Ionospheric corrections for GPS time transfer

Abstract

A real-time ionospheric mapping system is tested to investigate its ability to compensate for the ionospheric delay in single-frequency Global Positioning System (GPS) time transfer over Europe. This technique is compared with two other single-frequency systems: one that does not incorporate any ionospheric correction and one that uses the broadcast Klobuchar model. A dual-frequency technique is also shown as a benchmark. A period in March 2003, during a solar maximum, has been used to display results when the ionospheric delays are large and variable. Data from two European GPS monitoring centers were used to test the time-transfer methods. For averaging times between several minutes and a few hours, the instabilities in the time transfers were dominated by ionospheric effects. The instabilities at longer averaging times were found to be due to clock noise and hardware instabilities. Improvements in time-transfer instabilities are shown by using the ionospheric tomography system.

Improving Our Knowledge on the 229mThorium Isomer: Toward a Test Bench for Time Variations of Fundamental Constants

“…The accuracy of the 87 Rb clocks synchronously operated in the GPS satellite network (averaged over 24 h) amounts to about ±10 -13 , equivalent to a deviation of 10 ns per day. [31] Thus a nuclear frequency standard based on the thorium isomer may play a key role on the route toward (sub-)cm-scale global positioning. However, already the second-largest www.advancedsciencenews.com www.ann-phys.org contribution to the uncertainty originates from the stability of the clocks installed onboard the satellite network (typically four of them per satellite).…”

“…With innovative broadcasting methods already under study that aim to reduce or eliminate the influence of the ionosphere, ultimately the clock performance will be fundamental for the quality of any GNSS. [31] Thus a nuclear frequency standard based on the thorium isomer may play a key role on the route toward (sub-)cm-scale global positioning. In particular, its high resilience against external perturbations, ensuring a high drift stability of a nuclear clock, could avoid frequent resynchronization intervals and thus optimize the availability of the navigational systems' nuclear clock network.…”

Reconstruction of Storm‐Time Total Electron Content Using Ionospheric Tomography and Artificial Neural Networks: A Comparative Study Over the African Region

“…The ionospheric TEC and electron concentration are good indicators of the morphology of the ionosphere and can therefore be used for ionospheric studies and satellite applications (Mitchell & Spencer, 2003). There exist a number of studies related to ionospheric tomography imaging based on an inversion algorithm, namely Multi-Instrument Data Analysis System (MIDAS; Chartier et al, 2014;Dear & Mitchell, 2006;Giday et al, 2016;Jayawardena et al, 2016;Materassi & Mitchell, 2005;Meggs et al, 2005;Mitchell & Spencer, 2003;Muella et al, 2011;Rose et al, 2014;Yin et al, 2004). Using data from a network of GPS receivers over the U.S. midlatitudes, it has been proven that MIDAS can produce images of electron concentration and TEC during extreme geomagnetic conditions (K p = 9) that are in good agreement with observations (Yin et al, 2004).…”

“…MIDAS ionospheric tomographic imaging results were mainly focused on the midlatitudes (Chartier et al, 2012;Dear & Mitchell, 2006;Giday et al, 2016;Meggs et al, 2005;Rose et al, 2014;Yin et al, 2004). The few works that are related to ionospheric imaging for the low-latitude region were done for geomagnetically quiet conditions (Chartier et al, 2014;Materassi & Mitchell, 2005;Muella et al, 2011).…”

Very-Long-Baseline Interferometry

“…If timing measurements from four satellites are made, and corrected for propagation effects in the atmosphere, users can determine their positions in three coordinates and their clock errors. The accuracies available to civilian users have improved over about a decade from 100 ns in time (Parkinson and Gilbert 1983;Lewandowski et al 1999) to 1 ns (Rose et al 2014), and further improvement down to 100 ps is expected (Ray and Senior 2005). An analysis of the time-transfer problem, including relativistic effects, is given by Ashby and Allan (1979).…”