Wyniki wyszukiwania - BazTech

1

Study on secular change of the Earth’s rotation rate based on solar eclipse observation records on October 13, 443 BC

Ma Lihua

Artificial Satellites : Journal of Planetary Geodesy

|

2023

|

Vol. 58, No. 2

56--62

EN

An observation of a solar eclipse that occurred on October 13, 443 BC during the reign of the Duke Ligong of Qin was recorded in the Twenty-Four Histories (China’s dynastic histories from remote antiquity till the Ming Dynasty). With modern astronomical planetary ephemeris, the observation records were studied. The results showed that the eclipse probably occurred around sunset in Yongcheng, the capital of Qin, where the sunset time was exactly between the first contact stage (partial eclipse begins) and the fourth contact stage (partial eclipse ends) of the eclipse. Furthermore, secular change of the earth’s rotation rate at that time is investigated in this work.

2

Physical augmentation factor of precision in GNSS

Ma Lihua, Ai Guoxiang, Kong Ting

Artificial Satellites : Journal of Planetary Geodesy

|

2022

|

Vol. 57, No. 3

185--193

EN

The dilution of precision (DOP) in satellite navigation system provides a simple characterization of the user-satellite geometry and a quantitative assessment of the positioning constellation configuration. The essential idea of physical augmentation factor of precision (PAFP) proposed in this work, is that navigation signals are transmitted at multiple frequencies from each visible satellite in the positioning constellation, while users measure the corresponding multiple pseudoranges of satellites to achieve high precision code positioning. As the multiple pseudoranges of one satellite are measured independently by the corresponding navigation signals at different frequencies, it is reasonable to treat the measurement errors due to the satellite clock and ephemeris, the atmospheric propagation as uncorrelated, random, and identically distributed. The multipath effects and receiver noise are also processed with some empirical models. By measuring user-satellite code pseudoranges at different frequencies, the PAFP offers a scheme that produces the same effect as that of the redundant-overlapping constellation, thus equivalently improving the geometric DOP. It can effectively improve code positioning precision of satellite navigation system.

3

Quasi-1500-year-cycle signal in length-of-day change

Ma Lihua

Artificial Satellites : Journal of Planetary Geodesy

|

2021

|

Vol. 56, No. 2

10--17

EN

Length-of-day (LOD) change, i.e., variations in Earth’s rotation rate, includes the long-term slowdown trend, as well as periodic and irregular fluctuations. The current continuous sequence of the LOD change covers a time span of <400 years. Using astronomical records in ancient historical documents, combined with a modern astronomical ephemeris, it is possible to obtain ancient LOD change. Some scholars have given a discontinuous LOD data series for the past 4000 years. In this paper, the author uses the Lomb–Scargle periodogram to study the LOD series and finds a significant quasi-1500-yearcycle signal. Furthermore, with weighted wavelet Z-transform, time-varying characteristics of the cycle in the LOD change are obtained.