UCD problem in SSA/SpectrumDM

[Petr Skoda]

> I also think that a minor revision is warranted - mostly minor fixes
> (we have only a couple so far including Alberto's) and clarifications
> to text that was found to be insufficiently precise during the
> implementation phase.  We have been saving some of these up for the
> next doc update.

If the work on small changes starts, I would like to add more 
clarification to the concept of Flux calibration (e.g. the keyword 
NORMALIZED seems to bring some ambiguity (e.g. with respect to spectral 
synthesis models).

And maybe the required concepts of spectra cutout, rebining and 
normalization could be introduced here without changing the DM and 
protocol - just by some explanatory add-ons.

It would be good to start the discussion about the concept of the data 
collection as one service versus a buch a separate services (e.g. in ESO 
case - is it better to put all spectra from different spectrographs on one 
server with one URL ? or use several service URLs?

It is very difficult then to separate them as there is not even optional) 
query parameter to instrument or instrument mode and I think the 
collection is not what it could solve the problem .... Simply this 
requires little discussion and some practical rules ...

And what is an absolute must is a case of photometric series - e.g. the 
COROT archive in SSA is an example of service that is urgently needed for 
science work (and so cannot wait for proper definition in protocol, 
although is using the concept of Data model).

But the SSA clients are not properly understandig what to do with the 
data.

As was said the science should be the main driver of IVOA and so we should 
reflect this need ASAP.

Simply this minor revison (if it will be released) could correct many 
misunderstandings by more explanatory material (and correct errors) but 
will not introduce any new concepts - just may describe what is meant (and 
hint how to implement) the vaguely said concepts (e.g. Virtual data in 
sec.2 ) and extend the part of GetData (the section 5 is too sparse)  and 
AcRef.


And one practical issue for Take-up of IVOA - it is crucial to show the 
example how to prepare the VO-compliant SSA for spectra from GROUND-BASED 
telescopes - as there is a huge potential of spectra archives of smaller 
or medium-sized telescopes willing to publish their data but the people 
are still confused by the SSA a SDM (practical experience with several of 
them). The space data are usually handled by large groups who understand 
the IVOA docs.

And proper example of photometric series served by SSA (like COROT) would 
immediately force many smaller observatories and mainly advanced amateurs 
(who are eager for new technologies) to publish in VO (I know about many 
of them)



And just a science case confirming the need of postprocessing:

It is clearly seen that the spectrum cutout has to be supported on a 
reasonable high dispersion spectra

For  example - the  UVES or HARPS spectra inside the ESO network takes 
tens of sec to download - I can imagine how to get hundereds of them (e.g. for 
asteroseismology studies)

But you are still not able to display them on the screen - so usually must 
be zoomed - and the client may do it for a longer time than to download it 
repeatedly from server who will send only short pieces (not talking about 
memory limitations).

Simply I think that if we want the astronomers to use VO tools we have to 
solve the issues of fast response and large data volumes by clever design 
of particular service thinking about the practical impact on a user 
feeling. And my experience form practical usage of SSA services even on a 
high speed network is awfull  - you can show 10-20 spectra overploted 
after some time but not hundreds or thousands as would be expected from 
"petabyte science surveys"

So I strongly support the idea of minor SSA revison instead of waiting for 
SSA2 introducing fancy concepts of features required by few services (e.g. 
3D spactroscopy, IFU and so on ). I am sure that by proper hints and 
examples most of the useful things may be done already now - but is has to 
be said explicitly how.

Petr Skoda

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*  Petr Skoda                         Phone : +420-323-649201, ext. 361 *
*  Stellar Department                         +420-323-620361           *
*  Astronomical Institute AS CR       Fax   : +420-323-620250           *
*  251 65 Ondrejov                    e-mail: skoda at sunstel.asu.cas.cz  *
*  Czech Republic                                                       *
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