An Agile Very Low Frequency Radio Spectrum Explorer

TL;DR

This paper introduces an agile ground-based VLF radio spectrum explorer designed to study celestial VLF emissions, leveraging a new instrument with four antennas and advanced receivers, especially useful during periods of low ionospheric activity.

Contribution

The paper presents a novel, agile VLF radio spectrum explorer co-located with MUSER, capable of operating in 1-70 MHz range for celestial VLF studies, addressing challenges of ionospheric interference.

Findings

Successfully built and deployed the VLF spectrum explorer.

Demonstrated capability to observe VLF celestial emissions.

Instrument readiness for future VLF astronomical research.

Abstract

The very low frequency (VLF) regime below 30 MHz in the electromagnetic spectrum has presently drawing global attentions in radio astronomical research due to its potentially significant science outcomes exploring many unknown extragalactic sources, transients, and so on. However, the non-transparency of the Earth's ionosphere, ionospheric distortion and artificial radio frequency interference (RFI) have made it difficult to detect the VLF celestial radio emission with ground-based instruments. A straightforward solution to overcome these problems is a space based VLF radio telescope, just like the VLF radio instruments onboard the Chang'E 4 spacecraft. But building such a space telescope would be inevitably costly and technically challenging. The alternative approach would be then a ground based VLF radio telescope. Particularly, in the period of post 2020 when the solar and terrestrial ionospheric activities are expected to be in a 'calm' state, it will provide us a good chance to perform VLF ground-based radio observations. Anticipating such an opportunity, we built an agile VLF radio spectrum explorer co-located with the currently operational Mingantu Spectra Radio Heliograph (MUSER). The instrument includes four antennas operating in the VLF frequency range 1-70 MHz. Along with them, we employ an eight-channel analog and digital receivers to amplify, digitize and process the radio signals received by the antennas. We present in the paper this VLF radio spectrum explorer and the instrument will be useful for celestial studies of VLF radio emissions.