Towards Real-Time Impulsive RFI Mitigation for Radio Telescopes

Buch, Kaushal D.; Bhatporia, Shruti; Gupta, Yashwant; Nalawade, Swapnil; Chowdhury, Aditya; Naik, Kishor; Aggarwal, K. K.; Ajithkumar, B.

doi:10.1142/s225117171641018x

Cited by 11 publications

(7 citation statements)

References 11 publications

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“…We note that RFI has been a steadily worsening problem at the GMRT over the last decade and that online RFI mitigation techniques (e.g. Buch et al 2016) will be critical to deal with this issue. Since the observatory already owns most of the required land for the short-baseline expansion (for baselines 1.7 km; see Section 4.2), land acquisition is unlikely to be a serious problem here.…”

Section: Short Baselines: Surface Brightness Sensitivitymentioning

confidence: 99%

The expanded Giant Metrewave Radio Telescope

Patra

Kanekar

Chengalur

et al. 2018

Monthly Notices of the Royal Astronomical Society

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With 30 antennas and a maximum baseline length of 25 km, the Giant Metrewave Radio Telescope (GMRT) is the premier low-frequency radio interferometer today. We have carried out a study of possible expansions of the GMRT, via adding new antennas and installing focal plane arrays (FPAs), to improve its point-source sensitivity, surface brightness sensitivity, angular resolution, field of view, and U-V coverage. We have carried out array configuration studies, aimed at minimizing the number of new GMRT antennas required to obtain a well-behaved synthesized beam over a wide range of angular resolutions for full-synthesis observations. This was done via two approaches, tomographic projection and random sampling, to identify the optimal locations for the new GMRT antennas. We report results for the optimal locations of the antennas of an expanded array (the "EGMRT"), consisting of the existing 30 GMRT antennas, 30 new antennas at short distances, 2.5 km from the GMRT array centre, and 26 additional antennas at relatively long distances, ≈ 5 − 25 km from the array centre. The collecting area and the field of view of the proposed EGMRT array would be larger by factors of, respectively, ≈ 3 and ≈ 30, than those of the GMRT. Indeed, the EGMRT continuum sensitivity and survey speed with 550 − 850 MHz FPAs installed on the 45 antennas within a distance of ≈ 2.5 km of the array centre would be far better than those of any existing interferometer, and comparable to the sensitivity and survey speed of Phase-1 of the Square Kilometre Array.

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Section: Short Baselines: Surface Brightness Sensitivitymentioning

confidence: 99%

The expanded Giant Metrewave Radio Telescope

Patra

Kanekar

Chengalur

et al. 2018

Monthly Notices of the Royal Astronomical Society

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“…Quantitative improvement in the signal-to-noise ratio (SNR) was carried out using the metric shown in [4]. The improvement (dB) is given as 10 log 10 (S U /S F ) where S U and S F are the average mean-to-RMS ratios of the unfiltered and filtered signals respectively.…”

Section: A Test Schemesmentioning

confidence: 99%

“…RFI excision techniques use a robust statistical estimator to estimate the dispersion of the signal and the filtering thresholds [3], [4]. The signal values outside the threshold are blanked (replaced by zeros) or held at the threshold.…”

Section: Introductionmentioning

confidence: 99%

“…The system is released as part of the GWB and is currently undergoing system-level testing for understanding the effects of broadband RFI filtering. RFI excision techniques use a robust statistical estimator to estimate the dispersion of the signal and the filtering thresholds [3], [4]. The signal values outside the threshold are blanked (replaced by zeros) or held at the threshold.…”

Section: Introductionmentioning

confidence: 99%

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Implementing and Characterizing Real-Time Broadband RFI Excision System for the GMRT Wideband Backend

Buch

Naik

Nalawade

et al. 2018

IETE Technical Review

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The Giant Metrewave Radio Telescope (GMRT) is being upgraded to increase the receiver sensitivity. This makes the receiver more susceptible to man-made Radio Frequency Interference (RFI). To improve the receiver performance in presence of RFI, real-time RFI excision (filtering) is incorporated in the GMRT wideband backend (GWB). The RFI filtering system is implemented on FPGA and CPU-GPU platforms to detect and remove broadband and narrowband RFI. The RFI is detected using a threshold-based technique where the threshold is computed using Median Absolute Deviation (MAD) estimator. The filtering is carried out by replacing the RFI samples by either noise samples or constant value or threshold. This paper describes the status of the real-time broadband RFI excision system in the wideband receiver chain of the upgraded GMRT (uGMRT). The test methodology for carrying out various tests to demonstrate the performance of broadband RFI excision at the system level and on radio astronomical imaging experiments are also described.

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“…The RFI mitigation methods are broadly divided in two categories: pre-detection and post-detection strategies. The predetection techniques often use reference signals or relatively simple statistical criteria to identify and mitigate RFI signals in real time (e.g., Baan et al 2004;Buch et al 2016). These techniques are often more suitable for highly impulsive or narrowband RFI.…”

Section: Introductionmentioning

confidence: 99%

Fourier domain excision of periodic radio frequency interference

Maan

Leeuwen

Vohl

2021

A&A

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The discovery and study of pulsars and fast radio bursts (FRBs) in time-domain radio data is often hampered by radio frequency interference (RFI). Some of this terrestrial RFI is impulsive and bright, and relatively easy to identify and remove. Other anthropogenic signals, however, are weaker yet periodic, and their persistence can drown out astrophysical signals. Here we show that Fourierdomain excision of periodic RFI is an effective and powerful step in detecting weak cosmic signals. We find that applying the method significantly increases the signal-to-noise ratio of transient and periodic pulsar signals. In live studies we detected single pulses from pulsars and FRBs that would otherwise have remained buried in background noise. We show the method has no negative effects on pulsar pulse shape, and that it enhances timing campaigns. We demonstrate the method on real-life data from a number of large radio telescopes, and conclude that Fourier-domain RFI excision increases the effective sensitivity to astrophysical sources by a significant fraction, which can be even larger than an order of magnitude in the case of strong RFI. An accelerated implementation of the method runs on standard time-domain radio data formats and is publicly available.

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Towards Real-Time Impulsive RFI Mitigation for Radio Telescopes

Cited by 11 publications

References 11 publications

The expanded Giant Metrewave Radio Telescope

The expanded Giant Metrewave Radio Telescope

Implementing and Characterizing Real-Time Broadband RFI Excision System for the GMRT Wideband Backend

Fourier domain excision of periodic radio frequency interference

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