Spectral Data Model

SED/Spectrum

Holds metadata on per data point and per-observation basis for combining spectral observations

Implementations by Budavari, Busko

Related work by Osuna, Chiligarian

SAO implementation and Java library in work (McCusker)

Only minor changes in recent discussion

Updating to resolve conflicts with SSAP protocol document

Spectral Data Model - 2

Nomenclature

SED or Spectral or Spectrum or Spectrophotometric?

Model supports simple 1-D spectra

Also supports time series, aggregated SEDs

Doug suggests 'spectral' as a name that covers all cases even time series. Proposal to change “SED” data model name, utypes, etc. to “SDM” or “Spectral” or “spectrophotometric” ...?

Or, change references in Doug's doc to “SED”.

Spectral Data Model - 3

SSA protocol document

Query string and response votable use utypes which map to utypes in SED DM, so can harvest SSA data values from SED DM instance.

Minor changes to SED DM for compatibility –

SED.CreatorID changed to SED.DocURL

DataID.CreatorID added to complement DataID.DatasetID

Updated newly approved UCDs: instr.beam, em.wavenumber

Adding SED.DataModel for explicit version string.

Spectral Data Model - 4

Calibrated vs uncalibrated data

We identified at least 3 cases for spectra:

Raw counts, uncalibrated

Shape calibrated but not normalized

Fully calibrated

Other cases? e.g. Calibrated but bad at ends.. handle via error array values?

How do we encode this in the SSA query and in the DM data?

Spectral Data Model - 5

Doug suggested:

Accuracy.Calibration = “Asf”

Combines four specified axes in one string, hard to generalize

Modified suggestion:

Accuracy.Calibration.Time = “RELATIVE”

Values: CALIBRATED (default), RELATIVE, UNCALIBRATED ?

Generalizes to any other axis, can be used beyond SSA

Spectral Data Model - 6

I thought about using secondary UCDs

instr.uncal; instr.relcal

I don't like instr.* here, better suggestions?

We could use both approaches, but in the SSA context I think the Accuracy.Calibration.Time = ... is the way to go

Spectral Data Model - 7

One issue we haven't addressed: count spectra

In the X-ray domain, we don't flux our spectra

Just dividing counts by sensitivity is not a good way to go, although it may be adequate for SEDs

Characterization.Sensitivity.Spectral would allow us to store the sensitivity array, a better match to the way X-ray archives handle their data.

We should try and make this work following 1.0?

2005-05-10T09:47:56