光格子時計の測地学への活用における展望

摘要

Optical lattice clock is an epoch-making device that provides accurate relative physical height in addition to ultra-stable time frequency standard by detecting clock-rate variations. Conventionally, relative physical height is determined by time-consuming spirit leveling and gravimetry, for which it has been difficult to remove effects of vertical crustal deformation or tidal perturbation occurred during the measurements. In addition, the measurements suffer from cumulative errors resulting in decrease in accuracy over long distance. As a result, vertical reference surfaces realized from the conventional measurements are commonly not consistent between countries. Optical lattice clock has a capacity to provide accurate relative physical height even over long distance without the systematic errors, and hence is expected to contribute in developing accurate height reference across borders and throughout national land. In this paper, we discuss a possibility of utilizing optical lattice clock for geodesy, especially defining and maintaining geodetic reference frame of physical height.