Search

In this paper, a wideband Vivaldi phased array with double band-notched performance for radio astronomy is proposed. To address the issues of radio frequency interference from 5 G mobile communication (4.8–5 GHz) and C-band satellite communication (5.9–6.5 GHz) in radio astronomy system, the hairpin ring resonator (HRR), defected ground structure and λ/2 shorted-circuit stub are utilized together to realize the double notched bands with different bandwidth. The resonate mechanism of the proposed HRR is widely investigated, which exhibits independent and controllable resonances. Meanwhile, λ/2 shorted-circuited stub is adopted for the band notched performance. As the current on the stub is induced along the shorted via to the ground, without participating in radiation, thus the notched frequency is not affected by the scan angle. With these novel and dedicated design, the proposed phased array performs double band-notched performance with high skirt selectivity and deep suppression, within the notched band the maximum rejection level is better than 22.7 dB. This is the first work to implement double notched bands in phased array to the authors' best knowledge. Finally, a prototype composed of 8 × 9 elements is fabricated and measured. The measurements agree well with the simulated ones. [ABSTRACT FROM AUTHOR]

This paper introduces the first results of observations with the Ultra-Long-Wavelength (ULW) —- Low Frequency Interferometer and Spectrometer (LFIS) on board the selenocentric satellite Longjiang-2. We present a brief description of the satellite and focus on the LFIS payload. The in-orbit commissioning confirmed a reliable operational status of the instrumentation. We also present results of a transition observation, which offers unique measurements on several novel aspects. We estimate the RFI suppression required for such a radio astronomy instrumentation at the Moon-distances from Earth as order of − 80 dB. We analyse a method of separating Earth- and satellite-originated radio frequency interference (RFI). It is found that the RFI level at frequencies lower than a few MHz is smaller than the receiver noise floor. [ABSTRACT FROM AUTHOR]

After years of preparation, the Indonesia National Observatory, located in Mount Timau, Kupang Regency, is currently in the completion stage of research in astronomy and astrophysics and related subjects. An optic telescope with a 3.8 m diameter is expected to receive its first light in mid-2024. A feasibility study for Indonesia's radio telescopes and networks is in progress. A single-dish parabolic radio antenna with a diameter of 20 m is proposed to work in a frequency range of 1–50 GHz. An array dipole antenna with an area of 100 m × 100 m will also be installed at a 70–350 MHz frequency. A feasibility study about system design is in progress, and a radio frequency interference (RFI) survey has been underway since 2014. In this paper, we described the design of radio telescopes such as parabolic reflectors, horn antenna, and the radio frequency interference (RFI) in the surrounding area of the National Observatory, covering the frequency band from 45 MHz to 18 GHz. The frequencies in 45–85 MHz and 120–360 MHz intervals are still relatively quiet and suitable for developing radio telescopes. The selected higher frequency of 1.4 GHz for a neutral hydrogen (HI) spectral line, 6.6 GHz for a methanol (CH3OH) spectral line, and 8.6 GHz for a helium (3 He+) spectral line is still relatively quiet and suitable for the development of radio telescopes. [ABSTRACT FROM AUTHOR]

Low-frequency aperture arrays represent sensitive instruments to detect signals from radio astronomic sources situated in the universe. In Italy, the Sardinia Aperture Array Demonstrator (SAAD) consists of an ongoing project of the Italian National Institute for Astrophysics (INAF) aimed to install an aperture array constituted of 128 dual-polarized Vivaldi antennas at the Sardinia Radio Telescope (SRT) site. The originally envisaged 128 elements of SAAD were re-scoped to the 16 elements of its precursor named SADino, with the aim to quickly test the system with a digital beam-former based on the Italian Tile Processing Module (iTPM) digital back-end. A preliminary measurements campaign of radio frequency interference (RFI) was performed to survey the less contaminated spectral region. The results of these measurements permitted the establishment of the technical requirements for receiving a chain for the SADino telescope. In this paper, the design, implementation, and characterization of this signal acquisition chain are proposed. The operative frequency window of SAAD and its precursor, SADino, sweeps from 260 MHz to 420 MHz, which appears very attractive for radio astronomy applications and radar observation in space and surveillance awareness (SSA) activities. [ABSTRACT FROM AUTHOR]

Artificial intelligence is widely spreading in all modern technologies. Such a very powerful methodology can have important applications in radio astronomy technology, for instance, in the new DBBC4 VLBI backend development project and in the low frequency array AntArr under development on the Etna slopes in Italy. In the present paper, we describe the method currently adopted for those projects and some possible applications, which could provide substantial new features in this decade to the radio astronomy science and technology. [ABSTRACT FROM AUTHOR]

Radio astronomy uses radio telescopes to detect very faint emissions from celestial objects. However, human-made radio frequency interference (RFI) is currently a common problem faced by most terrestrial radio telescopes, and it is getting worse with the development of the economy and technology. Therefore, it is essential to monitor and evaluate interference during the planning, construction, and operation stages of the radio telescope and protect the quiet radio environment around the radio astronomical site. In this paper, we present a software for an RFI analysis of the radio environment around the telescope. In this software, information has been collected, including the location of the site; the technical specifications, such as aperture and the frequency range of the radio telescopes; and the terrain around the site. The software and its modules are composed of telescope, geographic, and meteorological databases, and analysis modules of terrestrial and space-based RFI. Combined with the propagation characteristics of radio waves, we can analyze and evaluate RFI on the ground and in space around the radio telescope. The feasibility of the software has been proved by the experimental implementation of the propagation properties and RFI source estimation. With this software, efficient technical support can be expected for protecting the radio environment around the telescope, as well as improving site selection for planned radio astronomical facilities. [ABSTRACT FROM AUTHOR]

In this paper we present details of the construction of a wideband, cryogenic receiver and its successful commissioning on the Arecibo Observatory 12 m telescope. The cryogenic receiver works in the 2.5–14 GHz frequency range. We upgraded the current narrow band, room temperature receivers of the telescope with the new wideband receiver. The current receiver is built around a Quadruple‐Ridged Flared Horn (QRFH) developed by Akgiray et al. (2013, https://doi.org/10.1109/tap.2012.2229953). To mitigate strong radio frequency interference (RFI) below 2.7 GHz, we installed a highpass filter before the first stage low noise amplifier (LNA). The QRFH, highpass filter, noise coupler and LNA are located inside a cryostat and are cooled to 15 K. The measured receiver temperature is 25 K (median value) over 2.5–14 GHz. The system temperature measured at zenith is about 40 K near 3.1 and 8.6 GHz and the zenith antenna gains are 0.025 and 0.018 K/Jy at the two frequencies respectively. We recommend the following improvements to the telescope system: (a) Upgrade the highpass filter to achieve better RFI rejection near 2.5 GHz; (b) Improve aperture efficiency at 8.6 GHz; (c) Upgrade the intermediate frequency system to increase the upper frequency of operation from 12 to 14 GHz. Key Points: Successful commissioning of a wideband, cryogenic receiver for the 12 m telescope at the Arecibo ObservatoryAchieved system temperature of 40 K and gains of 0.025 K/Jy and 0.018 K/Jy at frequencies 3.1 and 8.6 GHz respectively [ABSTRACT FROM AUTHOR]

The development of methods for the radio frequency interference mitigation becomes a fundamental challenge for any radio astronomy research. In this paper, we report on the development and creation of a new spectrometer designed for solar observations at the RATAN-600 radio telescope, capable of excising radio interference using a statistical algorithm based on the spectral kurtosis estimation. The implementation of the external analog interface and the operation of the digital signal processing system based on the FPGA are described. The maximum spectral resolution reached is 122 kHz in the frequency band of 1.0–3.0 GHz. The output spectrum has from 64 to 8192 frequency bins, depending on the requirements of the observer, the output rate is 120 spectra per second. The test results and the first observations of the Sun show that the research method can successfully detect and suppress interference from most of the local radio interference sources. [ABSTRACT FROM AUTHOR]

Large-scale non-geostationary orbit (NGSO) satellite communication systems (SCSs) are gaining interest from industries because of their ubiquitous wireless access and backhaul capabilities. However, the NGSO SCSs’ global downlink transmission can cause radio frequency interference (RFI) to the radio astronomy system (RAS) on earth. Thus, this paper first investigates RFI impacts of a large-scale NGSO SCS. Our RFI analyses show that a large-scale low earth orbit (LEO) SCS completely disrupts RAS’s continuum observation within or adjacent to the SCS downlink bands, which limits coexistence and growths of both SCS and RAS. To overcome such limitation, we propose a new paradigm where SCS and RAS are integrated into the NGSO satellite system, thus effectively creating large-scale telescopes in orbit. This integrated system not only avoids SCS’s RFI to RAS but also offers more spectrum access opportunities to both SCS and RAS. In addition, this paper addresses two related problems of the new paradigm, namely, the spectrum resource allocation problem and the RAS data transport problem. Our performance evaluation illustrates the advantages of the proposed paradigm in terms of accessible spectrum bands, RAS observation performance, and SCS maximum mean supportable data rate as well as enabling coexistence and growths of both types of services. [ABSTRACT FROM AUTHOR]

The search for astronomical pulsed signals within noisy data in the radio band is usually performed through an initial Fourier analysis to find "candidate" frequencies and then refined through the folding of the time series using trial frequencies close to the candidate. In order to establish the significance of the pulsed profiles found at these trial frequencies, pulsed profiles are evaluated with a χ2 test to establish how much they depart from a null hypothesis where the signal is consistent with a flat distribution of noisy measurements. In high-energy astronomy, the χ2 statistic has widely been replaced by the statistic and H-test, as they are more sensitive to extra information, such as the harmonic content of the pulsed profile. The statistic and H-test were originally developed for use with "event data" composed of arrival times of single photons, leaving it unclear how these methods could be used in radio astronomy. In this paper, we present a version of the statistic and H-test for pulse profiles with Gaussian uncertainties appropriate for radio or even optical pulse profiles. We show how these statistical indicators provide better sensitivity to low-significance pulsar candidates with respect to the usual χ2 method and a straightforward way to discriminate between pulse profile shapes. Moreover, they provide an additional tool for radio frequency interference rejection. [ABSTRACT FROM AUTHOR]

Based on the minimum noise subspace (MNS) method previously introduced in the context of blind channel identification, generalized minimum noise subspace (GMNS) is proposed in this paper for array processing that generalizes MNS with respect to the availability of only a fixed number of parallel computing units. Different batch and adaptive algorithms are then introduced for fast and parallel computation of signal (principal) and noise (minor) subspaces. The computational complexity of GMNS and its related estimation accuracy are investigated by simulated experiments and a real-life experiment in radio astronomy. It is shown that GMNS represents an excellent tradeoff between the computational gain and the subspace estimation accuracy, as compared to several standard subspace methods. [ABSTRACT FROM PUBLISHER]

The Pulsar Search Collaboratory (PSC) is a collaboration between the Green Bank Observatory and West Virginia University, funded by the National Science Foundation. The PSC program is currently expanding nationwide and engages high school students, teachers, and undergraduate mentors in real-world research by searching for pulsars in data collected with the 100-m Green Bank Telescope. In the process, students learn about observational radio astronomy, radio frequency interference, pulsar timing, and data analysis procedures. The primary goals of the PSC are to stimulate student interest in Science, Technology, Engineering, and Mathematics (STEM) careers, to prepare teachers in implementing authentic research with students by training them within a professional scientific community, and to promote student use of information technologies through online activities and workshops. In this paper, we provide an overview of pulsar science and the data analysis students undertake, as well as a general overview of the program. We then discuss evaluation data collected from participants through a series of survey questions to determine if the program's initial goals were met. The program had a positive impact on the students according to multiple measures, in particular, on their understanding of the nature of scientific inquiry and motivation to pursue STEM career paths. [ABSTRACT FROM AUTHOR]

The Ultralong‐Wavelength (ULW) regime of longer than 10 m (corresponding to frequencies below 30 MHz) remains as the last virtually unexplored window in radio astronomy and is presently attracting considerable attention as an area of potentially rewarding studies. However, the opaqueness of the Earth's ionosphere makes the ULW celestial radio emission very difficult to detect with ground‐based instrumentation. The impact of the ionosphere on ULW radio emission depends on the solar cycle activities and varies with time. In addition, the ULW spectrum region is densely populated by intensive artificial radio frequency interference. An obvious solution of these problems is to place an ULW radio telescope in space. However, this solution is expensive and poses nonnegligible technological challenges. An alternative approach is triggered by recent studies showing that the period of post 2020 will be most suitable for exploratory ground‐based ULW radio observations due to the expected "calm" state of the ionosphere; the ionospheric cutoff frequency could be well below 10 MHz, even in the day time. In anticipation of this upcoming opportunity, we propose and present in this paper a concept of an experimental ULW radio array, with the intention of setting it up in Inner Mongolia, China. This ULW facility will use the infrastructure of the currently operational Mingantu spectral radio heliograph. The proposed ULW array covers the frequency range from 1 to 72 MHz. This experimental array will be used for exploratory studies of celestial radio emission in the ULW range of the spectrum. Key Points: We propose an experimental Ultralong‐Wavelength (ULW) radio array operating in the frequency range of 1–72 MHzThe proposed ULW radio array is of low cost with easy implementability and will be useful post 2020 during the solar cycle minimum [ABSTRACT FROM AUTHOR]

Prospective authors are requested to submit new, unpublished manuscripts for inclusion in the upcoming event described in this call for papers. [ABSTRACT FROM AUTHOR]

At redshifts beyond z≳30 , the 21 cm line from neutral hydrogen is expected to be essentially the only viable probe of the three-dimensional matter distribution. The lunar far-side is an extremely appealing site for future radio arrays that target this signal, as it is protected from terrestrial radio frequency interference, and has no ionosphere to attenuate and absorb radio emission at low frequencies (tens of MHz and below). We forecast the sensitivity of low-frequency lunar radio arrays to the bispectrum of the 21 cm brightness temperature field, which can in turn be used to probe primordial non-Gaussianity generated by particular early universe models. We account for the loss of particular regions of Fourier space due to instrumental limitations and systematic effects, and predict the sensitivity of different representative array designs to local-type non-Gaussianity in the bispectrum, parametrized by fNL. Under the most optimistic assumption of sample variance-limited observations, we find that σ(fNL)≲0.01 could be achieved for several broad redshift bins at z≳30 if foregrounds can be removed effectively. These values degrade to between σ(fNL)∼0.03 and 0.7 for z=30 to z=170 , respectively, when a large foreground wedge region is excluded. This article is part of a discussion meeting issue 'Astronomy from the Moon: the next decades (part 2)'. [ABSTRACT FROM AUTHOR]

Radio astronomy organisations desire to optimise the terrestrial radio astronomy observations by mitigating against interference and enhancing angular resolution. Ground telescopes (GTs) experience interference from intersatellite links (ISLs). Astronomy source radio signals received by GTs are analysed at the high performance computing (HPC) infrastructure. Furthermore, observation limitation conditions prevent GTs from conducting radio astronomy observations all the time, thereby causing low HPC utilisation. This paper proposes mechanisms that protect GTs from ISL interference without permanent prevention of ISL data transmission and enhance angular resolution. The ISL transmits data by taking advantage of similarities in the sequence of observed astronomy sources to increase ISL connection duration. In addition, the paper proposes a mechanism that enhances angular resolution by using reconfigurable earth stations. Furthermore, the paper presents the opportunistic computing scheme (OCS) to enhance HPC utilisation. OCS enables the underutilised HPC to be used to train learning algorithms of a cognitive base station. The performances of the three mechanisms are evaluated. Simulations show that the proposed mechanisms protect GTs from ISL interference, enhance angular resolution, and improve HPC utilisation. [ABSTRACT FROM AUTHOR]

The Five-hundred-meter Aperture Spherical radio Telescope (FAST) has started the Commensal Radio Astronomy FasT Survey (CRAFTS). In this paper, we use the technical parameters of FAST derived from commissioning observations to simulate the completeness function for extragalactic H  i survey of CRAFTS, H  i galaxies from two kinds of mock catalogues are selected. One is generated by Monte Carlo simulation based on the interpolated mass–velocity width function of the ALFALFA |$100{{\ \rm per\ cent}}$| (a.k.a. α.100) catalogue. The other is constructed by semi-analytical N -body simulation based on the ΛCDM model. Our results suggest that a two-pass CRAFTS extragalactic H  i survey will be able to detect nearly 4.8 × 105 galaxies, from which the 'faint end' slope of the H  i mass function (HIMF) can be recovered to |$\mathrm{10^{7}\, M_{\odot }}$| and the 'knee mass' of the HIMF can be measured to a redshift of 0.1. Considering the radio frequency interference status and sensitivity limitation, CRAFTS will be efficient in detecting H  i galaxies at redshifts below 0.1, which implies a tremendous potential in exploring the galaxy interactions in different environments and the spatial distribution of H  i galaxies in the local universe. [ABSTRACT FROM AUTHOR]

The past two decades have witnessed a renewed interest in low frequency radio astronomy, with a particular focus on frequencies above 30 MHz e.g., LOFAR (LOw Frequency ARray) in the Netherlands and its European extension ILT, the International LOFAR Telescope. However, at frequencies below 30 MHz, Earth-based observations are limited due to a combination of severe ionospheric distortions, almost full reflection of radio waves below 10 MHz, solar eruptions and the radio frequency interference (RFI) of human-made signals. Moreover, there are interesting scientific processes which naturally occur at these low frequencies. A space or Lunar-based ultra-low-frequency (also referred to as ultra-long-wavelength, ULW) radio array would suffer significantly less from these limitations and hence would open up the last, virtually unexplored frequency domain in the electromagnetic spectrum. A roadmap has been initiated by astronomers and researchers in the Netherlands to explore the opportunity of building a swarm of satellites to observe at the frequency band below 30 MHz. This roadmap dubbed Orbiting Low Frequency Antennas for Radio Astronomy (OLFAR), a space-based ultra-low frequency radio telescope that will explore the Universe's so-called dark ages, map the interstellar medium, and study planetary and solar bursts in the solar system and search them in other planetary systems. Such a radio astronomy system will comprise of a swarm of hundreds to thousands of satellites, working together as a single aperture synthesis instrument deployed sufficiently far away from Earth to avoid terrestrial RFI. The OLFAR telescope is a novel and complex system, requiring yet to be proven engineering solutions. Therefore, a number of key technologies are still required to be developed and proven. The first step in this roadmap is the NCLE (Netherlands China Low Frequency Explorer) experiment, which was launched in May 2018 on the Chinese Chang'e 4 mission. The NCLE payload consists of a three monopole antenna system for low frequency observations, from which the first data stream is expected in the second half of 2019, which will provide important feedback for future science and technology opportunities. In this paper, the roadmap towards OLFAR, a brief overview of the science opportunities, and the technological and programmatic challenges of the mission are presented. [ABSTRACT FROM AUTHOR]

The electromagnetic spectrum is a valued shared resource. Its scientific use allows us to learn about our universe, measure and monitor our planet, and communicate scientific data. The use of the spectrum is managed by national, regional, and global regulatory frameworks. There are increasing demands for new or extended allocations because of vast technological advances in the past few years. Understanding spectrum management is important in the successful planning and execution of missions and instruments, as well as in determining the potential source of radio frequency interference in existing data and instruments, and in working to ameliorate its impact. This paper provides a summary of this framework for radio scientists and engineers. [ABSTRACT FROM AUTHOR]

Abstract In this paper, we present a deep learning-based recognition algorithm to identify pulsars by observing data containing millions of candidates including radio frequency interference and noise sources. The dataset is obtained from the High Time Resolution Universe survey created and updated by the Parkes telescope. We investigate several effective single and combined features via simple logistic regression. To deal with the imbalanced dataset, we oversimplify the original dataset at different sampling rates, which is also one of the learning parameters. After training the pre-processed dataset via a convolutional neural network, we provide a cross-validated evaluation of all candidates. Results show that the deep-learning based recognition algorithm can identify the pulsar and radio frequency interference signals with high accuracy. The precision and recall of radio frequency interference are both 100%, and those of pulsars are 91% and 94%, respectively. [ABSTRACT FROM AUTHOR]

We have demonstrated spectrum sharing and coexistence between a 5G network and a radio telescope without causing interference to the radio astronomer. This was realized by using optical heterodyning between two distributed feedback (DFB) semiconductor lasers as a flex-spectrum photonic RF transmitter. The 5G network was designed to identify and avoid any radio frequency interference (RFI). The generated 5G RF carrier signal is used as the primary RF data carrier for the 5G network. A second RF signal, acting as noise signal, is introduced to the 5G network using an electrical mixer. When the frequencies at the mixer ports are the same, an error signal is generated which triggers the control circuit of the 5G network to correct for the RFI by shifting the primary RF data carrier of the 5G network to a new RF carrier frequency. An impressive RFI correction time of about 3 milliseconds was recorded. [ABSTRACT FROM AUTHOR]

We report on the measurements of radio frequency interference (RFI) at Mount Timau, Kupang, Indonesia, which is intended to host a future radio astronomy observatory. These measurements were taken twice in October 2020 and December 2020 to obtain the RFI environment, at frequencies between 70 and 7000 MHz. Due to the limitations of the measurement data, the results presented in this paper are based on peak detection rather than statistical analysis. Based on the measurement results, the frequency interval between 70–88 MHz and 120–150 MHz is relatively quiet, and the frequency range of 150–300 MHz is relatively clear. The frequency interval of 300 to 800 MHz is relatively quiet, except at the frequency of 600 MHz. The frequency range of 800–1400 MHz is also relatively quiet. The predominant terrestrial services in this band are at 840 MHz, with an amplitude around 32 dB, and 916 MHz, with an amplitude around 12 dB, and the global system for mobile (GSM) signals around 954 MHz have an amplitude around 20 dB above the noise floor. The frequency range of 1400–7000 MHz is also relatively quiet. In this band frequency, we can see RFI at 2145 and 2407 MHz, emitted by local Wi-Fi, and at 2683 MHz, with amplitudes of 18, 40 and 15 dB, respectively, from the noise level. We conclude that, for this period, the frequency band allocated for astronomy can possibly be used for radio telescope development. [ABSTRACT FROM AUTHOR]

• Calibration algorithm of a radio telescope in the presence of man-made radio waves. • Array signal processing model that considers the presence of interferences. • Maximum likelihood estimation of the model parameters. • Development of a Space Alternating Generalized Expectation-Maximization algorithm. Radio interferometers are phased arrays producing high-resolution images from the covariance matrix of measurements. Calibration of such instruments is necessary and is a critical task. This is how the estimation of instrumental errors is usually done thanks to the knowledge of referenced celestial sources. However, the use of high sensitive antennas in modern radio interferometers (LOFAR, SKA) brings a new challenge in radio astronomy because they are more sensitive to Radio Frequency Interferences (RFI). The presence of RFI during the calibration process generally induces biases in state-of-the-art solutions. The purpose of this paper is to propose an alternative to alleviate the effects of RFI. For that, we first propose a model to take into account the presence of RFI in the data across multiple frequency channels thanks to a low-rank structured noise. We then achieve maximum likelihood estimation of the calibration parameters with a Space Alternating Generalized Expectation-Maximization (SAGE) algorithm for which we derive originally two sets of complete data allowing closed-form expressions for the updates. Numerical simulations show a significant gain in performance for RFI corrupted data in comparison with some more classical methods. [ABSTRACT FROM AUTHOR]

The increasing terrestrial and space-borne communications are causing major problems to the radio astronomy observations. Only a minor part of the frequencies is allocated to the passive services, such as Radio Astronomy Services (RAS). There are only a few, relatively narrow frequency bands below 20 GHz, which are still suitable for the radio astronomical observations. In addition, Out-of-Band (OoB) emissions will be a real threat to the observations on these bands. On behalf of all European radio astronomers, the Committee on Radio Astronomy Frequencies (CRAF) of the European Science Foundation (ESF) coordinates activities to keep the frequency bands used by radio astronomy and space sciences free of interference. Along with interference caused by active radio communication services, the local electronic device selection should be considered in the observatories. For instance, more common LED based lamps could cause harmful interference for the observations. Thus, it is very important to perform continuous radio frequency interference (RFI) monitoring locally, in each radio observatory. [ABSTRACT FROM AUTHOR]

Electromagnetic radiation from human activities, known as man-made Radio Frequency Interference (RFI), adversely affects radio astronomy observations. In the vicinity of the Upgraded Giant Metrewave Radio Telescope (uGMRT) array, the sparking on power lines is the major cause of interference at observing frequencies less than 800 MHz. A real-time broadband RFI detection and filtering system is implemented as part of the uGMRT wideband signal processing backend to mitigate the effect of broadband RFI. Performance analysis techniques used for testing and commissioning the system for observations in the beamformer and correlator modes of the uGMRT are presented. The concept and implementation of recording simultaneous unfiltered and filtered data along with data analysis and interpretation is illustrated using an example. For the beamformer mode, spectrogram, single spectral channel, and its Fourier transform is used for performance analysis whereas, in the correlator mode, the cross-correlation function, closure phase, and visibilities from the simultaneously recorded unfiltered and filtered is carried out. These techniques are used for testing the performance of the broadband RFI filter and releasing it for uGMRT users. [ABSTRACT FROM AUTHOR]

Abstract: In this paper, we investigated the radio frequency interference (RFI) that future Very Long Baseline Interferometer (VLBI) observations in Malaysia may encounter. Four frequency windows below 2.8GHz were chosen for this study and their spectra were measured at four sites. The frequency windows are 322–328MHz, 608–614MHz, 1660–1660.5MHz and 1660.5–1668.4MHz. The measured averaged RFI floor noise levels in these windows are −99.992 (±0.570)dBm, −99.907 (±0.639)dBm, −100.220 (±0.4941)dBm and −100.359 (±0.110)dBm, respectively. We found that only two bands below 2.8GHz are permitted for the purpose of radio astronomy in Malaysia. They are 608–614MHz and 1660–1660.5MHz. The RFI levels in these permissible bands at the best site (Langkawi) were also measured and concluded to be relatively low. Main sources of RFI in these bands in Malaysia were identified. We also reviewed several current VLBI observations in these two bands. [Copyright &y& Elsevier]

The population of artificial satellites and space debris orbiting the Earth imposes non-negligible constraints on both space operations and ground-based optical and radio astronomy. The ongoing deployment of several satellite 'mega-constellations' in the 2020s represents an additional threat that raises significant concerns. The expected severity of its unwanted consequences is still under study, including radio interference and information loss by satellite streaks appearing in science images. In this Letter, we report a new skyglow effect produced by space objects: increased night sky brightness caused by sunlight reflected and scattered by that large set of orbiting bodies whose direct radiance is a diffuse component when observed with the naked eye or with low angular resolution photometric instruments. According to our preliminary estimates, the zenith luminance of this additional light pollution source may have already reached ∼20 |$\mu$| cd m−2, which amounts to an approximately 10 per cent increase over the brightness of the night sky determined by natural sources of light. This is the critical limit adopted in 1979 by the International Astronomical Union for the light pollution level not to be exceeded at the sites of astronomical observatories. [ABSTRACT FROM AUTHOR]

The frequencies of interest for redshifted 21 cm observations are heavily affected by terrestrial radio-frequency interference (RFI). We identify the McGill Arctic Research Station (MARS) as a new RFI-quiet site and report its RFI occupancy using 122 h of data taken with a prototype antenna station developed for the Array of Long-Baseline Antennas for Taking Radio Observations from the Sub-Antarctic. Using an RFI flagging process tailored to the MARS data, we find an overall RFI occupancy of 1.8% averaged over 20–125 MHz. In particular, the FM broadcast band (88–108 MHz) is found to have an RFI occupancy of at most 1.6%. The data were taken during the Arctic summer, when degraded ionospheric conditions and an active research base contributed to increased RFI. The results quoted here therefore represent the maximum-level RFI environment at MARS. [ABSTRACT FROM AUTHOR]

The Tianlai project is a 21 cm intensity mapping experiment aimed at detecting dark energy by measuring the baryon acoustic oscillation (BAO) features in the large scale structure power spectrum. This experiment provides an opportunity to test the data processing methods for cosmological 21 cm signal extraction, which is still a great challenge in current radio astronomy research. The 21 cm signal is much weaker than the foregrounds and easily affected by the imperfections in the instrumental responses. Furthermore, processing the large volumes of interferometer data poses a practical challenge. We have developed a data processing pipeline software called tlpipe to process the drift scan survey data from the Tianlai experiment. It performs offline data processing tasks such as radio frequency interference (RFI) flagging, array calibration, binning, and map-making, etc. It also includes utility functions needed for the data analysis, such as data selection, transformation, visualization and others. A number of new algorithms are implemented, for example the eigenvector decomposition method for array calibration and the Tikhonov regularization for m -mode analysis. In this paper we describe the design and implementation of the tlpipe and illustrate its functions with some analysis of real data. Finally, we outline directions for future development of this publicly code. [ABSTRACT FROM AUTHOR]

This work sketches a possible design architecture of a low-frequency radio interferometer located on thelunar surface. The design has evolved from single antenna experiments aimed at the global signaldetection of the epoch of reionization (EoR) to thesquare kilometre array (SKA) which, when complete, will be capable of imaging the highly red-shifted H¹-signal from the cosmic dawn through to the EoR. However, due to the opacity of the ionosphere below10 MHz and the anthropogenic radio-frequency interference, these terrestrial facilities are incapable of detecting pre-ionization signals and the moonbecomes an attractive location to build a low-frequency radio interferometer capable of detectingsuch cosmological signals. Even though there areenormous engineering challenges to overcome,having this scientific facility on the lunar surfacealso opens up several new exciting possibilities forlow-frequency radio astronomy. [ABSTRACT FROM AUTHOR]

Quasiperiodic radio frequency interference (RFI), such as those generated by telecommunication and active radar systems, is commonly encountered in radio astronomy observations. Such RFI‐contaminated signals contain hidden periodicities due to cyclic features involved in their formation (e.g., carrier frequencies, periodic keying of the amplitude, and baud rates). RFI signal characterization and its subsequent excision based on the well‐known cyclic spectrum analysis have been previously demonstrated; however, the high complexity of the algorithm and the computational cost of its implementation have limited its utility in radio astronomy, rendering less sophisticated solutions. To overcome this challenge, we present a novel method for RFI detection and mitigation based on efficient estimation of the cyclic spectrum by compressive statistical sensing (CSS) of sub‐Nyquist data. CSS performs second‐order statistical estimation such as cyclic spectrum using a reduced number of input samples, thereby enabling accelerated performance. To validate the feasibility of the proposed method, we conduct experiments with simulated data and assess the detection and mitigation results under different parameter settings, for example, interference‐to‐noise ratio, additional RFI sources, frequency resolution, and input data size. We demonstrate the real performance of the method by analyzing radio astronomy data (∼1.3 GHz) acquired with the L‐wide band receiver at the Arecibo Observatory, which is typically corrupted by active air surveillance radars located nearby. Our CSS‐based solution enables robust and efficient detection of the RFI frequency bands present in the L‐band data, and subsequent excision by blanking is also demonstrated. Key Points: We present a novel method for RFI detection and mitigation based on cyclic spectrum analysis and compressive statistical sensingExperiments with synthetic radar‐based signals have been conducted, and accurate detection is achievedArecibo Observatory L‐band data contaminated with impulsive narrowband RFI from surrounding active radars are also used to demonstrate technique feasibility [ABSTRACT FROM AUTHOR]

Signal artifacts due to radio frequency interference (RFI) are a common nuisance in radio astronomy. Conventionally, the RFI‐affected data are tagged by an expert data analyst in order to warrant data quality. In view of the increasing data rates obtained with interferometric radio telescope arrays, automatic data filtering procedures are mandatory. Here, we present the results from the implementation of a RFI‐detecting recurrent neural network (RNN) employing long short‐term memory (LSTM) cells. For the training of the algorithm, a discrete model was used that distinguishes RFI and non‐RFI data, based on the amplitude information from radio interferometric observations with the Giant Metre‐Wave Radio Telescope (GMRT) at 610 MHz. The performance of the RNN is evaluated by analyzing a confusion matrix. The true positive and true negative rates of the network are ∼99.9 and ∼97.9%, respectively. However, the overall efficiency of the network is ∼30% because of the fact that a large amount non‐RFI data is classified as being contaminated by RFI. Matthews correlation coefficient is 0.42, suggesting that a still more refined training model is required. [ABSTRACT FROM AUTHOR]

Radio-frequency interference (RFI) can significantly contaminate the measured radiometric signal of current spaceborne L-band passive microwave radiometers. These spaceborne radiometers operate within the protected passive remote sensing and radio-astronomy frequency allocation of 1400-1427MHz but nonetheless are still subjected to frequent RFI intrusions. We present a unique surfacebased and airborne hyperspectral 385 channel, dual polarization, L-band Fourier transform, RFI-detecting radiometer designed with a frequency range from 1400 through ≈1550 MHz. The extended frequency range was intended to increase the likelihood of detecting adjacent RFI-free channels to increase the signal, and therefore the thermal resolution, of the radiometer instrument. The external instrument calibration uses three targets (sky, ambient, and warm), and validation from independent stability measurements shows a mean absolute error (MAE) of 1.0K for ambient and warm targets and 1.5K for sky. A simple but effective RFI removal method which exploits the large number of frequency channels is also described. This method separates the desired thermal emission from RFI intrusions and was evaluated with synthetic microwave spectra generated using a Monte Carlo approach and validated with surface-based and airborne experimental measurements. [ABSTRACT FROM AUTHOR]

We report the first measurements of radio frequency spectrum occupancy performed at sites aimed to host the future radio astronomy observatory in Indonesia. The survey is intended to obtain the radio frequency interference (RFI) environment in a spectral range from low frequency 10 MHz up to 8 GHz. The measurements permit the identification of the spectral occupancy over those selected sites in reference to the allocated radio spectrum in Indonesia. The sites are in close proximity to Australia, the future host of Square Kilometre Array (SKA) at low frequency. Therefore, the survey was deliberately made to approximately adhere the SKA protocol for RFI measurements, but with lower sensitivity. The RFI environment at Bosscha Observatory in Lembang was also measured for comparison. Within the sensitivity limit of the measurement equipment, it is found that a location called Fatumonas in the surrounding of Mount Timau in West Timor has very low level of RFI, with a total spectrum occupancy in this measured frequency range being about 1 %, mostly found at low frequency below 20 MHz. More detailed measurements as well as a strategy for a radio quiet zone must be implemented in the near future. [ABSTRACT FROM AUTHOR]

Farside Explorer is a proposed Cosmic Vision medium-size mission to the farside of the Moon consisting of two landers and an instrumented relay satellite. The farside of the Moon is a unique scientific platform in that it is shielded from terrestrial radio-frequency interference, it recorded the primary differentiation and evolution of the Moon, it can be continuously monitored from the Earth-Moon L2 Lagrange point, and there is a complete lack of reflected solar illumination from the Earth. Farside Explorer will exploit these properties and make the first radio-astronomy measurements from the most radio-quiet region of near-Earth space, determine the internal structure and thermal evolution of the Moon, from crust to core, and quantify impact hazards in near-Earth space by the measurement of flashes generated by impact events. The Farside Explorer flight system includes two identical solar-powered landers and a science/telecommunications relay satellite to be placed in a halo orbit about the Earth-Moon L2 Lagrange point. One lander would explore the largest and oldest recognized impact basin in the Solar System- the South Pole-Aitken basin-and the other would investigate the primordial highlands crust. Radio astronomy, geophysical, and geochemical instruments would be deployed on the surface, and the relay satellite would continuously monitor the surface for impact events. [ABSTRACT FROM AUTHOR]

We have searched for prompt radio emission from nine gamma-ray bursts (GRBs) with a 12 m telescope at 1.4 GHz, with a time resolution of 64 μs to 1 s. We detected single dispersed radio pulses with significances >6σ in the few minutes following two GRBs. The dispersion measures of both pulses are well in excess of the expected Galactic values, and the implied rate is incompatible with known sources of single dispersed pulses. The arrival times of both pulses also coincide with breaks in the GRB X-ray light curves. A null trial and statistical arguments rule out random fluctuations as the origin of these pulses with >95% and ∼97% confidence, respectively, although a simple population argument supports a GRB origin with confidence of only 2%. We caution that we cannot rule out radio frequency interference (RFI) as the origin of these pulses. If the single pulses are not related to the GRBs, we set an upper limit on the flux density of radio pulses emitted between 200 and 1800 s after a GRB of 1.27w–1/2 Jy, where 6.4 × 10–5 s < w < 32 × 10–3 s is the pulse width. We set a limit of less than 760 Jy for long timescale (>1 s) variations. These limits are some of the most constraining at high time resolution and GHz frequencies in the early stages of the GRB phenomenon. [ABSTRACT FROM AUTHOR]