Propagation Of Low-frequency Signals Research Articles

Two difference schemes for the numerical solution of Maxwell’s equations as applied to extremely and super low frequency signal propagation in the Earth-ionosphere waveguide

Two explicit two-time-level difference schemes for the numerical solution of Maxwell’s equations are proposed to simulate propagation of small-amplitude extremely and super low frequency electromagnetic signals (200 Hz and lower) in the Earth-ionosphere waveguide with allowance for the tensor conductivity of the ionosphere. Both schemes rely on a new approach to time approximation, specifically, on Maxwell’s equations represented in integral form with respect to time. The spatial derivatives in both schemes are approximated to fourth-order accuracy. The first scheme uses field equations and is second-order accurate in time. The second scheme uses potential equations and is fourth-order accurate in time. Comparative test computations show that the schemes have a number of important advantages over those based on finite-difference approximations of time derivatives. Additionally, the potential scheme is shown to possess better properties than the field scheme.

Precursory signature of several major earthquakes studied using 40 kHz low frequency signal

To investigate the precursory signature of earthquakes on low frequency (LF) signal propagation, six earthquakes, having magnitude greater than equal to 6.5 and depth less than equal to 30km, are being studied. The base line level of 40kHz signal, transmitted from JJY station, Japan, is analysed with respect to Vd statistical parameter. Results show that the Vd parameter values starts fluctuating from its ambient levels before and during the days of the earthquakes, with significant variation starting 1–3days prior to the earthquake concerned. This present study is an approach for identifying the precursory signatures of earthquakes on LF signal propagation using a new methodology with Vd parameter.

Integration of GPS and Loran-C / Chayka: A European Perspective

: Although the absolute accuracy of Loran-C is not very high (approximately 200–400 m), the overall system is superior to nonaugmented GPS with regard to some performance parameters (e.g., integrity). Notably, Loran-C's low-frequency signal propagation has a completely different immunity profile to noise, fading, and interference as compared with GPS. These complementary system features form a good basis for integrated (hybrid) navigation systems. In addition, Loran-C in Europe is operated under the auspices of the Northwestern European Loran-C System (NELS) Consortium and is under civil control, which addresses a key institutional question raised about GPS.