Minutes of ILRS Analysis Working Group Workshop

Matera, 9-10 November 2000

(written by C.Luceri, R.Noomen, R.Devoti)

List of Participants:

Graham Appleby, NERC, gapp@nerc.ac.uk
Richard Biancale, CNES, richard.biancale@cnes.fr
Roberto Devoti, Telespazio(ASI/CGS), roberto@caronte.mt.asi.it
Maurice Dube, Raytheon ITSS, dube@cddis.gsfc.nasa.gov
Ramesh Govind, AUSLIG, rameshgovind@auslig.gov.au
Van Husson, HTSI, van.husson@honeywell-tsi.com
Rainer Kelm, DGFI, kelm@dgfi.badw-muenchen.de
Cinzia Luceri, Telespazio(ASI/CGS), cinzia.luceri@asi.it
Maria Mareyen, BKG, mamy@ifag.de
Phil Moore, University of Newcastle, Philip.Moore@ncl.ac.uk
Ron Noomen, DEOS, ron.noomen@deos.tudelft.nl
Toshimichi Otsubo, CRL/NERC, otsubo@crl.go.ip
Matti Paunonen, Finnish Geodetic Institute, geodeet@csc.fi
Erricos Pavlis, JCET, epavlis@helmert.gsfc.nasa.gov
Mike Pearlman (Friday), CfA, mpearlman@cfa.harvard.edu
Paolo Rutigliano, Telespazio(ASI/CGS), rutigl@asi.it
Pete Shelus (Friday), McDonald Observatory, pjs@astro.as.utexas.edu
Mark Torrence, Raytheon ITSS, mtorrenc@magus.stx.com


THURDAY, November 9, 2000


(note: the paragraph numbering of the minutes follows the agenda items
numbering in appendix 1)

1. Opening

Brief introduction of the participants.

Noomen reports on the interest of the outside community and underlines
the importance of the workshop. The agenda is accepted (appendix 1).

2. Role of ILRS within IERS

Noomen gives an introduction on the ILRS products (coordinates,
velocities, EOPs, geocenter, etc.) and the ILRS clients (IERS,
the geophysical community and ourselves) (all material presented is
included in appendix 2).

Noomen illustrates the structure of the new IERS organization and
underlines the official status of the ILRS participation within IERS.
The new IERS organization is very well structured, with specific
Product Centers and Technique Centers (of which ILRS is one). ILRS will
be responsible for the provision, in the future, of one official product
to the respective IERS Product Centers; alternative solutions can be
submitted to the Combination Research Center. This can only be effective
after the ILRS has shown that its official product is of the best
possible quality. The new organization will probably be operational by
the summer of next year. Mareyen expresses her doubts about the
connection between the users and the IERS Directing Board. Kelm remarks
that IGN has been accepted as Product Center for the Terrestrial
Reference; IGN and DGFI have been assigned to Analysis Centers for
Terrestrial Reference. A call for participation to be a further
Analysis Center will be issued for others.

2.1. ITRF2000

Noomen summarizes the ITRF2000 workshop held in Paris
(2-3 November, 2000) underlining the fundamental role of SLR for the
definition of origin (all SLR solutions) and scale (all SLR and VLBI,
each technique contributing for 50%) for ITRF2000 and the large
number of contributions. He illustrates some results of a preliminary
ITRF2000 solution.

2.2. Operational products

The reasons for developing official products are discussed.
They are:

- ILRS term of reference
- Quality control (internal, external)
- Combination should be better (lower uncertainty, more reliable)
  than individual solutions (no degradation by poor solutions)
- Stimulus for improvements (quality, competition) and for
  operations (deadlines)
- Request of clients: Bulletin A (preferably now), other IERS
  products (in the future)
- Other services are providing (IGS) or about to provide
  (IVS, within a few days) official products
- Symbol of maturity


3. Action since AWG Delft

Noomen gives a summary of the main activities of the Analysis Working
Group from the very beginning (September 1998) until now (appendix 3).


4. Minutes AWG Delft

An overview of the action items from the minutes of the Delft meeting
(appendix 4). All have been satisfied, except for 2:

 1) Husson will get in contact with Pavlis for the eccentricity files.
 2) Husson will check if the description of the pilot projects is on the
    web pages. They are put on the list of action items of the Matera
    AWG meeting.


5. Pilot Project "Positioning and Earth Orientation"

5.1. Presentations of the contributions (station coordinates,
     earth orientation) to the pilot project (L1, L2 and L1&L2 solutions)
     are given:

Luceri (ASI) gives a general description of the analysis procedure
and a comparison of the results with ITRF97 (appendix 5).

Govind (AUSLIG) presents his strategy, which includes estimation of
range and time biases on a pass-by-pass basis. The results for the
rototranslation parameters and the coordinate residuals are identical
to ASI's (appendix 6).

Otsubo (CRL) presents his analysis. Here, a non-standard GM
value was adopted. Differences in scale factors of the submitted
solutions are highlighted (appendix 7).

Kelm (DGFI) presents his analysis. Here, a range bias is
estimated or modeled on a station-by-station basis. The internal
consistency between the L1 and L2 solutions is shown (appendix 8).

Biancale (GRGS) presents the solution: the range biases are adjusted,
the GRIM station coordinate standard errors are used to weight the
corresponding SLR observations. No a priori constraints are adopted,
even if the a priori matrix exists and shows significant constraints:
the SINEX file is probably wrong and needs to be checked (appendix 9).

Pavlis (JCET) weighs the SLR observations equally (apart from a few
exceptions); the range biases are adjusted (appendix 10).

Appleby (NERC) presents his solution. A non-standard GM value
was adopted (appendix 11).

Due to time constraints (too late) the meeting continues with
the SINEX format issues while a list of questions on the future
of “POS+EOP” is distributed to the audience to be
discussed tomorrow (appendix 12).


5.3. SINEX format

The ILRS interpretation of the SINEX format is discussed (appendix 13).

FILE/COMMENT: This section must include information on the analysis.
As a starting point, technical description file for submission to
IERS/ITRF can be used but, to fulfil the function properly, more
information must be added (appendix 14).

Information to be included in the FILE/COMMENT of the SINEX:
the one which is provided in the IERS technical description, plus:

- gravity field (static and time dependent) order & degree
- ocean tides
- solar radiation, thermal forces, albedo (visible) + earthshine (infrared)
  nutation, precession
- a priori EOP
- a priori station (position, velocity)
- ocean loading
- pressure loading
- geocenter (motion, tidal frequencies)
- range biases
- arc length
- estimated parameters
- empirical accelerations
- frequency of EOP solutions
- reference point for coordinate solutions
- wavelength of observations
- satellite used dynamic polar motion
- data weighting
- GM
- relativistic effects
- third body attraction
- atmospheric and earth tides
- tropospheric bias
- time bias
- minimum elevation
- site velocity
- constraints
- pole tide
- center of mass
- model for tropospheric delay

In order to properly represent biases, the participants agree to
also put the solved-for bias parameters in the SOLUTION parts of the
SINEX file. The range biases will be expressed in meters, time biases
in milliseconds, scale biases in part-per-billion and tropospheric biases
in meters. As far as the sign of the biases is concerned, the following
conventions apply: +1 m range bias means that the observation is 1 meter
long, time bias +1 sec. means that the observation is 1 sec. late.
The biases will be introduced in the SOLUTION/ESTIMATE, SOLUTION/APRIORI
and in a new BIAS/EPOCHS block. In the SOLUTION/ESTIMATE, and
SOLUTION/APRIORI blocks, the "parameter type" (A6) will indicate
the type of bias (RBIAS for range bias, TBIAS for time bias, SBIAS for
scale bias, ZBIAS for tropospheric bias, respectively), the "site
code" (A4) will provide the ID of the station, the "point code"
(A2) will provide the satellite (for now: L1 and L2 for LAGEOS-1 and
LAGEOS-2, respectively), the "solution id" (A4) will be used
as the indicator of the bias for this specific station (i.e. will be 1 if
only 1 bias is estimated) and "epoch" will refer to the beginning
date of the relevant time interval. To properly specify the actual time
interval of the bias solution, the new block BIAS/EPOCHS (similar to
SOLUTION/EPOCHS) will be used (appendix 14). Fields are to be interpreted
as described above; the "observation code" (A1) is to be used
to denote the type of bias (i.e. R, T, S or Z).

Regarding the SITE/ECCENTRICITY block, the analysis centers must
pay attention to the values specified here; eccentricities must be
subtracted if different from zero.

Scaling of solution
After a lengthy and detailed discussion, it was decided to
allow solutions in the SINEX files to be scaled by an internal
variance factor (all SOLUTION blocks consistently). This must be
done such that the standard deviation represent the actual
uncertainty (i.e. for the pilot project: 1 meter for coordinates).
The variance factor in the SOLUTION/STATISTICS block is for
information only.


FRIDAY, November 10, 2000


5.2. Presentation of comparison and combinations:

Pavlis (JCET) shows his comparison/combination results: the
estimation of rototranslation parameters, coordinate residuals
of the solutions among the L1&L2 solutions (appendix 10).
Geodesics show a scatter of about 10 mm, whereas variations in
scale and origin of 1-2 ppb and 10 mm, respectively are found.

Kelm (DGFI) presents his comparison/combination results, emphasizing
that loose constraints must indeed be loose (appendix 15).

Luceri & Devoti (ASI) give a comparison (Helmert parameters
based on coordinates only and on a combination of coordinates and
EOPs) and DOP analysis of EOPs. They recommend that no parameter
must be deleted from the normal equations because this is a
constraint not recoverable from the SINEX file. Also they notice
the poor quality of daily UT estimates using only LAGEOS-1
observations (appendix 16).

Husson (HTSI) gives extensive comparison results, addressing various
aspects of the dataset and the solutions. The network comparison is
done in terms of baselines, which appears to be a reliable tool for
assessing quality and scale. One comment from the audience is that
the variance/covariance should be considered (appendix 17).

Torrence (GSFC) provides a comparison in terms of baselines and uses a
NASA/GSFC solution as reference (appendix 18).

Moore (University of Newcastle) presents a combination of solutions
and a check on the agreement among the geocenter of the individual
solutions, of the combined solution and of ITRF97 (appendix 19).

5.5. Future of “POS+EOP”:

To illustrate the variety of problems that are related to
comparisons and combinations, Noomen gives an overview of the experiences
and suggestions by others, which is the result of a questionnaire sent
to various combination centers (AIUB, MIT, IGN, USNO, NRCan)
(appendix 20). Noomen shows a list of questions on the future the
"POS+EOP" project that must be answered by the audience
(appendix 21) on products, combination and comparison.

Products:

Product(s): official status?
Not yet, must await for a good quality first
-	Product(s): what? TRF: time series? Pos+Vel? EOP: time series
One of the objectives is to assess (and improve) the consistency
of the solutions. With this aim we should limit our products to time
series of EOP and station coordinates as done until now; velocities will
be considered at a later stage. The estimation of geocenter, as suggested
by Biancale, will be considered in the future.

Satellites?
A combined solution for LAGEOS-1 and LAGEOS-2 is required, optional
for LAGEOS-1 and LAGEOS-2 separately.

Total interval?
Noomen suggests one year of data and it is accepted. The time span
will go from January 3rd , 1999 to January 1st, 2000 (inclusive).
Husson and Dube will prepare the dataset by November 20th .

Frequency for TRF
One set of coordinates for intervals of 4 weeks. This is a problem
for GRGS,they need modification to the SW. The AWG recommends to do
these modifications.

EOP: length? product? epoch?
Pavlis underlines that daily solution with LAGEOS-1 and LAGEOS-2
are made since many years and that the community already has experience
on that argument  (cf. the products of the pilot projects until now),
that we should generate a LOD product instead of UT and that we need
to estimate rates for EOP. In order not to burden analysts with too much
work (SW modification), Noomen suggests to continue with the estimation
of UT and consider to make a change to LOD at the next stage.
Recommendation: daily EOP and UT at the midpoint of the day as before.
The equivalent of 1 meter as constraint.

Station: position? velocity?
ITRF97 a priori coordinates and velocities, Nuvel-1 velocity for
those stations not included in ITRF97. 1 meter constraints for
coordinates.

Timeline?
The analysis contribution must be submitted by February 1st, 2001.
The next meeting will be held on March 22nd and 23rd, 2001, the week
before the next EGS meeting.

Combinations/Comparisons:
Who? Backups?
To be seen in the future, depending on the progress made
during the next months.Official Request For Participation
(RFP) to the future “POS+EOP”? It is considered
too premature to release an official RFP now, since the community
needs to better understand the quality of data products itself,
first. Depending on the outcome of the pilot project during the
next months, there may be an official RFP which is to be released
by the ILRS GB. As for now, Noomen will prepare an invitation to
participate (as was done before), mail it around the AWG participants
for comments and then distribute it within the ILRS community
only. The official RFP should not be issued until after the next
meeting to give the SLR analysis centers the opportunity to increase
their experience and will be opened to all the centers. The combination
center(s) will be chosen on the basis of the answers to the RFP.

Demands on combination activity and results (internal, per
institute internal, w.r.t. mean external, w.r.t C04,
Bulletin B etc. external w.r.t. ITRF97, ITRF2000 etc. EOP alone?
TRF alone? POS+EOP?)?

The request to participate in the comparison/combination
should specify a minimum number of specific products that are
to be generated, in order to be able to compare the various
(comparison/combination) contributions and actually choose an
official combination center and backups. Within these
specifications, it is up to the center to make a comparison
and/or combination and choose the different parameters
(coordinates, baseline etc.) to consider.


6. Pilot Project "harmonization"

Husson gives a brief overview of the status. The differences have
been identified, the next step should be to have these reduced.


7. Pilot Project: Benchmarking

Husson will prepare an invitation to this project by the next AWG.


8. Pilot Project: Orbits

Nothing has been made but it remains on the table.


9. Miscellaneous

9.1 Report of the IVS/IGS/ILRS: Appleby comments on this activity.
In February a first meeting was held at Ktzting. Correspondence
among the participants to the WG is primarily made by e-mail. The
discussion is now on the possible contribution of VLBI to check the
bias and it is still going on. At the moment, no additional action
is given to ILRS; an invitation to ILRS to track intensively GPS35
and 36 is expected if the IVS community decides to start a tracking
campaign.

9.2 Data screening:
How to treat outliers in the observations? The audience agrees that
the matter should remain to the analysts, no edited data set will be
prepared for the community.

9.3 Data flow:
The labels for the solution for the new POS+EOP must be changed.
As an example bkg.990103.sol5.v1.snx, where the date is the
beginning of the 4-week data interval (including possible
leading zeroes) (and the other elements are as in the previous
definition.

- ITRF2000 methodology
Biancale reports on a request by Altamimi. He is asking the AWG to
identify a set of reliable (time span, data quality, station motion)
SLR stations to be used to define the origin and scale of the new
ITRF2000. He would like to do some analysis to see if this is a good
way to proceed toward ITRF2000. Biancale, Pavlis, Husson will make a
suggestion or this.

9.4	Next meeting:
March 22th and 23th, 2001, Nice, France


10. Action items

Noomen: prepare invitation to participate in "positioning +
	earth orientation" (time series solutions), distribute draft
	among AWG/Matera participants and next distribute within the
	ILRS community.

Noomen: prepare invitation to participate in "positioning + earth
	orientation"(comparison/combination), distribute draft
	among AWG/Matera participants and next distribute within the ILRS
	community.

Dube/Husson: prepare dataset for "positioning + earth orientation"

Husson: prepare plan of action for pilot project "Benchmarking"

Biancale/Husson/Pavlis: prepare list of SLR stations for definition of
			origin and scale in ITRF2000

Husson/Pavlis: prepare files with station eccentricities in NEU and XYZ
	       and put them on the ILRS web page

Husson: put description of pilot projects on the ILRS web page

Noomen/Husson: update description of SINEX for ILRS pilot project and
	       put on the ILRS web page. Inform Tom Herring


Appendices

1)	Agenda
2)	All material for item 2. Role of ILRS within IERS
3)	Activities AWG
4)	Action items from AWG Delft minutes
5)	POS+EOP solution ASI
6)	POS+EOP solution AUSLIG
7)	POS+EOP solution CRL
8)	POS+EOP solution DGFI
9)	POS+EOP solution GRGS
10)	POS+EOP solution and comparison/combination JCET
11)	POS+EOP solution NERC
12)	Questions on the future of POS+EOP project
13)	SINEX format
14)	Info for FILE/COMMENT and new SINEX labels
15)	Comparison/combination DGFI
16)	Comparison/combination ASI
17)	Comparison/combination HTSI
18)	Comparison/combination GSFC
19)	Comparison/combination NCL
20)	Comparison/combination experiences by others
21)	Future of POS+EOP

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