Instrument related UCDs

[Alberto Micol]

Dear UCDers,

I'm pretty aware that this email comes far too late, and I apologise 
for that.
Still, for the next round, I think that some of the UCD descriptions 
should be improved
to avoid confusion. But please keep reading, and imagine a naive user 
which might
or might not have deep knowledge on how an instrument works; still s/he 
is given the
task to assign ucds to different quantities. Here we go:


E instr.background:

    Is it the signal induced by e.g. the electronics of the detector,
    or, another example, by the heat of the detector?
    Note: it is not to be confused with the readout noise 
(instr.det.noise).
    If the answer is yes, then...

Q instr.skyLevel:

    ...Is it different than instr.background?
    If it is a "sky" level, why does it belong to instr?
    Also, why is it not marked with the syntax code "E"?


Q instr.det.psf:

    Is this the FWHM of the PSF, or the PSF itself?
    Maybe a better description to clarify...

    And why is it associated to instr.det?
    Usually the PSF is the product of the convolution of various 
components
    starting from the seeing; is this just only the component induced by 
the instrument
    optics (including the telescope itself), or is it really meant to be 
the component
    coming from the fact that the detector is sampled into pixels?

    I would think that the ucd for PSF FWHM is: 
phys.size;phys.resolution;instr
    (but phys.resolution does not exist).

instr.precision:

    Is it the sampling precision, or e.g. the astrometric accuracy?


instr.det.qe, instr.sensitivity:

    At first sight one might think that those two ucds are equivalent!
    I would recommend to change the description of instr.sensitivity
    to actually explicit the fact that the sensitivity includes
    BOTH the detector QE AND the transmission of the optics (at least 
that is my guess!).


Q instr.tel:

    Is it suppose to be the name of the telescope?
    Or is it just only an adjective (in which case Q should be changed 
to S)?

Q instr.tel.focalLength exists; what about instr.tel.diameter?


Let me end this with TRANSMISSION:

   Regarding transmission I would like to see explicited in the text that
   phys.transm is actually the covolution of various things, eg.:

    phys.transm = instr.sensitivity  *  instr.filter.transm

    (where I assume that

            instr.sensitivity  = instr.det.qe * instr.optics.transm

     and notice that I invented the last one, which does not exist)

   I think we have to make very clear such distinctions, otherwise people
   will use e.g. instr.sensitivity, while they mean phys.transm, or 
viceversa!


Alberto