On the importance of time and frequency in geodesy

According to Friedrich Robert Helmert geodesy is the science of the measurement and mapping of the figure of the Earth. With the advent of the space age it was possible to establish a global reference frame, which can relate different locations across the entire Earth with an accuracy of currently about 1 cm with respect to each other. A rapid development of highly precise and stable frequency standards took place at the same time and is an important prerequisite for the actual quality of this global terrestrial reference frame. In fact all measurement techniques in modern space geodesy are based on precise time and frequency. Growing demands for the monitoring of global change as one of several examples of the importance of a highly resolved reference frame require more than one order of magnitude improvement over the existing level of quality. Optical clocks, optical frequency combs and near lossless time and frequency transfer have the potential to provide significant improvements of the individual techniques of space geodesy. This talk reviews how time and frequency impacts space geodesy and how the observation techniques may benefit from the recent progress in this field.