Profile Ozone Adjustments

Procedure Used To Construct Profile Ozone Merged Data Sets

Assumptions

No external adjustments are applied when constructing the initial MOD Profile Data Set

In the inital MOD Profile data set, we use the SBUV Version 8 calibration as determined by the instrument teams, and do not apply any external adjustments to the data sets. This is a reasonable first approach, as the SBUV data have been internally calibrated to each other within the Version 8 algorithm. The NOAA 11 SBUV/2 absolute calibration is derived from overlap comparisons with measurements from the Shuttle SBUV (SSBUV) instrument. The calibrated NOAA 11 data are then used to determine the absolute calibration of the Nimbus 7 SBUV and NOAA 9 SBUV/2 instruments according to their respective overpass comparisons. The NOAA 16 SBUV/2, which do not have sufficient overlap with NOAA 11, are processed based on the calibration determined before launch. To date no time-dependent calibration adjustments are needed for NOAA 16. By adjusting the absolute calibration internally based on instrument intercomparisons, the Version 8 algorithm explicitly makes adjustments similar to those made when creating the MOD data set. This result is reflected in the generally lower external total ozone adjustments derived in this version of the MOD data set.

Methodology

Construct Zonal Average Data Sets

For each instrument, we construct 5° zonal mean monthly-mean data sets. Details of the averaging procedure and filtering requirements can be found under Profile Averaging Details. In this version we do not use coincident matches to compare the data, but instead compare the zonal monthly averages computed from all available data for each instrument.

SBUV Overpass Differences in Monthly Gridded Averages
Plotted in Broad Latitude Bands

SBUV Avg. Overpass vs. Altitude (% Difference)

Here we see the average differences between NOAA 11 SBUV/2, Nimbus 7 SBUV and NOAA 9 SBUV/2 are all within 5% in each latitude band. The average offset between NOAA 11 SBUV/2 and NOAA 16 SBUV/2 is a little larger, but still generally within 5%. Keep in mind that unlike Nimbus 7 and NOAA 9 data, the NOAA 16 data have not been adjusted to NOAA 11 within the Version 8 algorithm. In addition, the period of overlap between NOAA 11 and NOAA 16 is less than one year, where there are several years of overlap in each of the other comparisons.

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