WANG Na^1,2,3, LI Rui-min^1,2, SU Jian-feng¹

(1. National Time Service Center, Chinese Academy of Sciences, Xi′an 710600, China;

2. Graduate University of Chinese Academy of Sciences, Beijing 100039, China;

3. Key Laboratory of Time and Frequency Primary Standards, National Time Service Center,

Chinese Academy of Sciences, Xi′an 710600, China)

Abstract: For learning the practicality of Millington empirical formula in predicting the time delay of ground-wave propagating along piecewise smooth mixed path, the Millington empirical formula is compared with the strict Wait integral method. On the basis that the Wait integral method is realized with computer software, the secondary phase factors for the ground-waves propagating along several paths are calculated with the Millington empirical formula and the Wait integral method respectively. The calculations are compared and the results show that the Millington empirical formula can meet the requirements of practical engineering in ground-wave delay prediction.