Currently, no international framework has been established for the calibration of ultraviolet observation with a Brewer spectrophotometer. JMA defines the instrument constants for its Brewer spectrophotometers based on the irradiance of the NIST-certified standard lamps. The Aerological Observatory maintains domestic standard instruments evaluated with the NIST lamps. International comparison is not carried out at present under the framework of WMO, but as part of bilateral technological cooperation JMA compares its Brewer spectrophotometers with those of the Meteorological Service of Canada (MSC), which developed the Brewer spectrophotometer. Table 220.127.116.11 shows all past intercomparisons with MSC. The latest intercomparison was carried out in Toronto in 2010.
The Brewer spectrophotometers at the 3 stations in Japan have been calibrated about once every 3 years, on such occasions as intercomparison with national standard instrument to assure high precision of the observation instruments. Table 18.104.22.168 shows the dates of intercomparison of the Brewer spectrophotometers at 3 stations in Japan with standard instruments which have been carried out recently.
(Observation terminated in March 2005)
* calibration only
Besides intercomparisons, the Brewer spectrophotometers are inspected on a daily basis, including automated inspection using mercury lamps. Inspection is also performed regularly using external standard lamps (tungsten-halogen lamps) to monitor changes in wavelength-dependent sensitivity.
The broadband UV-B radiometer, which measures the total amount of global UV-B, is corrected using the monthly mean values from Brewer spectrophotometers in terms of changes in instrument sensitivity.
Brewer spectrophotometers at Syowa Station in Antarctica are calibrated by the national standard at the Aerological Observatory and sent to the station every 3 years to be used for observation. If an instrument needs to be used at the station successively for more than 3 years, another instrument calibrated at the Aerological Observatory is sent to Syowa Station, where the former instrument used for observation is compared with the latter instrument to assure high precision of the observation instruments. At Syowa Station, the inspections above are carried out as with other stations in Japan.