Remote seismic sensing

Claim 1

Apparatus for remotely measuring seismic signals at the surface of the earth, comprising: a laser for producing a laser beam of substantially monochromatic frequency, a beam splitter for splitting the laser beam into a sensing beam and a reference beam, an optical modulator for changing the frequency of the reference beam to produce a predetermined frequency offset between the frequency of the sensing beam and the frequency of the reference beam, a beam generating device for generating a preselected number of parallel sensing beams, a beam control and steering device for individually directing each of the parallel sensing beams to preselected locations on the earth's surface, a beam combining device located to intercept each reflected sensing beam and each reference beam and to individually combine an appropriate sensing and reference beam, an imaging device for imaging said combined beams onto a detection plane, a detector located at said detection plane for producing, at a frequency equal to the predetermined frequency offset, an individual beat signal varying in accordance with variations in the interference resulting from individually combining respective sensing and reference beams, and means electrically connected to said detector for processing each individual beat signal to measure variations in its phase or amplitude and determined seismic signals therefrom.