Very-Low-Frequency transmitters bifurcate energetic electron belt in near-earth space

Very-Low-Frequency (VLF) transmitters operate worldwide mostly at frequencies of 10–30 kilohertz for submarine communications. While it has been of intense scientific interest and practical importance to understand whether VLF transmitters can affect the natural environment of charged energetic particles, for decades there remained little direct observational evidence that revealed the effects of these VLF transmitters in geospace. Here we report a radially bifurcated electron belt formation at energies of tens of kiloelectron volts (keV) at altitudes of ~0.8–1.5 Earth radii on timescales over 10 days. Using Fokker-Planck diffusion simulations, we provide quantitative evidence that VLF transmitter emissions that leak from the Earth-ionosphere waveguide are primarily responsible for bifurcating the energetic electron belt, which typically exhibits a single-peak radial structure in near-Earth space. Since energetic electrons pose a potential danger to satellite operations, our findings demonstrate the feasibility of mitigation of natural particle radiation environment.

Signal transmission through seawater for MHz frequencies and medium distances (0–30 m) using ionic current waves

Electromagnetic (EM) signals can only be transmitted through seawater for short distances (<1 m) for frequencies (>1 MHz). Therefore a new technique, the ionic current wave (ICW), has been developed for signal propagation at MHz frequency. This technique uses the conduction current produced in seawater as a result of thermal ionisation releasing H+ and OH– ions. A small voltage (<1.5 V pk) is applied between two metal electrodes submerged in the seawater to avoid ionisation by the input electrical energy.<br/> A detailed theoretical analysis of the ICW process has shown that ionic currents can be transmitted at MHz frequency over distances of 10 m with low signal loss per decade. For longer propagation distances of 100 m the theory predicts a signal loss of –20 dB per decade.<br/> Propagation experiments have been carried out in Liverpool dock seawater for distances of 2 m–28 m between parallel 0.5 m × 0.3 m electrodes placed vertically in the seawater at a depth of 2 m. Signal frequencies within the range of 1 MHz–8 MHz have been investigated. In each experiment the received propa gated signal power was approximately –67 dBm (well above the dock electrical noise of –140 dBm) and only showed a small power loss over the full range of propagation.<br/> The ICW system will be able to measure longer propagation distances in deep seawater conditions suitable for ship and submarine communications. Its performance is comparable to that of sonar systems.