ZHANG Shi-tian, CHEN Lin-ru, WANG Yuan-xin

(Qingdao Branch, Chinese Research Institute of Radiowave Propagation, Qingdao 266071, China)

Abstract: The phase and field strength of VLF signals at three frequencies, which were transmitted from Novosibirsk, Krasnodar and Khabarovs stations of the Russian alpha hyperbolic navigational system, were measured with the alpha phase/field-strength monitor in Chongqing, Guilin and Qingdao respectively during a solar eclipse of July 22, 2009, and the measurements were analyzed. The ionospheric equivalent height in the total eclipse regions was derived by establishing the ionospheric model and considering the electromagnetic parameters for the propagation path. The relation between the sudden change in phase of VLF signal and the time when the solar eclipse took place were obtained for different propagation paths, and the cause of the relation were analyzed. Besides, the amplitude changes occurred during the solar eclipse for different propagation paths were analyzed and it was found that the phase change occurred earlier than the amplitude change.

Key words: VLF(very low frequency) abnormal propagation; eclipse; phase of propagation; Alpha navigation system