Seismic monitoring system for harsh environment (No semiconductor devices in sensors)
High-precision seismic observation is possible under the harsh environment, places where power cannot be supplied, high temperature where electronic devices do not operate and oil and gas field where explosion proof devices are required.
The phase-shifted optical interferometry enables highly accurate* seismic observation without power supply to the sensor.
* In a comparison of microtremor observation conducted in a quiet place, the same high sensitivity and low noise as the electric broadband seismometer were confirmed.
Optical interferometer can measure a very small distance change. However usual interferometer has only a half (1/2) wavelength of measurement range. Our patented phase shifted optical interferometer extends the range of up to thousands of wavelengths.
Noise spectra of an optical sensor seismic observation system, a servo accelerometer, and a broadband seismometer observed at the Tono Yamazaki Observatory of Tohoku University in Japan.
As the broadband seismometer is a velocity seismometer, the record of the broadband seismometer is differentiated and converted to acceleration. The optical sensor seismic observation system observes the ground motion of the observation tunnel from 0.1Hz to 30Hz, similar to the broadband seismograph. The noise level of the servo accelerometer is higher than that of the optical sensor seismic observation system and the broadband seismometer.
Waveform of the vertical component of the earthquake observed by the optical sensor system at the Tono Yamazaki Observation Tunnel of Tohoku University around 0:16 am on December 18, 2019. The waveform with the maximum amplitude of 0.02 Gal is clearly captured.