ROM SAF - NRT Notification Detail

NRT Notification Detail

GRAS/Metop-A Parameter Updates

DATE: 2013-06-26 14:04
TYPE: NRT-GTS

Description

Dear ROM SAF GTS User

Issued: 2013-06-26 14:05 UTC

Since the parameter upload to the GRAS instrument onboard Metop-A yesterday, many rising occultations did not reach below 20 km and were flagged as non-nominal by the ROM SAF. This was because the so-called L2 extrapolation had not yet been activated. The L2 extrapolation was activated starting with instrument sensing times of approx 10:00 UTC.

Please see detailed message from EUMETSAT below.

We apologize for any inconvenience.

With kind regards
The ROM SAF Team

Forwarded Message:
Subject: Once more: GRAS/Metop-A Parameter Updates
From : Christian Marquardt
Date: 2013-06-26 13:24 UTC

Dear all,

eventually, we (or rather Stig Syndergaard from DMI - many thanks, Stig!) noticed that after changing the onboard parameter settings for GRAS on Metop-A yesterday, we also should update the processing configuration to actually extrapolate the L2 data. We originally had the intention to do this in parallel with the implementation of the parameter change on the instrument - but I simply overlooked this. My apologies!

Since 10:00 UTC today, GRAS/Metop-A processing is fully consistent with the one for Metop-B.

On a different matter: As you might be aware, DMI (Stig again!) has reported increased refractivity differences against ECMWF data in the altitude range between 10 and 20 km for Metop-B data based on the extrapolated L2. Bending angle standard deviations against ECMWF do not show this behaviour and are indeed unchanged compared to the (old) Metop A products. As Chris Burrows (MetO) and Sean Healy (ECMWF) could then demonstrate, it appears that bending angle products for the new parameter configuration of the GRAS instruments produce increased vertical error correlations at impact parameters below 20 km. These are in fact consistent with the larger refractivity standard deviations Stig observed.

Some initial analysis on our side indicates that the increased error correlations are not due to the extrapolation in itself, but rather due to a rather poor implementation of the fitting algorithms involved. In particular, our prototype / future processing system does not seem to suffer from the correlation issue seen in the operational data. While the analysis is still ongoing, we will very likely backport the relevant algorithms update the operational processing in the July/August time frame to mitigate the error correlation (and thus increased refractivity error) issues. I will keep you updated.

Finally: Thank you *very* much Stig for being insistent!

Chris.

--
Dr. Christian Marquardt, Remote Sensing Expert, EUMETSAT Eumetsat-Allee 1, D-64295 Darmstadt, Germany
Tel: +49-6151-807-4560, Fax: +49-6151-807-8380

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