Large Radio Astronomy Research Articles

Bits Missing: Finding Exotic Pulsars Using bfloat16 on NVIDIA GPUs

The Fourier domain acceleration search (FDAS) is an effective technique for detecting faint binary pulsars in large radio astronomy data sets. This paper quantifies the sensitivity impact of reducing numerical precision in the graphics processing unit (GPU)-accelerated FDAS pipeline of the AstroAccelerate (AA) software package. The prior implementation used IEEE-754 single-precision in the entire binary pulsar detection pipeline, spending a large fraction of the runtime computing GPU-accelerated fast Fourier transforms. AA has been modified to use bfloat16 (and IEEE-754 double-precision to provide a “gold standard” comparison) within the Fourier domain convolution section of the FDAS routine. Approximately 20,000 synthetic pulsar filterbank files representing binary pulsars were generated using SIGPROC with a range of physical parameters. They have been processed using bfloat16, single-precision, and double-precision convolutions. All bfloat16 peaks are within 3% of the predicted signal-to-noise ratio of their corresponding single-precision peaks. Of 14,971 “bright” single-precision fundamental peaks above a power of 44.982 (our experimentally measured highest noise value), 14,602 (97.53%) have a peak in the same acceleration and frequency bin in the bfloat16 output plane, while in the remaining 369 the nearest peak is located in the adjacent acceleration bin. There is no bin drift measured between the single- and double-precision results. The bfloat16 version of FDAS achieves a speedup of approximately 1.6× compared to single-precision. A comparison between AA and the PRESTO software package is presented using observations collected with the GMRT of PSR J1544+4937, a 2.16 ms black widow pulsar in a 2.8 hr compact orbit.

A Digital Beamformer for the PHAROS2 Phased Array Feed

PHased Arrays for Reflector Observing Systems (PHAROS) is a C-band (4–8[Formula: see text]GHz) Phased Array Feed (PAF) receiver designed to operate from the primary focus of a large single-dish radio astronomy antenna. It consists of an array of 220-element Vivaldi antennas ([Formula: see text] polarization), cryogenically cooled at roughly 20[Formula: see text]K along with low noise amplifiers (LNAs), and of analogue beamformers cryogenically cooled at roughly 80[Formula: see text]K. PHAROS2, the upgrade of PHAROS, is a PAF demonstrator developed in the framework of the Square Kilometer Array Advanced Instrumentation Program (SKA AIP) with the goal of investigating the potential of the PAF technologies at high frequencies in view of their possible application on the SKA dish telescopes. The PHAROS2 design includes new cryogenically cooled LNAs with state-of-the-art performance, a digital beamformer capable of synthesizing four beams from a sub-array of 24 single-polarization antenna elements, and a C-band multi-channel Warm Section receiver capable of analogue filtering and down-converting the signals from the antennas to a suitable frequency range at the input of the digital backend, providing an instantaneous bandwidth of 275[Formula: see text]MHz for each signal. In this paper, we describe the design and performance of the PHAROS2 digital backend/beamformer, based on the Italian Tile Processing Module (ITPM) hardware, which was initially developed for the SKA Low Frequency Aperture Array (LFAA). The backend was adapted to perform the beamforming for our PAF application. We describe the implementation of the beamformer on the Field Programmable Gate Arrays (FPGAs) of the ITPM and how the backend was successfully used to synthesize four independent beams, both in the laboratory (across the entire 275[Formula: see text]MHz instantaneous bandwidth) and during on-field observations at the BEST-2 array (across 16[Formula: see text]MHz instantaneous bandwidth), which is a subset of the Northern Cross Radio Telescope (located in the district of Bologna, Italy). The beamformer design allows re-scaling to a greater number of beams and wider bandwidths.

In brief

PAGE 18 Researchers in Korea have proposed a method to significantly reduce the computation complexity of a phase rotation beamforming technique commonly used in medical ultrasound scanners. They demonstrate that it can be implemented on smartphone hardware and that the technique doesn't sacrifice image quality, either analytically or experimentally. PAGE 29 Optical cloaking of arbitrary cross-section cylindrical structures using scattering cancellation is presented in work from Iran. The approach uses nano-strips of silver in a dielectric host as a cloaking shell around the object and the work explores the effect of the nano-strip parameters on the cloaking efficiency. The computational complexity of the technique is improved sufficiently to run in realtime on a smartphone without compromising quality PAGE 51 A compact Ka-band full bandwidth 3-dB waveguide hybrid has been designed by researchers in China. With high directivity over the full bandwidth of the WR-28 standard waveguide. The hybrid can also be used as a two-way power divider and can be made with excellent repeatability at low-cost. Optical cloaking of cylindrical objects of arbitrary cross-section PAGE 12 Researchers in China present a surface diagnosis approach for large reflector radio astronomy antennas with active surface control systems. Based on microwave holographic techniques, it allows far field patterns to be measured in focus by actively adjusting the primary surface. The 3-dB waveguide hybrid can be fabricated at low-cost with excellent repeatability PAGE 36 A robust, portable stereoscopic system for rapid identification of hidden objects using only a small number of X-ray projections has been demonstrated in work from the US. The system uses a single fixed sensor and obtains different angles using a motion-controlled single X-ray source. With a known system geometry, a series of depth planes can be computed to allow rapid object identification and realtime operation. The approach applies techniques from microwave holography to large reflector radio astronomy antennas The single source, single sensor, portable X-ray system allows rapid identification of hidden objects

Scalable desktop visualisation of very large radio astronomy data cubes

Observation data from radio telescopes is typically stored in three (or higher) dimensional data cubes, the resolution, coverage and size of which continues to grow as ever larger radio telescopes come online. The Square Kilometre Array, tabled to be the largest radio telescope in the world, will generate multi-terabyte data cubes – several orders of magnitude larger than the current norm. Despite this imminent data deluge, scalable approaches to file access in Astronomical visualisation software are rare: most current software packages cannot read astronomical data cubes that do not fit into computer system memory, or else provide access only at a serious performance cost. In addition, there is little support for interactive exploration of 3D data.We describe a scalable, hierarchical approach to 3D visualisation of very large spectral data cubes to enable rapid visualisation of large data files on standard desktop hardware. Our hierarchical approach, embodied in the AstroVis prototype, aims to provide a means of viewing large datasets that do not fit into system memory. The focus is on rapid initial response: our system initially rapidly presents a reduced, coarse-grained 3D view of the data cube selected, which is gradually refined. The user may select sub-regions of the cube to be explored in more detail, or extracted for use in applications that do not support large files. We thus shift the focus from data analysis informed by narrow slices of detailed information, to analysis informed by overview information, with details on demand. Our hierarchical solution to the rendering of large data cubes reduces the overall time to complete file reading, provides user feedback during file processing and is memory efficient. This solution does not require high performance computing hardware and can be implemented on any platform supporting the OpenGL rendering library.

The self-cohering tied-array

Large radio astronomy multi-element interferometers are frequently used as single dishes in a tied-array mode when signals from separate antennas are added. Phase shifts arising during wave propagation through a turbulent atmosphere can significantly reduce the effective area of an equivalent single dish. I aim to give estimates of the impact of the ionosphere and troposphere on the effectiveness of a radio interferometer working in tied-array mode. Statistical estimates of the effective area are calculated and the power-law of turbulent atmosphere irregularities has been used. A simple method of tied-array calibration using optimization techniques is proposed. The impact of phase errors on the effectiveness of tied-arrays are given for low and high frequencies. Computer simulations demonstrate the efficacy of the proposed calibration algorithm.

Report indicates critical need for large radio astronomy facilities

The National Science Foundation has emphasized the critical need for new, large radio astronomy facilities to maintain the impetus of the U.S. effort in radio astronomy. This report was submitted to the Foundation by the ad hoc Advisory Panel for Large Radio Astronomy Facilities (the Dicke Panel). In the two years that have passed since the first meeting of the panel, new discoveries such as pulsars and the existence of then unsuspected interstellar molecules have been made in radio astronomy. The continued design studies for new facilities previously recommended by the panel have been substantially advanced, and the panel strongly urges that the Arecibo telescope be resurfaced to be useful at shorter wavelengths, and that the Owens Valley Array be constructed.