Recalibration of Dobson Field Spectrophotometers with a Travelling Brewer Spectrophotometer Standard

Abstract

The Brewer ozone spectrophotometer has been used to verify the calibration of Dobson spectrophotometers in the field on a trial basis. The test intercomparisons have demonstrated that the Brewer instrument verifies the double pair wavelength AD Dobson measurements of the type Direct Sun Ground Quartz Plate (AD DSGQP). The initial results from comparisons against a well maintained Dobson instrument (the Canadian standard #77) show agreement within 0.5% total ozone over an airmass range of 1 to 3. The method suggests that the recalibration of a Dobson containing major calibration errors can be achieved with respect to the double pair wavelength AD measurements and possibly identify the significant instrumental problems within the Dobson. Because the Brewer instrument is portable and can be easily transported without losing its calibration, it is ideal for carrying out field calibrations of instruments in the ozone network.