**Report of AWG Meeting, Eastbourne, UK, October 2, 2005.**

Note: since (the discussion of) some of the agenda items were moved to
the "Analysis" session on Monday October 3, a brief summary of the
outcome and resulting action items are attached at the end of these
minutes.

**Ad 1. Opening**

The ILRS AWG members met during Sunday October 2, 2005, preceding the
ILRS Workshop. The meeting began at 10.00 hrs. The agenda and list of
attendance are given in Tables 1 and 2, respectively. Noomen welcomed
the participants.

**Ad 2. Announcements**

On behalf of the CB, Pearlman also welcomed the participants.

Noomen made a remark about two ILRS papers during the IAG meeting in
Cairns, August 2005: a paper by Pavlis on the status of the ILRS
contributions to a new ITRF product, and a general ILRS poster by
Pearlman, Noll, Gurtner and Noomen. In addition, Müller, Willliams,
Turyshev and Shelus had a paper on lunar science capabilities.

**Ad 3. Pilot project \"positioning + earth orientation\"**

This agenda item took most of the day.

**Ad 3.1. Operational product**

Noomen made a brief introduction on the current ILRS activities on this
aspect. Weekly products on station coordinates and EOPs (1-day
resolution) are generated by 6 individual analysis centers (ASI, BKG,
DGFI, GFZ, JCET and NSGF), based on SLR data taken on LAGEOS-1 and --2
and Etalon-1 and --2. The current procedure is effectively working since
November 2003, and official since June 2004. Official ILRS combination
solutions are being produced by ASI (official primary) and DGFI
(official backup) and are available on Wednesday of each week.

Mareyen made specific remarks about the harmonization of the "pos+eop"
results, and would like to see more testing and evaluations of the scale
and weighting aspects. *Action item Mareyen*: make a proposal for this.

Mareyen also brought up the apparent difficulty in obtaining the
relevant information for the benchmark solutions and the operational
"pos+eop" solutions. *Action item Pavlis*: update description of
benchmark solutions and give better visibility. *Action item Noomen*:
update description of "pos+eop" products and procedures and give better
visibility. Both: send result and suggestions to Torrence.

Mareyen: there is serious concern about a so-called Sunday-effect: the
relatively small number of (accepted) NPs available on this day. In
particular, the situation is such that it results in poor solutions for
the EOPs on that day (accompanied by large standard deviations), but
that it also (potentially) affects the overall solution (including
station coordinates and other EOP solutions). This is claimed to occur
about once per month. Clearly, a reasonable amount of NPs is also
required for the Sundays. Another issue appears to be the geometry of
the (scarce) NPs: Pavlis showed plots of coverage of the globe from a
north pole and south pole perspective, which clearly shows the poor
orbital coverage afforded by the network and of course exacerbated by
significant numbers of stations not working 24/7 shifts.

König reported that this effect does not play a role for Champ and
GRACE, since GPS is the main tracking technique here. Torrence mentioned
that GFO and TOPEX/Poseidon would possibly be affected by this Sunday
effect as well, since SLR is the main technique. However, so far there
have been no signs of any (Sunday) dropoff. König mentioned that the
situation for ERS-2 is similar to that of GFO and T/P. *Action item
Noomen*: check out the situation for other satellites (status of
tracking, requirements on SLR). *Action item Noomen*: convey this
concern to the ILRS GB.

**Ad 3.2. ITRF2004: status ILRS 1993-2003**

As an introduction and representative for our customer IERS, Altamimi
gave a presentation on our "pos+eop" results (both on the operational
product and on the backwards solutions, covering the time-frame
1993-2003). He emphasized that IERS is interested in getting the best
from SLR, and that SLR provides a unique contribution for the TRF origin
and scale (scale shared with VLBI). Also, SLR is a unique contributor
for providing information on the vertical position (and motions). The
proposal for ITRF2004 is to convert the time-series of weekly
combination solutions for station coordinates into a linear model for
position and velocity, for each individual technique independently. As
the next (final) step, the pos+vel models coming from the various
techniques will be combined. The EOP information is also to be used for
the combination.

Altamimi presented time-series of the solutions (individual and
combination) of station coordinates. Issues addressed were outlier
rejection and the correlation with the estimation of troposphere biases
and range biases (which is not allowed for the core stations). A range
bias problem with the Graz data (1993-October 1996) proved to cause
unrealistic solutions for the vertical velocity; when a range bias for
this station is estimated, the jump disappears and the vertical velocity
for Graz improves, but the quality of the vertical solutions becomes
weaker and the consistency of the global scale estimates becomes worse.
Altamimi suggested that range biases are not estimated.

He is particularly interested in receiving an official ILRS contribution
for the ITRF2004 model, with the end of October as deadline. He made 3
suggestions to do so: (1) re-analyse 1993-2005 data, with a consistent
strategy (now) for treating range biases; (2) redo the combinations
only, with more strict outlier rejection; and (3) adopt the current v3
product as the ILRS contribution, and have ITRF/IERS do their editing at
their own liking. He also suggested to document instantaneous station
position shifts in a solution/discontinuity element in the SINEX files.

Bianco gave a series of presentations, also on behalf of Luceri and
Sciarretta. The v2 combination product was affected by weak tracking
data during the Christmas weeks, and errors in some of the contributions
(5 JCET solutions with duplications of site ids, 2 DGFI solutions with
too long EOP periods). The v3 combination solution, based on input from
ASI, DGFI, GFZ, JCET and NSGF, was derived after rigorous editing (all
parameters other than pos and EOPs were deleted) and a 5σ editing in the
combination process. Consistency checks were done for both the
individual solutions and for the combination product; they all yielded
the presence of yearly signals.

In a second presentation, discontinuities in the time-series were
addressed. Angermann (DGFI) had reported jumps in the station
coordinates for Graz and Riga, and Appleby had done some test
computations solving for RB for Graz. ASI found that this affected more
stations: 1864, 1868, 1884, 7210, 7237, 7403, 7811, 7835, 7839 and 8834.
The problem was aggravated by differences in treatment by the various
analysis centers. Bianco concluded that a more coherent treatment is
needed.

Next, ASI performed a new combination using different outlier-editing
procedures: individual solutions were eliminated if (1) the estimate was
too weak statistically; (2) there were too large differences w.r.t. a
reliable reference (ITRF2000) (how to handle stations that are not (good
enough) in ITRF2000 was not addressed); (3) a 5σ outlier editing. In the
result (v3.1), all problems that were reported by IGN were now captured
and eliminated at the combination step already, suggesting that this is
a better way to do the combination.

Finally, some ideas about the further development of the pos+eop product
were aired: (10 re-analyse 1993-2003 (also until 2005?) with a more
consistent treatment among analysts regarding RB; (2) also include other
contributions; (3) apply the v3.1 procedures; (4) use a 2-digit version
number (to allow more variations in the combination steps).

Pavlis gave an overview of the JCET procedure to obtain individual
pos+eop solutions. He elaborated on the on-line monitoring of
translation, scale, variance and observation statistics, that he is
routinely generating from the ILRSA (i.e. ASI combination) solutions.
This should be available as an open resource for anyone interested.
*Action item Pavlis*: make this available (as a link) through CDDIS.

The solutions for the geocenter showed evidence of El Niño. Solutions
for J~2~ showed a good agreement between SLR and GRACE (as determined by
CSR). To take the analysis back to 1976, Pavlis suggested that the
inclusion of other satellites (Starlette and Ajisaj) is essential
(LAGEOS-1 data are sparsely available; no LAGEOS-2 or any of the
Etalons, prior to 1989).

Kelm reported about new features in the DGFI combination software and
method. Some highlights: (1) A new rigorous variance component
estimation technique is used, which will identify problems with the
solutions of some of the (pos, EOP) parameter solutions; as a result,
these parameter solutions are typically edited out. (2) A comparison of
ILRSA and ILRSB results (coordinates, EOPs, Helmert parameters); a good
consistency between ILRSA and ILRS is observed. (3) It is recommended
that Graz becomes a core station only from October 1996 onwards. (4) Do
not solve range biases for the core stations. (5) Include the solutions
from Geosciences Australia. (6) Create an open directory for arbitrary
users in which most recent ILRS solutions are stored without version
number (to avoid confusion). *Action item Kelm*: rather than including
the differences w.r.t. ITRF2000 in the ILRSB SINEX files, statistics on
the differences w.r.t. some representative average is to be included.

On behalf of Eanes, Shelus gave an overview of recent pos+eop results at
CSR. Eanes gets post-fit rms values of about 5 mm (probably on a subset
of stations). Shelus report about bias results for a number of stations:
SHO, Maui, Zimmerwald, Changchun, Riyadh and Yarragadee.

After this, a lengthy discussion ensued on how to proceed further. In
summary:

The operational product will continue, albeit with more strict
procedures. For the core stations (currently, these are Graz, Greenbelt,
Hartebeesthoek, Herstmonceux, McDonald, Monument Peak, Mt Stromlo,
Riyadh, Wettzell, Yarragadee and Zimmerwald, as determined during the
2002 AWG meeting in Lanham). No bias will be modeled and/or estimated,
but time-series from these stations will be kept under review in order
to identify potential problems. For the non-core stations, an inventory
will be made for which station biases are needed and for which stations
they are not. *Action item Noomen and Bianco*: do this on the basis of
statistics from the ILRSA combination solutions (1992-2005). Level of
significance for bias jumps / height shifts: 15 mm. All analysts have to
do their re-analysis according to this standard.

*Action item AWG*: re-assess the choice for AWG core stations (at next
AWG workshop).

Backwards analysis (1993-2003): similar approach, similar action item by
similar people. Problems have been identified for the core stations Graz
and Wettzell. *Action item Noomen*: obtain realistic estimates for the
bias (jumps) from station representatives.

Combination products. *Action item ASI, DGFI*: apply their new criteria
and techniques.

Troposphere: for the time being (that is: the ITRF2004 contribution), we
stick to the Marini-Murray model (cf. agenda item 3.4).

Deadlines for various actions: October 15 for the reporting of the bias
values for Graz and Wettzell, as well as for the assessment of non-core
stations with a necessity to use biases and those without. October 31
for individual analysts to provide their new solutions (*action item
ACs*). November 7 for the combination solutions (*action item CCs*).

The analysis of pre-1993 data (input for ITRF2004) is not within
practical reach at this moment, but is left for the future (cf. agenda
item 3.5).

Satellites other than the LAGEOS and Etalons are not included in the
1993-2005 re-analysis.

Labeling: *action item Noomen*: ask Noll and Seemüller to generate 1
directory that is open to arbitrary users where the most recent ILRS
solutions (individual and combination) will be stored. Without a version
number in the name (it is present, directly or indirectly, in the
contents description). Other solutions are to be stored in a separate,
secluded sub-directory (with label numbers). This means there will be a
one-on-one copy in 2 subdirectories.

**Ad 3.3. Implementation station/satellite signature**

Considering the time, this item is deferred to the more general
discussion on Wednesday Oct 5.

**Ad 3.4. Implementation new troposphere model**

A discussion ensued about the value of the Mendes model as compared to
the older Marini-Murray model. The latter has the drawback that it has a
bias of about 1 mm at zenith, whereas the Mendes model is most likely
better suited to deal with the infrared frequencies of the MLRO system.
Initial tests (4 weeks) have shown that the Mendes model would result in
slightly larger values for the rms-of-fit, which is most likely due to
the fact that other elements of the computation model are unadjusted; in
particular, GM should have to be increased from .4415 to .4416
km^3^/s^2^ (fraction given here only). After some discussion, it was
decided to stay with the use of the Marini-Murray model for the time
being.

**Ad 3.5. ITR2004: plans ILRS 1983-1992**

Procedures and parameters were suggested during the AWG meeting in
Vienna. However, considering the time at the current meeting and the
large amount of work needed to be done for the 1992-2005 re-analysis and
the expected complications for handling this historic data, it was
decided to leave this interval to another round in the ITRF solutions.
Altamimi agreed.

**Ad 3.6. New products**

No new developments on this aspect.

**Ad 3.7. Other issues**

Nothing is reported here.

**Ad 4. Benchmark project: status**

BKG has passed the blind test in the middle of 2005, and has been
accepted as an official ILRS analysis "pos+eop" contributor. GA and GRGS
are in the process of doing this blind test, and are expected to hand in
their results to Pavlis by the end of October. *Action item Govind,
Exertier, Pavlis*.

**Ad 5. Miscellaneous**

Various brief agenda items.

**Ad 5.1. Status SLR tracking network**

The current situation with the NASA stations working only five-day
shifts was particularly detrimental to the products of the AWG and all
efforts should be made to rectify the situation and return to full 24/7
operations. NASA is in the process of bringing TLRS-4 to Maui. TLRS-3 is
being brought back into operational status at Arequipa. The French
system 7835 has officially stopped its operations. The lunar system 7845
is being redesigned at this moment, and will not be able to track
anything (operationally) for the coming 1-2 years (report Exertier). To
fill in the gap in the LLR tracking, MLRO (Matera) is requested to
concentrate more on lunar tracking than on the low-flying satellites.
*Action item Noomen*: convey this to the ILRS GB.

**Ad 5.2. Consistency QC reports**

This is left to the open discussion on Monday Oct 3.

**Ad 5.3. Analysis center categorization**

Recognizing the activities of a number of institutes to pass the
benchmark test, this issue is deferred to a next meeting.

**Ad 5.4. Procedure for assessing quality of new SLR system**

In the AWG meeting in Vienna (2005), DGFI volunteered to do this task. A
secondary aspect is the generation of station coordinates, which can be
used for QC evaluations. These should be consistent within the ITRF2000
frame. If possible, use should be made of ITRF2000 information on
related sites (e.g. GPS occupations), or a common and reliable solution
should be estimated otherwise (including position and velocity). This
solution is to be used (and kept fixed) by the QC centers.

**Ad 5.5. Station performance card**

This is a continuing activity at ILRS CB. It is used as input for the
evaluations of the stations for AWG-Core status evaluations.

**Ad 5.6. Analysis documentation**

Driven by financing from the INDIGO project, CDDIS has been asked to
document the various analysis standards (and approaches?) of the various
individual pos+eop contributors. The choice is between something that
comes out directly of our SINEX files (the description block), and the
use of the format that is in use by IGS and IDS already. The former has
the advantage of being a minimum effort; the latter provides consistency
all over the geodetic services (it is mainly aimed at external users
that are not familiar with any of the techniques). It was decided to go
for the latter option, since this is (in principle) a one-time effort.
*Action item Noomen*: complete the empty standard format as much as
possible, and send this to the analysis centers contributing. *Action
item ACs*: complete and send to Noll. *Action item ACs*: keep
up-to-date. This is not relevant for the combination product, CCs.

**Ad 5.7. IERS EOP Prediction Comparison Campaign**

This was initiated by the IERS. Some people have expressed their doubts
about the procedures proposed for this project. There is no official
ILRS involvement here, although individual analysis centers are
encouraged to get involved.

**Ad 5.8. CONT\'05 Campaign**

This IERS project evolved form an IVS project. It basically aims at
intensified SLR tracking of radionavigation satellites and satellites
that are equipped with multiple tracking techniques. Essentially, this
is to be done for the period September 1-28. No further official
analysis involvement of ILRS (individual groups may do their analysis,
of course).

**Ad 5.9. Galileo**

The ILRS will introduce the tracking of the two Galileo test bed
satellites (GSTB-V2/A and --V2/B) in the tracking schemes. These are due
for launch in December 2005 and February 2006. In the future, it may
very well be possible that ILRS is asked to range on the full
constellation of some 30 operational Galileo satellites.

**Ad 6. Next meeting**

A new venue in connection with the AGU meeting in San Francisco was
proposed, but it turns out that we have a very limited representation of
ILRS analysts. Instead, it was decided to organize a (full-day) AWG
meeting in conjunction with the next EGU meeting in Vienna, April 3-7,
2006.

**Ad 7. Action items**

See Table 3. Standing action items from the meeting in Vienna 2005 are
not addressed.

**Ad 8. Closure**

The meeting adjourned at 18.30 hrs. The chairman thanked the
participants for their input in presentations and discussions.

## Analysis session ILRS Workshop, October 3: relevant aspects

Stations, when going after financial arrangements with funding agencies,
can ask the ILRS (CB, chairman, analysis coordinator) and/or IERS
(chairman, Altamimi, Noomen) for a letter of support. They can also use
the science material that is available on the ILRS web pages. Pearlman
noted that an overview paper on the value of SLR, given for GA managers
in August 2005, was well received and would be similarly useful for
"selling" SLR to others.

In a discussion about the contribution of SLR to the TRF (introduction
Pavlis), Pavlis emphasized the need for implementation of atmospheric
pressure loading. Altamimi stressed not to do this for the ILRS ITRF2004
contribution.

It was remarked by various people that the ILRS (analysts) should be
more aggressive in highlighting problems, so that external people are
aware of the importance of activities and products. Full operations
("24-7") by the global network is a good example, and should be strongly
recommended to the stations.

After introductions on the error budget of SLR observations (Schillak)
and the modeling of tropospheric corrections (Riepl), a long discussion
on the latter ensued. The importance of two-color ranging was
recognized. The value of truly differential observations, using a streak
camera, is of utmost importance. Since MLRO is the only system currently
capable to obtain such measurements, this station was encouraged to
range on those LEO satellites with a unique and unambiguous CCR
signature: CHAMP, GRACE-A and GRACE-B (*i.e.* single-reflector
satellites). More studies should be done on various aspects of the
tropospheric delay (gradients, wavelength dependencies, etc.).

Next the subject changed to the semi real-time quality control
activities of a number of analysis centers (introduction Noomen), the
results and the interpretation of that. Range biases as "observed" by
different analysis centers may show remarkable differences. This may be
due to a number of aspects, of which station coordinates is a reputed
one. To improve upon this, (1) these centers should all use ITRF2000 for
now; (2) stations either not included or poorly-determined in ITRF2000
should be analysed with a consistent and common (new) position/velocity
solution; (3) the development of ITRF2004 will of course also result in
a new, SLR-only position+velocity model for use by these QC centers
(consistent with current reference frame); updates should be made with a
frequency of e.g. once per year, to also include new stations (but with
a consistent reference frame) (recommendation Altamimi). As a general
advice, stations are advised to ignore (absolute) reported biases
smaller than about 30 mm.

Gurtner gave a brief presentation of a recent manoeuvre of GPS-35, which
was observed by station Herstmonceux and analysed by the CODE group.

October 28, 2005

R. Noomen, G. Appleby, P.J. Shelus

**Table 1: Agenda**

(Note: ordering slightly adapted w.r.t. original agenda)

1\. opening

2\. announcements

3\. pilot project \"positioning + earth orientation\"

3.1. operational product

3.2. ITRF2004: status ILRS 1993-2003

3.3. implementation station/satellite signature

3.4. implementation new troposphere model

3.5. ITRF2004: plans ILRS 1983-1992

3.6. new products

3.7. other issues

4\. benchmark project: status

5\. miscellaneous

5.1. status SLR tracking network

5.2. consistency QC reports

5.3. analysis center categorization

5.4. procedure for assessing quality of new SLR system

5.5. station performance card

5.6. analysis documentation

5.7. IERS EOP Prediction Comparison Campaign

5.8. CONT\'05 Campaign

5.9. Galileo

6\. next meeting

7\. action items

8\. closure

**Table 2: Attendance**

Zuheir Altamimi <altamimi@ensg.ign.fr>

Graham Appleby <gapp@nerc.ac.uk>

Giuseppe Bianco <giuseppe.bianco@asi.it>

Christopher Clarke <christopher.clarke@honeywell-tsi.com>

Ludwig Combrinck <ludwig@hartrao.ac.za>

Mark Davis <mdavis@ssdd.nrl.navy.mil>

Howard Donovan <howard.donovan@honeywell-tsi.com>

Pierre Exertier <pierre.exertier@obs-azur.fr>

Vladimir Glotov <vladimir.glotov@mcc.rsa.ru>

Ramesh Govind <ramesh.govind@ga.gov.au>

Werner Gurtner <gurtner@aiub.unibe.ch>

Julie Horvath <julie.horvath@honeywell-tsi.com>

Rainer Kelm <kelm@dgfi.badw.de>

Rolf König <koenigr@gfz-potsdam.de>

Kazimirs Lapushka <riglas@lanet.lv>

Maria Mareyen <maria.mareyen@bkg.bund.de>

Ron Noomen <ron.noomen@deos.tudelft.nl>

Toshi Otsubo <otsubo@nict.go.jp>

Erricos C. Pavlis <epavlis@jcet.umbc.edu>

Mike Pearlman <mpearlman@cfa.harvard.edu>

Peter J. Shelus <pjs@astro.as.utexas.edu>

Mark Torrence <mark.h.torrence.1@gsfc.nasa.gov>

Scott Wetzel <scott.wetzel@honeywell-tsi.com>

Matt Wilkinson <matwi@nerc.ac.uk>

**Table 3: action items**

(Note: some of these action items remain after the AWG meeting in
Vienna; others are the result of the Eastbourne workshop)

ACs submit new individual pos+eop solutions 1993-2005 (deadline: Oct 31)

ACs complete INDIGO description analysis and submit to CDDIS and EDC

ACs, CCs general: submit solutions to both CDDIS and EDC

Appleby extend table with CoM values

ASI apply new combination approach

AWG re-assess AWG core stations status

CCs generate new combination pos+eop solutions 1993-2005 (deadline: Nov
7)

DGFI apply new combination approach

Exertier submit blind test benchmark project

Govind submit blind test benchmark project

Gurtner develop proposal for orbit product (with Ries, Müller,
Sciarretta, König)

Kelm include residuals in ILRSB summary files w.r.t. combined solution

Mareyen develop proposal for testing and evaluating scale and weighting
aspects of pos+eop solutions

Noomen, Gurtner, Shelus develop new AC/AAC categorization

Noomen, Pearlman, Gurtner homogenization of QC reports

Noomen update description of pos+eop products and procedures

Noomen make inventory of Sunday effect for different geodetic missions

Noomen, Bianco make assessment of bias-need for core and non-core
stations 1993-2005

Noomen obtain realistic estimates for bias jumps for Graz and Wettzell
(1996) (deadline Oct 15)

Noomen ask Noll and Seemüller to "redesign" pos+eop subdirectories, plus
change in naming and handling

Noomen complete INDIGO description analysis as much as possible and
submit to ACs

Noomen make and distribute list for unambiguous station treatment for
ITRF2004 contribution

Pavlis update description of pos+eop products and procedures

Pavlis make pos+eop statistics from ILRSA available through CDDIS link

Pavlis evaluate blind test benchmark project results GA and GRGS

Pearlman convey MLRO tracking priorities to GB (*i.e*. LAGEOS and
higher)

Pearlman convey concern on Sunday effect to GB

Actions items after "Analysis" session on October 3:

AWG make overview of station activities 1993-2005, based on eccentricity
file and "pos+eop" info

AWG develop yearly linear SLR-only position model for QC purposes

Glotov use ITRF2000 in QC analyses

Müller use ITRF2000 in QC analyses

Noomen get letter expressing general support for ILRS activities from
IERS chairman