A high performance GPS based autonomous event time-tagging system with application in a next generation extensive air shower array

Two prototype, low-cost event time-tagging systems have been constructed using commercially available Global Positioning Satellite (GPS) receivers. The systems are capable of operating independently of one another and may be physically separated. By the use of special techniques the relative accuracy of the event time-tags has been much improved, and the effects of the selective availability (SA) system degradation eliminated. With the two systems co-located the time interval measurement accuracy, when matching pairs of event times are subtracted from one another, has an average offset error of 5 ns, and random error having an average standard deviation of 6 ns. When the systems are separated by 500 m there is no detectable degradation of this performance. The maximum time interval measurement errors recorded over 8 days of operation, both co-located and 500 m separated, with 800 000 test events, were +21 ns and -35 ns.