Systems, devices and methods for borehole gravimetry
First Claim
1. A method for measuring gravitational acceleration, the method comprising:
- locating a gravimeter within a borehole, wherein the gravimeter includes a proof mass that is constrained by at least one spring, an open loop optical interferometer having a reference component located in a fixed position relative to the proof mass, and a light source, with said proof mass allowed to freely move against the spring to a position of gravitational equilibrium without feedback;
generating a light path from the light source to a reflective surface on the proof mass; and
determining spatial displacement of the proof mass from a reference position of the reference component to a position of gravitational equilibrium by (i) determining a number of interference fringes between the reference position and the position of gravitational equilibrium with the open loop optical interferometer, and (ii) determining a change in length of the light path based on the number of interference fringes.
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Abstract
A gravimeter, a gravimeter system, and a method for measuring gravitational acceleration within a borehole are described herein. The gravimeter includes a proof mass that is constrained by springs and an optical interferometer for measuring displacement of the proof mass. The optical interferometer generates a light path from a light source to a reflective surface on the proof mass. Spatial displacement of the proof mass from a reference position to a position of gravitational equilibrium is determined by measuring a change in length of the light path. In turn, gravitational acceleration can be determined from the spatial displacement of the proof mass. A number of such gravimeters can be used in a gravimeter system to make measurements of gravitational acceleration in variety of different directions.
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Citations
29 Claims
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1. A method for measuring gravitational acceleration, the method comprising:
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locating a gravimeter within a borehole, wherein the gravimeter includes a proof mass that is constrained by at least one spring, an open loop optical interferometer having a reference component located in a fixed position relative to the proof mass, and a light source, with said proof mass allowed to freely move against the spring to a position of gravitational equilibrium without feedback; generating a light path from the light source to a reflective surface on the proof mass; and determining spatial displacement of the proof mass from a reference position of the reference component to a position of gravitational equilibrium by (i) determining a number of interference fringes between the reference position and the position of gravitational equilibrium with the open loop optical interferometer, and (ii) determining a change in length of the light path based on the number of interference fringes. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9)
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10. A gravimeter comprising:
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a proof mass that is constrained by at least one spring and that is displaceable in response to gravitational acceleration; an open loop optical interferometer for measuring displacement of the proof mass without feedback, wherein the optical interferometer comprises a reference component in a fixed position relative to said proof mass and a light source and is configured to generate a light path from the light source to a reflective surface on the proof mass; and a processor in electronic communication with the optical interferometer, wherein the processor is configured to determine spatial displacement of the proof mass from a reference position of said reference component to a position of gravitational equilibrium by (i) determining a number of interference fringes between the reference position and the position of gravitational equilibrium and (ii) determining a change in length of the light path based on the number of interference fringes. - View Dependent Claims (11, 12, 13, 14, 15, 16, 17, 18, 19, 20, 21, 22, 23, 24, 25, 26, 27, 28, 29)
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Specification