Preface

Summary

This preface of the book provides the driving motivation for the development of ultra-stable and highly sensitive inertial rotation sensing for applications in the geosciences. It identifies the exact observation of the rotation rate and the orientation of the rotation axis of the Earth as the important connecting link between the terrestrial reference frame and the long-term-stable celestial reference frame. The former is important because we navigate in this frame, while the latter is the frame in which navigation satellite motion is defined. With the precise knowledge of Earth rotation, one can transform from one reference frame to the other. At this point in time, space geodesy still awaits a self-contained continuously observing high resolution inertial sensor for this demanding task. Large ring laser gyroscopes are currently the only promising technique for this task.