OMI Anomalies

Past anomalies

Anomaly Start Date Start time Start orbit Resume Data Date Resume Data orbit Resumption Special Remarks Further information
FMM February 28 2006 00:23:13 8631 March 2 2006 8676 No calibration and irradiance for which FMM was needed June 12 2006 running fully nominal. First irradiance in orbit 10152
OMI survival 2016 May 29 2016 21:30 63151 June 14 2016 6372 This is release date of the data OMI was switched on June 9 2016. But temperatures and performance not yet stable
OMI survival 2017 March 12 2017 18:19 67329 xxxxxxxxxxxx xxxx This is release date of the data OMI was switched on March 16 2017. Data taking resumed March 17 2017 (orbit 67392) But temperatures and performance not yet stable

Present anomalies

Background information

FMM Background information

The Folding Mirror Mechanism (FMM) behaviour changed in the last week of February 2006 and on the 28th of February 2006 the FMM did not return to it's nominal position. What followed where many discussions of what could be the problem, and many tests of the mechanism to confirm our suspicions. This greatly improved our understanding of the FMM, but the FMM moved smoothly during all of our tests and none of our suspicions were confirmed. However, since we suspected the bouncing of the FMM against the end-stop to be the cause of the anomaly that occured on February 28th 2006, we decided to change the way the FMM is operated. This entailed updating all the calibration measurements that use the FMM and testing of all the updated measurement code. After 2 years all the calibration measurements have been updated.

Row Anomaly

In 2007 OMI started to experience the so-called row anomaly. Two rows seemed to be (partially) blocked. This row anomaly was follwed by another row anomaly in 2008. Like the first row anomaly a few rows seemed to be (partially) blocked. But these rows also suffered from reflected sunlight during part of the orbit and earthshine from another scene. This second row anomaly is changing through time (see below for more details). We had many discussions and looked at many pictures of the instrument, but have not been able to find a satisfying explanation for all the row anomalies. Corrections (if possible) and a flagging algorithm are being developped and for an update of the situation, please see the "Important Information for OMI Data Users" below.

Important Information for OMI Data Users

Row Anomalies

OMI has suffered from a so-called “row anomaly”. It affects particular viewing directions, corresponding to rows on the CCD detector, hence the name “row anomaly”. Other viewing directions are of optimal quality. Please read this information carefully prior to using OMI data.

The first appearance of the row anomaly is on June 25th, 2007. At that time, it appeared only in rows 53 and 54 (zero-based). From May 11th, 2008, cross-track scenes 37-41 (0-based) are affected as well. In January 2009 the range of rows extended to 27 - 44, while the original rows 53 and 54 remain affected. Since then the behavior of the row anomaly has remained dynamic. Which rows are affected and to what extent varies with time. Please visit the “Overview” section of our detailed technical information page for the most up to date information and details. A graphical overview of the affected rows is available on the background page.

Recommendations To Users

At the moment no corrections have been implemented in the operational level 1B and level 2 data. Please use the flagging provided in the level 1B and level 2 products to filter out affected data. All other OMI data, meaning unflagged scenes and earlier observations, is of optimal quality. Level-3 products are being produced after filtering for the flagged scenes.

Please visit the README and Data Product Quality Information for the OMI data product of your interest at the NASA DISC pages for OMI data.

Row Anomaly Corrections

The OMI team is aware of the anomaly and is currently investigating whether corrections for the effects can be implemented in the data-processing software. Please visit this information page regularly for updates on the status of corrections implemented and visit our detailed technical information page.

Row Anomaly Flagging

The Level 1B data are flagged for the row anomaly via the XTrackQualityFlags field. Most level 2 products have this information available now, either by copying the XTrackQualityFlags field into the level 2 product or via other newly defined flags in the level 2 product. Please check the README file of the L2 products for more information. Please visit our detailed technical information page for details on the current flagging status of the Level 1B and Level 2 products.

Row anomaly RSS feed

We have set up a row anomaly RSS feed where we post updates to our flagging. You can subscribe to the row anomaly feed via the link. An archive of the messages is here.

© OMI -- Last update: Tuesday, 09-May-2017 03:04:18 UTC. --