Very Low Frequency Propagation Phase Prediction And Study On C-layer Effect

Using half-empiric method, C-layer effect of very low frequency (VLF) propagation phase is analyzed and modeled, moreover, the function of VLF phase prediction is modified. Through analyzing experimental data of signals of "Alpha (α)" VLF navigation system in Russia, C-layer effect which is one of especial effect of VLF propagation phase at sunrise is discovered. Base on the former research production of the low ionosphere, the characteristic analysis of configuration and diurnal variation of C-layer in low ionosphere and the reason of C-layer effect are showed. Base on the wave-guide model theory of VLF propagation, the timing pattern of VLF phase velocity and the regression function of VLF phase prediction are established. On the condition of known space-variety coefficients, time-variety coefficients are obtained by the experimental data and liner regression method. It is obvious that C-layer effect is more intense in summer and autumn than winter and spring by the results of liner regression. Furthermore, the results of liner regression indicate that the most intense change occurs happen between April and May. Accuracy improvements of phase prediction have been achieved in the new model which is decided by the coefficients of liner regression. The important meaning of study on C-layer effect is proved by predicting results of the new model which considers the influence of C-layer as compared with that of the sixth model of America. The precision of the new model is about 3.35 cec higher than that of the sixth model of America at the time from sunrise to noonday.