ROM SAF - NRT Notification Detail

NRT Notification Detail

Scheduled outage of GRAS level 1b data

DATE: 2009-12-08 16:13
TYPE: NRT-GTS

Description

Dear GRAS SAF GTS User Issued : 2009-12-08 16:12 Due to a scheduled Metop-A in-plane manoeuvre and a GRAS SLTA update there will be an outage of GRAS SAF products this Thursday, 2009-12-10. Please see the message from EUMETSAT below. -- snip --- Dear all, this coming Thursday is going to be a busy day for GRAS... In the afternoon, an in-plane maneouvre will be performed for Metop around 15:31 UTC. As we (as usual) expect to have to reset the GRAS Precise Orbit Determination (POD) afterwards, we will stop the dissemination of operational GRAS products around that time and enable it again after the orbit has converged to its nominal quality. GRAS products will be flagged as being of poor bending angle quality for 8 hours after the reset, i.e. probably until midnight (00:00 UTC on 11 Dec 2009). In the morning (currently scheduled for 08:40 UTC), we also intend to change several parameters affecting the raw sampling peformance of the GRAS receiver. In particular, we will - increase the altitude range for which raw sampling data is available in rising occultations to (nearly) the tropical tropopause, in order to fill gaps in closed loop data in the upper troposphere. This will only affect rising occultations. - decrease the lowest altitude at which raw sampling data can be measured by the instrument, from (currently) -140 km Straight Line Tangent Altitude (SLTA) to -300 km SLTA. This change aims at making research data available to study the role of signals propagating deep behind the atmosphere in tropospheric RO retrievals. This change will affect both rising and setting occultations. The closed loop measurements should not be affected much by these parameter settings, so we do not expect changes in the quality of the current operational GRAS products. There might be a small increase in the lower impact altitude for setting occultations. Please let us know if this poses a significant problem for you. There probably also is a small risk that the parameter change (which will be accompanied by a 2 minute data gap) may trigger another POD reset. We'll let you know should this indeed happen. Due to the increased length and size of individual occultations caused by the second parameter change described above, we also expect that the number of daily occultations might be slightly reduced. Therefore, the test is initially planned to last one week only. If the loss of occultations turns out to be acceptable, we will extend the test over the Christmas period; if our worst case scenario comes true (foreseeing losses in the order of ~50 occultations/day), we will restore the current default settings. We expect that make reconstructed amplitude and phase data available to the interested science community as soon as possible after we have have been able to make an initial assessment of the instrument performance. Given that we have the holidays coming up, I hope you'll won't mind too much if this will only happen after Christmas - probably in early January. If you are interested in this data (and havent discussed this with us before), please send me a short email so that we can inform you once the data is available. Kind regards, Christian Marquardt. -- snip --- Kind regards The GRAS SAF Team

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