NRT Notification Detail
| Changes to the Metop-A NRT refractivity product |
| DATE: 2013-06-18 14:49 TYPE: NRT-GTS |
| Description |
| Dear ROM SAF GTS Users Issued: 2013-06-18 14:50 UTC On June 25, 2013, EUMETSAT CF will upload the parameter configuration that is currently on Metop-B/GRAS to the Metop-A/GRAS instrument (see message from EUMETSAT below). At the same time EUMETSAT CF will enable the so-called L2 extrapolation. This will make Metop-A data have the same characteristics as Metop-B data. After the upload, the ROM SAF NRT refractivity product from Metop-A (product id GRM-01) will therefore become similar to that of Metop-B (product id GRM-40). The characteristics of the GRM-40 product was described in a ROM SAF users notification on April 8, 2013, and is repeated below. Since the upload of the change to the Metop-B/GRAS instrument in late March, the ROM SAF Team have analyzed the GRM-40 product and concluded that the increased standard deviation between 10 and 20 km that is observed for rising occultations is due to an increased vertical correlation of the bending angles, which in turn is caused by the L2 extrapolation and a few bad outliers. The standard deviation of nominal profiles from rising occultations can be reduced by an enhanced QC, which the ROM SAF plan to implement on June 20, 2013. After this date, about 6-7% more rising occultations from Metop-B/GRAS will be flagged as having non-nominal refractivity (there will be no changes to the data characteristics of the GRM-40 product as such, only more profiles flagged as non-nominal). With the upload to Metop-A/GRAS on June 25, the same enhanced QC will automatically take effect also on the GRM-01 product. Please do not hesitate to contact us if you have any questions related to the data. We would also be very interested in learning about your experience and analysis of the Metop-B/GRAS data. With kind regards The ROM SAF Team ------ Forwarded Message: Subject: Upload of new onboard threshold parameters to GRAS/Metop-A on 25/06/2013 From: Christian Marquardt Date: 6. June 2013 12:43 UTC Dear all, as you know, we carried out several parameter test campaigns on the GRAS instrument on Metop-B at the beginning of the year, and have been operating GRAS on Metop-B with the new, enhanced parameter set since 25th March. Our operations team intends to upload the enhanced parameter set to the GRAS instrument on Metop-A on 25th June 2013. This will make GRAS/Metop-A data provide the same data characteristics as Metop-B does since late March. I have attached the announcement email for the activation of the new parameters on Metop-B from March, as it contains a summary of the changes and how they affect the bending angle data quality. Note in particular that there are a few profiles which now penetrate deeper into the troposphere than before, not necessarily providing good measurements as we are still running a geometrical optics retrieval. We do have a report describing more details of the parameter set tests; please let me know if you are interested in receiving a (pdf) copy. As I am writing to you - we are going to have a scheduled manoeuvre for Metop-A on 26th June. I will let you know the precise times closer to the event. With kind regards, Christian. -- Dr. Christian Marquardt, Remote Sensing Expert, EUMETSAT Eumetsat-Allee 1, D-64295 Darmstadt, Germany Tel: +49-6151-807-4560, Fax: +49-6151-807-8380 Email: christian.marquardt@eumetsat.int, Web: http://www.eumetsat.int ------ Excerpt from ROM SAF message issued on 2013-04-08 11:45 UTC: EUMETSAT CAF has implemented a change in the Metop-B/GRAS instrument configuration and enabled the so-called extrapolation of the L2 signal. This means that we are able to process more occultations to lower altitudes, but also that the quality of the retrievals are different than for Metop-A. In the lower troposphere (below 8 km), Metop-B/GRAS refractivity, when compared to ECMWF forecasts, shows a significant negative bias (larger for rising than for setting), and also a larger standard deviation. For rising occultations we have also observed a larger standard deviation between 10 and 20 km (up to 100% larger), which is currently under investigation. The quality of setting occultations above 10 km is unaltered. It should be recalled that the current Metop-B/GRAS produts are derived from a geometric optics algorithm (and using closed loop data only) which means that the data are of limited use below a height of about 10 km. |
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