Patent ID: 9625348
Date: 2017-04-18
CPC Classifications: F17D,G01D,G01H,G01M,G01P

Claim:
1. A method of detecting P and S waves in a solid medium comprising: repetitively launching at least a first optical pulse and a second optical pulse into a optic fibre located, at least partly, within said solid medium wherein the first and second pulses have a first optical frequency difference; detecting light which is Raleigh backscattered from the optic fibre; analysing the backscattered light to determine a measure of disturbance for each of a plurality of discrete longitudinal sensing portions of the optic fibre, analysing the evolution of a disturbance in the discrete longitudinal sensing portions together with the location of each discrete longitudinal sensing portion to identify a first wavefront followed by a second, slower wavefront to detect P and S waves, and analysing the detected P and S waves to determine their origin using the differences in time of arrival of the P and S waves at two or more different discrete longitudinal sensing portions by the further steps of: