Fwd: [nvo-techwg] Time series data

[Rob Seaman]

FWIW:

Begin forwarded message:

> From: Doug Tody <dtody at nrao.edu>
> Date: June 7, 2007 10:49:32 AM MST
> To: NVO Technical Working Group <techwg at us-vo.org>
> Subject: [nvo-techwg] Time series data
>
> Hi All -
>
> The issue of time series data came up briefly in the NVO telecon  
> today.
> Since all the attention has been focused on spectra little has been
> done about this yet, although the Spectrum/SED data model upon which
> SSA is based was always intended to be general enough to support time
> series data as well.  Both are spectrophotometric sequences, with
> the spectral coordinate varying in one case, and time in the other.
>
> It was mentioned that VizieR is a major resource for light curves
> so I had a look to get a better feel for current practice.  What we
> have now for SSA could probably already be used for light curves such
> as we see in VizieR, but there are two areas where it could stand
> improvement for this data.  The support for photometric systems could
> be better - but we need this for spectra and images as well.  This was
> a major topic of dicussion at the recent Spectroscopy in VO workshop
> in Madrid for example.  The second thing is that it would be good to
> be able to have multiple flux values (photometric systems or filters)
> associated with each time value, as time series data often measures
> the object in multiple standard filters/bandpasses/photometric systems
> for each time sample.  A final issue is segmentation, as large time
> series taken over a long period of time are often segmented, with
> big time caps between the segments.
>
> All of these issues came up in connection with SSA and spectra as
> well, but they were second order features (for spectra) and lower
> priority for the first version of SSA, hence were deferred.  But with
> the completion of SSA and the Spectrum data model, Characterization,
> etc., we are probably 90% of the way there already.
>
> In terms of the data interface, it appears that a SSA service could be
> trivially modified to support time series data.   The query interface
> would probably work as-is.  For simple light curves, CSV/TSV output
> would probably be popular, and is essentially what existing services
> such as VizieR return now.  HTML or JPEG for a direct graphical view
> is also popular, and VOTable would be ideal for serious analysis;
> again this is much the same as for simple 1-D spectra.
>
> 	- Doug

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