Two eyes, two views of the cosmos: Europe’s largest radio telescope finds a new role
Space weather refers to phenomena occurring in the Sun, Earth’s magnetosphere, ionosphere and thermosphere arising from solar activity. These include flares, coronal mass ejections, solar wind and the emission of energetic particles. “To study space weather phenomena, we need to be able to observe events that happen at different regions in our Solar System and at different time scales,” notes Carla Baldovin, project manager of the EU-funded LOFAR4SW project. “Ideally, we would like to track all chains of events originating from the Sun, how they unfold in the yawning space between Earth and Sun, and how they impact on our ionosphere.”
Preparing the largest radio telescope for a new role in space
Observing all these processes simultaneously using a single telescope is challenging. This is where LOFAR4SW steps in. “LOFAR4SW planned a significant upgrade for the Low-Frequency Array (LOFAR) telescope. Besides detecting radio waves from astronomical radio sources, the telescope will assume a new, parallel role: it will serve as a space weather facility that will simultaneously monitor the Sun, the heliosphere and the ionosphere,” remarks Baldovin. LOFAR is currently the world’s largest radio telescope, formed by an antenna network with its core located in the Netherlands and spreading across seven other European countries. Utilising a novel phased array design, it covers the largely unexplored low-frequency range from 10 to 240 MHz and is used for various astrophysical use cases. Unlike single-dish telescopes, LOFAR is a multipurpose sensor network with an innovative computer and network infrastructure that can handle extremely large data volumes. “The phased array technology makes LOFAR a flexible instrument, opening up the possibility to design a fully independent system that can function as a space weather facility in parallel to astronomical use cases using an upgraded version of the existing hardware,” explains Baldovin.
Tweaking the antenna technology to produce two beams
A fundamental part of the LOFAR4SW upgrade was the redesign of LOFAR’s high-band antennas. “By modifying the analogue beamforming system, we succeeded at prototyping a high-band antenna capable of producing two beams that can be pointed at different directions,” adds Baldovin. “The idea behind the hardware upgrade was to provide the high-band antennas with the capability of producing two independent beams, pointing at two different objects in the sky at the same time: one beam dedicated to radio astronomy and the other to space weather monitoring. It sounds like offering the telescope two eyes that can work independently,” notes Baldovin. Another fundamental aspect of the LOFAR telescope is that it relies on software rather than hardware to produce science-ready data. This means the signal is digitised early and processed using CPU-based software. LOFAR4SW developed software prototypes to perform monitoring programs that can quickly react to space weather events and to process the data of the different use cases. LOFAR4SW will be able to perform routine observations of the ionosphere using passive radar techniques that monitor ionospheric disturbances. Considering interplanetary scintillation, it will observe the heliosphere daily to capture both the speed and density of solar wind. It will also perform daily monitoring of the Sun in dynamic spectra and high-resolution imaging. The telescope upgrade is still ongoing but once completed, LOFAR will be one of Europe’s best space weather observing systems capable of shedding new light on a variety of space weather events.
Keywords
LOFAR4SW, LOFAR, space weather, ionosphere, Sun, high-band antenna, heliosphere, beamforming
