坪井賞受賞記念論文
レーザー干渉法の精密測地観測への応用
2010 年 56 巻 1 号 p. 1-12
詳細
2010 年 56 巻 1 号 p. 1-12
Laser interferometers are widely used for accurate measurements in fundamental physics, metrology, telecommunication, and so on. The most outstanding feature of laser light is its coherent optical waves, and once the laser wavelength is stabilized it provides a significantly stable and accurate standard of length for measurements. The excellent wavelength stability in various time scales is useful, especially for geodetic observations that often measure small crustal deformations for a long period of time. In this article, after describing the principles of a laser interferometer and its possible errors, three geodetic applications are shown: a laser strainmeter, an absolute gravimeter, and a satellite gravity mission. A laser strainmeter installed 1000 m underground in Kamioka Mine showed low background noise and clearly detected earth tides, whose waveforms agreed with theory within 5%. With the instrument, far-field crustal deformations associated with earthquakes were successfully observed with sufficient precision to provide geodetic constraints on fault parameters and dislocation theory. Absolute gravimeters, meanwhile, are commercially available at present. Their dimensions, weight, and price, however, are not suitable for field observation, such as dense network observation surrounding a volcano and installation in boreholes and the ocean bottom. A compact absolute gravimeter has been developed using newly devised methods for signal processing, seismic-noise correction, and a compact free-fall mechanism. A prototype worked almost as designed and showed 0.8 µgal precision during a 2-day observation. These achievements will be utilized to develop a more compact, practical absolute gravimeter in the near future. Finally, laser interferometers are useful for a satellite gravity mission that needs to measure the precise displacement of a reference mass due to gravity, in which compact instruments are necessary. The development of an accelerometer to be used in the DECIGO Pathfinder project is also presented.
