Accuracy of GPS Time Transfer Verified by Closure Around the World
BUREAU INTERNATIONAL DES POIDS ET MESURES SEVRES (FRANCE)
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The precision of time transfer over intercontinental distances by the GPS common-view method, using measurements of ionospheric delays, precise ephemerides provided by the DMA and a consistent set of antenna coordinates, reaches 3-4 ns for a single 13-min measurement, and decreases to 2 ns when averaging several measurements over a period of one day. It is thought that even this level of precision can be bettered by improving the ionospheric measurements, the ephemerides of the satellites and the antenna coordinates. In the same conditions, an estimation of the accuracy is attained by using three intercontinental links encircling the Earth to establish a closure condition The three independant time links should add to zero. We have computed such a closure condition over a period of thirteen months using data recorded at the Paris Observatory in Paris France, at the Communications Research Laboratory in Tokyo Japan and at the National Institute for Standards and Technology in Boulder, Colorado USA. The closure condition is verified to within a few nanoseconds but a bias, varying with time, can be detected.
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