arXiv subjects

Liroy Lourenco

Publications and source records attributed to Liroy Lourenco.

3 recordsLinked to original sources

arXiv2026

SNIFFLES I: Intended Emission, Unwanted Emission, and Unintended Radiation from Low-Earth Orbiting Satellites Impacting Radio Astronomy from 1-26 GHz

We present the first results of SNIFFLES, an ongoing observational programme to characterise intended emission, unwanted emission, and unintended radiation from NGSO systems across common radio astronomy receiver bands from 1-26 GHz (L, S, C, X, and K bands). Using the Australian 22 metre Mopra radio telescope near Coonabarabran, New South Wales, with followup observations from a single dish of the ATCA interferometer and its new BIGCAT backend, we conducted 4629 tracked observations of satellites from four NGSO constellations (Starlink, OneWeb, Amazon Leo, and Guowang), amounting to 375.9 hours of telescope time. Satellite identification was confirmed by correlating detected Doppler shifts with predicted ephemerides. We detected 2345 instances of intended emission, unwanted emission, and unintended radiation at 300+ unique frequencies from three of the four systems. The detections span all three interference classes affecting radio astronomy: (1) intended emission (including DTD), (2) unwanted emission (OOBE, including up to the fourth harmonic of the Starlink DTD signal at approximately 2.6 GHz, with the fourth harmonic detected near 10.5 GHz), and (3) unintended radiation from satellite platform electronics. Several detections fall within primary radio astronomy allocations, including 1613.19 MHz within the protected OH line band, and at 2690.76 MHz and 2700 MHz. At 2700 MHz, unintended radiation was detected in 76.9 percent of all observations of the relevant satellite version. ATCA followup measurements confirm flux densities up to eleven orders of magnitude brighter than typical astronomical sources, well in excess of levels that saturate radio astronomy receivers.

astro-ph.IM↗

arXiv2026

Towards Genuine Coexistence: Per-Satellite Emission and Radiation Limits to Protect Radio Astronomy and Geodetic VLBI at 1-14 GHz from Satellite Constellations

Geodetic very long baseline interferometry (VLBI) is a vulnerable application of the radio astronomy service (RAS): it provides the fundamental link between the celestial and terrestrial reference frames, and is the only technique that uniquely determines UT1-UTC. The next-generation geodetic VLBI Global Observing System (VGOS) achieves millimetre accuracy by synthesising group delay across 3-14 GHz using 32x32 MHz channels, most of which lie outside RAS primary allocations. The SNIFFLES-I survey (Indermuehle et al 2026) measured intended emissions, unwanted emissions (spurious emissions, notably harmonics), and unintended electromagnetic radiation (UEMR) of NGSO systems from 1-26 GHz. On this basis we model the equivalent power flux density (EPFD) of current and future constellations and compare against protection criteria of ITU-R RA.769. The analysis extends to frequencies without radio astronomy allocations where SNIFFLES-I made detections. For geodetic VLBI, we run a Monte-Carlo EPFD model at the AuScope VGOS stations and scale the aggregate from the present catalogued fleet (~12000 satellites) to the hundreds of thousands on file with a validated method. Inverting the EPFD analysis against the interpolated RA.769 thresholds yields maximum tolerable per-satellite levels for spurious emissions and for UEMR, expressed as a field-strength limit in dB(uV/m) at 10 m for standard-setting bodies. We treat proposed orbital-data-centres in Sun-synchronous orbit as a distinctively UEMR-dominated case. We find that already today the single-dish protection criteria are exceeded in two primary RAS bands. For geodetic VLBI, the dominant threat is spurious emission from the 2620 MHz Direct-to-device (DTD) downlink, whose second harmonic at 5240 MHz already causes at least 59% data loss today. (Abstract modified for arxiv limits)

astro-ph.IM↗

arXiv2024

Mitigation of self-generated RFI using ASKAP's phased array feeds

This paper presents the effects of radio frequency interference (RFI) mitigation on a radio telescope's sensitivity and beam pattern. It specifically explores the impact of subspace-projection mitigation on the phased array feed (PAF) beams of the Australian SKA Pathfinder (ASKAP) telescope. The goal is to demonstrate ASKAP's ability to make science observations during active RFI mitigation. The target interfering signal is a self-generated clock signal from the digital receivers of ASKAP's PAFs. This signal is stationary, so we apply the mitigation projection to the beamformer weights at the beginning of the observation and hold them fixed. We suppressed the unwanted narrowband signal by 31dB, to the noise floor of an 880s integration on one antenna, with a typical degradation in sensitivity of just 1.5%. Sensitivity degradation over the whole 36 antenna array of 3.1% was then measured via interferometric assessment of system equivalent flux density (SEFD). These measurements are in line with theoretical calculation of noise increase using the correlation of the beam weights and RFI spatial signature. Further, degradation to the main beam's gain is 0.4% on average at the half-power point, with no significant change to the gain in the first sidelobe and no variation during extended observations; also consistent with our modelling. In summary, we present the first demonstration of mitigation via spatial nulling with PAFs on a large aperture synthesis array telescope and assess impact on sensitivity and beam shape via SEFD and holography measurements. The mitigation introduces smaller changes to sensitivity than intrinsic sensitivity differences between beams, does not preclude high dynamic range imaging and, in continuum 1MHz mode, recovers an otherwise corrupted holography beam map and usable astronomical source correlations in the RFI-affected channel.

astro-ph.IM↗