Abstract: Gravity gradient measurements taken by an accelerometer type gradiometer are optimized by tilting the measuring plane of the instrument by a selected angle above and below the horizontal to obtain data that can be differenced or otherwise processed to remove instrument bias and by taking data at first and then at a second orthogonal azimuth heading to obtain absolute non-relative gradient measurements.

Abstract: A gravity gradiometer including first and second proof masses and a device for providing simultaneous free flight of the proof masses under the influence of the gravitional force in which the gradient is to be measured and a capacitance device for monitoring the movement of the centers of mass with respect to each other during free flight by monitoring capacitance between portions of the two proof masses.

Abstract: The mass of stockpiled materials is determined from detailed measurements of the elevation of the pile surface at many points and the measurement of the gravitational field along several profile lines across the surface of the stockpiled material. The elevation measurements allow the calculation of the pile volume. Measured gravity values are adjusted using standard gravity corrections in such a manner as to imply all gravity data are collected along the same reference datum. Variations in the corrected gravity values are assumed to be caused solely by the pile material. The gravity measurements are interpreted using analytical and statistical methods to determine the volume-average bulk density value of the pile material. The pile volume is multiplied by the volume-average bulk density to obtain the weight of the stockpiled material.

Abstract: Apparatus for measuring gravitational fields comprising a superconducting string (1) fixed at both ends and forming part of a closed superconducting loop inductively coupled to two driving solenoids (L.sub.d1, L.sub.d2). Displacement of the string in response to a gravitational field is sensed by two magnetic flux transformers each comprising a signal coil and two pick-up coils ((L.sub.p1, L.sub.p2). Pairs of pick-up coils lie in two perpendicular planes providing two independent channels of measurements. The two arms of each flux transformer are balanced to convert only the amplitudes of the string's antisymmetric natural modes into an output voltage. The output voltage of each channel is used to produce a feed-back current distribution (L.sub.y1, L.sub.y2) proximate and parallel to the string.

Abstract: This invention concerns improvements to gravity gradient instruments (GGI) and in particular to the accelerometers that are paired within these instruments. Accelerometers have a proof mass suspended by a spring within a magnetic field. An internal feedback loop provides a signal related to movement of the proof mass back through a reaction coil retaining the proof mass in the magnetic field, to maintain the proof mass stationary. An external feedback loop adjusts the accelerometer scale factor. The internal feedback loop provides second order compensation to the proof mass and the spring stiffness. In a further aspect the invention is a method of matching accelerometer pairs.

Abstract: This invention concerns improvements in the performance of a mobile gravity gradient instrument (GGI). Gravity gradiometers measure one or more components of the gradient of gravity which is expressed as the gradient of a gravity vector, or in other words a tensor. The instrument comprises a first, second, third and fourth accelerometer equally spaced around the circumference of a circle, with their sensitive axes tangential to the circle, and arranged in opposing pairs with the first accelerometer opposite the second, and the third accelerometer opposite the fourth. In use the accelerometers are spun around an axis normal to the circle which passes through its center. A summing amplifier receives the outputs of the accelerometers and combines them in a manner to cancel the common mode output signals and so produces all instrument output. One or more feedback loops extend from the instrument output to one or more of the accelerometers to compensate for errors.

Abstract: A method of obtaining gravity gradient well logs over selected baselines, using a well log tool having first and second gravity meters separated by a fixed distance, referred to as the baseline, is disclosed. Gravity gradient measurements are obtained in the wellbore by stepping the tool along the wellbore, where readings at adjacent depths are obtained by setting one of the gravity meters at the same depth at which the other gravity meter is or was located in another reading; alternatively, the well log tool may include a single gravity meter, with readings at adjacent depths made by moving the tool along the wellbore by the baseline. The user or computer system selects a virtual baseline, corresponding to a multiple of the gravity gradient measurements. The gravity gradient is then obtained by summing the individual gravity gradient measurements and dividing by the number of summed measurements.

Abstract: A proof mass support system has a pair of alignment coils for controlling the rest position of an elongate proof mass. The alignment coils are constructed to provide a levitation force when they carry electric currents which varies along the length of the proof mass. The relative strength of the electric currents are tuned in the alignment coils to cause the proof mass to take up a predetermined orientation with respect to one or more degrees of freedom defined by the alignment coils. In an alternative, one or more anti-rotation coils may be arranged to apply a restoring force to the proof mass when electric currents pass therethrough. The proof mass is formed so as to cooperate with the restoring force which acts against rotation of the proof mass away from a predetermined orientation. The system is typically provided as part of a superconducting accelerometer or gravity gradiometer.

Abstract: A gravity gradiometer for measuring off-diagonal components of the gravitational gradient tensor includes a housing comprising a pair of electromagnetic shield enclosures (22, 23) arranged one inside the other, and a body (25) including superconducting material mounted within the inner enclosure (23) for fine pivotal flexure about an axis passing substantially through the center of mass of the aforesaid body. An array of superconducting coils (30) is supported by the outer enclosure (22) and positioned in close proximity to the aforesaid body (25) for diamagnetically applying a rotational force to the body with respect to the axis of flexure and/or for responding by modulation of inductance to pivotal flexure of the body arising from a gravitational gradient across the body. The array is arranged to apply the rotational force in both rotational directions and to respond to flexure in either rotational direction.

Abstract: A gravity gradiometer capable of obtaining the vertical component T.sub.zz of the gravity gradient tensor out of the two horizontal components T.sub.xx and T.sub.yy based on Laplace equation: T.sub.zz =-(T.sub.xx +T.sub.yy) comprises a single disc, and two pairs of radially-oriented horizontal axis accelerometers oppositely-mounted on such disc along respective X and Y axes, each pair being capable of providing, respectively, T.sub.xx =T.sub.x1 -T.sub.x2 and T.sub.yy =T.sub.y1 -T.sub.y2 where T.sub.x1 and T.sub.x2 are the respective outputs of the X axis accelerometers and T.sub.y1 and T.sub.y2 are the respective outputs of the Y axis accelerometers. The gravity gradiometer is also capable of obtaining all five independent components of the gravity gradient tensor based on the above Laplace equation and tensor symmetry as follows: One of the above pairs of horizontal axis accelerometers further comprises tangentially oriented horizontal accelerometers capable of providing by subtraction the T.sub.

Abstract: The gravimetry apparatus includes two rigidly connected accelerometer triads and a global positioning system antenna defining a kinematic reference point. The apparatus has a specific layout where the nominal center of the accelerometer triads and the kinematic reference point are collinear and the corresponding accelerometers of the two triads are parallel. In this gravimetry system, the lever arm correction is measured internally and the magnitude of gravity is calculated without the need for stabilized platforms or measurement of the spatial orientation of the gravimeter.

Abstract: A toilet seat alarm comprising a housing unit having pegs for insertion into a toilet seat, resembling a standard bumper placed on the underside of a toilet seat. A timing device-alarm, power source, speaker and position sensor are located within said housing unit. When the toilet seat is placed in the raised position, the position sensor activates the timing device-alarm which in turn causes the speaker to emit a series of beeps at predetermined intervals to alert the user to the position of the toilet seat.

Abstract: A method of analyzing geological survey data of the potential field measurement type is disclosed. According to the disclosed method, discrete measurement values of the potential field, either the gravitational or magnetic field, are retrieved from memory, corresponding to either a one-dimensional or two-dimensional survey region of the earth. The discrete values are first preconditioned by the application of a noise-reduction digital filter, preferably of the Weiner type. The disclosed method then performs decomposition of the filtered discrete values using the Daubechies scale function and wavelet function of length 2. According to the preferred method, the second level low-frequency component of the first level high-frequency component is generated, and expanded by a factor of four to correspond to the range of the input discrete values. Interpolation is performed to fill in values between adjacent coefficients of this component.

Abstract: A gravity gradiometer for measuring off-diagonal components of the gravitational gradient tensor includes a housing having a pair of electromagnetic shield enclosures (22, 23) arranged one inside the other, and a body (25) including superconducting material mounted within the inner enclosure (23) for fine pivotal flexure about an axis passing substantially through the centre of mass of the aforesaid body. An array of superconducting coils (30) is supported by the outer enclosure (22) and positioned in close proximity to the aforesaid body (25) for diamagnetically applying a rotational force to the body with respect to the axis of flexure and/or for responding by modulation of inductance to pivotal flexure of the body arising from a gravitational gradient across the body. The array is arranged to apply the rotational force in both rotational directions and to respond to flexure in either rotational direction.

Abstract: A gravity meter has a portable housing for holding a corner cube retroreflector that can be dropped within the housing. The housing also holds a laser and an optical fiber having a first end in light communication with the laser. Additionally, the fiber has a second end which terminates at a ferrule. Light from the laser propagates through the optical fiber, and a portion of the light is reflected by the second end of the fiber back through the optical fiber to a beam splitter, while another portion of the light propagates through the second end of the fiber and is reflected by the falling corner cube back through the fiber to the beam splitter. The two reflected portions of the laser light interfere with each other to generate an interference fringe pattern which is extracted by the beam splitter.

Abstract: A proof mass support system has a pair of alignment coils for controlling the rest position of an elongate proof mass. The alignment coils are constructed to provide a levitation force when they carry electric currents which varies along the length of the proof mass. The relative strength of the electric currents are tuned in the alignment coils to cause the proof mass to take up a predetermined orientation with respect to one or more degrees of freedom defined by the alignment coils. In an alternative, one or more anti-rotation coils may be arranged to apply a restoring force to the proof mass when electric currents pass therethrough. The proof mass is formed so as to cooperate with the restoring force which acts against rotation of the proof mass away from a predetermined orientation. The system is typically provided as part of a superconducing accelerometer or gravity gradiometer.

Abstract: A gravity meter has a portable housing for holding a corner cube retroreflector that can be dropped within the housing. The housing also holds a laser and an optical fiber having a first end in light communication with the laser. Additionally, the fiber has a second end which terminates at a ferrule. Light from the laser propagates through the optical fiber, and a portion of the light is reflected by the second end of the fiber back through the optical fiber to a beam splitter, while another portion of the light propagates through the second end of the fiber and is reflected by the falling corner cube back through the fiber to the beam splitter. The two reflected portions of the laser light interfere with each other to generate an interference fringe pattern which is extracted by the beam splitter.

Abstract: An apparatus and method for conducting a precise gravimetry survey downhole in an earth formation. The apparatus includes an elongated closed, hollow, cylindrical pressure vessel. The vessel is suspended from a vessel cable which is used for lowering and raising the vessel within a borehole. A stepper motor is mounted inside a top portion of the vessel, and includes control electronics which communicates with and is controlled by a surface system located on the surface. The stepper motor is geared to drive a winch with a gravity meter cable attached to a gravity meter so that the gravity meter cable may be used to precisely raise and lower the gravity meter inside and along the length of the elongated vessel. When the stepper motor is activated and rotates the winch, the gravity meter cable raises and lowers the gravity meter. The stepper motor is geared to the winch in a fashion so that one step of the motor corresponds with a displacement of the gravity meter in a range of from about 0.01 to about 0.

Abstract: A gravity meter includes a support framework which supports a suspension system having a weight beam to which a reaction mass is attached. The reaction mass includes a dielectric mass which extends partially within first and second cavities formed between respective first and second pairs of conductors. Changes in either the ambient gravitational field or the electric potential on the conductors causes the dielectric mass to move into the first cavity between the first pair of conductors and out of the second cavity between the second pair of conductors or vice-versa, with the force on the dielectric mass being linearly proportional to the voltage between the conductors. An optical detector system determines the position of the weight beam, thus the position of the dielectric mass, and is connected to the voltage source for the plates so that, by adjusting the electric potential between the plates, the weight beam can be moved to a nulled position.

Abstract: A terrain estimation system and procedure in which prior knowledge of terrain configuration is taken as a starting point in the estimation procedure. The gravity field of the earth is sensed by a gradiometer which measures the gravity gradient as the gradiometer is transported by a moving platform past the earth's surface to obtain data of the topology of the earth's surface and of the geology of the terrain including subterranean oil and iron deposits. Optimal filter means, operative in response to a statistical model of terrain and residual geology predict values of gravity gradient to be sensed by said gradiometer at successive locations along a path of travel. Comparison is made between measured and predicted values of gravity gradient to update terrain altitude data by nulling a difference between measured values and predicted values of gravity gradient.

Abstract: A gravity gradiometer and method for measurement of changes in the intensity of a gravitational field experienced during traversal over earth's terrain, or past a massive object, has a set of eight accelerometers disposed on rotating disc, or on a pair of parallel discs, and arranged uniformly about a central rotational axis of the disc, or of the pair of discs. Each accelerometer develops a signal for maintaining a pendulum in its position of swing along an input axis of the accelerometer. Each input axis, for all of the accelerometers, is perpendicular or parallel to a radius of a disc. The accelerometers are treated as two groups of four accelerometers wherein, in each group, the accelerometers are disposed in pairs about perpendicular diameters of the disc or the pair of discs.

Abstract: A gravity gradiometer instrument alternately and sequentially rotatable in opposing angular increments provides a measure of the gravity gradient in-line and cross components without requiring real-time generation of trigonometric harmonic components, continuous demodulation to separate the component data signals, or filtering. Demodulation of the output data is accomplished by simple summing of the data from successive angular positions of radially opposing accelerometers. Precise control of the rotational speed is not required. Further, the accelerometer complement is minimal and because the direction of rotation is periodically reversed, a twist capsule is used rather than slip rings, thereby avoiding the noise and maintenance problems associated therewith.

Abstract: A superconductive gravimeter comprises a spool (12, 14, 16) and a circumferential magnet (20, 22, 24), both of which are covered with superconductive material (48, 52, 58, 60) except at the magnetic field gaps (54, 56, 62, 64) between them. A force rebalance coil (28, 30) lies in these gaps and supports a superconductive plate (70) above them. Leakage flux flows through the space between the plate and the circumferential magnet. Variations in gravity result in variations in the weight of the plate, resulting in variations in the height of the space, resulting in variations in the flux in the space, which are detected by a pick up coil (74).

Abstract: A method of making for an area a map or a representation of regional variations in the position of the geoid which have an amplitude less than about 1 m. and are caused by density variations in the underlying sea floor. The map or representation is intended primarily for use in the determination of part areas of the sea floor with increased probability of deposits of natural resources, the density of which part areas distinguishes from that of the surroundings.

Abstract: The invention is a neutral atom (and/or molecule) matter-wave interferometer (and/or set of interferometers) that can be used as an inertial sensor with a sensitivity exceeding that of conventional mechanical sensors and multiple circuit optical interferometers (including ring lasers) by many powers of ten. An interferometer in which matter-wave propagation beam paths enclose a finite area will sense rotations via the Sagnac effect. One with the paths displaced from each other will sense acceleration plus gravity. Interferometers with paths that follow a figure-eight pattern yield a gravitational gradiometer. Laser cooling and slowing of a beam of neutral atoms provides a low energy nearly monochromatic source. Diffraction gratings are employed as beam splitters. Such gratings may consist of apertures in a sheet of solid material, near-resonant standing-wave laser beams, or crystal faces.

Abstract: An apparatus and method for measuring the vertical gradient of the vertical gravitational field using a gravity gradiometer comprising a housing containing a fluid, a float buoyantly supported within the fluid, mechanism for varying the metacentric height of the float, and apparatus for obtaining a measure of the gravitational gradient acting on the float resulting from varying the metacentric height.

Abstract: Apparatus and method for establishing a level plane and with respect to the level plane, vertically aligning an acceleration sensitive axis of a gravity measurement device (10). The gravity measurement device includes an accelerometer (68), which is rotatably mounted on a gimbal shaft (62) within a gimbal frame (54). The gimbal frame is also rotatable about a longitudinal axis that is preferably oriented at a right angle to the longitudinal axis of the gimbal shaft. A stepping motor (20) is connected through an antibacklash gear (30), an idler gear (32) and an antibacklash gear (48) to a drive shaft (50). Rotation of this drive shaft causes the accelerometer to rotate about the gimbal shaft. In a similar fashion, a stepping motor (22) is drivingly connected to a drive shaft (56), used to rotate the gimbal frame.

Abstract: A system which detects the presence and bearing of a mass M implemented by having a first field or wave interact with the motion of a charged mass m to produce a second field or wave which is modulated by the tidal effect of mass M. The second field or wave with unique tidal signal is then detected. The system can be implemented as a magnetic resonance spectrometer, gyrotron, cyclotron, Fourier Transform-Mass Spectrometer (FT-MS), or even as a large spinning mass and permits the substantial increase in the sensitivity of practical gravitational mass detectors and gradiometers and thereby permitting the detection of earthbound objects such as ore deposits, ships, submarines, tanks, artillery, and small concealed handguns and may extend gravitational mass detection capabilities to space and galactic objects.

Abstract: Each accelerometer includes a cylindrical proof mass made of a superconducting material. Each proof mass includes annular upper and lower hollowed out portions longitudinally surrounded by a cylindrical exterior wall. Common mode and differential mode sensing coils are arranged adjacent a bottom-side surface of the proof mass in one hollowed out annular portion and a levitation coil is arranged adjacent a bottom-side surface of the proof mass in the other hollowed out annular portion. The common mode, differential mode and levitation coils are connected in respective first, second and third superconducting circuits. The first circuit produces common mode signals indicative of forces acting on both accelThis invention was made with government support under Contract No. NAS 8-36165 awarded by the National Aeroanutics and Space Administration. The government has certain rights in this invention.

Abstract: A digitizer for a gravity meter having a rotatable gradient readout dial and a null indicator, the digitizer comprising a shaft position sensor attached to the readout dial for providing a digital output signal representation of clockwise and counterclockwise rotation of the readout dial during nulling of said indicator, a microprocessor coupled to the shaft position sensor for receiving and storing the sensor digital output signal representation and means in the microprocessor for analyzing the stored digital output signals from the shaft position sensor and producing and storing a digitized output signal representing the gravity in the form of the average position of the readout dial on the gravity meter.

Abstract: A continuous gravimetry survey is carried out with a gravity logging tool having a column of fluid within the tool. First and second pressure sensors are located at spaced-apart axial positions within an upper portion of the fluid column. Third and fourth pressure sensors are located at spaced-apart axial positions within a lower portion of the fluid column. The outputs from the first and second pressure sensors are differenced to produce a first pressure difference signal. The outputs of the third and fourth pressure sensors are also differenced to produce a second pressure difference signal. The difference between these first and second pressure difference signals is related to the gravity gradient along the earth formation adjacent the fluid column. Such a gravity gradient is a continuously moving gradient that is insensitive to acceleration effects from unsteady motions of the logging tool as it traverses the earth formation during the gravimetry survey.

Abstract: A tuned borehole gravity gradiometer comprises a dipole mass system having means for selectively tuning the sensitivity of the gravity gradiometer to detect variations in the earth's gravity gradient within a borehole. The tuning means includes varying the metacentric height of the dipole mass system by selectively varying the center of gravity of the dipole mass system with respect to the metacenter of the dipole mass system.

Abstract: Method and apparatus for determining the vertical gradient of the vertical gravitational field by a single measurement, for example, adjacent an earth formation of interest, are provided.

Abstract: A gravity anomalometer has dual units arranged in longitudinal alignment in a tube which in turn is maintained in substantially constant alignment with the center of gravity of the earth. Each unit has an upper electric member providing support for the mass and a similar lower electric member, with each member having an opening facing the opposite member. A single sensing mass initially supported in the upper member of each unit falls under the influence of gravity when the upper member is deenergized and is caught by the lower member when the latter is energized, after which the mass is returned to the upper field in a repeating cycle. Electronic means measure the rate of each fall of the mass. Since the mass in the upper unit is further from the earth's center of gravity than the mass in the lower unit the time consumed in a corresponding fall is less in the upper unit than in the lower unit. The difference in rate accordingly is made use of in determining the gravity gradient in a selected area.

Abstract: A gravity gradiometer disposed upon a gyroscopically stabilized platform in a vehicle can be modified, without impairment of its normal operation, to perform compassing functions.

Abstract: An instrument for detecting and making use of a charged particle located in a vacuum and contained by a cubic array of electrically chargeable electrodes is programmed to have the charged particle constantly in motion. A sensing means for each of three sets of plates becomes operative when the particle reaches a preset distance from the center of the array to trigger a pulse adapted to reverse the direction of movement of the particle. The instrument is one capable of detecting and measuring acceleration along three coordinate axes and rotational translations relative to inertial space and/or a gravity reference. It is also one for static and in-motion gravity and gravity gradient measurement. There is additionally a built-in detector of comparable accuracy capable of using the same particle to detect malfunction of the instrument.

Abstract: The output of the vertical accelerometer of a ships inertial navigation sem (SINS), in pulse form, is first counted and scaled to provide an output related directly to the total acceleration. The SINS computer provides the latitude, and north and east velocities of the ship, which are then converted into the theoretical gravity and the Coriolis error. These two factors are subtracted from the total scaled acceleration, and the resultant output is passed through a filter that corresponds to a particular weighting function (heavily weighted for the middle time) to remove the factor of ships heave acceleration. The final output is the free-air gravity anomaly in terms of real time.

Abstract: Gravity gradiometer including a ring laser cavity, two modulator elements in the path of the laser beam, and spaced masses attached to the modulator elements to provide a differential modulation of circular polarization modes proportional to the difference in gravity at the location of the two masses. In one form, a biasing element is added to shift the operating point of the laser system to improve performance.

Abstract: To locate potentially hydrocarbon-bearing subsurface formations, tiltmeters measure the time of arrival and the apparent direction of a lunar/solar induced earth tide at an array of points on the earth's surface. The measurements are combined to determine the shape of the tidal wave in a region of interest. The shape is indicative of subsurface viscosity in the region. Subsurface formations having an abnormally low viscosity are considered potentially hydrocarbon bearing.

Abstract: A gravity gradiometer using at least one mass dipole mounted in a laser force-measurement system to detect the torque on the mass dipole generated by gravity gradient. The mass dipole is mounted on one end of a photoelastic modulator element positioned in the laser beam to differentially modulate circular polarization modes in response to application of a torque. In a preferred form, two mass dipoles are mounted on opposite ends of the modulator element which is rigidly supported at its center to improve noise rejection.