[GENESIS Newsletter]: February 2003

[newsletter-admin@sayatnova.jpl.nasa.gov]

Dear Colleagues,

Many of you attended the International Workshop on GPS Meteorology in
Tsukuba last month. It was a great success and we were all impressed with
the progress that has been made in both ground and spaceborne GPS
meteorology. One thing that we at JPL came away with is the need to
stress the experimental nature of the occultation instruments on CHAMP
and SAC-C. These are entirely new instruments developed from scratch and
the flight software is still being refined. One persistent issue has been
receiver mistracking in the lower troposphere, which gives rise to
refractivity biases in some retrievals. This is entirely expected until
the full "open loop" reception capability is implemented, as it
will be shortly. Open loop tracking will allow accurate signal phase (on
perhaps multiple tones) to be reliably recovered in ground processing,
and will greatly reduce the observed refractivity biases. There have been
a number of other receiver performance anomalies, particularly on SAC-C,
which has served as the primary test bed for new software, and which has
a balky oscillator on its "A side" receiver. 

For those interested we have compiled a chronology of the performance
status of each receiver, identifying those intervals where the
performance was generally satisfactory. This is available on GENESIS
at:

ftp://sideshow.jpl.nasa.gov/pub/genesis/level0/sac-c/Documents/SACC_recvr.html
ftp://sideshow.jpl.nasa.gov/pub/genesis/level0/champ/Documents/CHAMP_recvr.html

But bear in mind that these are developmental units intended to serve as
test beds for occultation software and tracking techniques. Changes are
made regularly. It may be another year before a highly stable version of
flight software is ready, and probably more than that before ground
retrieval algorithms have matured to the point where the promise of
minimally biased, super-precise GPS retrievals is fully realized.

By all evidence, there are no serious barriers to achieving that promise.
Those of you who followed the GPS geodesy saga will recall that it took
roughly ten years from the time, in the early 1980s, when the potential
of GPS geodesy was first recognized to the time that potential was
achieved. Today, another ten years later, that perceived early potential
has been far surpassed, and many unforeseen geodetic applications have
become routine. We can expect to witness a similar flowering of GPS
occultation science, and a future beyond what we can now hope to
describe. It promises to be an exciting decade. 

Tom

=========================================
GENESIS
Monthly Newsletter 
=========================================
HIGHLIGHTS 
 1. 
Alert to GENESIS Data Users:  New FTP Server
 2.  Anomalous occultation data periods
 3.  Jason-1 GPS flight data now available
 4.  ICESat launched carrying Blackjack POD receivers 
 5.  Science and technical
highlights 
 6.  New online publications
 7.  Recent/upcoming events
 8.  Occultation Missions Status
 9.  Hot Topics
10. Feedback
=========================================

1. Alert to GENESIS Data
Users:  New FTP Server
Beginning February 3, 2003, GENESIS data
comprised of:

 a.  Level 0-3 data
 b.  Orbits data
 c.  LEO-POD data

will be made available for download via an account-based FTP server at
sayatnova.jpl.nasa.gov. 
Access to this data from its current location at
sideshow.jpl.nasa.gov
will be  removed on March 14, 2003.  At this time, you may
register for an account on:
http://sayatnova.jpl.nasa.gov/genesis/cgi-bin/register.cgi

Apologies for the inconvenience.

2. Anomalous occultation data
periods
As noted in the introduction, you can obtain a
chronology of the performance status of each occultation receiver from
the GENESIS web site.  See links cited above.

3. Jason-1 GPS flight data now
available
JASON flight GPS Data (for POD only) from year
2002/doy 013 through year 2003/doy 023 is now available for download
at:
ftp://sayatnova.jpl.nasa.gov/pub/genesis/rinex/jason

Note from CNES README.txt:

"Even though these data are publicly available, they are being used
by the members of the TOPEX/Jason POD Working Team as part of their
CALVAL activities during the verification phase.

It should also be understood that these data are preliminary and might
still contain errors."

4.  ICESat launched on
Monday, January 13, 2003 00:45 UTC carrying Blackjack POD-only receivers
Blackjack Receiver #1 and its antenna were
powered on and the first GPS data were recorded at about 15:30 UTC
Friday, January 17, 2003.  According to Bob Schutz, GLAS science
team leader for ICESat:

" BJ#1 has performed as expected, tracking up to 9 satellites during
normal operations. ICESat commissioning is underway by Ball Aerospace
with a series of orbital maneuvers to place the satellite into the
desired calibration orbit, an 8-day repeat ground track. Initial
operation of GLAS is planned for early February. Availability of GPS
RINEX data will be announced via IGSLEO."

Bob Schutz's IGSLEO update is available via IGSLEO at:
 http://igscb.jpl.nasa.gov/mail/igsleo/2003/msg00002.html

The official ICESat website is at:
http://icesat.gsfc.nasa.gov

Other available data products are available
at:
ftp://sayatnova.jpl.nasa.gov

Check on the current status of level0 and glevel data for SAC-C and
CHAMP.
http://genesis.jpl.nasa.gov/html/index.html

5. Science & Technical
Highlights
On the technical side, the SAC-C spacecraft
encountered power supply problems several weeks ago.  The spacecraft
is still operating but with reduced capability.  As a result, we are
only getting 20 MBytes of GPS data per day instead of the previous
40.  This means ionospheric occultations must be kept off and
atmospheric occultations must be limited to about 200 per day with the
current starting altitude of 150 km.

The SOLVE campaign was running throughout January and part of
February.  The SAC-C receiver was configured to allow normal
occultations at latitudes above 50 degrees during this period to minimize
occultation data gaps.

Further, we have indications that the high-vertical resolution of radio
occultations can be used to capture thin moisture layers, and that
solving the dry-wet ambiguity without ancillary data is not an impossible
task (see paper by M. de la Torre Juarez & M. Nilsson accepted in
JGR-Atmospheres as 2002JD002880, also in the GENESIS Eprint
repository:
http://genesis2.jpl.nasa.gov/archive/200302001/

6. Online Publications
The GENESIS library of online preprints,
presentations, and other publications can be accessed at:
http://genesis2.jpl.nasa.gov

If you have materials you would like to make
available, please register:
http://genesis2.jpl.nasa.gov/perl/set_password

and log on:
http://genesis2.jpl.nasa.gov/perl/users/home

Latest Additions: 
* On the detection of water vapor profiles and thin moisture layers from
the atmospheric radio occultations
http://genesis2.jpl.nasa.gov/archive/200302001/
* Ionospheric Data Assimilation of Ground GPS TEC by Use of the Kalman
Filter
http://genesis2.jpl.nasa.gov/archive/200212031/
* Improved Resolution and Accuracy of Temperature Retrievals from GPS Occultations
http://genesis2.jpl.nasa.gov/archive/200212032/

7. Recent/Upcoming Events 
* ESIP Federation Assembly - 6-10 January 2003, Pasadena, California:
http://www.esipfed.org/Library/meetings/10th_fed_meeting/10th_fed_meeting.html
* EGS-AGU-EUG Joint Assembly - 6-11 April 2003, Nice, France:
http://www.copernicus.org/egsagueug/index.html
* Second CHAMP Science Meeting - 1-4 September 2003, GeoForschungsZentrum, Potsdam:
http://op.gfz-potsdam.de/champ/main_CHAMP.shtml

8. Occultation Missions Status 
* CHAMP - operational; averaging 138 occultations per day since January 1, 2003:
http://op.gfz-potsdam.de/champ/index_CHAMP.html
* SAC-C - serving as the principal test bed for improved occultation software; remains operational for occultations with occasional outages for new software tests:
http://www.conae.gov.ar/sac-c/index.html
* GRACE - in commissioning phase; occultation start date not yet set:
http://www.csr.utexas.edu/grace/
* ICESat - in commissioning phase; occultation start date on Friday, January 17, 2003 at about 15:30 UTC;  Bob Schutz's update is available via IGSLEO at:
 http://igscb.jpl.nasa.gov/mail/igsleo/2003/msg00002.html
The official ICESat website is at:
http://icesat.gsfc.nasa.gov

 9. Hot Topics 
* Open-Loop Tracking: Implementation of open-loop tracking is progressing with recent software tests on SAC-C.  Roll out date for open loop is not yet set.
* N-bias: It is expected that when finally implemented, the open-loop tracking technique will lead to a substantial reduction on the N-bias in the lower troposphere. 

10. Feedback
If you have any question, comments, and/or suggestions to improve this newsletter -- or on other GENESIS topics -- please send them to:
mailto:leoops@sdsio.jpl.nasa.gov

Thank you for your attention.