Imaging data from upcoming radio telescopes requires distributing processing at large scales. This paper presents a distributed Fourier transform algorithm for radio interferometry processing. It generates arbitrary grid chunks with full non-coplanarity corrections while minimising memory residency, data transfer and compute work.
We utilise window functions to isolate the influence between regions of grid and image space. This allows us to distribute image data between nodes and construct parts of grid space exactly when and where needed. The developed prototype easily handles image data terabytes in size, while generating visibilities at great throughput and accuracy. Scaling is demonstrated to be better than cubic in baseline length, reducing the risk involved in growing radio astronomy processing to the Square Kilometre Array and similar telescopes.
Get PDF Email Share Share with Facebook Tweet This Post on reddit Share with LinkedIn Add to CiteULike Add to Mendeley Add to BibSonomy Get Citation Copy Citation Text J. C. Kent, "Fabrication of Graded Filters for Knife-Edge Replacement in Laser Schlieren Optical Systems," Appl. Opt. 8, 2148_1-2149 (1969) Export Citation BibTex Endnote (RIS) HTML Plain Text Citation alert Save article
We analyze data from the Hydrogen Epoch of Reionization Array. This is the third in a series of papers on the closure phase delay-spectrum technique designed to detect the HI 21cm emission from cosmic reionization. We present the details of the data and models employed in the power spectral analysis, and discuss limitations to the process. We compare images and visibility spectra made with HERA data, to parallel quantities generated from sky models based on the GLEAM survey, incorporating the HERA telescope model. We find reasonable agreement between images made from HERA data, with those generated from the models, down to the confusion level. For the visibility spectra, there is broad agreement between model and data across the full band of $\sim 80$MHz. However, models with only GLEAM sources do not reproduce a roughly sinusoidal spectral structure at the tens of percent level seen in the observed visibility spectra on scales $\sim 10$ MHz on 29 m baselines. We find that this structure is likely due to diffuse Galactic emission, predominantly the Galactic plane, filling the far sidelobes of the antenna primary beam. We show that our current knowledge of the frequency dependence of the diffuse sky radio emission, and the primary beam at large zenith angles, is inadequate to provide an accurate reproduction of the diffuse structure in the models. We discuss implications due to this missing structure in the models, including calibration, and in the search for the HI 21cm signal, as well as possible mitigation techniques.
The future of radio astronomy will require instruments with large collecting areas for higher sensitivity, wide fields of view for faster survey speeds, and efficient computing and data rates relative to current capabilities. We describe the first successful deployment of the E-field Parallel Imaging Correlator (EPIC) on the LWA station in Sevilleta, New Mexico, USA (LWA-SV). EPIC is a solution to the computational problem of large interferometers. By gridding and spatially Fourier transforming channelized electric fields from the antennas in real time, EPIC removes the explicit cross-multiplication of all pairs of antenna voltages to synthesize an aperture, reducing the computational scaling from |$\mathcal {O}(n_\mathrm{ a}^2)$| to |$\mathcal {O}(n_\mathrm{ g} \log _2 n_\mathrm{ g})$|, where na is the number of antennas and ng is the number of grid points. Not only does this save computational costs for dense arrays but it produces very high time resolution images in real time. The GPU-based implementation uses existing LWA-SV hardware and the high performance streaming framework, Bifrost. We examine the practical details of the EPIC deployment and verify the imaging performance by detecting a meteor impact on the atmosphere using continuous all-sky imaging at 50 ms time resolution.
RF sensor methods for motion correction require no (or minimal) additional hardware, are sequence independent and have high temporal resolution. Several RF sensor-based methods for rigid-body head motion detection have been demonstrated but which method offers the most sensitivity to motion is yet unknown. We aim to compare the sensitivity of PT and pTxS methods by simultaneously measuring these signals during continuous motion, training a linear model from EPI registered images and analysing the ability to predict rigid head positions. Currently, we see little difference in their ability to predict rigid head motion but further investigation is needed.
Motivation: Fast and accurate B1+ mapping is critical for parallel transmission in ultra-high field MRI, but several options exist, and which is the most optimal is unknown. Goal(s): To evaluate three FLASH-based volumetric B1+ mapping methods; 2D SatTFL, 3D SA2RAGE and 3D Sandwich. Approach: We acquired fully sampled absolute B1+ maps at 7T in a realistic human head phantom across multiple transmission voltages to establish a ground truth and assess the dynamic range of each method. Results: SA2RAGE and Sandwich both enable low-power non-selective RF pulses and maintain accuracy for low B1+ regions. Sandwich has a 60% shorter acquisition time than SA2RAGE. Impact: This study will help to inform a choice of B1+ mapping sequences when imaging at ultrahigh field.
In this paper, we describe our efforts towards the development of a real-time radio imaging correlator for the Long-Wavelength Array station in Sevilleta, New Mexico. We briefly discuss the direct-imaging algorithm and present the architecture of the GPU implementation. We describe the code-level modifications carried out for one of the modules in the algorithm that improves GPU-memory management and highlight the performance improvements achieved through it. We emphasize our ongoing efforts in tuning the overall run-time duration of the correlator which in turn is expected to increase the operating bandwidth in order to address the demands of wide-band capability for radio transient science.
'%3e%3cpath fill='%23001489' d='M0 0v6h9V0z'/%3e%3cpath fill='%23e03c31' d='M0 0v3h9V0z'/%3e%3cg stroke='%23fff' stroke-width='2'%3e%3cpath id='d' d='m0 0 4.5 3L0 6m4.5-3H9'/%3e%3cuse xlink:href='%23b' stroke='%23ffb81c' clip-path='url(%23c)'/%3e%3c/g%3e%3cuse xlink:href='%23d' fill='none' stroke='%23007749' stroke-width='1.2'/%3e%3c/g%3e%3c/svg%3e)
'%3e%3cpath fill='%23012169' d='M0 0v30h60V0z'/%3e%3cpath stroke='%23fff' stroke-width='6' d='m0 0 60 30m0-30L0 30'/%3e%3cpath stroke='%23C8102E' stroke-width='4' d='m0 0 60 30m0-30L0 30' clip-path='url(%23b)'/%3e%3cpath stroke='%23fff' stroke-width='10' d='M30 0v30M0 15h60'/%3e%3cpath stroke='%23C8102E' stroke-width='6' d='M30 0v30M0 15h60'/%3e%3c/g%3e%3c/svg%3e)