[mmaimcal] Implementation of ALMA correlator multi-resolution modes

[Bryan Butler]

we have already had a number of proposals for EVLA that use what i think 
you're referring to as "multi-resolution" modes.

any time you want to resolve a very narrow line (masers, the ammonia 
hyperfine transitions, etc.), that has continuum associated with it is 
going to want this kind of mode (some narrow-band subbands and some 
wide-band ones).

so i think you definitely want the capability of specifying different 
bandwidths and resolutions between subbands.

i don't think you would ever need the flexibility of specifying 
different numbers of polarization products within the subbands, or at 
least i can't think of a use case for that.

i also don't think you need different sampling characteristics between 
subbands (nyquist or number of bits).

	-bryan


Al Wootten wrote, On 5/4/10 08:30:
> Rich Lacasse asked me:
> 
> "ALMA Memo 556, by Escoffier et al.,
> 
> http://edm.alma.cl/forums/alma/dispatch.cgi/almamemos/showFile/100591/d20080819212956/No/ALMA%20Memo%20556.pdf
> 
> describes observational modes supported by the ALMA 64-Antenna 
> Correlator.  One class of modes is called "multi-resolution" modes.
> 
> It has recently been found that this class of modes is only partially 
> implemented.  It is also not clear which aspects of this class of modes 
> are scientifically valuable (i.e., would actually be used).  Before 
> changing the interface with the Computing IPT and before changing 
> correlator firmware, we thought it would be valuable to have a short 
> discussion with you to get some perspective on exactly what should be 
> implemented. I, for one, have too often been the designer (victim?) of 
> elaborate hardware and software features that have never been used."
> 
> We're having a discussion about this at NTC on Thursday morning, which 
> I'll attend.  I'd be very interested in your views and on specific 
> examples of multi-resolution modes for which you would be a proponent.
> 
> At ALMA we have already attempted the mode in which we have a low 
> resolution 2GHz window in  which to identify features (unwanted spectral 
> features in this case) but then to further characterize them had a high 
> resolution window superposed.  We discovered that the software did not 
> support this mode after some amount of effort was expended on it.
> 
> A clear science case is in planetary atmospheres, where 
> pressure-broadened wings skirt a narrow line core; inversion of the 
> whole profile provides a good probe of atmospheric physics.
> 
> Clear skies,
> Al
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