The patent badge is an abbreviated version of the USPTO patent document. The patent badge does contain a link to the full patent document.
The patent badge is an abbreviated version of the USPTO patent document. The patent badge covers the following: Patent number, Date patent was issued, Date patent was filed, Title of the patent, Applicant, Inventor, Assignee, Attorney firm, Primary examiner, Assistant examiner, CPCs, and Abstract. The patent badge does contain a link to the full patent document (in Adobe Acrobat format, aka pdf). To download or print any patent click here.
Patent No.:
Date of Patent:
Feb. 22, 1994
Filed:
Sep. 18, 1992
Albert J Berni, Houston, TX (US);
Shell Oil Company, Houston, TX (US);
Abstract
A remote sensing system is provided which operates as a bipolarized, differential mode, LDI (laser differential interferometry) system to detect motion at a remote location. The system is adapted to reduce the effects of turbulence induced frequency fluctuations by using a retroreflector apparatus which converts a single sensing beam into a single return beam having two overlapping transversely polarized sensing signals; thus, turbulence induced noise will be common mode to both return signals and cancel at the receiver. In preferred embodiments, the system is used to detect seismic motions. The retroreflector apparatus is coupled to ground motions at a selected location where it separates the sensing beam into two polarized sensing signals, frequency modulates one of the polarized sensing signals to contain frequency components that represent selected ground motions, and combines the polarized sensing signals into the return beam. The return beam is detected. The return sensing signals are separated from the beam and combined by electronic and/or by optical heterodyning techniques to cancel common mode signals (including turbulence induced noise) on the sensing and return beam, thereby leaving a difference signal which represents the selected ground motions. In one preferred embodiment, the target is illuminated with a horizontal sensing beam; a polarizing beamsplitter splits the sensing beam into a first and a second polarized sensing signal. The beamsplitter Doppler shifts the first signal and also deflects the first signal to a vertical path where it reflects from an inertially isolated retroreflector. The second signal travels along a horizontal-inline path where it is reflected and Doppler shifted by a seismically coupled retroreflector. The Doppler shifted signals are combined in the beamsplitter to form the return signal. The first signal contains Doppler shifted frequency components which represent vertical and horizontal-inline ground motions. The second return sensing signal contains Doppler shifted frequency components which represent horizontal-inline ground motions. The common mode signals (the horizontal-inline frequency components and turbulence induced noise) are canceled in the receiver, leaving a difference signal which represents vertical motions.