高精度国际时间比对的进展

The Progress on Precise Time Transfer and Comparison between Remote Sites

在过去的４５ｙｒ中原子频标的性能大约每７ｙｒ提高一个数量级，从国际标准时间和各国高精度守时的需要出发，远距离的高精度时间频率传递比对技术也有与之相适应的很大的发展。ＧＰＳ卫星在近２０ｙｒ中不仅成为导航定位不可缺少的工具，在时间、频率的传递方面也发挥出巨大威力；近年来多通道“全视接收”技术的发展使得时频传输比对的稳定性有了重大改善；ＧＬＯＮＡＳＳ卫星系统在高精度时间比对方面正在成为ＧＰＳ系统的重要补充手段ＳＴＷＳＴＴ的出现及发展在２１世纪将具有广阔的应用前景。介绍了近年来该领域的进展与初步实验结果，还简单介绍了 ＬＡＳＳＯ和 Ｃａｒｒｉｅｒ ｐｈａｓｅ技术的情况。

Since about 15 years ago, when GPS receivers were used to accurate time and frequency transfer by common-view observations of GPS satellites, significant improvements have occurred in time comparisons with the uncertainties reaching 10-20 at first and then having further reduced to about 3 nanoseconds. Today the sole method of comparing clocks contributing to TAI is the GPS single channel common-view technique. However, over the past 45 years, the performance of the atomic frequency standards has been improved on average by an order of magnitude every seven years, and the metrology is experiencing the birth of many new and innovative frequency standards which seem to be approaching 1 x 10-15 in accuracy and a short-term stability of 1 x 10-16. The needs for their future distant comparison challenge the adequate progress in time and frequency transfer. The recent progress resulting from the use of GPS and GLONASS multi-channel observations, GLONASS P-code, and the specially protected receiver antennas indicates that GPS and GLONASS, as time transfer systems, should have a stability of one part in 10~15 over one day and will eventually reach several parts in 10~16 in the next few years. The two-way satellite time and frequency transfer (TWSTT or TWSTFT) is currently taken as one of the most precise and accurate methods for time comparisons between remote sites. The most recent experiments with GPS carrier phase measurements on time and frequency transfer show the extremely promising potential in this field. This paper mainly focuses on the recent progress of GPS single channel, GPS/GLONASS multi-channel and GLONASS p-code commonview technique with the newly developed receivers, and TWSTT. The comparisons between these techniques are described. The GPS carrier phase measurements are mentioned briefly.