Circular 1
JCR01.1. Formation of the Joint Committee
The Joint Committee on general relativity
for reference systems and metrology, hereafter referred to as Joint Committee
on Relativity (JCR), has been created by the Bureau International des Poids
et Mesures (Approval
by the Comite International des Poids et Mesures, September 1997) and the
International Astronomical Union (Resolution B3 (1997) at the Kyoto General
Assembly).
For the CIPM, the JCR replaces the
Working Group on the application of general relativity to metrology (AGRM).
This group has worked since 1993 under the chairmanship of B. Guinot. In
his Circular 13 (16 October 1997), he exposed the new situation and thanked
the members for their contribution. Here I want to thank B. Guinot for
his work, which built the foundations of the JCR. I am glad that he and
several members of the past AGRM will continue to contribute to the JCR.
The JCR will issue circulars as required
by the amount of new work or information. Distribution will be made to
all members by e-mail. Contributions by members will be directly redistributed
to all members if they are sent to the address jcr@bipm.org. Otherwise contributions
can be sent to the chairman (gpetit@bipm.org). A home page will be accessible
on the BIPM Web site when it is open (this should occur at the end of this
year).
JCR01.2. Membership
The initial membership (October 24,
1997) is given below. It includes mostly persons that have been proposed
by the CIPM and the IAU and there should be some extension of the membership
by the IAG. The special category of corresponding members has been proposed
and appears below, but will be merged with regular members unless a clear
distinction is found.
Name Affiliation e-mail
Ashby N. U. Colorado Boulder, USA n_ashby@mobek.colorado.edu
Brumberg V.A. IAA St Pestersburg, Russia
brumberg@ipa.rssi.ru
Damour T. IHES Bures s Yvette, France
damour@ihes.fr
Groten E. TH Darmstadt, Germany groten@ipg.verm.th-darmstadt.de
Guinot B. Obs. Paris, France BGuinot@compuserve.com
Han C. ISM Zhenzhou, China ljx@public.zz.ha.cn
Klioner S.A. TU Dresden, Germany klioner@rcs.urz.tu-dresden.de
Kopeikin S.M. U.Jena/Germany S.M.Kopeikin@tpi.uni-jena.de
Kovalevsky J. OCA Grasse, France kovalevsky@mfg.cnes.fr
McCarthy D.D. USNO Washington DC, USA
dmc@Maia.usno.navy.mil
Petit G. BIPM Sevres, France gpetit@bipm.org
Petley B.W. NPL Teddington, UK bwp@newton.npl.co.uk
Ries J. U.Texas Austin, USA ries@moebius.csr.utexas.edu
Sazhin M.V. Sternberg I. Moscow, Russia
sazhin@sai.msu.su
Soffel M.H. TU.Dresden, Germany soffel@rcs.urz.tu-dresden.de
Standish E.M. JPL Pasadena, USA ems@smyles.jpl.nasa.gov
Wolf P. BIPM Sevres, France pwolf@bipm.org
corresponding
Ray J. USNO Washington DC, USA jimr@maia.usno.navy.mil
Seidelmann P.K. USNO Washington DC,
USA pks@spica.usno.navy.mil
JCR01.3. Program of work
(Contributors: G. Petit and P. Wolf)
At the Kyoto General Assembly, the
IAU has endorsed both the continuation of the WG on Relativity in Celestial
Mechanics and Astrometry (RCMA) under the chairmanship of M. Soffel and
the creation of the Joint Committee on Relativity (JCR). Therefore the
first task is to specify what should be the goals of each. In this aim,
the following list of tasks is proposed, along with the rough outline of
cooperation among the JCR and the RCMA. One should bear in mind that one
of the aims of the JCR is that, as mentioned in the IAU Resolution B3 (1997),
"the organizations taking part in the Joint Committee adopt Resolutions
or Recommendations .... with the aim of having identical definitions, conventions
and notations based on the conclusions of the Committee". So the JCR should
be involved in all decisions that affect several fields of applications.
All members are asked to comment and
make suggestions on this document. All members are also invited to contribute
by indicating possible fields and techniques where general relativity has
to, or might have to, be taken into account and for which the formulation
in the framework of GR has to be considered. Please send your contribution
to jcr@bipm.org for automatic redistribution to the whole group, otherwise
to gpetit@bipm.org.
1) One of the major tasks for all fields
is the specification of higher order terms of the metric for barycentric
as well as planetocentric (in particular geocentric) reference systems.
- It is necessary for celestial mechanics
and astrometry at 1PN level and at current observational accuracies.
- It implies a choice of coordinate
conditions (spatially isotropic (conformally cartesian), harmonic, standard
PN).
Work on this task should result in
expressions that provide all necessary information for use at the 1PN level
whilst remaining as simple and as close to practical applications as possible.
This should be one of the main tasks
of RCMA. Some consultation between RCMA and JCR in particular concerning
the rationale for making decisions and the form in which the results are
expressed would, however, be desirable.
2) A number of other problems can only
be ultimately resolved once this first task is accomplished. For example:
- Define the fundamental constants
and quantities (parameters) appearing in the expressions (GM, multipole
expansions...) and establish proceedures to obtain their numerical value.
- Examine how certain basic concepts
can be maintained in the new framework and define them (e.g. TT, geoid,
centre of mass...).
- Interpret models which are based
on space-time references (e.g. precession, nutation...).
- Interpret the results (coordinates,
ephemerides, fundamental constants and other parameters) of different realizations
of space-time references and of the models used for the treatment of measurements.
These tasks are of more general nature
than those mentioned in 1). They could be the subject of collaboration
between JCR and RCMA following a final agreement on the results of 1).
3) Other tasks can be resolved within
the existing framework (IAU Resolution A4, 1991). These include also, to
a limited extent, some of the problems mentioned in 2):
- Clarify some of the basic concepts
and definitions (e.g. meaning of GME (two values given by IERS
Standards (1992) only one in IERS standards (1996) but not compatible with
Resolution A4).... ), definition of the astronomical unit, role of Recommendation
IV (IAU 1991), ......), or their realization (e.g. treatment of tides in
the definition of TT or in the transformation from proper time to coordinate
time).
- Interpret the results (coordinates,
fundamental constants and other parameters) of different realizations of
space-time references and of the models used for the treatment of measurements
(as far as this is possible within the IAU 1991 framework).
- Establish a uniform system of notations
for quantities and units and apply it to future official texts and to rewrite
past texts if necessary.
These problems concern a broad community
(astronomy, geodesy, metrology, geophysics). They could be treated by JCR
with frequent discussions (comments, exchanges of opinions) between JCR
and RCMA.
We suggest that initially RCMA focuses
on item 1 (new metric) and JCR on item 3 (as much as can be done in the
existing framework). Then the extension to item 2. should occur naturally.
Looking forward to your contributions,
Gerard Petit |