OMI Calibration: Instrument Status Collection 3
All data presented hereafter are based on level 1b metadata and various TMCF products. The purpose is to provide OMI data users with detailed information on what was measured, how it was measured and its quality. In the measurement types section an overview of all instrument measurement modes is given as well as all orbits in which they were executed. The daily reports section is ordered by date and gives additional information on ground track coverage and the derived level 1b products. Information on the quality of the instrument and the level 1b data for the complete duration of the mission can be found in the Performance, Telemetry and Quality Flag sections. All exceptions and anomalies, including solar eclipses and the budgets for the life-limited items of the instrument are also provided.
- Rows 27-44 anomaly
Since 24 January 2009 the signal suppression in the radiance (earth) measurement data observed since May 2008 and described below has worsened. This anomaly is now visible in binned rows 27-44 in the UV2 and VIS channels (zero based) and binned rows 15-22 in the UV1 channel (zero based) in the global earth measurements (binning factor 8) for the complete illuminated part of the orbit. In addition, in the UV1 channel the signal increase is now observed in rows 15-22 (zero based), but still only for northern latitudes, at Solar Zenith Angles (SZAs) larger than 44.0 degrees for the affected rows.
The origin for the deterioration is currently not known.
The anomaly is currently under investigation. It is recommended for now that the rows in question are not used for further data analysis, until a correction in the level-1b and level-2 data has been implemented.
- Rows 53-54 anomaly
Rows 38-41 (UV2, VIS) and rows 18-21 (UV1) anomaly
Since 25 June 2007 a signal suppression is observed in the radiance (earth) measurement data in rows 53-54 of the UV2 and VIS channels (zero based) over the complete illuminated orbit. Since 11 May 2008 another signal suppression is observed in the radiance (earth) measurement data in rows 38-41 of the UV2 and VIS channels (zero based), while a signal increase is observed for the UV1 channel for rows 18-21, but only for northern latitudes. The signal suppressions are tentatively attributed to Multi-Layer Insulation (MLI) blocking part of the field of view and the signal increase is tentatively attributed to sun light being reflected into the radiance (earth) entrance port of the instrument by the same material that is responsible for the partial blocking of the field of view.
The irradiance (sun) measurement data are not affected by any of the row anomalies.
Both anomalies are currently under investigation. It is recommended for now that the rows in question are not used for further data analysis at the latitudes specified above for both row anomalies, until a correction in the level-1b and level-2 data has been implemented.
- Azimuth angle in irradiance measurements exceeding maximum calibrated angle, 20 October - 21 November 2008
As a direct result of the EOS-Aura rephasing that took place in 2008 the azimuth angle on the on-board diffuser used in the irradiance measurements exceeded the maximum angle for which the calibration is most accurate in the time period 20 October - 21 November 2008. The maximum calibrated azimuth angle is 31.2 degrees and in the time period in 2008 mentioned above the azimuth angle reached a value of 31.7 on 4 November 2008. This may lead to less accurate level-1b irradiance data products for that time period.
- OMI instrument software anomaly 27 September - 1 October 2008
No measurements were performed from 27-29 September 2008 as a result of an OMI instrument software anomaly. Measurements were resumed on 30 September 2008, without calibration measurements that use one or more mechanisms. Regular instrument operations were resumed on 2 October 2008. In the period 30 September 2008 to 1 October 2008 only limited calibration data are available, leading to a gap in some of the figures.
- Commissioning phase
From the launch on 15 July 2004 until 26 September 2004 the commissioning phase activities were performed. This implies that the OMI instrument was not operated using a nominal regular in-flight operations scenario and that in-flight calibration and characterisation measurements were performed that are not performed in the nominal in-flight operations scenario. In addition, the optical bench and detector temperatures may have been different from their nominal in-flight values. Although the measurement data from the commissioning phase can be used for scientific purposes, it is good to keep this in mind.
Additional commissioning measurements were performed in the time period 19 November 2004 until and including 1 December 2004.
- Update frequency daily reports
The daily reports are updated every night. However, it may occur that not all data are available at that time, which can lead to a small backlog. This is automatically corrected after approximately 3-4 days.
- Update frequency mission duration reports
The performance and quality reports are updated every week. Therefore, these plots do not contain the most recent orbits.
- Folding Mirror Mechanism Anomaly
The folding mirror was not used nominally between 28 February 2006 and 11 June 2006 (orbit range 8631-10146). In this period only limited calibration data are available, leading to a gap in some of the figures.
After 11 June 2006 the folding mirror mechanism was used nominally.