New Total Column Ozone Data from GOME

Reaching the Accuracy of Ground-Based Measurements with GDP 4.0

The Global Ozone Monitoring Experiment (GOME) has been measuring global distributions of total ozone since July 1995. Operational GOME data products are generated by the GOME Data Processor (GDP) on behalf of ESA, at the German Processing and Archiving Facility (D-PAF) at DLR.
A new total column algorithm, GDP 4.0, has been developed by scientists from BIRA, SAO and DLR funded by ESA. Independent geophysical validation shows that the average agreement of GDP 4.0 with correlative ozone column measurements is now at the “percent level”, that is, comparable to the precision level of ground-based sensors.

The current quality of the GOME ozone data meets the requirements for the most demanding geophysical research applications such as ozone trend analysis and polar process studies.

Long-term global monitoring of total ozone from European spectrometers is moving with GDP 4.0 into a new era. The GOME and GOME-2 sensor series (the first one scheduled for launch in early 2006) will provide a unique data record covering a time period of over 25 years.

Data Distribution

The complete GOME data record from July 1995 onwards has been reprocessed with GDP 4.0:

GDP 4.0 Total Column Algorithm

The Differential Optical Absorption Spectroscopy (DOAS) approach adopted in GDP consists of the spectral fitting of the apparent slant column amount, followed by its conversion into vertical column amount using a calculated Air Mass Factor (AMF) and the correction for cloud contamination using cloud information inferred from GOME measurements.

The main GDP 4.0 algorithm characteristics are:

  • improved correction for Raman scattering
  • AMFs determined iteratively using on-line radiative transfer forward model calculations
  • new cloud algorithms
  • effective absorption temperature derived by spectral analysis
  • improved atmospheric and surface databases

A detailed description of the GDP 4.0 algorithm can be found in the Algorithm Theoretical Basis Document (ATBD).

GDP 4.0 Validation

The GDP 4.0 algorithm has been validated by scientists from BIRA and AUTH. GOME ozone total column data was compared with pole-to-pole ground-based measurements from SAOZ/DOAS UV-visible Brewer and Dobson spectrometers, and with data from other satellite sensors.

In general, the average agreement of GDP 4.0 with correlative ozone column measurements falls to the percent level. At polar latitudes, and at solar zenith angles beyond 80°, preliminary validation indicates that the agreement is slightly worse, but do not exceed 5%. A remarkable feature of the GOME data record is that, despite the anticipated degradation of the instrument with time, the ozone total column product does not suffer from any long-term drift of quality.

A detailed description of the quality and validation of the GOME products can be found in the Product Disclaimer, the Delta Validation Report and the GOME Validation sites BIRA and AUTH.

Technical Documentation

The following documents contain technical information relevant to GDP 4.0:

Contact

For further information please contact Diego Loyola at DLR.