An interference detection strategy for Apertif based on AOFlagger 3
arXiv:2301.01562 · doi:10.1051/0004-6361/202245022
Abstract
Context. Apertif is a multi-beam receiver system for the Westerbork Synthesis Radio Telescope that operates at 1.1-1.5 GHz, which overlaps with various radio services, resulting in contamination of astronomical signals with radio-frequency interference (RFI). Aims. We analyze approaches to mitigate Apertif interference and design an automated detection procedure for its imaging mode. Using this approach, we present long-term RFI detection results of over 300 Apertif observations. Methods. Our approach is based on the AOFlagger detection approach. We introduce several new features, including ways to deal with ranges of invalid data (e.g. caused by shadowing) in both the SumThreshold and scale-invariant rank operator steps; pre-calibration bandpass calibration; auto-correlation flagging; and HI flagging avoidance. These methods are implemented in a new framework that uses the Lua language for scripting, which is new in AOFlagger version 3. Results. Our approach removes RFI fully automatically, and is robust and effective enough for further calibration and (continuum) imaging of these data. Analysis of 304 observations show an average of 11.1% of lost data due to RFI with a large spread. We observe 14.6% RFI in auto-correlations. Computationally, AOFlagger achieves a throughput of 370 MB/s on a single computing node. Compared to published machine learning results, the method is one to two orders of magnitude faster.
arXiv comment15 pages, 10 figures. Accepted for publication in A&A
References in corpus (16)
- LOFAR: The LOw-Frequency ARray
- The Murchison Widefield Array: the Square Kilometre Array Precursor at low radio frequencies
- A morphological algorithm for improving radio-frequency interference detection
- The low-frequency environment of the Murchison Widefield Array: radio-frequency interference analysis and mitigation
- The LOFAR radio environment
- Absolving the SSINS of Precision Interferometric Radio Data: A New Technique for Mitigating Faint Radio Frequency Interference
- FLAGCAL:A flagging and calibration package for radio interferometric data
- Deep residual detection of radio frequency interference for FAST
- First release of Apertif imaging survey data
- Statistically Stable Estimates of Variance in Radioastronomical Observations as Tools for RFI Mitigation
- SERPent: Automated reduction and RFI-mitigation software for e-MERLIN
- Automated Editing of Radio Interferometer Data with Pieflag
- Spectral Kurtosis Based RFI Mitigation for CHIME
- Continuum source catalog for the first APERTIF data release
- Apercal -- The Apertif Calibration Pipeline
- Removal and replacement of interference in tied-array radio pulsar observations using the spectral kurtosis estimator