Computation of amplitude and phase of VLF radio waves: Results from comparative study between wave-hop and waveguide mode theory

We present a comparative study of the wave-hop theory and waveguide mode theory (namely, Long Wavelength Propagation Capability (LWPC)) for computing the amplitude and phase of VLF signals in the context of Indian sub-continent. We use the Indian Navy VTX station transmitting at 18.2 kHz as an example of the source and compute the propagation characteristics. We find the signal amplitudes as a function of distance from the transmitter using wave hop-theory for VTX-Kolkata propagation path and compare with the same obtained from the LWPC code (Version 2.0) which uses the mode theory. The diurnal and seasonal behaviour of the amplitude of VTX signal using wave-hop code is also presented here. We further compared the azimuthal variation (0-360⁰) of attenuation rate and phase velocity of VTX-signal at day and night using LWPC (Version 2.0) code and modified LWPC code which includes International Geomagnetic Reference Field (IGRF) model.