[IGSMAIL-5855]: ITRF2008 Call for Participation

Tue Nov 11 04:55:11 PST 2008

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IGS Electronic Mail      11 Nov 04:55:13 PST 2008      Message Number 5855
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Author: Zuheir Altamimi (forward by J. Ray)

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IERS Message No. 137                                   November 11, 2008
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ITRF2008 Call for Participation

Dear colleagues,

Please find below the call for participation for the ITRF2008.

Best regards
Zuheir Altamimi

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ITRF2008 Call for Participation

Background

For the first time in the ITRF history, the ITRF2005 used time series of
station positions and EOPs: weekly from satellite techniques (SLR, GPS,
DORIS) and session-wise from VLBI. Time series are now essential to
account not only for station non-linear motions, but also to evaluate
the stability over time of the frame parameters, mainly the physical
ones, the origin and the scale. For the first time also, the ITRF2005
rigorous combination provides self-consistent series of EOPs, including
Polar Motion from VLBI and satellite techniques and Universal Time and
Length of Day from VLBI only.

While the ITRF2005 marked considerable progress compared to past ITRF
versions, some weaknesses were underlined in the individual technique
solutions that were used as well as their co-locations. An ITRF2008
becomes now necessary to benefit from the expected improvement of the
reprocessing effort being undertaken by the Technique Centers (IVS,
ILRS, IGS, IDS).

ITRF2008

Since the release of the ITRF2005 we can note the following changes:

- Three years of additional data have become available
- New sites added to the ITRF network
- A few new local ties are now available
- The processing strategies of the individual techniques have
  improved and self-consistent reprocessed solutions are
  expected to be available.

In order to take benefit of these new developments, the ITRS Center,
together with the ITRS Combination Centers, is planning to generate a
new ITRF solution (ITRF2008) and solicits inputs from the IERS Technique
Centers (TC) and their related Analysis Centers. Official combined time
series of the four TCs are preferred. In case that this requirement
could not be reached by the TCs within the ITRF2008 schedule (see
below), at least three individual AC solutions are requested. The TCs
are requested to provide as long time series as possible and preferably
covering the full history of observations of each technique, such as for
instance VLBI and SLR data since the eighties.

It is requested NOT to correct for any geophysical fluid loading
effects, except for tidal ocean loading.

Long Time Series Contributions

Contributed time series (weekly/daily) solutions to be included in the
ITRF2008 should be provided in SINEX format and comply with one of the
following constraint categories:

- Solutions with removable constraints
- Loosely constrained solutions (constraint level: Sigma > 1 m)
- Solutions with TRF minimum/inner constraints
- Free singular normal equations

The SINEX files have to follow the SINEX Version 2.0 format standard and
should contain for one week (Sunday to Saturday) - a session in the case
of VLBI - station positions, a set of EOPs for each day (offsets and
rates fitted over 24-hr intervals for polar motion, UT1 and LOD, where
only VLBI provides UT1). IVS is highly encouraged to provide nutation
offsets and quasar coordinates for future studies by the ITRS
Combination Centers. If the SINEX files contain a variance-covariance
matrix (eventually except minimal constraints or loose constraints), all
constraints applied to the solution should be given in the a priori
variance-covariance matrix.

All solutions should conform to the IERS Conventions, including updates
posted at:

http://tai.bipm.org/iers/convupdt/convupdt.html

Whenever departures from the recommendations of the IERS Conventions are
preferred, it is requested that the effects of those deviations be
documented. Based on experiences with ITRF2005 some specific model
updates are requested:

- Thermal expansion of the VLBI antennas causes a significant annual
  frame scale variation if it is not modeled. If feasible, IVS is
  encouraged to consider modeling that effect, provided that no net
  artifactual scale offset/drift is introduced.

- Appropriate modeling of SLR station range biases is needed to minimize
  frame scale effects.

- Long-term GPS solutions compatible with modern operational products
  are needed for full consistency.

- Appropriate DORIS analysis strategy to minimize possible scale
  discrepancies between ACs.

Solicited solutions to be considered are of three types:

A) Official single-technique combined time series solutions from the
   Technique Centers

B) If solutions of type A are not available, or for specific reasons
   (e.g. longer time span, more stations, more homogeneous processing),
   individual Analysis Center time series solutions are solicited under
   the coordination of the corresponding Technique Center.

C) Solutions that result from a combination of various techniques at the
   observation level may be submitted as well.

A summary file describing the strategy adopted to generate the time
series should be submitted together with the SINEX files, as well as all
information related to station position discontinuities.

ITRF2008 Analyses and Results

The general analysis strategy planned by the ITRF CCs will follow
closely the procedure used for ITRF2005 and will consist of the
following steps:

- Remove original constraints (if any)

- Use as they are the minimally constrained solutions

- Perform per-technique combinations (TRF + EOP) of each individual time
  series: stacking/accumulating the weekly time series. The outputs of
  this step will be full SINEX file per technique/AC, containing station
  positions, velocities and daily EOPs.

- Identify and reject outliers and properly handle discontinuities,
  using break-wise approach

- Combine if necessary all solutions of a given technique into a unique
  solution

- Combine the per-technique combinations adding local ties in
  co-location sites. This global combination will constitute the
  ITRF2008 solution.

The expected main results will be:

- Positions and velocities for a global network of tracking stations and
  related markers of the four techniques (VLBI, SLR, GPS, DORIS), with
  full variance/covariance information provided in SINEX format.

- Fully consistent EOPs: daily polar motion and their rates, UT1 and LOD

- Per-technique solutions of station positions and velocities and daily
  EOPs, with full variance/covariance information provided in SINEX
  format.

- Residual time series as result from the per-technique time series
  combinations

- Geocenter offset time series from satellite solutions (SLR, GPS,
  DORIS)

Instructions

The Technique Centers and individual Analysis Centers that intend to
contribute their long time series of SINEX files should submit these
series by February 10, 2009 at the latest. Earlier submissions are most
welcome and very much encouraged.

To submit a time series of SINEX files please send an e-mail to:

ITRS Center: itrf at ensg.ign.fr
and
IERS Central Bureau: central_bureau at iers.org

The e-mail should contain the detailed instructions on where the
solutions can be downloaded, their present naming convention, etc. The
submitted SINEX files will be archived in the IERS Data and Information
System and the ITRS Center.

Schedule:

November 11, 2008      Dissemination of the Call for Participation

February 10, 2009      Deadline for solution submissions by
                       Technique/Analysis Centers

April 19-24, 2009      First results and discussions at EGU
                       General Assembly

Until May 10, 2009     Analysis by the ITRS CCs

May 10 - June 10, 2009 Preliminary ITRF2008 solution available
                       for evaluation by the Technique/Analysis
                       Centers

July 15, 2009          Final ITRF2008 solution ready.

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