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From: SCHILDKNECHT THOMAS
Reply-To: SCHILD@aiub.unibe.ch
To: jimr@Maia.usno.navy.mil, cthomas.bipm.fr@UBECLU.unibe.ch
Cc: BEUTLER@aiub.unibe.ch, SPRINGER@aiub.unibe.ch, ROTHACHER@aiub.unibe.ch,
GURTNER@aiub.unibe.ch, Gregor.Dudle@eam.ejpd.inet.ch,
Beat.Jeckelmann@eam.ejpd.inet.ch, Leon.Prost@eam.ejpd.inet.ch,
Ulrich.Feller@eam.ejpd.inet.ch, Frederic.Overney@eam.ejpd.inet.ch,
SCHILD@aiub.unibe.ch
Message-Id: <009C3235.10F15126.329@ubeclu.unibe.ch>
Subject: IGS/BIPM Project: Response to Call for Participation
Status: RO
Please find attached our response to the CALL FOR PARTICIPATION in the IGS/BIPM
PILOT PROJECT.
Best regards,
Thomas Schildknecht
------------------------------------------------------------------------------
Response to CALL FOR PARTICIPATION in an
IGS/BIPM PILOT PROJECT TO STUDY ACCURATE TIME AND FREQUENCY
COMPARISONS USING GPS PHASE AND CODE MEASUREMENTS
Agency or group: Joint Proposal AIUB/OFMET
AIUB - Astronomical Institute University of Bern
Sidlerstrasse 5
CH-3012 Bern
Switzerland
OFMET - Swiss Federal Office of Metrology
Lindenweg 50
CH-3084 Wabern
Switzerland
Contact person(s): Dr. Thomas Schildknecht, AIUB
Dr. Tim Springer , AIUB
Mr. Fr‚d‚ric Overney , OFMET
Dr. Ulrich Feller , OFMET
E-mail address(es): schild@aiub.unibe.ch
springer@aiub.unibe.ch
Frederic.Overney@EAM.ejpd.inet.ch
Ulrich.Feller@EAM.ejpd.inet.ch
Areas of participation:
1) Deployment of GPS receivers: Yes
2) GPS data analysis: Yes
3) Analysis of instrumental delays: Yes
4) Time transfer comparisons: No
6) Other: ----
Limitations on participation: ---
Comments or suggestions:
***********************
Preamble:
--------
The AIUB is engaged since 1992 in the International GPS Service as an IGS
Analysis Center (IGS=International GPS Service for Geodynamics). The CODE
Analysis Center (CODE=Center for Orbit Determination in Europe) is a joint
venture of AIUB, the Federal Office of Topography, the French Institut
G‚ographique National and the German Bundesamt fr Kartographie und
Geod„sie (BKG).
The OFMET, Swiss Federal Office of Metrology, is among other responsible for
time and frequency maintenance and dissemination in Switzerland. Within
this field of activities time and frequency transfer over a wide range of
distances using many different methods (among other TV-Methods, GPS
common view techniques, etc.) are of primary interest.
At the CODE Analysis Center of the IGS originally "only" geometrical
quantities, like satellite orbits, station coordinates and velocities,
Earth Orientation Parameters (EOPs) and Earth Rotation Parameters (ERPs)
were estimated on a daily basis. Later on (since spring 1995) tropospheric
zenith corrections (time resolution of 2 hours) were and are estimated for
those stations which are routinely analysed by the CODE Analysis Center.
Since 1995 global Ionosphere models are regularly computed and made
available.
The software used is the Bernese GPS Software Version 4 (Rothacher and
Mervart, 1997). The Bernese GPS Software originally was a pure
double-difference software package. For more information concerning the
CODE processing center and its performance within the IGS we refer to
Appendix A (Annual Report 1996 of the CODE Analysis CENTER for the IGS)
For the IGS/BIPM project it was essential to upgrade the software to allow
for zero difference processing. This actually happened in September 1995 (see
appendix A). Since January 1997 the CODE satellite clock estimates are of
comparable accuracy as those of other IGS Analysis Centers. Internally,
not only satellite clocks, but also receiver clocks are estimated using
several combinations of code and phase zero difference observations.
In summary we believe that the present version of the Bernese GPS software
is very well capable of producing interesting results for the IGS/BIPM
Pilot project.
A common project of OFMET and AIUB to develop time transfer terminals based
on geodetic GPS receivers with the goal of comparing time offsets with
sub-nanosecond accuracy and frequencies with 10**(-15) over one day
accuracy of two or more (GPS external) clocks was started in 1991. It was
clear from the outset that optimum use should be made of GPS code AND phase
measurements and that only geodetic-type GPS equipment should be used. The
emphasis in this project was put on the comparison of external (as opposed
to receiver internal) clocks. Calibration of delays in cables, temperature
dependent delays, etc., were and are of major interest in the context of
the joint OFMET/AIUB project. We emphasize at this point that the control of
these delays is absolutely mandatory for time transfer. (The corresponding
requirements are much less stringent for frequency
transfer.)
Today two prototype geodetic time-transfer terminals (GeTT terminals) are
available, an additional terminal will become available in the near future.
The terminals contain modified ASHTECH Z-12 receivers. A description of
the state of the art of the time-transfer terminals is given in Appendix B.
Remarks concerning the Areas of Participation
---------------------------------------------
1) Deployment of GPS receivers:
---------------------------
After two experiments on European baselines in 1997 (OFMET-NPL, PTB-NPL)
the GeTT terminals will be deployed on a transatlantic baseline during
the second half of 1998. (This will in fact be the first comparison of the
GeTT method with the independent two-way satellite technique (TWSTFT) on an
intercontinental baseline.)
Clearly we wish that these terminals be deployed at National Time
Laboratories. It is assumed that they are connected to the best available
time standards at these sites. Site-log information will be made available
to the IGS Central Bureau (according to the procedure defined in the Call
for Participation). Data will be made available to the IGS (no
restrictions) to allow inclusion into the final IGS product computation
(depending on the selected sites a delivery to meet the IGS rapid products
deadline might be possible).
Further deployments may of course be discussed and fine-tuned with the
management of the IGS/BIPM pilot project.
2) GPS data analysis
-----------------
Within the framework of this project we plan to perform two different
types of analysis:
(1) We will deliver (the satellite and) receiver clock estimates
as they emerge from the daily CODE routine processing. In this routine
processing up to 80 globally distributed (IGS) stations are used to
generate satellite and receiver clock estimates with a sampling
rate of 5 minutes. Currently only "smoothed code" observations are
used but it is planned to use the code and phase observation
simultaneously in the near future.
In a first phase clock estimates will be available together with the final
CODE products only which means with a delay of about 5 days.
(2) A special routine time-transfer routine processing will be set up.
In this processing we will use the CODE and/or IGS products like,
e.g. orbits, EOPs, station coordinates, and troposphere delays,
to determine receiver (and satellite) clock corrections.
In this special processing we will focus on a selected set of
stations, like e.g. receivers at timing-laboratories and of course our
own receivers (the GeTT-terminals).
In this setup code and phase measurements will be used! The results will
be based on either the "rapid" or "final" products depending on the
requirements of the project.
Furthermore we also would like to point out that, starting 1 January, 1999
our group will be "ex officio" involved in this analysis part of the project
(Tim Springer will be the new IGS Analysis Center Coordinator).
3) Analysis of instrumental delays
-------------------------------
Many of the development of the OFMET/AIUB time transfer project are
intimately related to issues listed in this area. We may of course make
available our papers dealing with these topics (see appendix B). We would
be very much in favour of the establishment of a special working group
dealing with instrumental delays, etc., and we would be willing to
contribute to such activities. It might be a good idea to organize a
session dealing with that topic at one of the future major "time
conferences".
Appendix A: Annual Report 1996 of the CODE Analysis Center
Appendix B: Short technical description of the GeTT terminals
EFTF Paper 97
EFTF Paper 98
------------------------------------------------------------------------------
****************************************************************************
Thomas Schildknecht Internet: SCHILD@AIUB.UNIBE.CH
Astronomical Institute SCHILD@130.92.4.11
University of Berne HEPNET/SPAN: 20579::49202::SCHILD
Sidlerstrasse 5 Phone: +41-31-6318594 (91)
CH-3012 Bern, Switzerland Fax: +41-31-6313869
****************************************************************************
From Leon.Prost@EAM.ejpd.inet.ch Wed Mar 25 05:03 EST 1998
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To: "'E-Mail BIPM C. Thomas'" ,
"'E-Mail USNO J. Ray'"
Cc: "'E-Mail AIUB T. Schildknecht'" ,
Feller Ulrich EAM ,
Jeckelmann Beat EAM
Subject: IGS/BIPM
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Status: RO
Conc. : IGS/BIPM Pilot Project=0D
=0D
We want to inform you that the contact person=0D
at the Swiss Federal Office of Metrology (OFMET/EAM) is now : =0D
Dr. Leon Prost=0D
The corresponding E-Mail address is :=0D
leon.prost@eam.ejpd.inet.ch=0D
From 6.4.1998:=0D
leon.prost@eam.admin.ch=0D
=0D
The official abreviation of our office is OFMET. =0D
We also want to inform you that we are interested in the meeting =0D
of the CCTF working group on June 22,23.=0D
=0D
Regards Leon Prost=0D
=0D
*****************************************************=0D
Leon Prost, Swiss Federal Office of Metrology,=0D
Lindenweg 50, CH-3084 Wabern, Switzerland=0D
Tel:(+41 31) 323 33 01, Fax: (+41 31) 323 32 10=0D
E-Mail: leon.prost@eam.ejpd.inet.ch=0D
From 6.4.1998:=0D
leon.prost@eam.admin.ch=0D
*****************************************************=0D
From Ulrich.Feller@eam.admin.ch Fri Aug 28 11:40:47 EDT 1998
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From: Feller Ulrich EAM
To: "'Jim Ray'"
Subject: AW: Clock Format -- CORRECTION
Date: Fri, 28 Aug 1998 17:38:30 +0200
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Status: RO
Dear Jim
I'm still on the mailing list of the joint IGS/BIPM project. Since some
time, I'm no longer involved directly in the the project work. In order to
avoid further reception of mails, I kindly ask you to remove me from the
mailing list.
Kind regards, Ulrich Feller