SPECIAL NOTE ON GPS-PRN32 and LEVEL-1 READ SOFTWARE

The GPS satellite PRN32 (SVN23) was set "healthy" as of Feb 26, 2008.
Tracking of this satellite was therefore enabled on GRACE.
The Level-1B data since Feb 26, 2008 contains GPS tracking data from PRN32.

The software to convert from GRACE GPS1x format to Rinex format has been
updated to handle the presence of data from PRN32.

Users should download and re-install the entire Level-1 Read software suite
(RELEASE_2008-03-20) from the here.

GRACE is a joint partnership between the National Aeronautics and Space Administration (NASA) in the United States and Deutsches Zentrum Für Luft und Raumfahrt (DLR) in Germany. Prof. Byron Tapley of The University of Texas Center for Space Research (UTCSR) is the Principal Investigator (PI), and Prof. Markus Rothacher of the GeoForschungsZentrum (GFZ) Potsdam is the Co-Principal Investigator (Co-PI). The Jet Propulsion Laboratory carries out project management and systems engineering activities.

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The twin GRACE satellites were launched on March 17, 2002. Since that time, the GRACE Science Data System (SDS) has produced and distributed estimates of the Earth gravity field on an ongoing basis. These estimates, in conjunction with other data and models, have provided observations of terrestrial water storage changes, ice-mass variations, ocean bottom pressure changes and sea-level variations. This portal, together with ISDC, is responsible for the distribution of the data and documentation for the GRACE project. A brief overview of the science data flow is given at http://www.csr.utexas.edu/grace/asdp.html and more details are provided in the project documents. A complete list of relevant project documents has been made available (click here). Users are strongly urged to read these documents before proceeding with data analysis.

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A Guide To Available Data
(April 24, 2008)

The newest Level-1B and Level-2 products are made available at approximately monthly intervals.

Level-1B data refer to the collection of ranging, accelerometry, attitude and related ancillary data. All products have been created by the NASA/JPL element of the SDS. At present, data prior to Jan 1, 2005 are labeled Release-00, and all the data, thereafter, are labeled Release-01. Please see NOTE-1 below for special remarks on AOD1B products from June 2006 to Sep 2007.

Level-2 data refer to monthly estimates of spherical harmonic coefficients of the Earth gravity field. Please see NOTE-3 below for special remarks on re-processed Level-2 products from June 2006 through September 2007. Data products from all three centers are available, as follows:

NOTE-1 (Feb 12, 2008):If you downloaded AOD1B RL04 products for the period June 23, 2006 until September 20, 2007 prior to November 30, 2007 please be sure to download these files again because the oceanic contributions to these products are wrong (by mistake twice reduction of atmospheric S2 tide from surface pressure data used to force the OMCT model). Please also see NOTE-3 below for impact on Level-2 GSM products. The correct AOD1B RL04 products for this range of dates have to have a product creation date later than November 2007 within the header information, e.g.

PRODUCT CREATE START TIME(UTC): 2007-11-08 10:51:24.000

PRODUCT CREATE END TIME(UTC)  : 2007-11-08 13:19:25.000

NOTE-2 (Nov 20, 2007): If you downloaded CSR-RL04 solution for July 2007, labeled

GSM-2_2007182-2007212_0028_UTCSR_0060_0004

before Nov 19, 2007, please be sure to download this file again. The correct file should have the comment line:

CMMNT Updated GSM file based on run n28b (updated on 15 November 2007)

NOTE-3 (Feb 29, 2008): The influence of the error in AOD1B product, described in NOTE-1, on the Level-2 gravity field products, though small, is not negligible. Therefore all GSM-products between June 2006 and September 2007 have been reprocessed with the correct AOD1B. Click Here for a summary of the principal changes in the Level-2 fields in this duration.

The previously released Level-2 products for this span have been replaced with the re-processed fields in the archives. Specifics for each SDS center are described within the Release Notes, and are summarized here:

• UTCSR: The GSM, GAC and GAD product files between Jun 2006 and Sep 2007 have been replaced. The new files are distinguished by the comment line:

CMMNT Solution was reprocessed using corrected AOD product

• GFZ: The GSM product files between Jun 2006 and Sep 2007 have been replaced. The influence of the wrong AOD1B products on the GAA/B/C/D products is negligible, thus these products are only re-distributed if the number of days used to create GSM products has changed during reprocessing. Further details are given in the release notes. The new files are distinguished by the comment line:

  CMMNT Generated with correct AOD1B RL04 product (see SDS Newsletter October 2007)

• JPL: The new GSM and GAx product files will be made available after re-processing.

Please review this page often, as it contains timely updates and information regarding the latest product releases.