N. Ashby

Publications163
h-index23
Citations2,405
Highly Influential Citations122
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Relativity in the Global Positioning System
  • N. Ashby
  • Physics
    Living reviews in relativity
  • 28 January 2003
TLDR
The conceptual basis, founded on special and general relativity, for navigation using GPS, and experimental tests of relativity obtained with a GPS receiver aboard the TOPEX/POSEIDON satellite will be discussed.
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Relativity and the Global Positioning System
We need general relativity to understand extreme astrophysical realms. But the theory also turns out to be essential for the many mundane activities that nowadays rely on the precision of the GPS.
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Discrete simulation of power law noise
A method for simulating power law noise in clocks and oscillators is presented based on modification of the spectrum of white phase noise, then Fourier transforming to the time domain. Symmetric real…
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Future gravitational physics tests from ranging to the BepiColombo Mercury planetary orbiter
Milani et al. recently have published careful and fundamental studies of the accuracy with which both gravitational physics information and the solar quadrupole moment can be obtained from…
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An assessment of relativistic effects for low Earth orbiters: the GRACE satellites
The GRACE mission consists of two identical satellites orbiting the Earth at an altitude of ∼500 km. Dual-frequency carrier-phase Global Positioning System (GPS) receivers are flying on both…
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Relativistic effects in the global positioning system
TLDR
The essential role of special and general relativity in the GPS is explained and a chain of thought leads to the breakdown of simultaneity, the Sagnac effect, the first-order Doppler effect, gravitational frequency shifts, and time dilation.
First accuracy evaluation of NIST-F2
We report the first accuracy evaluation of NIST-F2, a second-generation laser-cooled caesium fountain primary standard developed at the National Institute of Standards and Technology (NIST) with a…
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The Sagnac Effect in the Global Positioning System
In the Global Positioning System (GPS) the reference frame used for navigation is an earth-centered, earth-fixed rotating frame, the WGS-84 frame. The time reference is defined in an underlying…
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Precision atomic spectroscopy for improved limits on variation of the fine structure constant and local position invariance.
TLDR
Tests of local position invariance and the variation of fundamental constants from measurements of the frequency ratio of the 282-nm 199Hg+ optical clock transition to the ground state hyperfine splitting in 133Cs show results similar to those reported for the absolute optical frequency measurements in H and 171Yb+ vs other 133Cs standards.
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Testing local position invariance with four cesium-fountain primary frequency standards and four NIST hydrogen masers.
TLDR
The mostsensitive tests to date of the assumption of local position invariance (LPI) underlying general relativity, based on a 7 yr comparison of cesium and hydrogen atomic clocks (frequency standards), place an upper limit that is over 20 times smaller than the previous most sensitive tests.
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