[IGSMAIL-5881]: IGS Reference Frame Coordinator - Call for Participation

Mon Jan 12 13:35:31 PST 2009

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IGS Electronic Mail      12 Jan 13:37:53 PST 2009      Message Number 5881
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Author: Via IGS Central Bureau

*Apologies for multiple postings*

INTERNATIONAL GNSS SERVICE

CALL FOR PARTICIPATION

January 9, 2009

IGS REFERENCE FRAME COORDINATOR

2010 -2013

Summary

The IGS invites proposals for a new Reference Frame (RF) Coordinator,
whose key responsibilities include forming the weekly SINEX
combination of Analysis Center solutions for global station
coordinates & velocities, Earth rotation, and apparent geocenter
parameters.  The new RF coordinator will replace Remi Ferland (Natural
Resources Canada) by the end of 2009 with a prior transition and
validation phase of no less than six months.

This is a core task within the IGS.  Expressions of interest are
requested at the earliest opportunity, with a proposal due by 31 March
2009.  It is expected that a final selection will be made by 1 May
2009 and a hand-over process begun by 1 June 2009.

The charter for the reference frame working group can be found at:

http://igs.org/projects/reference_frame/rfwg_charter.html (also
attached).

Background

The IGS Reference Frame Coordinator, who also chairs the Reference
Frame Working Group (RFWG), forms the official combination of Analysis
Center (AC) solutions for station coordinate, Earth rotation, and
other frame-related parameters.  Weekly submissions of AC solutions in
SINEX format, including full variance-covariance information, are
combined using rigorous mathematical methods.  The results of this
step are subsequently used by the Analysis Center Coordinator (ACC) to
form the IGS combined orbits and clock products in a way that
maintains a high level of overall internal consistency.

Since May 1999, Natural Resources Canada (NRCan) has supported Remi
Ferland as IGS RF Coordinator, and since March 2000 (week 1050), the
NRCan SINEX combination has provided the official frame products for
the IGS [Ferland, 2000].  A new orbit alignment procedure was adopted
at the same time to ensure consistency in the IGS Final products
[Springer, 2000a,b].  The general methodology now used was discussed
and agreed at the IGS Analysis Center Workshop held in Darmstadt in
1998 [Kouba et al., 1998].

After more than a decade, NRCan will terminate their sponsorship of
this important activity at the end of 2009.  In order to provide an
orderly transition of responsibilities and modify inter-agency
interfaces, it is expected that parallel operations and testing by the
new RF Coordinator will begin by 1 June 2009.  Full operational
responsibility should be in place by 1 January 2010.

The RF Coordination requires approximately one full-time person plus
additional backup support to provide year-round coverage. Proposals
where resources are leveraged with other closely related activities
and experience will be considered.   Weekly SINEX combinations are
normally released by the RF Coordinator each Wednesday, 11 days after
the end of each GPS week, followed the next day by the production of
consistent IGS orbits and clocks by the ACC.

Specific Tasks

The tasks of the RF Coordinator are to:

1) Chair the IGS RFWG and direct its activities.  Details are given at:

http://igs.org/projects/reference_frame/index.html

In this capacity, the RF Coordinator is also a voting member of the
IGS Governing Board.

2) Lead the RFWG in specifying and selecting a globally distributed
set of GNSS stations to realize an IGS reference frame, and ensure its
accurate alignment to the International Terrestrial Reference Frame
(ITRF).  The coordinates and velocities of the IGS RF are determined
from a long-term accumulation of IGS combined SINEX solutions.  New RF
realizations are issued at irregular intervals, usually synchronized
to new ITRF releases.  The continued reliability and consistency of
individual RF stations must be continuously monitored and occasional
updates announced to users.

3) Combine the weekly SINEX submissions from the IGS ACs into a
unified global frame aligned to the current IGS RF. This involves
checking and validating the input AC solutions, detection and removal
of outliers, reweighting of input solution covariances, alignment of
all input frames to the current IGS RF, rigorous combination of AC
solutions with full covariance information, and the output and
distribution of the combination products, consisting of weekly station
coordinate frames and covariances, daily Earth rotation parameters,
weekly geocenter offsets, and other frame-related parameters.  This
processing is normally done each Wednesday, 11 days after the end of
each GPS week.  Suitable electronic interfaces must be established
with the ACC and IGS Data Centers to enable the subsequent orbit and
clock combination to be performed in a consistent way.  In addition,
an accumulation of weekly frame solutions is updated weekly to form a
continuously evolving secular GNSS RF with linear station velocities.
A summary of the weekly combination statistics shall also be prepared.

4) Maintain the combination software, either that developed at NRCan
(which may be exported to the new RF Coordinator under agreement), or
an independent combination system, provided that it possesses similar
functionality.  The NRCan combination uses standard least-squares
adjustment theory for the various component tasks [Ferland et al.,
2000]:

            variance factor estimation

            removing constraints

            addition of normals

            rejection of outliers

            addition of inner constraints.

Comparable estimation schemes and algorithms are well documented in
most geodesy textbooks on least-squares.  In actual practice, most
effort is needed to interpret and check results in a "relatively
automated" way to give reliable results, rather than on the mechanics
of the combination process itself.

5) Detect station discontinuities. In order to accumulate the time
series of weekly frames, it is necessary to detect and accommodate any
discontinuities in the linear evolution of station positions, which
are caused by changes of receiver equipment, tectonic events, or other
causes, both known and unknown.  Abnormal station behaviors should be
reported via the agreed to procedures, to the IGS Central Bureau,
station operators and data analysts.  The set of coordinate and
velocity discontinuities shall be continuously documented, updated,
and published in SINEX format for general use.

6) Accumulate Earth Rotation Parameters (ERP) files. The weekly SINEX
combinations also produce an update of the accumulated estimates of
daily Earth rotation parameters, consisting of the coordinates of the
pole of rotation, the rates of change of the polar coordinates, and
the excess length of day.  While other ERP files are also generated by
the ACC from the various IGS orbit combination processes, the weekly
Final ERPs from the RF Coordinator are the definitive IGS products.

7) Report the residuals of the coordinates, ERPs, and apparent
geocenter estimates of the AC solutions with respect to the weekly
combined solution, as well as the residuals of the AC solutions with
respect to the reference frame realization and the cumulative solution.

8) Compute and report accumulated coordinates, residuals, and summary
files. Time series of the coordinates and residuals files shall also
be updated weekly and made available.  Plots of those time series and
residuals shall also be updated weekly and made available. Time series
and plots from the summary files shall also be reported.

9) Provide the official IGS submissions to the ITRF.  Based on the
regular combined RF products, the IGS RF Coordinator will interact
with the ITRF Product Center of the International Earth Rotation and
Reference Systems Service (IERS) and provide the official submissions
for the ITRF updates.

10) Provide satellite antenna offsets. Certain other frame-related
parameters may be reported in AC SINEX solution files, such as the
phase center offsets of the GNSS satellite antennas.  From time to
time, the RF Coordinator will assist the chair of the IGS Antenna
Working Group in examining and updating estimates of the satellite
offsets based on these parameter estimates.

11) Periodically reprocess and recombine new AC submissions. From time
to time, the IGS expects to reprocess all GNSS observational data
using the latest models and procedures to achieve the highest possible
product accuracy and to maintain long-term consistency.  The RF
Coordinator should be prepared to contribute to such irregular
campaigns by reprocessing and recombining new AC submissions similar
to the regular weekly tasks.

12) Investigate improvements and assess performance of participating
ACs. The RF Coordinator, in collaboration with the RFWG, IGS ACC, the
IERS, and other scientists, will investigate improvements in the IGS
products through refinements in analysis, modeling, and combination
algorithms. As needed, feedback should be provided to existing ACs
when significant changes occur and to new candidate ACs to assess
their performance.

13) Provide, as needed to the users, information about the combined
SINEX products.

14) Document and submit regular reports of results of each weekly
SINEX combination to be distributed by the IGS. An example of the
SINEX combination report for GPS week 1500 is given at:

http://igscb.jpl.nasa.gov/mail/igsreport/2008/msg00942.html

15) Prepare other reports and scientific papers to document
accomplishments and future developments.

Responses

Expressions of interest should be addressed to the IGS Central Bureau
at anytime to

igscb at igscb.jpl.nasa.gov

Proposal responses to this CfP are due by March 31, 2009 and should
contain at least the following information:

            Names of key personnel, especially the proposed new RF
Coordinator

            Level of support to be provided

            Software system to be used for tasks

            Available starting date

            Duration of commitment

Schedule

            12 Jan 2009             Call for proposals released

            Jan  March            Expression of interest, email to igscb at igscb.jpl.nasa.gov

            31 Mar 2009            Due date for submission of
proposal responses

            01 May 2009            Selection of new Reference Frame
Coordinator

            01 Jun 2009            Beginning of test and validation
phase

            01 Jan 2010            Full operational responsibility by
new Coordinator

Any questions on proposal preparation and submission, or
clarifications on the above technical tasks, can be directed to:

John Dow, Chair, IGS Governing Board

John.Dow at esa.int, +49-6151-90-2272

Remi Ferland, IGS Reference Frame Coordinator

Remi.Ferland at NRCan-RNCan.gc.ca,+1-613-995-3215

Ruth Neilan, Director, IGS Central Bureau

Ruth.E.Neilan at jpl.nasa.gov, +1-818-354-8330

References

R. Ferland (2000) SINEX Products Status Changes, IGS Mail 2740, 10 Mar
2000,

http://igscb.jpl.nasa.gov/mail/igsmail/2000/msg00080.html

R. Ferland, J. Kouba, D. Hutchison (2000) Analysis methodology and
recent results of the IGS network combination, Earth Planets Space,
52, 953-957

http://acc.igs.org/trf/sinex-combi_ferland_eps00.pdf

J. Kouba, J. Ray, M.M. Watkins (1998) IGS Reference Frame Realization,
in 1998 IGS Analysis Center Workshop Proceedings, European Space
Operations Centre, Darmstadt, Germany, pp 139-171, available at:

http://igscb.jpl.nasa.gov/igscb/resource/pubs/wksp_2.pdf

T. Springer (2000a) IGS Final orbit changes, IGS Mail 2750, 17 Mar 2000,

http://igscb.jpl.nasa.gov/mail/igsmail/2000/msg00090.html

T. Springer (2000b) Clarification of IGS Final orbit changes, IGS Mail
2751,18 Mar 2000,

http://igscb.jpl.nasa.gov/mail/igsmail/2000/msg00091.html

==============================================================

CHARTER
For the
IGS REFERENCE FRAME WORKING GROUP

Remi Ferland

Geodetic Survey Division

Natural Resources Canada

Ottawa, Ontario, Canada

INITIAL GOALS

The collective effort of the working group participants is to generate
the official IGS station coordinates and velocities, Earth Rotation
Parameters (ERP) and geocenter estimates along with the appropriate
covariance information. The estimated parameters will be aligned to
the International Terrestrial Reference Frame (ITRF). The group will
strive for consistency, reliability and accuracy of the above products.

The station coordinates and ERP information from the Analysis Centers
(AC), the Global Network Associate Analysis Centers (GNAAC), the
Regional Network Associate Analysis Centers (RNAAC) and potentially
other sources will be compared and used to generate and validate the
IGS official products. A new solution will be computed and made
available regularly. It will initially contain station coordinates,
daily ERP, weekly geocenter estimate, and relevant information on the
equipment used at each station.

The "epoch" estimated station coordinate solutions will be added to
the cumulative solution. The cumulative solution will contain at least
a set of estimated coordinates and velocities at a reference epoch for
each station. The AC, GNAAC, RNAAC, "epochs", cumulative, ITRF and
potentially other solutions will be compared and residual files will
be made available. The cumulative solution will be submitted as needed
to IERS in order to contribute to the definition of ITRF. The
solutions will be limited to about 200 to 250 well distributed and
high quality stations, forming an IGS polyhedron.

Abnormal station coordinates behavior will be reported. Potential
inconsistencies in the past and current coordinates solutions will be
investigated and corrected whenever possible. The performance and long
term characteristics of the network based on the station coordinate
time series will be monitored and reported. The network will consist
of a number of well-distributed and quality stations. In collaboration
with interested users, the network will be reassessed regularly as
part of the maintenance.

The IGS Reference Frame working group will promote improvements to the
products through refinement in the analysis, modeling and algorithms.
As a result, enhancements to current exchange standards and reports
may be proposed. This group will collaborate with other groups and
scientific organizations to improve the IGS products and to promote
their use.

The use of the IGS realization of ITRF will also be promoted. The
products will be suitable for other IGS products as well as various
studies such as plate tectonic, regional deformations, temporal
variations. The definition of national reference systems can also
benefit from the IGS realization of ITRF.

STRUCTURE

The working group will be composed of one coordinator with a number of
active members. The working group reports to the IGS Governing Board.
Modifications to the goals and working plan will be arrived at through
consultation among the working group.

WORKING PLAN

In coordination with the group members, the ongoing objectives are to:

            Analyze the time series station coordinates residuals;
report on the findings and if appropriate implement improvements to
the processes.

            Compare the products with other solutions/models, report
the findings and if appropriate implement improvements to the processes.

            Analyze/compare ERP solutions, report the findings and if
appropriate implement improvements to the processes.

            Inform responsible groups/organizations to help resolve
station related inconsistencies.

In coordination with the group members, the objectives for the first
year are to:

            Get the weekly combination and reporting procedure to run
smoothly, with a concise and informative weekly report.

            Reanalyze the AC and/or GNAAC and/or RNAAC stations
coordinates solutions available since GPS week 837 and report the
results.

            In coordination with the group members, the objectives
for the second year are to:

            Monitor and report the performance and long term
characteristics of the network based on the stations coordinates time
series

            Continue the analysis with emphasis on the reliability
and accuracy of the products

            Include AC and/or GNAAC and/or RNAAC stations coordinates
solutions available before GPS week 837 and report the results.

In coordination with the group members, the following objectives will
be considered as time and resources are available to:

            Provide graphical interface for the reporting of the time
series residuals and other types of data.

MEMBERS

The working group will be potentially composed of the IGS coordinator,
the Director of the IGS Central Bureau, one representatives from each
AC, one from each GNAAC and one from the ITRF/IERS section. Other
members may be added as required.