Dear Pascal,

thanks a lot for your fast and thoughtful comments on the IERS CPP.

> My only concern is that you totally leave the responsability of 
> declaring a "technique-unified" solution "operational" to the techniques 
> services themselves. Don't you want to verify this point through the 
> campaign itself? 

I agree that we will have to have a very very good idea of the performance
of the intra-technique combinations, because we will (if there is only one
solution per technique left) fully rely on just a single solution per
technique.
On the other hand, I expect that the Technique Services will eventually
produce the information we need, namely how different the individual
solutions are and what systematic effects exist between the
individual solutions of one technique. I think that when it comes to
the details the experts of the respective techniques are best suited
to clarify such issues. Therefore the Technique Centers should take over
and keep this repsonsibility for their official solutions.
I know, it will take some time to arrive at really good combined
intra-technique solutions: first, the systematic biases
between the individual ACs will have to be identified and corrected,
and only then a reasonable combination will be possible. To correct
for systematic biases migth take a lot of time (it took, e.g., a big effort
within the IGS to get the geocenter shifts due to different orbit
parameterization under control and the problem is still not completely
solved).

> In terms of delays and precision, you put for this 
> Pilot Project more stringent requirements that the techniques could want 
> to apply for their own goals. You may want to verify during some period 
> of time (6 months?) that effectively the unified solution is more 
> precise, more reliable and is delivered in a timely manner. In my
> opinion, it is only after such an "observation period" that you could 
> get rid of the individual solutions as proposed in the long-term scheme.

It is clear, that it would be easiest to start the IERS CPP only after
each of the techniques has its official, consistent, reliable, and timely
combined solution available. But I think that the exactly the IERS CPP is
essential to get such developments going, going into a common direction.
So, we will have to live with this somewhat hybrid situation, where
the IERS CPP is already started, but some intra-technique combinations are
not yet fully validated and operational. I think, that the IERS CPP
should not take over the responsibility for the INTERNAL validation of the
intra-technique combinations, which is the task of the Technique Service,
but only for the EXTERNAL validation and combination.

> The consequence is that I will send you soon a IGN/JPL proposal on the 
> DORIS solution as the IDS unified solution cannot be considered as 
> operational at this point. I will tell you where to find those files. 
> Naming conventions are almost the same, so there should be no problem.

That's fine with me. With your solutions available, the various groups
can already start to gather some experience with DORIS solutions.
We should also keep in mind that, because the number of groups
performing combinations is small anyway, there will always be quite
some overlap between the groups working on Step 1, Step 2, and Step 3
(e.g. DGFI, producing intra-technique solutions for SLR is also going to
generate inter-technique solutions).
An important point for me is, that we get the IERS CPP going, thereby
taking the Technique Services with us on this way ... making sure that
they can identify themselves with both, their own Technique Service
and the IERS goals.

> I still suggest (if it is not already done) that you contact directly 
> IDS, ILRS and IVS and ask them to encourage individual groups within 
> their techniques to submit proposal for the IERS campaign when needed, 
> at least for the time being, as the initial call for participation was 
> not clear enough and led to different interpretations.

I hope that the Technique Services read these lines and think about
their opinion concerning this point. I will contact the Analysis
Coordinators to get once more a clearer idea of their time line
and their thoughts about this hybrid phase we are in right now.

Best regards,
                       Markus

--------------------------------------------------------------------------------
Prof. Dr. Markus Rothacher                   Phone : ++49-89-289-23191
Forschungseinrichtung Satellitengeodaesie    Fax   : ++49-89-289-23178
Technische Universitaet Muenchen             E-mail: markus.rothacher@bv.tum.de
Arcisstrasse 21
D-80290 Muenchen / Germany