[Pafgbt] save PAF cross-correlations rather than formed beam outputs

[Brian Jeffs]

Rick,

I agree that you have much more flexibility to try different beamformer designs, detection algorithms, interference mitigation techniques, superresolution, calibration correction, etc. if you store and operate on the accumulated cross products (correlation matrices).  However, you give up the ability to do fine resolution spectral processing.  You are stuck with the coarseness of the correlator's frequency channelization.  I don't know how problematic this is for some applications, such as pulsar searches, where fine spectral resolution may be needed.

Brian

On May 20, 2013, at 6:38 AM, Anish Roshi wrote:


Yes indeed. We can form images with beams with different optimization if the correlations are recorded.
Anish


On Sun, May 19, 2013 at 9:57 AM, Rick Fisher <rfisher at nrao.edu<mailto:rfisher at nrao.edu>> wrote:
Brian, Karl,

In trying to understand the ASKAP data processing architecture, I'm
beginning to understand the fundamental importance of saving the
cross-products between array element outputs in our own PAF data
processing.  In forming beams you throw away a lot of information in the
array's field of view that can be recovered only by forming many beams
with very close spacing (much closer than HPBW/2).  This has important
consequences for the sensitivity to point sources, as in the search for
pulsars.  Hence, I would suggest that the most important archived outputs
from your signal processor are the cross-products rather than formed
beams.  For a given data storage volume, there's more information in the
cross-products than in the formed beam outputs.  In some respects, the
"beam" concept is a holdover from a waveguide feed where there's only one
output, and most of the information in the focal plane is reflected back
into the sky.

Rick
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