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This paper presents a new technique to reject the radio frequency interference (RFI) from the nearby radar at 9.4 GHz, which causes about 20% blockage of the sky coverage in the Very Long Baseline Inter ferometry (VLBI) telescope at the Goddard Geophysical Astronomical Observatory (GGAO), in Greenbelt, MD. An internal notch filter is proposed by inserting and optimizing two-quarter wavelength slots...
In preparation for the SKA, many new RFI (radio frequency interference) mitigation algorithms have been developed. However, these algorithms usually assume that the RFI source is in the far-field and that the array is calibrated. In this paper, the recovery of astronomical signals from uncalibrated RFI-corrupted LOFAR visibility data using spatial filtering methods are presented. For this demonstration,...
A modern radio astronomy observatory needs continuous monitoring of the radio spectrum to detect and characterise the sources of RFI, and ever improving plans for mitigation against such sources. With increasing population densities, accompanied by modernization in transport and communication facilities, the sources of external RFI affecting a radio observatory increase with time. The problem is aggravated...
A group of Mauritian scientists are building a Low/Mid Frequency array called the Mauritius Deuterium Telescope (MDT) in Mauritius. Additionally, the country is one of the SKA partner countries and will host one or more nodes of the Square Kilometer Array (SKA) project. To preserve current and future radio astronomical endeavors, it is critical that the radio frequency interference is monitored and...
We describe the design and implementation of an extremely scalable real-time RFI mitigation method, based on the offline AOFlagger. All algorithms scale linearly in the number of samples. We describe how we implemented the flagger in the LOFAR real-time pipeline, on both CPUs and GPUs. Additionally, we introduce a novel simple history-based flagger that helps reduce the impact of our small window...
Modern radio telescopes were designed for wider bandwidth to use the interference free bands for radio astronomy. Many intentional radiations are directional and line of site, pointing can be avoided to prevent receiver saturation. About 35000 Satellites are in space to provide voice and data service, navigation, GPS, weather, military and various space programs. These satellite footprints are larger...
The radio frequency environment in which the SKA Phase 1 telescopes should operate is characterised at locations within the proposed spiral arm layout. The total integrated power level of the radio frequency interference at the various locations is determined.
The Global Precipitation Measurement (GPM) Microwave Imager provides a valuable case study to evaluate levels and distribution of observable radio frequency interference (RFI) in semi-protected bands above 10 GHz from terrestrial and space-based sources. The GMI views the earth from a variety of different observation geometries and polarizations. The GMI detects significant earth-based RFI at 10.65...
A real-time spatial RFI mitigation experiment has been conducted with an ASKAP test array in Australia at GPS L2 frequencies. The goal of the study was to observe and image a bright astronomical source in a corrupted environment. The RFI spatial information was estimated in real-time with Phased Array Feed sample Array Covariance Matrices in order to update a spatial filter based on subspace projection...
Passive microwave remote sensing of the Earth from space provides information essential for understanding the Earth's environment and its evolution. Parameters such as soil moisture, sea surface temperature and salinity, and profiles of atmospheric temperature and humidity are measured at frequencies determined by the physics (e.g. sensitivity to changes in desired parameters) and by the availability...
Radio frequency interference (RFI) is a significant concern for radio astronomy, even in radio-quiet reserves. Whereas frequency-based algorithms are well suited for detecting and classifying intentional RFI (like communication links), the identification of unintentional RFI events (like those from devices such as relays or electric motors) is far more difficult. In this work we describe a novel way...
Radio frequency interference (RFI) is a significant concern for radio astronomy. Identifying unintentional RFI signals (for example, from equipment operating in the vicinity of radio telescopes) is a challenging topic due to the highly non-ergodic nature of such signals. Another non-ergodic signal type which has been very well researched is human speech, for which hidden Markov model-based approaches...
Real-time RFI excision is developed for the GMRT wideband correlator as part of the upgraded GMRT (uGMRT) project. The technique uses robust statistical estimation and a nonlinear filter to excise broadband and narrowband RFI. This paper provides an overview of the technique and its real-time implementation. The results showing improvement in the signal-to-noise ratio and cross-correlation performance...
It is known that Radio Frequency Interference affects a significant fraction of data from radio telescopes. These bad data must be carefully identified and eliminated before further processing. Current approaches require manual labor for tuning the parameters of auto flag algorithms or even marking individual regions of the data on a visual display. This paper presents a technique that can help automate...
We present the results of a radio frequency interference (RFI) study conducted using the Boolardy Engineering Testing Array (BETA) phased array feeds (PAFs) built for the Australian Square Kilometre Array Pathfinder (ASKAP) and located at the same site as the Australian component of the Square Kilometre Array (SKA). We first provide a brief overview of the radio quiet zone (RQZ) set up around the...
In recent years, three instruments have been launched into orbit with the aim of producing global maps of sea surface salinity and soil moisture using the 1400–1427 MHz band: SMOS, Aquarius and SMAP. Although this frequency band is allocated to passive measurements only, RFI (Radio-Frequency Interference) is present in the data of all three missions. On a global scale, the three sensors have observed...
BIGHORNS is a total power radiometer developed to identify the signal from the Epoch of Reionisation in the all-sky averaged radio spectrum at low frequencies (70–300 MHz). In October 2014, the system with a conical log spiral antenna was deployed at the Murchison Radio-astronomy Observatory (MRO) and has been collecting data since then. The system has been monitoring the radio frequency interference...
We investigate the bias of the Spectral Kurtosis Estimator induced by the quantization and bit truncation of the accumulated spectral power, which are standard signal manipulation operations performed by radio astronomy instruments that produce Power Spectral Density (PSD) estimates by means of sequential Discret Fourier Transform (DFT) operations. We demonstrate that these bias may be properly accounted...
Radio-frequency interference (RFI) has negatively impacted scientific measurements of passive remote sensing satellites. This has been observed in the L-band radiometers Microwave Imaging Radiometer with Aperture Synthesis (MIRAS) for the Soil Moisture and Ocean Salinity (SMOS) mission, Aquarius and more recently, Soil Moisture Active Passive (SMAP). RFI has also been observed at higher frequencies...
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