[Passband] a useful self contained model?

[Anita Richards]

I take Jonathan's points, the main one being that in the data itself
almost evey parameter can be complicated and we can't assume that linear
relationships will do in every case.  However to make things managable we
will initially provide the simpler means of conversion e.g. energy units,
or point to a data-provider or user-supplied algorithm, if we can
incorporate that concept it might bring the model back to Martin's initial
motivation which was for something quick and simple... or perhaps just
good old 'other'.

1)
> > A spectral region ... can be divided into channels
>
> I don't want to mandate the 'regular spacing', the whole game
> with optical spectra is that you need to at least polynomial-fit the
> channels.
......

2)
> This corresponds to considering a spectrum with N channels as N independent
> photometry filter measurements.
..
> So to rephrase the question Martin then asked - 'would this work
> if each channel was a separate Passband?', we can ask
> 'should the Passband object include the concept of Resolution as
> well as Sensitivity/Passrate, or should a contiguous, multichannel
> spectrum be modelled by a compound Passband?'. Either will work
> in an abstract sense, but using the Resolution concept will, I believe, map
> better to current practical implementations of astronomical data; if
> we do the compound passband approach, it will be harder to keep the
> normalizations straight and it will be messy to even define Resolution.

I wasn't trying to say that channels have to be regular, only that if they
are, it is unneccessarily complicated to model each one separately. The
Allen telescope array, for example, will produce 4x10^9 1-Hz channels. By
regular I mean that there is some available and usable function which
describes the spectral resolution, I should ahve made it clear that
Gaussians were just an example.  This is case 1) above and as Jonathan
says we can model this by Resolution.  When it gets too complicated we can
revert to case 2) and make each channel a separate passband.   It should
be obvious which regime we are in and it is only a pragmatic, not a
fundamental distinction if some cases end up as e.g. multiple passbands
when resolution might suffice (as long as there aren't 10^9).

Would this work?



- - - - - - - - - - - - - - - - - - - - - - - - - - - - - - - -
Dr. Anita M. S. Richards, AVO Astronomer
MERLIN/VLBI National Facility, University of Manchester,
Jodrell Bank Observatory, Macclesfield, Cheshire SK11 9DL, U.K.
tel +44 (0)1477 572683 (direct); 571321 (switchboard); 571618 (fax).