Hi,

following Jim latest email, I would like to continue the discussion 
on these important points.

First of all, concerning the need for long-term solutions before 
starting the combination. There are basically 2 cases. Either these 
solutions already exist at the Technique Data centers or not. This 
point was discussed at Nice already and the decision was to ask the 
technique or directly the ACs within a few weeks to provide those. 
Was it done?

People like Detlef and Zuheir know perfectly well where to find these 
solutions even if they are not officially at the IERS ftp site, for a 
reason that is still quite obscure to me. So they don't need to wait 
or to do "a solution in isolation".

For other solutions (some are currently being recomputed) it is not 
sure that they will be available before san Francisco. So we should 
start with what we have now and most probably recompute new 
combinations when we have more available solutions. It would be 
probably a good idea for groups who are in the process of submitting 
new long-term solutions to give a preliminary schedule of what they 
plan to do. We could then see if it make more sense to wait or not. 
Without any further information, I think people should start without 
waiting. The same issue was raised in Nice and I don't think that any 
new long-term solution has been provided since.

Concerning the local ties issue, some people have done quality 
analysis of local ties so I think that the situation is fortunately 
better now that 3 years ago and I am sure that Zuheir keeps an eye on 
those regularly. Even if we need the long-term a centralized archive 
for all local ties, this does not prevent us to start. I guess this 
point was also discussed in Nice.

In my opinion, the goal of the campaign is not to provide a 
"bullet-proof" product for weekly coordinates since the very first 
weekly combination but to do it and by doing it to assess the 
technical difficulties and the problems in combination and 
validation. The solutions are not going to be made available 
worldwide at present. My understanding is that it is only for our own 
investigations. One day, when everything will have converged we may 
distribute them broadly but we are far from it.

Maybe the conclusion is that these inter-technique combination will 
not provide any useful feed-back for the techniques as stated by Jim. 
For the time being, I don't know the answer to this question. Let's 
try it and see if it is useful or not.

Following Jim's remark, I agree that it would seem very strange to go 
to the meeting in December if no combination has effectively been 
done at all before the meeting. It would seem to me also as a waste 
of time. Combinations groups need to start something, that will not 
be perfect, that will not be compatible and by assessing the quality 
of those we will learn something and we will be able to go another 
step further and improve.

I also agree that we should discuss results before the meeting 
exchanging emails. The results won't appear by magic the first day of 
the meeting.

My guess is that when the first group will provide a first weekly 
inter-technique combination, other groups will join and a technical 
discussion will start. Before this happens, we are almost exactly at 
the same point as several months ago at the meeting in Nice.

Best regards
Pascal
-- 
Pascal Willis
Jet Propulsion Laboratory, MS 238-646     Ph : 1-818-393-4748
4800 Oak Grove Drive                      FAX: 1-818-393-4965
Pasadena CA 91109                         Em : Pascal.R.Willis@jpl.nasa.gov