Propagation of low frequency signals in oceanic environments; theory, simulation and experimentation

The excitation and propagation of extremely, super and ultra low frequency signals (ELF, SLF and ULF) in the range of 30 Hz to 3,000 Hz associated with ocean environments are of particular interest for applications dealing with deep-water communications or sub-surface emissions caused by power generation devices and lines. Due to the relatively long wave-lengths on the order of hundreds of meters or so in saltwater and the high-power nature of the sources, it is possible to detect these signals several kilometers from the source. In the current age in which sophisticated electromagnetic modeling tools have been developed for high frequency applications, the question has been asked whether these same tools can be applied to ELF, SLF and ULF applications (referred to as just ELF in subsequent discussions). In particular, we wish to ascertain the usefulness and robustness of the finite-difference, time-domain (FDTD) method, commercial codes (e.g. HFSS and Maxwell), and layered media modeling using Sommerfeld and quasi-electrostatic methods as applied to the ELF propagation problem. Each of these approaches has its strengths and weaknesses, as described in the ensuing sections.