AVERAGING SATELLITE TIMING DATA FOR NATIONAL AND INTERNATIONAL TIME COORDINATION

摘要

The International Bureau of Weights and Measures (BIPM) calculates International Atomic Time (TAI) and Coordinated Universal Time (UTC) using data from many national metrology institutes and timing laboratories. An important part of these data are the measured time differences between GPS (or GLONASS) time and the realization of UTC by each of the laboratories, UTC (lab). These time differences are acquired using tracking schedules published by the BIPM and are based on 1-second measurements averaged as specified in the corresponding technical directives. The concept of a tracking schedule and the algorithms that are used for averaging the data were designed many years ago when all of the contributing laboratories used single-channel receivers with relatively slow internal processors. Although these receivers are still in use, many laboratories also use multi-channel receivers with much greater processing power. In addition, the speed of the network that links the contributing timing centers continues to increase and the cost of storage devices continues to decrease. Both of these developments make it feasible to acquire and store more data. Given these advances, it is appropriate to reconsider the design of the averaging algorithms. In particular, I will show that the current 13-minute averaging scheme is not optimum in general, and that a shorter and simpler averaging scheme would provide a better means of handling the effects of multipath reflections and similar problems, which are not attenuated by common-view subtraction. In addition to remaining compatible with the method used in the existing receivers, it is desirable to design an averaging algorithm that could be compatible with data acquired by geodetic (carrier-phase) receivers, which typically report measurements every 30 s. In principle, these data cannot be made compatible with the algorithms currently specified for the 13- minute tracks; the incompatibilities will be most serious at sites with large multipath reflections or other noise sources that are not attenuated by common-view subtraction.