| 摘要 |
A time offset measurement system for the timing of events at spaced apart locations comprising at each location, a dual frequency Global Positioning System (GPS) receiver having operatively associated with it a GPS antenna, wherein both the GPS receiver and the antenna are dual frequency (L1, L2), and the former is capable of both Coarse Acquisition (C/A) Code and carrier phase measurements, a frequency reference source giving local time, a data-logger for logging GPS data, a Time Interval Counter (TIC) used to measure the time of a local event as defined by the frequency reference source relative to time as defined in dependence on GPS data and further comprising a central processor system (CPS), and a communication system via which the logged GPS data and time interval data, are received at the CPS from each location, the CPS being arranged to derive in accordance with a predetermined algorithm, for each pair of sites a primary time-offset figure based on a direct signal path between the sites, and a secondary time-offset figure based on at least one indirect signal path between the sites, wherein confidence that correct system operation obtains is indicated in dependence upon correspondence between the primary and secondary time-offset figures.
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