Novel Earth Observation Based on Quantum Optics and Relativity

Recent developments in fundamental physics (in theory as well as in technology) provide novel capabilities for geodetic applications such as refined observations of the Earth's gravity field. We will focus on two new concepts: one applies atomic interferometry for (satellite) gravimetry, the other uses clock measurements for observing potential differences at Earth surface. In the first case, gravity anomalies are determined by observing free-falling atoms (quantum gravimetry), such technique can also be applied for future gradiometric measurements in space. In the second case according to Einstein's theory of general relativity, frequency comparisons of highly precise optical clocks give access to differences of the gravity potential - even over long distances (relativistic geodesy). Also laser interferometry between test masses in space with nanometer accuracy belongs to these novel concepts. For the latter, technology developed for gravitational wave detection and successfully tested in the LISA/pathfinder mission is being prepared for geodetic measurements. Those concepts are recently elaborated in close cooperation between physicists and geodesists at the University of Hannover under the umbrella of the Collaborative Research Center SFB 1128 "Relativistic geodesy and gravimetry with quantum sensors (geo-Q)". We will give a few examples where geodesy will potentially benefit from these novel developments and show future perspectives. The direct determination of physical heights and the connection of distant tide gauges are just two examples. We will also illustrate the application of the new methods for Earth observation, where local and global mass variations can be observed with unforeseen accuracy and resolution, benefitting a wide range of geosciences.