ROM SAF - NRT Notification Detail

NRT Notification Detail

Degration of GRAS level 1b data

DATE: 2010-04-07 12:45
TYPE: NRT-GTS

Description

Dear GRAS SAF GTS User Issued: 2010-04-07 13:45 UTC GRAS level 1b products have been degraded since Monday afternoon (2010-04-05) and as a consequence GRAS SAF level 2 products have also been degraded. The quality of both the GRAS level 1b products and GRAS SAF level 2 products are expected to be back to normal later today. Please see detailed message from EUMETSAT below. Kind regards The GRAS SAF Team Forwarded message: Subject: GRAS Processing Anomalies and POD reset Date : 2010-04-07 Dear all, starting in the early afternoon of Monday,5 Apr 2010, we observed anti- symmetric high altitude biases in the order of up 2-3 microradians (positive for rising, negative for setting occultations) in GRAS bending angle products. The situation partially recovered during yesterday, but higher altitude bending angles remained to exhibit biases in the order of 1 microradian, with opposite signs for rising and setting occultations. In order to get back to the nominal quality of our data products, we have now performed a POD reset. Accordingly, GRAS products from measurement time 09:06 UTC onwards is flagged as degraded. We expect that the data quality will be nominal again for sensing times around 13:00 UTC. Note that the data will remain to be flagged as containing bad bending angle data until 17:06 UTC. Some more details on what had happened: - Starting in the early Monday afternoon, the estimated position of Metop in the operational processing has been drifting off by up to 3 meters from our reference POD, giving rise to clock inconsistencies and thus high altitude systematic bending angle biases. Things did improve during yesterday, but the POD recovery process eventually stalled around around a 1 meter position bias. - We currently believe that the root cause is a strong geomagnetic storm that occurred on Monday (see, e.g., http://www.spaceref.com/news/viewsr.html?pid=33826) The sequential filter in use in our operational processing is not able to update the increase in atmospheric density related to such events quickly enough; hence the systematic problems in the orbit determination, clock error estimation and bending angle data quality. - We are extremely grateful to Michael Rennie (MetOffice & GRAS SAF) and Sean Healy (ECMWF & GRAS SAF), who very quickly helped us to identify the impact of the data degradation on their operational systems, and gave us continued feedback on the GRAS data. We apologize for the inconvenience that this renewed POD reset might have caused on your side. Christian. -- Dr. Christian Marquardt, Polar System Product Expert EUMETSAT, Am Kavalleriesand 31, D-64295 Darmstadt, Germany

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