DBPapers
DOI: 10.5593/sgem2017/21/S08.135

THE INCREASE OF THE ACCURACY OF THE LASER-BASED MEASUREMENT OF ULTRA-LOW TIDAL DEFORMATION OF ROCKS

V. Zhmud, V. Semibalamut, L. Dimitrov, Y. Fomin
Wednesday 13 September 2017 by Libadmin2017

References: 17th International Multidisciplinary Scientific GeoConference SGEM 2017, www.sgem.org, SGEM2017 Conference Proceedings, ISBN 978-619-7408-01-0 / ISSN 1314-2704, 29 June - 5 July, 2017, Vol. 17, Issue 21, 1069-1076 pp, DOI: 10.5593/sgem2017/21/S08.135

ABSTRACT

The laser meter of super small rock displacement under the influence of gravitational forces from the moon and the sun allows registering the regular fluctuations in the Earth’s crust. These fluctuations provide small difference in the distances between the rocks edges in the two orthogonal directions inside the shaft structure drilled in the rock. Laser-based displacement meter converts the distance change into the increment of the phase difference in the two light beams in the interferometer. The photo detector converts the light beam into an electric signal, and the phase meter allows measuring of the phase difference obtained as the result of the measurement of the increments of length difference in the two arms of the interferometer meter. This paper summarizes the measurement principles and gives method to improve the accuracy and reliability of these measurements. The essence of the proposed way for increasing of the accuracy is based on the alternative method and hardware for the measuring of the phase difference. This method is based on analog-to-digital conversion of the signal from photo detectors with the use of original algorithm of calculating of coherent and quadrature components (X and Y) and calculation of the phase as function atan2X/Y.

Keywords: earthquake precursors, laser metrology, measurement of ultra-low displacement and vibration, measurement of the phase difference

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