Measuring height by connecting clocks
How far above sea level is a place located? And where exactly is "sea level"? It is one objective of the geodesists to answer these questions with 1 cm accuracy. Conventional measurement procedures or GPS technologies via satellites, however, reach their limits here. Now optical atomic clocks offer a new approach, because the tick rate of a clock is influenced by gravity. This well-known, but tiny effect was measured with unprecedented precision in 2010 using two optical clocks – however, they were located at the same institute. Now, up to 2000 km may lie between them. Using commercial optical fibers and a sophisticated amplifier technique, the frequency of one of the atomic clocks can be transported to the other where the frequencies may then be compared.