Modified Integral Equation Method With Time-Varying Factors for Low-Frequency Ground-Wave Propagation Delay Prediction

A large amount of long-term measurements illustrate that the propagation delay of low-frequency (LF) ground-wave exhibits complex temporal variation properties. In this letter, we present a modified integral equation (IE) method to be capable of predicting the temporal variation of propagation delay. The modified method introduces suitable time-varying conductivity and refractivity models to characterize the temporal variation of propagation channel in terms of two aspects of ground and atmosphere. Comparisons between the modified method and experiment data along two actual propagation paths show good agreement. The effect of the time-varying factors controlling the conductivity and refractivity on propagation delay is further analyzed. It is found that compared to the refractivity, the time-varying factors in the conductivity have greater influence on the propagation delay.