[IGSMAIL-3606]: GPS occultation data from CHAMP

Tue Nov 20 16:24:44 PST 2001

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IGS Electronic Mail      20 Nov 16:24:47 PST 2001      Message Number 3606
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Author: Tony Mannucci and Tom Yunck

We are pleased to announce the release of GPS occultation data from 
NASA's Blackjack receiver aboard the German CHAMP mission, which is 
managed by GFZ in Potsdam.  These new data join NASA's SAC-C 
occultation data released earlier this year.  Both data sets are 
available via anonymous ftp from JPL's GENESIS web site 
(http://genesis.jpl.nasa.gov).

A first validation of the Champ GPS data has been carried out by GFZ 
and JPL.  Preliminary results by both centers for precise orbit 
determination and atmospheric retrievals on CHAMP have appeared in 
the scientific literature.

For each occultation event, raw phase observables are acquired at 
both GPS frequencies from two GPS satellites tracked through the 
rear-facing antenna: the occulting satellite and a higher elevation 
calibration satellite.  Phase and pseudorange observables from all 
the GPS antennas are included in the files. Detailed information for 
data download is provided at the end of this notice. The GPS data, 
along with other CHAMP mission data, are also accessible via GFZ's 
CHAMP Information System and Data Center at 
http://isdc.gfz-potsdam.de/champ.

Users of the CHAMP and SAC-C GPS data should be aware that this is 
still an area of intensive development at JPL.  The BlackJack is an 
all new design attempting to make measurements in the lower 
troposphere never before accomplished.  CHAMP and SAC-C are serving 
as vital developmental test beds for experimental GPS remote sensing 
techniques. We have previously announced the availability of raw data 
from the SAC-C Blackjack receiver. Please see:
ftp://sideshow.jpl.nasa.gov/pub/genesis/level0/sac-c/Documents/announcement.010913 
.

As we gain knowledge and experience, we will continue to make changes 
to the flight software on both CHAMP and SAC-C.  We hope many of you 
will be able to join in this process of discovery, and contribute to 
the many insights and advances that we can expect as these missions 
proceed.

The CHAMP receiver is being managed by GFZ Potsdam, and changes to 
the GPS receiver acquisition modes may occur from time to time. A 
history of upgrades, operational modes, and software changes for 
CHAMP is available in the GENESIS ftp area at: 
ftp://sideshow.jpl.nasa.gov/pub/genesis/level0/champ/Documents/CHAMP_recvr.html. 
Similar information for the SAC-C receiver can be found at:
ftp://sideshow.jpl.nasa.gov/pub/genesis/level0/sac-c/Documents/SACC_recvr.html 
.

We ask that users who choose to download these data fill out the 
registration form appended to this email and send it to: 
leoops at sdsio.jpl.nasa.gov. Send inquiries to Gerald Manipon at 
leoops at sdsio.jpl.nasa.gov.

The binary data are primarily intended for groups familiar with the 
technical details of occultation processing.  Retrieved atmospheric 
profiles of refractivity, temperature, etc. generated at JPL will be 
made available in a few weeks from GENESIS.  Similar quantities are 
also generated at the GFZ ISDC. Please contact that center for 
further details.

High-rate ground data useful in processing these occultations are 
available from the International GPS Service (IGS) (See IGSLEO 
message number 9 at 
http://igscb.jpl.nasa.gov/mail/igsleo/igsleo.html).

Precise orbit determination data from the CHAMP and SAC-C 
zenith-viewing antennas are available from GENESIS in RINEX format, 
Version 2.1, as are CHAMP and SAC-C precise orbit solutions computed 
at JPL for occultation processing (see below).

The availability of these data is the result of outstanding effort 
from a number of individuals within the following groups and 
institutions:

The CHAMP project managed by GFZ Potsdam - see http://op.gfz-potsdam.de/champ

GENESIS group at JPL
GPS Earth Observatory group at JPL
GPS Systems group at JPL
International GPS Service
NASA
Orbiter and Radiometric Systems group at JPL
Raytheon Technical Services Company
Satellite Geodesy and Geodynamics Systems group at JPL

DATA DOWNLOAD INFORMATION
-------------------------
Data are available via GENESIS at http://genesis.jpl.nasa.gov. The 
ftp link to Level 0 data becomes visible after clicking on 
"Atmosphere Data and Products".  Anonymous ftp clients can be 
directed to the following address: 
ftp://sideshow.jpl.nasa.gov/pub/genesis/level0/champ/

Data are in subdirectories yYYYY/dDDD, where YYYY is the four-digit 
year and DDD is the three-digit day of year.

GPS data are in files named, e.g 
CH-0-RDC-DMP-SC+NZ_2001_311_04_20_2_b.gpsM, where 2001_311_04_20 
indicates the time of the dump:
   2001_311 is the year and day of year (1-366)
   04_20 is the hour and minute,
and .gpsM indicates GPS raw data from the Main GPS receiver (.gpsR 
indicates the Redundant receiver). Occultation data are not present 
for all days. See the receiver operations file for more information.

The data are stored in Blackjack format with a TRSR (Turborogue Space 
Receiver) wrapper, with a second wrapper added by GFZ.  We provide a 
utility to remove the GFZ wrapper (champ_unwrap.c).  We provide a 
reader, BJfmtl, which removes the TRSR wrapper and writes the data in 
ASCII format. The source code is provided in the following directory:
ftp://sideshow.jpl.nasa.gov/pub/genesis/level0/champ/Software .

Additional documentation is provided in the directory
ftp://sideshow.jpl.nasa.gov/pub/genesis/level0/champ/Documents .

README.011112 provides information on the data.
CHAMP_recvr.html provides information on satellite and GPS receiver operations.
README.satellite lists some satellite specifications.

RINEX format files for the 10-second rate GPS data from the 
zenith-viewing antenna are available at:
ftp://sideshow.jpl.nasa.gov/pub/genesis/rinex/champ .

File names are, e.g. cham3120.01o.gz in subdirectory y2001/ for day 
of year 312 in 2001.  Directory history is provided in:
ftp://sideshow.jpl.nasa.gov/pub/genesis/rinex/champ/Documents .

Orbit files in both earth-fixed and earth-centered inertial 
coordinates are provided in:
ftp://sideshow.jpl.nasa.gov/pub/genesis/orbits/champ/quick .

The orbits are described in:
ftp://sideshow.jpl.nasa.gov/pub/genesis/orbits/champ/quick/Documents/README.quick.

These are quick-look orbits which were used for processing the 
occultations.  To obtain an orbit estimate for arbitrary times, we 
typically use Lagrange polynomial interpolation (polynomial of degree 
10).   A software utility for this purpose will be available shortly 
in the ftp area.

Please submit a registration form (see below) or register on the 
GENESIS web site. If you have questions about downloading data, 
please contact leoops at sdsio.jpl.nasa.gov .

General information on the CHAMP satellite is available from:
http://op.gfz-potsdam.de/champ

--
Tony Mannucci ,Task Manager, GPS Earth Observatory project
and
Tom Yunck, Manager, GPS Observatories Office
Jet Propulsion Laboratory, California Institute of Technology

Email:
Tony.Mannucci at jpl.nasa.gov
Tom.Yunck at jpl.nasa.gov

Postal address (Mannucci):
Jet Propulsion Laboratory, California Institute of Technology
MS 138-308
4800 Oak Grove Drive
Pasadena, CA 91109

Begin Registration Form
-----------------------
Please complete this form and send to leoops at sdsio.jpl.nasa.gov using 
the following text in the subject heading: "New User Registration". 
Or, register your interest on the GENESIS site.

Name:

Affiliation:

E-mail Address:

Please select your area(s) of interest:

(  ) Climate and Global Change
(  ) Ionosphere and Space Weather
(  ) Geodesy and Solid Earth Science
(  ) Weather Prediction
(  ) Precise Orbit Determination
(  ) Other (enter in "Comments")

Please indicate spacecraft of interest (check all that apply):
(  ) CHAMP
(  ) SAC-C

Comments or Additional Information:

End Registration Form
---------------------
-- 
Tony Mannucci
Supervisor, Ionospheric and Atmospheric Remote Sensing Group
  Mail-Stop 138-308B,                     Tel > (818) 354-1699
  Jet Propulsion Laboratory,              Fax > (818) 393-5115
  California Institute of Technology,     Email > Tony.Mannucci at jpl.nasa.gov
  4800 Oak Grove Drive,                   http://genesis.jpl.nasa.gov
  Pasadena, CA 91109