Have you ever thought to use a clock to identify mineral deposits or concealed water resources within the Earth? An international team headed by astrophysicists Philippe Jetzer and Ruxandra Bondarescu from the University of Zurich is convinced that ultraprecise portable atomic clocks will make this a reality in the next decade. The scientists argue that these atomic clocks have already reached the necessary degree of precision to be useful for geophysical surveying. They say that such clocks will provide the most direct measurement of the geoid the Earth's true physical form. It will also be possible to combine atomic clocks measurements to existent geophysical methods to explore the interior of the Earth.
Determining geoid from general relativity
Today, the Earth's geoid the surface of constant gravitational potential that extends the mean sea level can only be determined indirectly. On continents, the geoid can be calculated by tracking the altitude of satellites in orbit. Picking the right surface is a complicated, multivalued problem. The spatial resolution of the geoid computed this way is low approximately 100 km.
Using atomic clocks to determine the geoid is an idea based on general relativity that has been discussed for the past 30 years. Clocks located at different distances from a heavy body like our Earth tick at different rates. Similarly, the closer a clock is to a heavy underground structure the slower it ticks a clock positioned over an iron ore will tick slower than one that sits above an empty cave. "In 2010 ultraprecise atomic clocks have measured the time difference between two clocks, one positioned 33 centimeters above the other," explains Bondarescu before adding: "Local mapping of the geoid to an equivalent height of 1 centimeter with atomic clocks seems ambitions, but within the reach of atomic clock technology."
Geophysical surveying with atomic clocks
According to Bondarescu, if
|Contact: Ruxandra Bondarescu|
University of Zurich