Research Projects |
Strain MetersThe Gravity Group also uses fiber optic instruments to build strain meters in boreholes and on the seafloor. Following are some examples of our work in geodesy.Strain in an ice sheet borehole -- Siple Dome AntarcticaOne example of applying fiber optics to strain problems is our development of A Time-of-Flight Fiber Optic Borehole Strain Sensor in Antarctica.Borehole optical fiber strainmeter -- Long Vall ey exploratory wellWe have deployed an optical fiber strainmeter similar to the one used at Siple Dome to monitor strain in the Long Valley exploratory well near Mammoth Mountain, California. It is located over the resurgent dome in the Long Valley Caldera, a site of current volcanic unrest with great societal relevance due to a high potential for an eruptive event. Seafloor strainmeter (see FOSS)We developed an optical fiber strainmeter intended for measuring tectonic strains on the seafloor. In this instrument, an optical fiber is stretched between two points fixed to the ocean bottom; relative displacement of these points causes a change in the elongation of the fiber. This associated change in optical path length is monitored by an electronic distance meter. The dominant sources of noise in determining the optical path length of the fiber stem from the dependence of the fiber's index of refraction on both wavelength and temperature. In a 50 day long experiment performed in the shallow ocean, a test fiber was installed along a 210 m long baseline on the bottom. The RMS variation in length was 5 mm except for two displacements of order 10 cm caused by known effects. People |