Improved Techniques for the Surveillance of the Near Earth Space Environment with the Murchison Widefield Array

We present the first survey of radio frequency interference (RFI) at the future site of the low frequency Square Kilometre Array (SKA), the Murchison Radio-astronomy Observatory (MRO), that both temporally and spatially resolves the RFI. The survey is conducted in a 1 MHz frequency range within the FM band, designed to encompass the closest and strongest FM transmitters to the MRO (located in Geraldton, approximately 300 km distant). Conducted over approximately three days using the second iteration of the Engineering Development Array in an all-sky imaging mode, we find a range of RFI signals. We are able to categorise the signals into: those received directly from the transmitters, from their horizon locations; reflections from aircraft (occupying approximately 13% of the observation duration); reflections from objects in Earth orbit; and reflections from meteor ionisation trails. In total, we analyse 33 994 images at 7.92 s time resolution in both polarisations with angular resolution of approximately 3.5 $^{\circ}$ , detecting approximately forty thousand RFI events. This detailed breakdown of RFI in the MRO environment will enable future detailed analyses of the likely impacts of RFI on key science at low radio frequencies with the SKA.

Section: In-orbit Object Backscatter/transmissionmentioning

confidence: 99%

A survey of spatially and temporally resolved radio frequency interference in the FM band at the Murchison Radio-astronomy Observatory

Tingay

Sokołowski

Wayth

et al. 2020

“…In this paper, we focus on the development of non-coherent techniques for space surveillance by the MWA. The development of coherent techniques is described by (Hennessy et al, 2019) and in an upcoming article by Hennessy et al (2019, IEEE submitted). Tingay et al (2013b) carried out observations during the commissioning phase of the MWA as a proof-ofconcept for the non-coherent passive radar technique.…”

Section: Introductionmentioning

confidence: 99%

The development of non-coherent passive radar techniques for space situational awareness with the Murchison Widefield Array

Prabu

Hancock

Zhang

et al. 2020

The number of active and non active satellites in Earth orbit has dramatically increased in recent decades, requiring the development of novel surveillance techniques to monitor and track them. In this paper, we build upon previous non-coherent passive radar space surveillance demonstrations undertaken using the Murchison Widefield Array (MWA). We develop the concept of the Dynamic Signal to Noise Ratio Spectrum (DSNRS) in order to isolate signals of interest (reflections of FM transmissions of objects in orbit) and efficiently differentiate them from direct path reception events. We detect and track Alouette-2, ALOS, UKube-1, the International Space Station, and Duchifat-1 in this manner. We also identified out-of-band transmissions from Duchifat-1 and UKube-1 using these techniques, demonstrating the MWA's capability to look for spurious transmissions from satellites. We identify an offset from the locations predicted by the cataloged orbital parameters for some of the satellites, demonstrating the potential of using MWA for satellite catalog maintenance. These results demonstrate the capability of the MWA for Space Situational Awareness and we describe future work in this area.

“…The MWA can observe the sky at 70-300 MHz and was primarily designed for radio astronomy purposes (Bowman et al 2013;Beardsley et al 2019). The MWA has detected satellites in the past using two different techniques, namely coherent detection (Palmer et al 2017;Hennessy et al 2019) and non-coherent detection (Tingay et al 2013b;Zhang et al 2018;Prabu et al 2020b) methods.…”

Section: Introductionmentioning

confidence: 99%

“…The coherent detection method uses the MWA's high time and frequency resolution voltage capture system (VCS) (Tremblay et al 2015) and performs detections using matched filters designed using the transmitted FM signal (Hennessy et al 2019), while the non-coherent detection system uses interferometer correlated data (Prabu et al 2020b) along with wide-field imaging techniques. The blind detection pipeline developed here uses the non-coherent detection method, including the use of the DSNRS techniques established by Prabu et al (2020b).…”

Section: Introductionmentioning

confidence: 99%

A low-frequency blind survey of the low Earth orbit environment using non-coherent passive radar with the Murchison widefield array

Prabu

Hancock

Zhang

et al. 2020

We have extended our previous work to use the Murchison widefield array (MWA) as a non-coherent passive radar system in the FM frequency band, using terrestrial FM transmitters to illuminate objects in low Earth orbit (LEO) and the MWA as the sensitive receiving element for the radar return. We have implemented a blind detection algorithm that searches for these reflected signals in difference images constructed using standard interferometric imaging techniques. From a large-scale survey using 20 h of archived MWA observations, we detect 74 unique objects over multiple passes, demonstrating the MWA to be a valuable addition to the global Space Domain Awareness network. We detected objects with ranges up to 977 km and as small as $0.03$ ${\rm m}^2$ radar cross section. We found that 30 objects were either non-operational satellites or upper-stage rocket body debris. Additionally, we also detected FM reflections from Geminid meteors and aircraft flying over the MWA. Most of the detections of objects in LEO were found to lie within the parameter space predicted by previous feasibility studies, verifying the performance of the MWA for this application. We have also used our survey to characterise these reflected signals from LEO objects as a source of radio frequency interference (RFI) that corrupts astronomical observations. This has allowed us to undertake an initial analysis of the impact of this RFI on the MWA and the future square kilometer array (SKA). As part of this analysis, we show that the standard MWA RFI flagging strategy misses most of this RFI and that this should be a careful consideration for the SKA.