Direct-Sun column ozone retrieval by the ultraviolet multifilter rotating shadow-band radiometer and comparison with those from Brewer and Dobson spectrophotometers

A methodology for direct-Sun ozone retrieval using the ultraviolet multifil ter rotating shadow-band radiometer (UV-MFRSR) is presented. Total vertical column ozone was retrieved in three stations: Mauna Loa, Hawaii, in the U. S., and Regina, Saskatchewan, and Toronto, Ontario, in Canada, from direct solar irradiances of the UV-MFRSR at 325-, 305-, 332-, and 311-nm channels (2-nm FWHM). The total uncertainty of ozone retrievals in this study is +/- 2.0%. For Mauna Loa the mean ratios of the UV-MFRSR column ozone retrievals to the collocated Dobson and Brewer were 0.998 and 0.986 between May and S eptember of 1999. The mean ratio of UV-MFRSR retrievals to the collocated B rewer retrievals was 1.012 in Toronto between April and August of 1999, and the mean ratio of retrievals of the UV-MFRSR to the collocated Brewer was 0.988 in Regina between June and September of 1999. Total vertical column o zone values for solar zenith angles of > 70 degrees were not considered, be cause of the signal-to-noise ratio and the angular response of the instrume nts, and were not used in the evaluation. The advantages of total vertical column ozone retrieval using UV-MFRSR include relatively low cost, computer -controlled operation, automated calibration stability checks, and minimal maintenance. It allows for the real-time measurement of total vertical colu mn ozone. The UV-MFRSR is being used at 28 sites across the United States a nd 2 sites in Canada that form the U.S. Department of Agriculture W-B Radia tion Monitoring and Research Program. This constitutes a unique network of total Vertical column ozone measurement.