Observation and Analysis of the Sunrise Effect of 19.8kHz Signal in Xinjiang

Very low frequency waves (VLF) have a frequency of 3~30kHz. They are transmitted over long distances in the earth-ionosphere waveguide, with small propagation loss and high skin depth, so they are widely used in navigation, submarine communication and other fields. In addition, it has important significance in ionospheric remote sensing. During the period from April 22 to May 22, 2021, a very low frequency receiver was used in the Yili area of Xinjiang to observe the 19.8kHz signal from the Australian NWC, and the characteristics and laws of its amplitude response during the sunrise were counted. The statistical results found that the amplitude response of different test points all showed minimum values, showing certain regularity and consistency as a whole, and the minimum value appeared almost all later than the sunrise time. Observing a certain observation point at different times, the angle between the sunrise terminator and the propagation path gradually decreases, and the time interval between the sunrise time and the time when the minimum value appears becomes larger. When observing different observation points at the same time, the angle of the sunrise terminator does not change. The smaller the angle between the propagation path and the sunrise terminator, the greater the time interval between the sunrise time and the occurrence time of the minimum.