability in total ozone measurement by (i) station to station-or 'short-range' intercomparisons of daily means and (ii) a several days' direct intercomparison at Arosa in spring 1978. The regression analysis with the Hohenpeissenberg data-covering the five month autumn-winter 1977/78 period with highly variable ozone-shows that the filter instrument's direct-sun modeX_AD total ozone values were systematically too low by a conversion factor of 0.93. The excellent proportionality between the instruments is indicated by the standard deviation of only 1,3%. The (-7.0±1.3%) bias perfectly agrees with the result reported byBASHER [1] for a similar, yet direct, intercomparison. During the direct Arosa intercomparison the filter instrument also tracked down short-time variations in a remarkable, though biased, parallelism with the Dobson instruments, and theX_AD daily means fit well into the 'prognostic' relationship derived from the preceding autumn-winter 'short-range' intercomparison. A creeping deterioration of the characteristics of the 305.5 nm 'double filter' then prevented any furtherX_AD total ozone intercomparison. No final decision is possible whether this behaviour after a half year's run is typical or just an unusual exception. The otherwise excellent long-term stability is demonstrated by the comparison of theX_CD daily means with the HohenpeissenbergX_AD data for a 1 1/2 year's period (autumn 1977-spring 1979), resulting in the same bias relationship as for theX_AD total ozone measurements.