May 16, 2012
Introduction of the GDR-D standard in the Jason-2 near real time products
We are pleased to announce the implementation of the next evolution of the product processing and format standard for Jason-2 data, known as GDR-D, in the Jason-2 Near Real Time (NRT) products.
It is planned to introduce the change in the EUMETSAT and NOAA NRT processing systems on the 31 July 2012, and it will affect the Jason-2 OGDR, OGDR-SSHA and OGDR-BUFR products disseminated via EUMETCast, the GTS and the EUMETSAT Data Centre.
In order to prepare your systems for the use of these new data, you may find useful the following advanced information, containing a summary of the changes.
Two changes are to be considered. First, the suffix '.nc' will be added to the netCDF products (OGDR and OGDR-SSHA). Additionally, the new product version ('d') will be reflected in the filenames of all products (OGDR, OGDR-SSHA and OGDR-BUFR).
Examples of new filenames (changes in bold):
The format changes affect the netCDF products only and can be summarised as follows:
Several global attribute changes to better record the processing and instrument configuration for each product.
Inclusion of the altimeter surface type and the ice flag in the OGDR-SSHA products.
The Advance Microwave Radiometer (AMR) surface type definition has changed, in order to include a new value for coastal areas.
Addition of smoothed AMR brightness temperature for all channels.
Several new variables, based on an improved processing of the AMR data have been added for rain and sea ice flagging, as well others specifically related to coastal processing.
The atmospheric attenuation correction for radar backscatter will be provided as an integer field.
Removal of the value for the platform off-nadir angle and associated flag.
Meaningful use of the currently existing orbit state flag after a re-definition of the variable.
Meaningful use of the currently existing variable to flag the availability of ECMWF-based atmospheric corrections.
Inclusion of new parameters for Ku-band range, backscatter, wind and significant wave height, based on a new MLE3 re-tracking solution. This is in addition to the MLE4 re-tracking solution parameters included currently in the products. The MLE3 fields are explicitly named so in the variable name, e.g., ‘sig0_ku_mle3’ vs the current MLE4-based ‘sig0_ku’ field.
As a consequence of the above changes, the product sizes will increase approximately as follows:
OGDR-BUFR: no change
Here are the main product content changes relevant to the NRT products:
Calibration of the wind speed retrieval.
New models for tide corrections, mean sea surface and mean dynamic topography.
The off nadir angle field in the OGDR-BUFR products is now set to missing.
The AMR instrument identifier in the OGDR-BUFR has been corrected.
OGDR-BUFR encoding with version 16 of the WMO BUFR tables, which will be activated already on the 18 July.
For more details regarding the changes on product file names, format and contents listed above, we encourage you to inspect closely the new Product Format Specification and Jason-2 Handbook. For your convenience, a set of products generated following the new GDR-D standard for NRT processing can be found on our ftp site. Finally, an update of the reading tools kindly provided by NOAA is also available in the Jason-2 NetCDF OGDR Reader Package.
The graphs below provide a comparison example between the current and new standard for Ku-band SWH and wind speed during the Jason-2 cycle 1. A full analysis of the OGDR-D data quality is being carried out at the moment and more details will be provided in the coming weeks, highlighting the major improvements and remaining open issues. We encourage you however already to refer to the Jason-2 handbook for a summary of the main product performance indicators for range, wind and significant wave height.
Figure 1: Ku-band Significant Wave Height and Wind Speed histograms corresponding to Jason-2 cycle 1 reprocessed with the OGDR-D standard.
In green Jason-1, in red the Jason-2 current operational standard and in blue the GDR-D standard.
After the improvements introduced, both parameters align better now with those from Jason-1. Graphs courtesy of CNES.
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