DiFX

DiFX
Name	DiFX
Developer	Australian Long Baseline Array; Swinburne University of Technology; International VLBI Service
Released	2000s
Latest release	ongoing
Programming language	C++ and Fortran
Operating system	Linux
License	Open-source (GPL)

DiFX DiFX is a software correlator used in very long baseline interferometry (VLBI) for radio astronomy and geodesy. It performs cross-correlation of radio telescope data streams to produce interferometric visibilities for instruments such as the Very Long Baseline Array, the European VLBI Network, and the Australian Square Kilometre Array Pathfinder. DiFX has been employed in campaigns associated with the Event Horizon Telescope, the International VLBI Service for Geodesy and Astrometry, and projects linked to the Square Kilometre Array Organisation.

Overview

DiFX is an FX-style correlator designed to replace hardware correlators for arrays including the Australia Telescope Compact Array, the Atacama Large Millimeter/submillimeter Array, and the Green Bank Telescope. It supports multiple data formats used by systems such as the Mark5A, Mark5B, and VDIF recorders, interfacing with observatories like the Very Large Array, the Effelsberg 100-m Radio Telescope, and the Westerbork Synthesis Radio Telescope. DiFX integrates with software packages such as AIPS, CASA, and HOPS for post-correlation calibration and imaging in studies like pulsar timing at the Parkes Observatory and black hole imaging at the Event Horizon Telescope.

History and Development

Development of DiFX originated at the Swinburne University of Technology and the Australian Long Baseline Array to address limitations of hardware correlators used by arrays including the Very Long Baseline Array and the European VLBI Network. Early versions were tested in campaigns involving the Metsähovi Radio Observatory and the James Clerk Maxwell Telescope. Contributors have included researchers from the National Radio Astronomy Observatory, the CSIRO Astronomy and Space Science division, and the Max Planck Institute for Radio Astronomy. DiFX evolved through collaborations with projects such as the VLBA Sensitivity Upgrade and the Global Millimeter VLBI Array, enabling experiments pursued with the IRAM 30m Telescope and the Plateau de Bure Interferometer.

Architecture and Components

DiFX follows an FX correlator architecture used historically in systems like the Mark II and Mark III correlators. Core components include the "Datastream" module compatible with Mark5 recorders and the "F engines" that perform Fourier transforms similar to designs used at the Jodrell Bank Observatory and the Cambridge Radio Telescope. The "X engines" compute cross-multiplications and integrate visibilities akin to operations in the Haystack Observatory correlator. DiFX is implemented in C++ and Fortran, runs on Linux clusters such as those at Curtin University and the University of Manchester, and leverages libraries like FFTW and MPI implementations used at the National Center for Supercomputing Applications.

Applications and Use Cases

DiFX has been applied to high-resolution imaging projects led by teams from the Harvard-Smithsonian Center for Astrophysics, the Max Planck Institute for Radio Astronomy, and the Observatoire de Paris. Use cases include geodetic VLBI campaigns coordinated by the International VLBI Service, pulsar astrometry performed with the Parkes Observatory and the Lovell Telescope, and transient event follow-up involving the Australian Square Kilometre Array Pathfinder and the MeerKAT telescope. DiFX supports experiments for international consortia such as the Event Horizon Telescope consortium, the Global mm-VLBI Array, and surveys linked to the Sloan Digital Sky Survey teams.

Performance and Benchmarks

Benchmarks for DiFX have been reported in contexts including the VLBA sensitivity comparisons and the European VLBI Network throughput studies. Performance scales with cluster size used at centers like the Max Planck Computing and Data Facility and the Australian National Computational Infrastructure. DiFX performance metrics were validated against hardware correlators at facilities such as the Joint Institute for VLBI ERIC and the Haystack Observatory, demonstrating comparable fidelity for spectral line observations at telescopes including the Nobeyama Radio Observatory and the IRAM 30m Telescope.

Adoption and Collaborations

DiFX is widely adopted by organizations including the Australian Telescope National Facility, the National Radio Astronomy Observatory, and the Joint Institute for VLBI ERIC. Collaborative users include the Event Horizon Telescope collaboration, the European VLBI Network, and the International VLBI Service for Geodesy and Astrometry, with development contributions from institutions such as the Swinburne University of Technology, the Curtin University node of ICRAR, and the Max Planck Institute for Radio Astronomy. DiFX continues to be integrated into pipelines used by projects coordinated by the Square Kilometre Array Organisation and research groups at the University of California, Berkeley and the University of Oxford.

Category:Radio astronomy software Category:Interferometry