[GENESIS Newsletter] February 2003

Mon Sep 20 15:09:27 PDT 2004

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 <http://icesat.gsfc.nasa.gov/>

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

_* 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: <mailto:leoops at sdsio.jpl.nasa.gov>leoops at sdsio.jpl.nasa.gov 
<mailto:leoops at sdsio.jpl.nasa.gov>

_Thank you for your attention.
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://sayatnova.jpl.nasa.gov/pipermail/newsletter/attachments/20040920/b36285b9/attachment-0001.htm