CHIME runs 2048 feeds into an FX correlator with 1/2 GHz bandwidth.
We form beams in real time and interrogate them at better than ms
cadence for transients (frb).
The system is a bit big to picture hiding it in an airport.
mark
On 2020-07-20 07:12, Neil Salmon wrote:
Hi Danny,
Yes I can appreciate the difference here with respect to integration
times. Furthermore, as our arrays tend to be more fully filled, some
form of FT beam-former might be more efficient than a correlator.
However, things do get more complicated in the near-field security
screening scenarios where the FT relationship between physical space and
spatial frequency space breaks down.
Cheers,
Neil
*From:*Danny Price <[email protected]>
*Sent:* 20 July 2020 14:44
*To:* Neil Salmon <[email protected]>; [email protected]
*Subject:* RE: [casper] references to recent cross-correlator technology
developments
Hi Neil,
The correlation is indeed done in real time using stream processing
frameworks for most interferometer telescopes. Conversion from (very
sparse) visibilities to images is generally done offline (this can be
very time consuming!).
There are a few real-time imaging systems: the EPIC correlator that Jack
mentioned, and the realfast system on the VLA
(https://science.nrao.edu/facilities/vla/observing/realfast) are good
examples.
Cheers,
Danny
On 20 July 2020 at 9:55:06 pm, Neil Salmon ([email protected]
<mailto:[email protected]>) wrote:
Hi Danny,
Thank you for these references.
For security screening systems the name of the game is real-time, ie
an image in less than 1 second. However, I see a great many
references to GPU based correlators. I was used to seeing these
devices as off-line correlators, as in software correlators. Are the
GPUs being used by the radio astronomy community as real-time
correlators, or as software correlators?
Many thanks,
Neil
*From:*Danny Price <[email protected] <mailto:[email protected]>>
*Sent:* 20 July 2020 12:21
*To:* [email protected] <mailto:[email protected]>
*Subject:* Re: [casper] references to recent cross-correlator
technology developments
Hi Neil,
To add to Jack's post, allow me to plug some overview articles that
may be of interest. The first, https://arxiv.org/abs/1702.00442, was
for an introduction for a special issue of JAI on DSP in radio
astronomy in 2016. Table 1 summarises some of the larger
correlators: the references therein may be of use. Jack (et al)'s
CASPER article in said JAI special issue is also a font of
references: https://arxiv.org/abs/1611.01826. The full special issue
article listing is up here:
https://www.worldscientific.com/toc/jai/05/04.
More recently, here's my book chapter on real-time stream processing
in radio astronomy, https://arxiv.org/abs/1912.09041, which delves a
bit deeper into technical details for common approaches.
In terms of cutting edge, there are various groups working with the
Xilinx RFSoC components for next-gen systems -- you will no doubt
have seen some traffic on this list. The ASKAP telescope group have
plans to use an Alveo Xilinx U280 accelerator card for high time
resolution imaging + dedispersion, which is an alternative to the
GPU correlator.
GPU correlators are still the most widespread for O(100) antennas.
There's some discussion on GPU correlator performance in J. Kocz et
al 2014 (https://arxiv.org/abs/1401.8288); for O(100) inputs a GPU
correlator will likely be memory bandwidth bound.
Cheers,
Danny
On 18 July 2020 at 7:54:49 pm, Neil Salmon ([email protected]
<mailto:[email protected]>) wrote:
I need references on recent developments in cross-correlator
technology for an IEEE paper on the subject of aperture
synthesis imaging in the area of security screening of people
for concealed weapons. Typical requirements for this application
are cross-correlators that can process in real-time signals from
hundreds of receiver channels with around 1 GHz of RF bandwidth.
As none of this technology is commercially available
off-the-shelf I’m dependent on the radio astronomy community to
get the latest information of correlator development. This might
be just technical knowhow on the building of correlators, or
communities who would be willing to supply for a fee correlators
to a security screening technology development company.
Could anyone provide me with any references of papers on recent
correlator development that I could include in this paper?
Many thanks,
Neil
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