Radio telescopes that aim to find astroparticles rely on the detection of impulsive, short-lived and transient radio signals produced primarily via the geomagnetic emission effect. One of the main challenges of this detection method is the presence of abundant radio backgrounds produced by human activity, both continuous (as in intentional emission for telecommunications) and impulsive (for example, unintentional emission associated with the use of large electrical currents and voltages). It is impossible to separate the origin of impulsive signals (astrophysical or anthropogenic) if they have very similar shapes.
Therefore, radio telescopes are usually placed in remote and geographically advantageous regions where the radio background is the lowest, and they carefully characterize their continuous radio backgrounds near the horizon in order to perform their research. Transient radio telescopes have also focused on near-vertical radio emission, which allows for a closer match to our models of geomagnetic emission.
However, next-generation radio detectors aim to also detect radio signals from near-horizontal sources, in particular the interactions of Earth-skimming neutrinos. Modeling of radio propagation near the surface of Earth needs to include complex geometrical effects and include possible interactions with the non-smooth lower layers of the atmosphere. This need is further evidenced by reports from multiple radio observatories of an excess of near-horizon impulsive signals that could not be reconciled with sources at the horizon so-far.
In this work, we consider the possibility of secondary radio reflections of originally terrestrial sources as the cause of the near-the horizon excess transient events.
A simple model of low-altitude clouds shows that they cannot be ruled out as the source of sporadic radio reflections.