Important Information for OMI Data Users

Row Anomalies

Several row anomalies have occurred in the recent past. These anomalies affect the quality of the Level 1B and Level 2 data products. Please read this information carefully prior to using OMI data. Please respect the dates mentioned as the anomalies have occurred recently.

Anomaly 1: Since June 25th, 2007, cross-track scenes 53-54 (0-based).

Anomaly 2: Since May 11th, 2008, cross-track scenes 37-44 (0-based)

Anomaly 3: Since January 24th, 2009, cross-track scenes 27-44 (0-based).

Please be aware that for all other rows the data are of optimal quality and not affected.

Also all OMI data before these anomalies are of optimal quality.

Row Anomaly Corrections

Please be aware that these anomalies are known to the OMI team and are currently under investigation to examine whether corrections for the effects can be implemented in the Level 1b data. Please visit this information page regularly for updates on the status of corrections implemented and visit our detailed technical information.

Row Anomaly Flagging

The Level 1B data are partially flagged for the anomalies listed above. Please visit our detailed technical information for details on the current flagging status of the Level 1B and Level 2 products.

Recommendations To Users

At the moment no corrections have been implemented in the operational Level 1B and Level 2 data. It is recommended not to use the affected cross-track scenes.

Please respect the dates mentioned above. All other OMI data, meaning other cross track scenes and earlier observations, is of optimal quality.

Level-3 products are being produced after filtering for the cross track scenes mentioned per anomaly.

Collection 3 data

Almost all OMI swath or orbital (Level-1B, Level-2), Global Binned (L2G) and Global Gridded (Level-3) data are available in Version-3 collection from the NASA DISC website.

README files

Users are advised to read data quality documents available from the NASA DISC website and validation documents as provided by the algorithm leads carefully before using the OMI data for research purposes. Our data quality and validation documents are updated regularly with the latest information. In case of questions please feel free to contact the respective algorithm lead.

Technical Information for OMI Data Users

Several row anomalies have occurred in the recent past. These anomalies affect the quality of the Level 1B and Level 2 data products. Please read this information carefully prior to using OMI data. Please respect the dates mentioned as the anomalies have occurred recently.

Anomaly 1

Since June 25th, 2007 an anomaly is present in (cross-track) scenes 53-54 (0-based). The anomaly comprises a decrease in the radiance signal, with secondary effects.

The Level 1B data has been flagged for this anomaly for (cross-track) scenes 53-54 (0-based).

All Level 2 data products are affected by this anomaly.

Anomaly 2

Since May 11th, 2008 an anomaly is present in (cross-track) scenes 37-44 (0-based) towards the northern end of OMI orbit. The anomaly comprises a decrease or increase in the radiance signal depending on position in orbit.

On December 3rd, 2008, this anomaly expanded to cross-track position 44 (0-based) and along the full length of the orbit.

All Level 2 data products are affected by this anomaly.

Anomaly 3

Since January 24th, 2009 an anomaly is present in (cross-track) scenes 27-44 (0-based). The anomaly comprises a decrease and increase in the radiance signal depending on position in obit.

All Level 2 data products are affected by this anomaly.

Row Anomaly Flagging Overview

The flags for the row anomaly are stored in the Level 1B data product in the new field 'XTrackQualityFlags'. When Level 2 products are generated, this field is copied in the Level 2 orbit data files. In addition, the Radiance Error bit or Radiance Warning bit in the Fit Quality flags of the Level 2 product are raised, depending on the status of the Level 1B corrections.

• Anomaly 1: The Level 1B data has been flagged for this anomaly for (cross-track) scenes 53-54 (0-based). Level 2 data products have NOT been flagged at the moment.

• Anomaly 2: The Level 1B data has NOT been flagged for this anomaly for (cross-track) scenes 37-44 at the moment. Level 2 data products have NOT been flagged at the moment.

• Anomaly 3: The Level 1B data has NOT been flagged for this anomaly for (cross-track) scenes 27-44 at the moment. Level 2 data products have NOT been flagged at the moment.

Additional Notes

The OMI cross track positions mentioned here are 0-based and hold for UV2 and VIS channels only. For the UV1 channel all number should be divided by 2 and rounded to the nearest integer.

OMI flags are documented in the GDPS Input/Output Data Specification (IODS) (volume 2) of the Level 1B software, available from the NASA DISC: http://disc.sci.gsfc.nasa.gov/Aura/OMI/documents/v003/SD467_IODS_Vol_2_issue5.pdf

The flags for the row anomalies are implemented with version 1.1.2 of the Level 1B software that has been operational from October 8th, 2008 onwards.