Geophysical applicability of atomic clocks: direct continental geoid mapping

Abstract

The geoid is the true physical figure of the Earth, a particular equipotential surface of the gravity field of the Earth that accounts for the effect of all subsurface density variations. Its shape approximates best (in the sense of least squares) the mean level of oceans, but the geoid is more difficult to determine over continents. Satellite missions carry out distance measurements and derive the gravity field to provide geoid maps over the entire globe. However, they require calibration and extensive computations including integration, which is a non-unique operation. Here we propose a direct method and a new tool that directly measures geopotential differences on continents using atomic clocks. General Relativity Theory predicts constant clock rate at sea level, and faster (resp. slower) clock rate above (resp. below) sea level. The technology of atomic clocks is on the doorstep of reaching an accuracy level in clock rate that is equivalent to 1 cm in determining equipotential surface (including geoid) height. We discuss the value and future applicability of such measurements including direct geoid mapping on continents, and joint gravity and geopotential surveying to invert for subsurface density anomalies. Our synthetic calculations show that the geoid perturbation caused by a 1.5 km radius sphere with 20% density anomaly buried at 2 km depth in the crust of the Earth is already detectable by atomic clocks of achievable accuracy. Therefore atomic clock geopotential surveys, used together with relative gravity data to benefit from their different depth sensitivities, can become a useful tool in mapping density anomalies within the Earth.

Express Letter. 21 pages, double spaced, 3 figures, final accepted version

References in corpus (4)

• Frequency Comparison of Two High-Accuracy Al+ Optical Clocks
• A Single-Ion Nuclear Clock for Metrology at the 19th Decimal Place
• Relativistic theory for time and frequency transfer to order c^{-3}
• A coherent optical link through the turbulent atmosphere

Cited by in corpus (26)

• Optical two-way time and frequency transfer over free space
• Atomic Clocks for Geodesy
• Experimenting an optical second with strontium lattice clocks
• Entanglement-enhanced quantum metrology: from standard quantum limit to Heisenberg limit
• Point-to-Point Stabilised Optical Frequency Transfer with Active Optics
• Comparing optical oscillators across the air to milliradians in phase and $10^{-17}$ in frequency
• Determination of a high spatial resolution geopotential model using atomic clock comparisons
• Demonstration of quantum synchronization based on second-order quantum coherence of entangled photons
• Improving cold-atom sensors with quantum entanglement: Prospects and challenges
• A cavity-stabilized laser with acceleration sensitivity below $10^{-12}$/g
• Laser frequency stabilization based on steady-state spectral-hole burning in Eu${}^{3+}$:Y${}_2$SiO${}_5$
• Atomic clocks as a tool to monitor vertical surface motion
• The unit of time: present and future directions
• Intermittent optical frequency measurements to reduce the dead time uncertainty of frequency link
• Stabilized free-space optical frequency transfer
• Non-linear Spectroscopy of Sr Atoms in an Optical Cavity for Laser Stabilization
• Probing Multiple Electric Dipole Forbidden Optical Transitions in Highly Charged Nickel Ions
• Absolute and relative stability of an optical frequency reference based on spectral hole burning in Eu${}^{3+}$:Y${}_2$SiO${}_5$
• Chronometric geodesy: methods and applications
• Post-Newtonian reference-ellipsoid for relativistic geodesy
• Excited-Band Coherent Delocalization for Improved Optical Lattice Clock Performance
• Atomic clocks: new prospects in metrology and geodesy
• Higher-Order Allan Variance for Atomic Clocks of Arbitrary Order: Mathematical Foundation
• Normal gravity field in relativistic geodesy
• Two null gravitational cones in the theory of GPS-intersatellite communications between two moving satellites. I. Physical and mathematical theory of the space-time interval and the geodesic distance on intersecting null cones
• Preliminary experimental results of determining the geopotential difference between two synchronized portable hydrogen clocks at different locations