Litton Systems, Inc.

Shell Oil Comapny

James Brett Bunn

David Barnett Hall

Donald A Frederick

Steven James Maas

James S Bunn, Jr

An integrated seismic system and method for monitoring seismic parameters of a subsurface structure is provided. The integrated seismic system includes a base station; a plurality of mobile satellite nodes, each of the plurality of mobile satellite nodes having sensor stations for collecting seismic data from the subsurface structure; and a fiber optic cable extending from the base station to the plurality of mobile satellite nodes and operatively linking the plurality of mobile satellite nodes and the sensor stations; the base station comprising: a light source for sending a light through the fiber optic cable, the light being distributed to the sensor stations and, in the sensor stations, experiencing a change or phase shift related to a physical property being measured; and a seismic acquisition unit for receiving seismic signals from the plurality of mobile satellite nodes via the fiber optic cable and generating seismic parameters therefrom.

Integrated seismic monitoring system and method

The invention is a method for obtaining a measure of the light propagation time difference for two light-propagating-media paths. The first step consists of generating two substantially-identical frequency-modulated light waves whereby the frequency of the light waves is offset from a reference frequency by a different frequency increment for each basic time interval in each of a plurality of groups of three or more basic time intervals. Each frequency increment is the sum of a specified increment and a frequency-modulation-error increment. The frequency-modulation-error increments associated with the specified increments are independent of each other and unknown. The second step consists of feeding the two light waves into the entry points of two light-propagating-media paths having a light propagation time difference and obtaining a combination light wave by summing the light waves emerging from the exit points of the two light-propagating-media paths. The third step consists of calculating an estimated corrected or estimated uncorrected phase measure of the light propagation time difference for the two paths for a plurality of groups using only measured properties of the combination light wave.

Method for determining the phase difference of light waves propagated

An interferometer amplitude modulation reduction circuit coupled to receive an interferometer output signal from the output of a fiber optic interferometer sensor. The interferometer sensor is excited by a frequency modulated input light signal from a light source having an unwanted amplitude modulation and intensity noise signal component. The interferometer output signal has both wanted interference induced intensity modulation and also unwanted amplitude modulation and intensity noise from the unwanted amplitude modulation and intensity noise signal components present on the frequency modulated input light signal. The invention circuit has a sampling means for sampling a sample portion of the frequency modulated input light signal from the output of the light source. The sampling means detects and the sample portion signal to provide a detected sample intensity signal having a detected unwanted amplitude modulation and intensity noise signal component. A detector detects the interferometer output signal from the output of the fiber optic interferometer sensor and converts the interferometer output signal into a detected AM modulated phase-generated carrier signal containing a detected unwanted amplitude modulation and intensity noise signal component. A divider scales and divides the detected AM modulated phase-generated carrier signal by the detected sample intensity signal to provide a corrected interferometer output signal. The detected unwanted amplitude modulation and intensity noise signal components common to both the detected sample intensity signal and the detected AM modulated phase-generated carrier signal are substantially canceled by the division process.

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Austin, TX, United States of America

James Brett Bunn