Minutes ILRS/AWG Workshop #11
June 5, 2004, San Fernando, Spain

Saturday June 5

Welcome by Noomen. Approval of agenda (Table 1). The names and e-mail addresses of the participants are listed in Table 2.

2. Pilot project "positioning and earth orientation"

Noomen gave a short introduction of this ILRS AWG pilot projects, in particular on the customers (IERS Bulletin A, IERS Combination Pilot Project) and the most recent refinements (after the AWG meeting in Nice, April 2004).

2.1. Individual contributions

In the discussion that took place during the AWG meeting in Nice, a number of criteria were selected to document and evaluate the quality of the solutions for station coordinates and EOPs. The ones for documentation (like number of stations, number of passes, etcetera; cf. Table 4 of minutes AWG meeting Nice 2004) are not addressed here any further. The ones that have been identified for quality evaluation purposes in particular are reflected in tabular form in Table 3.

The various contributors to the ILRS products were given the opportunity to comment on their most recent activities. The providers of individual solutions present here (ASI, DGFI, JCET and NSGF) as well as the combination centers present (ASI and DGFI) gave a few remarks, where appropriate. The time for this agenda item was mainly filled with the completion of Table 3. This gives an overview of the various numerical estimates of various quality aspects, both of the individual solutions and of combination solutions. After each entry, the name of the source of the specific number is given; in principle, a particular aspect may have been addressed by more than one group. The table has been completed as much as possible.

2.2. Comparisons and combinations

See remarks under 2.1 "individual contributions".

2.3. External evaluation of combination solutions

IGN

On behalf of Altamimi, Noomen presented the IGN evaluation of the combination solutions generated by ASI. Because of time constraints, Altamimi was unable to address any of the other (individual and/or combination) solutions, and the evaluation of the ASI solutions, too, was restricted to a few aspects only.

Altamimi compared the ASI combination solution with an intermediate combination solution, which is based on 10 years of SLR, 6 years of GPS, 14 years of VLBI and 10 years of DORIS data. This may introduce an offset w.r.t. the other comparisons which used ITRF2000 as a reference, and therefor, the results are not included in Table 3, but will be reported in this part of the minutes only. The following ranges were observed for the origin differences of ASI's combination solution versus this internal IGN solution: -15 - 35 mm (X), -35 - 20 mm (Y) and 0 - 40 mm (Z). Neither clear signals nor significant outliers were detected. As for scale, the values typically range between -15 and 0 mm (corresponding to about -2 - 0 ppb), with an individual outlier of -40 mm (or 6 ppb). The differences w.r.t. this new IGN combination solution show values of, on average , 10 - 20 mm for 2D WRMS, and a similar range (and pattern) for the up component (making the total 3D difference 15 - 30 mm WRMS).

OdP

Based on input provided by Altamimi, Gambis showed a plot of the EOP residuals for x-pole and y-pole of the ASI combination solution w.r.t. IERS C04 (Gambis was not present; Noomen presented on his behalf). The rms value of these differences amounts to about 0.3 mm for the x-component and about 0.4 mm for the y-component (ignoring a small group of individual outliers at the level of up to 20 marcsec).

2.4. Selection of ILRS combination center and backup

In this part of the meeting, two main questions needed to be answered: ( i ) is the quality of the combination solutions better than that of the individual solutions, and ( ii ) which institute will act as the official primary ILRS combination center, and what will be the role for the others?

The first question can be answered positively by inspecting Table 3: there is a small improvement in the residual rms w.r.t. ITRF2000, but this can possibly be explained by imperfections in this reference model at the level of a few mm. More striking, however, is that the Helmert parameters (in particular those for our unique products, i.e. origin and scale) when mapping into ITRF2000 show a much better consistency (cf. Table 3). Also, EOP statistics for the combination solution (ASI's solution could be evaluated only) turn out to be significantly better than those for the individual solutions. In conclusion, there was a positive conclusion on this part of the evaluation.

The second question proved a bit harder to answer, if only because the information that was present to evaluate and compare the 3 combination solutions was sparse. There was a debate on whether to postpone this important decision or not, but in view of the requirements of our external clients (IERS, with various products) and the likely date for a next AWG meeting, it was generally accepted that a decision was to be made here.

At this point, it was generally agreed by the members present that ASI has done an outstanding performance throughout the pilot phase (history), and has taken a large variety of roles within the ILRS analysis community, always with a positive attitude. After some debate, it was decided to give the role of official primary ILRS combination center to ASI, and the role of official backup ILRS combination center to DGFI. Representatives of the two institutes present agreed with this outcome. It was emphasized by the chairman that it requires strict adherence to the timelines as followed now during the testing phase of the operational procedures, irrespective of the actual role. Holidays and other occasions cannot be taken as an excuse to not have a particular analysis done, by neither of the centers. Since NCL was not present, no information was available on the actual performance of this combination product, and the combination product information to the analysis community has been difficult sometimes, it was decided to give NCL the status of ILRS combination center in development; NCL is strongly encouraged to further develop their procedures and results.

There are a number of action items that come out of this decision: Noomen will iron out the exact details of the combination products (computer location, naming etc.) and will convey the outcome to IERS. The decision will be formalized by sending an official letter on the outcome to ASI and DGFI representatives ( action item Noomen, Pearlman ). The current selection will be effective until the next International Workshop on Laser Ranging, to take place in Canberra in October 2006. Then, the performance of the current two (plus additional candidates, like NCL) combination centers will be evaluated again. It was decided to retain this performance evaluation, of ASI and DGFI as a minimum, as a standard agenda item in upcoming AWG meetings.

Although the decision has been made, Altamimi and Gambis will be asked to complete their evaluation of the results as they are now ( action item Noomen ). Irrespective of the outcome, this will not change the decision made here, but it will be used as additional monitoring input. Preferably this should be ready by July 15. Kelm and Altamimi need to get in contact on technical problems of the DGFI solutions ( action item Kelm ).

2.5. Other issues

No issues here.

3. Next meeting

The next AWG workshop has not been scheduled yet. Very likely, there will be one in conjunction with the EGU meeting in Spring 2005 (Vienna, Austria). If deemed necessary, an additional AWG meeting may be organized in the mean time, but if possible preference will be given to email correspondence.

4. Action items

In view of the time, no overview of the standing and new action items was given. All standing action items remain, and new ones are added (cf. Table 4).

5. Closure

Noomen thanked the participants for their contributions and their input in the discussions.

June 25, 2004

Table 1: Agenda

Table 2: Attendance

Table 3: Overview of aspects for evaluation of individual and combination solutions and their values; institute names after numbers represent source of data.

Table 4: ILRS AWG action items

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