The data is calculated on a convective cloud differential (CCD) algorithm and averaged whereby only the position of the central coordinate is considered.
The tropospheric column can then be calculated by the difference between the stratospheric column and the total column. The stratospheric column being estimated as above the high reaching convective clouds (cloud cover >0.8 and >8km in height). To reduce the error above the clouds from up draught of tropospheric pollution a clean reference region 70°E to 170°W representitive of the latitude band.

For the Total column only cloud free observations are considered (<10%). This method assumes the stratospheric ozone is constant throughout each month and for one latitude band limit the CCD algorithm to the tropics (20°S to 20°N).

SCIAMACHY (Scanning Imaging Absorption Spectrometer for Atmospheric CHartographY) is
a multi-channel UV-Vis-NIR spectrometer launched on the ENVISAT platform in 2002. Its
primary mission objective is the global monitoring of trace gases in the troposphere and in the
stratosphere. The solar radiation transmitted, backscattered and reflected from the atmosphere is
recorded at medium resolution (0.2 nm to 1.5 nm) over the range 240 nm to 1700 nm, and in
selected regions between 2.0 µm and 2.4 µm. SCIAMACHY is particular since it has three
different viewing geometries: nadir, limb, and sun/moon occultation, which yield total column
values as well as distribution profiles in the stratosphere and upper troposphere. In this project
both nadir and limb measurements are used in Channels 1, 2 and 3. In nadir view, used for ozone
total column and vertical profile retrievals, the ground pixel size for channels 2-3 is 30x60 km2,
i.e. a resolution intermediate between GOME and OMI. The swath width of SCIAMACHY at
nadir is similar to GOME (960 km), however due to the alternate nadir and limb mode operation,
global coverage is only obtained in approximately 6 days. In limb view, ozone number density
profiles are derived in the stratosphere by exploiting the Hartley and Chappuis spectral
absorption bands in channels 1 and 3. SCIAMACHY data are available from July 2002 till April
2012 when communication with ENVISAT was lost.