Abstract Details

Name: Kaushal Buch
Affiliation: Giant Metrewave Radio Telescope, NCRA-TIFR
Conference ID: ASI2021_463
Title : Online Broadband RFI Excision for the Upgraded GMRT: Techniques, Results, and Performance Aspects
Authors and Co-Authors : Kaushal D. Buch (GMRT, NCRA-TIFR, Pune, India), Ruta Kale (NCRA-TIFR, Pune, India), Mekhala V. Muley (GMRT, NCRA-TIFR, Pune, India), Sanjay Kudale (GMRT, NCRA-TIFR, Pune, India), and Ajithkumar B. (GMRT, NCRA-TIFR, Pune, India)
Abstract Type : Poster
Abstract Category : Instrumentation and Techniques
Abstract : The recently upgraded Giant Metrewave Radio Telescope (uGMRT) provides a near-seamless observing in the range of 130 - 1450 MHz with a maximum receiver bandwidth of 400 MHz. One of the impairments affecting the quality of astronomical data is the broadband Radio Frequency Interference (RFI) from high-power transmission lines and associated systems. We describe the implementation and testing of a robust filtering technique which operates on Nyquist-sampled digital time-series per antenna and polarization. This online RFI filtering technique uses robust estimation of signal dispersion using Median-of-MAD (MoM) for detecting longer bursts of interference. Using threshold-based detection, the RFI samples are replaced by digital noise with statistical properties similar to the parent distribution. After undergoing a rigorous system-level testing, the online excision feature is available for use during uGMRT observations. As part of the RFI excision system testing, relative improvements in signal-to-noise ratio (SNR), uncertainty in the cross-correlation function and closure phase relation were measured in the different uGMRT bands. Test observations on calibrator radio sources and extended sources showed improvement in the spatial cross-correlation spectrum (visibilities) at short baselines in the form of reduced standard deviation by a factor of two or more and qualitatively as improved image fidelity. For time-domain signals, pulsar observations in the incoherent array mode show SNR improvement by a factor of three over the unfiltered signal. We describe the tests specifically designed to address the finer aspects of excision and the results achieved. This paper shall deal with the above-mentioned aspects of the system in greater detail along with other ongoing efforts for improving it.