The Ozone Hole
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December 2002 

NASA Earth Probe TOMS  Images

Ozone Measurement

1 Dobson Unit (DU) is defined to be 0.01 mm thickness at STP (standard temperature and pressure). Ozone layer thickness is expressed in terms of Dobson units, which measure what its physical thickness would be if compressed in the Earth's atmosphere.

NASA decided to change the EP/TOMS operational processing configuration in order to apply a correction for the cross-track bias errors that have grown large over the past year or so. These data are being made available at the TOMS web site on an operational basis. Data starting August 1, 2001 will be reprocessed with this configuration and made available as well to provide a consistent data set over the 2001 ozone hole season. The data previous to August are the old data, so a discontinuity will be seen at the July 31 / August 1, 2001 boundary. The reprocessed ozone images will also use the new color scale. The cross-track bias correction will remove almost all of the cross-track bias, but will not remove residual long-term changes in ozone due to related instrument degradation. The current EP/TOMS data should not be used for studies of long-term changes in ozone beyond the summer of 2000.

The white area on the images is where data cannot be retrieved in the earth's shadow or polar night regions by the satellite.