The total ozone maps are based on ground-based measurements available
from the World Ozone and
Ultraviolet Radiation Data Centre. Preliminary near real-time data
from ground-based observations were also used for the most recent
maps. Total ozone values are given in
Dobson Units.
The numbers represent observations taken from ground stations situated
at the bottom left corner of the number.
Maps of deviations represent total ozone
deviations from the
1978-1988 level estimated using
Total Ozone Mapping Spectrometer
(TOMS) data for all areas except the Antarctic and from the
pre-1980 level estimated using Dobson data over the Antarctic.
Over areas with poor data coverage
adjustments are made according to
TOMS on Nimbus-7, Meteor-3, ADEOS and Earth Probe satellites. Over
the polar night area Dobson and Brewer moon observations and/or
NOAA's TIROS Operational Vertical Sounder (TOVS) satellite data
are used. TOVS data are also used when the more reliable TOMS data are
not available. The mapping algorithm is similar to those used by the
WMO Ozone Mapping
Centre.
The day part of the “Start date”
can specify a day (1 to 31), a mean over the entire month (1-end) or
the mean of a “10-day” period during the month (1-10, 11-20 or 21-end,
which might be 8 or 9 or 11 days). It must logically correspond to the
unit of the “Interval”.
