12/07/2006

GNSS Radio Occultation Community:

GRACE-A (a.k.a. GRACE-1) occultation products from 2006 Oct 10 through
the present have been republished and are now available from the GENESIS
FTP server (sayatnova.jpl.nasa.gov). 

Additionally, GRACE-A Blackjack raw data are now online on the GENESIS
FTP server in the level0 subdirectory of the ftp area.

The data files include only the following
(1) All OBSDqfit packets for the POD antenna.
(2) All OBSDqfit packets for the limb antenna
(3) All NAVGants packets
All other data are stripped out.

The format is the same as for CHAMP except
(1) There is no GFZ integrity wrapper.
(2) The POD OBSDqfit data are 10 second packets, as for CHAMP, but they also include 1 Hz phase residuals.

There is no tracking of occultation reference satellites, which is OK because of the stability of the clock.  The POD data can be used instead if desired.  (The clock is very stable, but has a significant rate, and the clock offset is allowed to drift far off zero.  In particular, recently, the clock offset has been allowed to drift very far (<~ 0.9 sec), which caused our occultation processing software a little problem.  We delayed publication of the raw data until we were sure the data were still OK.)

We've put the last month's data online, and will be putting data online ~ every 12 hours.  If you are interested in older data, please let us know.

The following are currently not online, but will be:
(1) Documentation
(2) Orbits

BJfmtl.c, the reader for CHAMP, also works for GRACE, except that it does not interpret the 1 Hz POD phase residuals properly, though that is a minor problem.
The reader still works for the 10 second POD data and limb data.

Please let us know if you have any questions.

GENESIS Team