Hi Neil,
We have a GPU-based direct imaging correlator (EPIC - E-Field
Parallel Imaging Correlator) implemented and tested on one of the LWA
stations at Sevilleta. In EPIC we directly grid the fourier transformed
voltages from the individual antennas and form real-time dirty maps without
having to estimate the visibilities. EPIC can essentially produce images at
high time resolution on the order of a few ms. Currently we are optimizing
the GPU-part of EPIC to increase the operating bandwidth per node for a
commensal transient imaging backend at LWA-SV.
You can refer to the following publications for more details on EPIC
https://academic.oup.com/mnras/article-abstract/486/4/5052/5484888
https://academic.oup.com/mnras/article/467/1/715/2917985
Regards,
Hari
On Mon, Jul 20, 2020 at 7:12 AM Neil Salmon <[email protected]> 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]) 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]>
> *Sent:* 20 July 2020 12:21
> *To:* [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]) 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
>
> "Before acting on this email or opening any attachments you should read
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