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 7.3.7.1 shows all past intercomparisons with MSC. The latest intercomparison was carried out in Toronto in 2010.
|
Table 7.3.7.1 Brewer spectrophotometer intercomparison for the Japanese standard. |
| Year | Venue |
|---|---|
| 1994 | Boulder, USA |
| 1997 | Toronto, Canada |
| 2002 | Toronto, Canada |
| 2006 | Toronto, Canada |
| 2010 | Toronto, Canada |
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 7.3.7.2 shows the dates of intercomparison of the Brewer spectrophotometers at 3 stations in Japan with standard instruments which have been carried out recently.
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Table 7.3.7.2 Brewer spectrophotometer comparison for the Japanese network. |
| Station | Sapporo | Kagoshima | Naha |
|---|---|---|---|
| Time of Comparison |
February 1996 July 1997 October 2000 August 2001 November 2001 July 2003 October 2007 October 2010 |
October 1995 October 1997 September 1998 March 2000 August 2001 November 2001 November 2002 May 2005 (Observation terminated in March 2005) |
October 1996 November 1999 May 2000* August 2001 December 2001 November 2001 November 2004 September 2006 April 2010 * 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.
GAW stations for the ozone layer and ultraviolet radiation observation | Ultraviolet radiation observation | Calibration for ultraviolet observation