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利用卫星进行时间、频率比对的技术已为测量远地时钟之间的时间差及频率差提供了条件并大大地提高了测量精度。本文将对各种远地时钟比对技术做一扼要回顾,而重点放在全球定位系统(GPS)上。 GPS系统的问世首先为低成本、高精度、自动化地进行国际时间、频率的比对创造了条件。已经证明,当已知卫星星历表在几米之内时,这折算成地球表面上的两个远地时钟在同时接收GPS信号的时差仅为几个毫微秒。两个远地时钟的时差是简单地通过两地读数相减得到的,而每一地的读数则从共视测量值中减去一个差动延迟常数而得到。延迟常数可通过一开始的计算或测量获得。利用这种同时观测技术也可将其他共模误差如GPS时钟误差、电离层误差等消除或减少。由于GPS卫星轨道的黄道(ecliptic)的倾角很高,因此基本上可以做到所有北半球各观测点之间具有共视能力,而南半球的主要观测点则与北部的关键定时中心之间具有共视能力。本文也将对其他技术如“双向”卫星技术、LASSO、STIFT、GOES气象卫星系统及其有关技术等做一回顾和讨论。上述技术的现状将在对它们的用途和特点的叙述时一并讨论。有关将来的发展计划也将论及。
The technology of time and frequency alignment using satellites has provided the conditions for measuring the time difference and frequency difference between remote clocks and has greatly improved the measurement accuracy. This article will make a brief review of the various remote clock alignment techniques, with a focus on the Global Positioning System (GPS). The advent of the GPS system first of all for low-cost, high-precision, automatic time and frequency of international comparison and creation of the conditions. It has been shown that when the known satellite ephemeris is within a few meters, this translates to a time difference of only a couple of nanoseconds when two remote clocks on the surface of the earth are simultaneously receiving GPS signals. The time difference between the two remote clocks is simply subtracted from the readings of the two places, and the readings for each are subtracted from the common-view measurements by a differential delay constant. The delay constant can be obtained from the first calculation or measurement. The use of such simultaneous observation techniques can also eliminate or reduce other common-mode errors such as GPS clock errors, ionospheric errors and the like. Due to the high dip of the ecliptic orbit of the GPS satellite orbit, it is possible to achieve commonality between all the observation points in the northern hemisphere, while the main observation points in the southern hemisphere have a common view with the key timing centers in the north ability. This article will also review and discuss other technologies such as “two-way” satellite technology, LASSO, STIFT, GOES meteorological satellite systems and their related technologies. The status of the above technologies will be discussed in conjunction with their use and features. The future development plan will also be discussed.