Abstract
Lightning and transient luminous events (TLEs) emit a short burst
(~1 ms) of broadband electromagnetic waves, whose
frequencies can range from a few Hz to the optical band, but the bulk of
their energy is radiated as longwaves (<500 kHz). These
longwave radio signals are named radio atmospherics, or colloquially
sferics. Due to their low frequency, sferics can propagate in the
Earth-ionosphere waveguide at global distances with relatively low
attenuation (~3 dB per 1000 km). This allows a sparse
network of longwave receiver stations, placed hundreds of kilometers
apart, to geolocate lightning strikes at a global scale. Hardware
performance of the receivers at these stations significantly impacts the
data quality and determines the detection efficiency and location
accuracy of the lightning detection network. In this work, we present a
low-frequency remote sensing instrument for lightning geolocation in the
form of an ultra-sensitive broadband electric field receiver. It is
capable of detecting extremely weak sferics, enabled by its ideal
sensitivity of 1 nV/(m√Hz), or 0.003 fT/√Hz. We present this receiver’s
antenna-amplifier co-design and the design considerations to achieve
this low sensitivity. We then report its performance characteristics,
validated both theoretically and empirically. Finally, we present some
of the novel applications of this device in the scope of lightning
geolocation and remote sensing.