From jimr@maia.usno.navy.mil Mon Jul  9 11:47:36 EDT 2001
Received: (from jimr@localhost)
	by maia.usno.navy.mil (8.9.3 (PHNE_22672)/8.9.3) id LAA09531
	for gpst; Mon, 9 Jul 2001 11:46:35 -0400 (EDT)
From: Jim Ray (USNO 202-762-1444) 
Message-Id: <200107091546.LAA09531@maia.usno.navy.mil>
Subject: [GPST] report to the CCTF
To: gpst@maia.usno.navy.mil
Date: Mon, 09 Jul 2001 11:46:35 EDT
X-Mailer: Elm [revision: 212.5]
Status: RO

Dear Colleagues,

I represented the IGS/BIPM Pilot Project as an invited guest at the
15th meeting of the Consultative Committee on Time and Frequency (CCTF)
at the BIPM on 20-21 June.  This is the formal technical oversight
group for the T/F functions of the BIPM and consists of delegates from
the various national timing laboratories.  Prof. Sigfrido Leschiutta
(IEN) is the CCTF President.  The previous CCTF meeting was held in
April 1999.  In addition, the CCTF Working Group on TAI held its 5th
general meeting on 19 June; Paul Paquet is the chair of this group.

A copy of the report to the CCTF prepared by Felicitas Arias and me is
available at .  This
summary was accompanied by the more detailed group proceedings paper
from the IGS/BIPM workshop held in Sept. 2000, which was published in
the IGS special issue of GPS SOLUTIONS (vol. 4, no. 4).  A preprint of
this paper is available at
.

[Any Pilot Project participant who did not receive a copy of this special
issue of GPS SOLUTIONS can do so by sending me your postal mailing address.
The contents are at .]

I gave an oral presentation on the status of the IGS clock products at
the TAI meeting, focussing on a description of the new clock combination
products that began last November (thanks to the efforts of the IGS
Analysis Centers, Jan Kouba, and Tim Springer) and the new IGS time scale
being developed by Ken Senior at USNO (available only in a preliminary
form now but soon to be released for public examination).  The new time
scale uses the IGS combined clocks to synthesize an internal frequency
scale from a weighted ensemble of the high-stability frequency standards
available within the IGS network.  This will overcome the current time
scale limitations associated with the IGS use of linearized GPS time.

Prior to the BIPM meetings, the Analysis Centers were questioned about
possibilities for "densifying" the IGS clock products to include more
high-quality clocks and to ensure that all time labs will be incorporated.
The ACs producing clocks agreed that they could augment their clock
submissions by using the precise point positioning method to efficiently
generate additional clock estimates fully consistent with their standard
IGS products.  It is hoped that over the next few months this augmentation
will be adequate to fulfill the requirements of the BIPM and the timing
community.  If not, then it may be necessary to consider a new role of
Associate Analysis Center for Timing to perform the augmentation of the
IGS clock producs (again using the PPP method but applied to the IGS
products).

For the CCTF meeting, I summarized the status of the Pilot Project
activities in general terms.  An updated recommendation was adopted
urging greater participation by the timing labs in the IGS network
with installation of calibrated geodetic receivers.  Currently, the
participation is somewhat limited and no calibrated receivers are
available yet.  (Some of the labs that do participate are not included
in the current IGS clock products due to the densification problem
described above.)  But the climate and prospects have improved markedly
over the past two years.  Most of the major labs are actively involved
in installing geodetic receivers, mostly Ashtech Z12T receivers.  The
BIPM has developed a calibration method for these receivers and is now
circulating a reference receiver to differentially calibrate the Z12Ts
that are installed (see the previous e-mail from Gerard Petit).

I ended my CCTF presentation by urging that carrier-phase clock results
be incorporated into TAI as soon as they become available, initially for
comparison purposes only.  By the time of the next CCTF meeting,
sufficient experience should have accumulated, including direct
comparisons with results from the common-view and two-way satellite
methods, that a decision should be possible regarding the operational use
of carrier-phase clocks.  My personal goal is to end the Pilot Project by
the end of 2002 and transition to an operational or quasi-operational mode.

Please let me know if you have any questions.
Best regards,
--Jim

---------------------------------------------------------------------------
IGS/BIPM Pilot Project website          http://maia.usno.navy.mil/gpst.html