Improved calibration of NOAA-9 and NOAA-11 SBUV/2 total ozone data using in-flight validation methods

The Solar Backscattered Ultraviolet (SBUV)/2 instrument on-board the National Oceanic and Atmospheric Administration (NOAA)-9 satellite monitored global total ozone and its vertical distribution from 1985 to 1998. The instrument's diffuser reflectivity calibration system failed early in the mission and an alternative calibration procedure with a time extrapolation was used for an initial processing (Version 6.1 data). The total ozone data shows a +3% drift from 1992 to 1998 as well as large seasonal variations with respect to ground based and other satellite data. Using two internal data validation techniques the total ozone data quality is significantly improved. One method, the 'D-pair Method', which is analogous to the method used for the Nimbus 7 SBUV, corrects the diffuser reflectivity calibration and eliminates the drift in total ozone for NOAA-9. The D-pair Method applied to NOAA-11 SBUV/2 data from 1989 to 1994 shows good agreement with the NOAA-11 on-board diffuser reflectivity calibration system. The second validation method, the 'PMT System Method', is a new method that corrects the Photomultiplier Tube System Nonlinearity Characterization in Range 3 thereby reducing the seasonal variation in total ozone. The PMT System Method corrects both the NOAA-9 and NOAA-11 data.