Abstract: A method of geologic exploration for subsurface deposits includes the steps of: emitting energy below a surface of the earth; sensing a plurality of reactive electro-magnetic waves resulting from the emitted energy; outputting signals from a plurality of sensors to a vehicle corresponding to the sensed reactive electro-magnetic waves; determining position data for the plurality of sensors; generating position marked data corresponding to the outputted signals and the position data; uploading the position marked data from the vehicle to a satellite; and relaying the position marked data from the satellite to a remote analyzing station.

Abstract: A non-destructive inspection apparatus includes a transmitting section, a reception section and a processing unit. The transmission section irradiates an electromagnetic wave signal toward an inspection target. The reception section receives a reflected electromagnetic wave signal from the inspection target to generate a received wave signal. The processing unit generates a fundamental reflected wave signal predicted to be received from each reflection point of the inspection target, and determines the existence or nonexistence of any defects in the inspection target and the details of the defect, if it exists, based on a pattern matching between a waveform of the received wave signal and a waveform of a linear combination of fundamental reflected wave signals.

Abstract: An electromagnetic prober comprising a transmission antenna, a reception antenna, a reception signal processing section for generating an analytic signal on the basis of a detection signal of the reception antenna, and an analytic processing section for performing a predefined analytic process on the basis of the analytic signal, wherein the analytic processing section divides the analytic signal into a plurality of time-based ranges and performs a predefined computation on average cycle periods in the respective time-based ranges of the analytic signal to calculate average dielectric constants in depth ranges of the medium corresponding to the respective time-based ranges.

Abstract: A system for detecting or determining the nature of a subterranean reservoir. An electromagnetic field is applied using a dipole antenna transmitter and this is detected using a dipole antenna receiver. The measurements are taken with the antenna both in-line and parallel and the difference between the two sets of measurements is exploited. A characteristic difference indicates a high resistive layer, which corresponds to a hydrocarbon reservoir.

Abstract: An induction logging tool is used on a MWD bottom hole assembly. Due to the finite, nonzero, conductivity of the mandrel, conventional multi frequency focusing (MFF) does not work. A correction is made to the induction logging data to give measurements simulating a perfectly conducting mandrel. MFF can then be applied to the corrected data to give formation resistivities.

Abstract: A method and apparatus for minimizing direct coupling between transmitters and receivers on a downhole logging tool are disclosed. One embodiment includes a transmitter, a bucking device, and a plurality of receivers, where signals may be directly coupled from the transmitter into the receivers and signals may be indirectly coupled from the transmitter into the receivers through the formation and borehole environment. The bucking device minimizes the magnitude of the signals that are directly coupled from the transmitter into multiple receivers within the plurality. By varying the current in the bucking device, the bucking device minimizes the magnitude of the directly coupled signal of each receiver in the plurality, and each receiver may utilize a common bucking device.

Abstract: A method for mapping a submarine or subterranean reservoir by conducting an electromagnetic survey using an electromagnetic field in the form of a wave. An electromagnetic field is applied by a transmitter on the seabed and detected by antennae. The nature of the detected reflected waves is used to determine whether the reservoir contains water or hydrocarbons, which may then be produced from a well that penetrates the reservoir.

Abstract: A method and apparatus for use within a borehole for simultaneously determining the horizontal resistivity, vertical resistivity, and relative dip angle for anisotropic earth formations. An antenna configuration in which a transmitter antenna and a receiver antenna are oriented in non-parallel planes such that the vertical resistivity and the relative dip angle are decoupled. Preferably, either the transmitter or the receiver is mounted in a conventional orientation in a first plane that is normal to the tool axis, and the other antenna is mounted in a second plane that is not parallel to the first plane. Also included are a method and apparatus for steering a downhole tool during a drilling operation in order to maintain the borehole within a desired earth formation. The steering capability is enabled by computing the difference or the ratio of the phase-based or amplitude-based responses of the receiver antennas which are mounted in planes that are not parallel to the planes of the transmitter antennas.

Abstract: A system for investigating subterranean strata. An electromagnetic field is applied using a dipole antenna transmitter and this is detected using a dipole antenna receiver. Phase information is extracted from a refracted wave response and used to identify the presence and/or nature of a subterranean reservoir.

Abstract: A system for investigating subterranean strata. An electromagnetic field is applied using a fixed dipole antenna transmitter and this is detected using a dipole antenna receiver. The receiver is moved from one location to another in dependence upon the strength of the detected signal.

Abstract: Methods and devices are disclosed for determining if hydrocarbons or water is present in a subterranean reservoir are described. Certain embodiments involve an electromagnetic field applied by a transmitter on the seabed and detected by at least one antenna also on the seabed, wherein a refracted wave component is sought in the wave field response, and is analyzed to determine the nature and contents of the resevoir.

Abstract: An in-line system and method for determining T-top gate dimensions is provided. The system comprises a wafer structure undergoing a T-top gate formation process; a scatterometry system coupled to the formation process for directing light at and collecting reflected light from the wafer structure; a signature store; a T-top gate formation analysis system coupled to the scatterometry system and to the signature store for determining the T-top gate dimensions; and a feedback control system coupled to the T-top gate formation analysis system for optimizing T-top gate formation. The method comprises providing a wafer structure having a T-top gate formed thereon; generating a signature associated with the T-top gate; comparing the generated signature with a signature store to determine the dimensions of the T-top gate; if the dimensions of the T-top gate are not within a pre-determined acceptable range, then adjusting T-top gate process parameters using feedback control.

Abstract: The invention relates to techniques for locating and determining the orientation of a fracture in an earth formation. Systems and methods for detecting a fracture in an earth formation using a propagation tool include producing electromagnetic fields using a TMD transmitter in the tool; measuring corresponding voltage signals detected with one or more TMD receivers in the tool; determining harmonics from the measured signal responses by shifting the responses (e.g. by 90 degrees) and performing an addition or subtraction using the shifted response. In some embodiments, the second harmonic is processed to determine the fracture orientation.

Abstract: A system for investigating subterranean strata. An electromagnetic field is applied using a fixed dipole antenna transmitter and this is detected using a dipole antenna receiver. The receiver is moved from one location to another in dependence upon the strength of the detected signal.

Abstract: The invention relates to techniques for locating and determining the orientation of a fracture in an earth formation. Systems and methods for detecting a fracture in an earth formation using a propagation tool include producing electromagnetic fields using a TMD transmitter in the tool; measuring corresponding voltage signals detected with one or more TMD receivers in the tool; determining harmonics from the measured signal responses by shifting the responses (e.g. by 90 degrees) and performing an addition or subtraction using the shifted response. In some embodiments, the second harmonic is processed to determine the fracture orientation.

Abstract: A system for determining the nature of a subterranean reservoir whose position and geometry is known from previous seismic surveys. An electromagnetic field is applied by a transmitter 18 on the seabed 14 and detected by antennae also on the seabed. The nature of the detected reflected waves is used to determine whether the reservoir contains water or hydrocarbons.

Abstract: Well logging apparatus and methods for determining formation resistivity at multiple (>3) depths of investigation. At least one transmitter antenna and at least two receiver antennas are mounted in a logging tool housing, on substantially a common axis. The antennas are untuned coils of wire. Electromagnetic energy is emitted at multiple frequencies from the transmitter into the formation. The receiver antennas, which are spaced apart from each other and from the transmitter, detect reflected electromagnetic energy. Formation resistivity at multiple depths of investigation is determined using only phase differences in the reflected energy at the different frequencies, minimizing false indications of invasion due to mismatch of vertical response with attenuation measurements and also permitting correcting for the effects of varying dielectric constant of the formation.

Abstract: A method for investigating subterranean strata. An electromagnetic field is applied using a dipole antenna transmitter and this is detected using a dipole antenna receiver. Phase information is extracted from a refracted wave response and used to identify the presence and/or nature of a subterranean reservoir.

Abstract: A system for investigating subterranean strata. An electromagnetic field is applied using a fixed dipole antenna transmitter and this is detected using a dipole antenna receiver. The receiver is moved from one location to another in dependence upon the strength of the detected signal.

Abstract: A system for determining the nature of a subterranean reservoir 12 whose position and geometry is known from previous seismic surveys. An electromagnetic field 24, 25, 26, 27 is applied by a transmitter 18 on the seabed 14 and detected by antennea 21, 22, 23 also on the seabed 14. The nature of the detected reflected waves 25, 26, 27 is used to determine whether the reservoir 12 contains water or hydrocarbons.

Abstract: The invention subject of this application pertains to a method and apparatus for measuring the subterranean lithology using electromagnetic energy. The invention is applicable to the measurement from within uncased boreholes, i.e., and open-holes. The present invention transmits and receives electromagnetic energy deep into a geologic formation from a borehole, while also providing high resolution for distant measurements and the ability to control the direction in which the measurements are taken. The invention does not require a receiver to be located at the ground surface or in another borehole. In simple terms, the apparatus of this invention is able to “look around” into the surrounding geologic formation from a stationary position.

Abstract: A monitoring device defines a boundary for movement of an underground object such as a booring tool. The underground object generates a magnetic field which is detected by the monitoring device. The monitoring device then determines the position of the underground object relative to itself, and hence to the boundary. The movement of the underground object can then be controlled so that it does not cross the boundary. The monitoring device may therefore define a protection zone so that a buried object within that protection zone will not be contacted by the moveable underground object.

Abstract: Most mines and underground facilities employ standardized construction techniques and materials. Such also cannot avoid having some above ground openings to receive utilities, fresh air, supplies, etc. Those or other surface openings are also universally used to discharge ground water, wastes, and other materials. Typical underground facilities have abundant electrical wiring and power demands, both of which can be detected at the surface. Levees with leakage pathways also form electrical conductors. When properly illuminated with remotely generated electromagnetic (EM) radiation, many of these features will “glow” or reradiate the radio energy in an electronic signature unique to the underground facility. Synchronized EM-gradiometer transponders are situated nearby on the ground surface to collect and analyze the “glow”. Alternative transmitting devices further includes ways to generate the illumination, and computers for characterizing the return signatures.

Abstract: This invention is directed to a downhole method and apparatus for simultaneously determining the horizontal resistivity, vertical resistivity, and relative dip angle for anisotropic earth formations. The present invention accomplishes this objective by using an antenna configuration in which a transmitter antenna and a receiver antenna are oriented in non-parallel planes such that the vertical resistivity and the relative dip angle are decoupled. Preferably, either the transmitter or the receiver is mounted in a conventional orientation in a first plane that is normal to the tool axis, and the other antenna is mounted in a second plane that is not parallel to the first plane. This invention also relates to a method and apparatus for steering a downhole tool during a drilling operation in order to maintain the borehole within a desired earth formation.

Abstract: A system for investigating subterranean strata. An electromagnetic field is applied using a dipole antenna transmitter and this is detected using a dipole antenna receiver. Phase information is extracted from a refracted wave response and used to identify the presence and/or nature of a subterranean reservoir.

Abstract: A system for investigating subterranean strata. An electromagnetic field is applied using a fixed dipole antenna transmitter and this is detected using a dipole antenna receiver. The receiver is moved from one location to another in dependence upon the strength of the detected signal.

Abstract: Most mines and underground facilities employ standardized construction techniques and materials. Such also cannot avoid having some above ground openings to receive utilities, fresh air, supplies, etc. Those or other surface openings are also universally used to discharge ground water, wastes, and other materials. Typical underground facilities have abundant electrical wiring and power demands, both of which can be detected at the surface. Levees with leakage pathways also form electrical conductors. When properly illuminated with remotely generated electromagnetic (EM) radiation, many of these features will “glow” or reradiate the radio energy in an electronic signature unique to the underground facility. Synchronized EM-gradiometer transponders are situated nearby on the ground surface to collect and analyze the “glow”. Alternative transmitting devices further includes ways to generate the illumination, and computers for characterizing the return signatures.

Abstract: This patent application is to use dynamic electromagnetic wave reflection and refraction methods for prospecting for oil directly. The available geophysical methods including the most used seismic reflection method are all prospecting for oil indirectly, viz., aiming at finding the geological structures and stratigraphic traps, etc. The high contrasts of electric permittivity between oil cord the surrounding geological formations of rocks including gas, water (fresh and salt), on the other hand, make it possible to use the dynamic electromagnetic wave reflection and refraction methods for prospecting for deep seated oil directly.

Abstract: Apparatus and method is provided for performing detailed mine detection over variable terrain. An articulated robotic scanner comprises an articulated arm mounted to any vehicle such as a robot. One or more mine detectors mounted at the end of the arm. The arm operates autonomously to repetitively sweep the mine detector in ever forward advancing side-to-side arcs over the terrain. The vehicle can operate autonomously or be tele-operated. The position of the mine detector is monitored and known with respect to a known coordinate system. Sensors measure their position relative to the ground and relative to known co-ordinates of the mine detector. A controller determines the relative position of the ground and the mine detector and dynamically adjusts the mine detector's position to maintain a constant separation over variable terrain without ever contacting the ground or objects thereon.

Abstract: An electromagnetic (EM) survey system for determining the presence of liquid or gaseous deposits within the earth's interior. The system includes an EM pulse generator for generating the EM pulses, a data acquisition system for receiving and processing reflected signals from the earth's interior caused by the EM pulses, and a data processing system for analyzing the reflected signals to determine the presence of fluids in the earth's interior. Delivery of the EM pulses to the earth's interior can be accomplished either invasively or non-invasively. In an invasive manner, the EM pulse is delivered to the earth's interior via a set of electrodes buried shallow into the ground. In a non-invasive coupling, the EM pulse is delivered to the earth's interior via a wire loop. The reflected signals are received from the earth's interior via one of a wire loop, set of electrodes, wire antenna, or rod antenna array.

Abstract: A multisensor vehicle-mounted mine detector having one or more sensors leading the vehicle for detecting objects in the ground while moving. A navigational system tracks the coordinates of the detected objects, performs data fusion, declares whether the object is a target worthy of interest and if so, stops the vehicle with a trailing thermal neutron activator sensor (TNA) over the coordinates of the object and interrogating the object with slow neutrons to confirm whether it contains sufficient nitrogen to indeed be a mine. The TNA confirmation is kept brief due to the use of a strong source coupled with means for analysing the resultant pulses and rejecting piled-up pulses. The difference between an integration of the entire pulse and a portion of the pulse is compared against a predetermined difference for a normal pulse wherein variations therebetween are indicative of a piled-up pulse which is then rejected.

Abstract: Apparatus, and related method, for remotely measuring at 1east one environmental condition includes an electromagnetically resonant sensor having a measurable resonance characteristic (e.g., center resonance frequency, quality factor, or bandwidth) that varies in correspondence to changes in the environmental condition present at the sensor. The sensor emits an electromagnetic return signal representative of a state of the resonance characteristic when an electromagnetic excitation signal impinges on the sensor. The electromagnetic excitation signal is generated by a generator located separate and away from the sensor, and the excitation signal is then directed at the remote sensor. The sensor thus remotely detects and measures the environmental condition. In one embodiment, the sensor is an electromagnetically resonant electrical circuit. In another embodiment, the sensor is an antenna resonator (e.g., a half-wavelength antenna) made of a conductive material.

Abstract: Apparatus for use in a geophysical prospecting method from a vehicle for site plan pictorial representation of inclusions present in substratum soil which reflect modulated electromagnetic oscillations. This apparatus is particularly useful for detecting inclusions such as veins of water, ore beds, pipelines, unexploded bombs, cavities, ammunition and residual fissures. A transmitter and receiver are mounted in the vehicle with a common quartz oscillator in a sawtooth generator. A transmitting antenna and receiving antenna are provided with an amplifier connected to the latter. A pulse shaper employs the width of received triangular pulses from the amplifier to give needle pulses and a color transmitter has four power amplifiers and is a goniometrically scanned four-cycle transmitter, and accordingly the cathode ray tube has four crosswise arranged horizontal sweep coils in addition to the frame coil.

Abstract: An intrapipe work robot apparatus includes an intrapipe work robot and an operation unit. The intrapipe work robot is inserted into a pipe so as to perform a work while performing automotive traveling in the pipe. The operation unit designates travel and other actions of the robot externally of the pipe. The operation output signal is transmitted from at least the operation unit to the intrapipe work robot through a radio communicating device having special antenna units.

Abstract: A method of and apparatus for the deconvolution of response data obtained from transmission of a maximum length sequence, wherein the samples of incoming data are deconvoluted and stored in a reconstruction buffer as said samples are received. It is possible in this way to employ a reconstruction buffer shorter than that necessary to store the complete deconvoluted waveform.

Abstract: A ground condition monitor includes a housing for disposal underground, a power source disposed in the housing, and a controller disposed in the housing and in communication with the power source and with a plurality of sensors. The sensors are adapted to receive signals from the controller and in response thereto to send electromagnetic excitation signals into surrounding earth, receive reflective electromagnetic signals from the surrounding earth, and feed the reflective signals to the controller, which is adapted to convert the reflective signals to data indicative of electromagnetic properties of the surrounding earth, and to transmit the data.

Abstract: A device for detecting the position of a physical defect on a buried pipe includes a leak-of-fluid signal detector, a number of vibration signal detectors, and a device body and can detect the position of a site of a leak, into the ground, of a fluid running through a fluid pipe buried beneath the ground surface. The device body calculates vibration amplitudes and speeds via associated vibration signal detectors with the use of the outputs of the respective vibration signal detectors, calculates cross-correlation functions of the vibration amplitudes and speeds with the use of the vibration amplitudes and speeds and the output of the leak-of-fluid signal detector, calculates the amplitude intensity for each cross-correlation function, and generates resultant vector data representing the position of the leak-of-fluid site with the use of the vibration intensity.

Abstract: Earth formation evaluation for detection of hydrocarbon fluids is carried out by a microwave frequency range sensor (antenna or wave guide) disposed in the face of a diamond or PDC drill bit configured to minimize invasion of drilling fluid into the formation ahead of the bit. The sensor is connected to an instrument disposed in a sub interposed in the drill stem for generating and measuring the alteration of microwave energy. In particular, the dielectric constant of the earth formation in a zone which is substantially uninvaded by drilling fluid may be detected and compared with density and/or porosity logs to determine the presence of hydrocarbons in relatively thin layers of formation material.

Abstract: A method in accordance with the invention is implemented via a computer program to determine the density and water (or other fluid) content of the various layers within a multilayer system. For convenience, the program is referred to as SIDARS. A conventional ground penetrating radar (GPR) system is used to obtain digitized images of a reflected radar signal from a multilayer pavement system. From these images standard mathematical techniques are applied to determine the number of layers, the thickness of each layer, and the dielectric constant for each layer within the multilayer system. SIDARS takes advantage of the fact that each layer is itself composed of three distinct types of material: solids, fluids, and gases. Thus, the dielectric constant obtained for a layer is in fact a composite value, namely a combination of the layer's solid, fluid, and gas dielectric constants. SIDARS employs a wave propagation model of the pavement system to generate a synthetic reflected radar signal.

Abstract: An underground radar tomography in which an electromagnetic wave is radiated into the ground, the amplitude and propagation time of a transmitted wave, a reflected wave or a diffracted wave of the electromagnetic wave are measured at a number of points, and signal processing is performed on the result of measurement to thereby obtain the distribution of strata and soil in the ground as section information with a high accuracy. By use of two pseudo random signals which are slightly different in period but the same in code pattern, measurement time which is expanded relative to propagation time is obtained to thereby make the measurement accuracy high.

Abstract: A pavement structure examination vehicle capable of mounting all necessary equipments and instruments therein; including a body of a rear gate type having a rear door which rotates vertically to open and close, underground radar means attached to the body vertically movably relative to the direction of traveling, a stand for boring operation to be removably attached to the door, a radar system comprising underground radar control means for controlling the underground radar means and observation data recording means for recording the observation data of the underground radar means, the radar system recording in the data recording means information of the distance covered by the vehicle received from covered distance detection means which detects the distance covered by the vehicle, together with the observation data of the underground radar means, and an image processing system for photographing a surface of an inner circumferential wall of a bored hole and processing images thus photographed.

Abstract: A tool for evaluating electrical properties of an earth formation surrounding a borehole while drilling the borehole is disclosed. The tool includes a housing for connecting upper and lower portions of a drillstring, a transmit antenna for generating electromagnetic waves at least two receiving antennas for receiving electromagnetic waves and magnetic elements associated with each of the antennas for electromagnetically coupling each of the antennas with the formation. The tool provides improved transmit efficiency and improved receiving sensitivity.

Abstract: In a logging tool which transmits electromagnetic radiation into adjacent formations, and including such tools which operate as low as 20 Khz (typical for induction logs) up to as high as the gigahertz range, an improved antenna system is set forth. The antenna preferably transmits a circular polarized signal so that reflected and refracted return constituents in the receiver signal can be sorted out. For intermediate frequencies, the antenna can be potted in a high dielectric constant material.

Abstract: An apparatus and method for detecting vertically or horizontally oriented underground electrical conductors such as electrical wiring or rails in tunnels thin conducting ore veins surrounded by less conducting rock, or boreholes filled with conductive water or lined with a conductive casing. The apparatus includes a surface or downhole transmitter and a downhole receiver connected to a coherent frequency source unit by fiber optic cables. The source unit generates two phase synchronized frequency signals in the range of one hundred to three hundred kHz. The receiver includes a vertical or horizontal magnetic dipole antenna, e.g. a ferrite rod antenna, and the transmitter includes a vertical or horizontal magnetic dipole antenna in the downhole configuration or at least one long cable or loop antenna in the surface configuration.

Abstract: If electromagnetic waves are emitted from a plurality of points on the ground surface above a material (TG) buried under the ground, an echo image (EP) formed from the data of propagation times of reflected waves at each of the points describes a hyperbola as a result of expansion of the transmitted electromagnetic waves. An operation is carried out to overlap on the echo image (EP) a false echo image (DM) which lies on the same coordinate system and which consists of a similar hyperbolic image. If the two echo images (DM, EP) are overlapped upon each other as the result, the vertex position and the expansion of the opening of the echo image (EP) can be determined from the data of the false echo image (DM). The propagation velocity of electromagnetic waves under the ground is then calculated from the data that represents the vertex position and the expansion of the opening.

Abstract: An object detection method and apparatus in which, in order to distinguish only an echo wave which is returned back from an object of interest, such as an underground buried object, from those echo waves returned back from another object of objects, the observation signal is divided (an electromagnetic wave as an echo wave) into portions, and the signal portion is converted into a corresponding frequency region to evaluate that spectral distribution and computes frequency parameter values from the spectrum distribution. The object of interest is detected by comparing the reference data of various fields with the parameters of the object of interest, extracting only an echo wave returned back from the object of interest and displaying a corresponding image.

Abstract: A method and apparatus for producing data indicative of the presence of buried objects, wherein two waveforms I(t) Q(t) are combined with two reference waveforms Ir(t) Qr(t) using filters 10, 12, 14, 16 of two types A, B. Type A has time response Ir(-t) and type B has time response Qr(-t). The products {I(t)@Ir(t)}.multidot.{Q(t)@Qr(t)} and {I(t)@Qr(t)}.multidot.{Q(t)@Ir(t)} from multipliers 18, 20 are subtracted to give V1 and added to give V2 in the combiner 30. A list of object distances (36) is derived from V1. A list of object orientations (46) is derived from V2. Object times (34) are used to section V2 at (40) on a time basis. A correlation operation is represented by @. The invention is particularly applicable to location of buried pipes using ground probing radar, but is also useful in locating planar objects and in other systems. The waveform combination suppresses noise and clutter. I(t) and Ir(t) are quadrature versions of Q(t) and Qr(t). The emitted radiation is circularly polarized.

Abstract: A method for determining a sonde error characteristic of an induction tool is disclosed. The method includes the step of measuring an electrical characteristic which may be the real or quadrature component of conductivity, at two or more different heights above the earth. The sonde error characteristic is determined as a function of a predetermined relationship between the desired sonde error characteristic and the measurements of that characteristic at two or more different heights above the earth. The method may be performed with the tool disposed substantially parallel to the earth. Alternatively, the tool may be disposed substantially perpendicularly to the earth.

Abstract: In a shield machine, there are provided an electromagnetic wave transmitting and receiving unit mounted on the top of the shield machine for radiating electromagnetic impulse wave toward an underground and for receiving the electromagnetic wave reflected from the underground, and a position sensor for collecting an information regarding the position of the electromagnetic wave transmitter and receiver unit. Data processing unit is provided for processing the signals from transmitter/receiver and the position sensor and sent through a transmission line. The data processing unit continuously displays the condition of the underground at the cutting face.

Abstract: A method of seismic prospecting using electromagnetic grounded antennas to detect electromagnetic waves that are produced from acoustic waves in the earth's formation. Seismic waves reflected by a formation in the earth are converted into electromagnetic waves in the vicinity of the antenna according to the streaming potential theory. The antenna has two electrodes which detect the horizontal component of the electromagnetic waves, thus providing additional seismic information that is not readily available using standard geophones. Antennas are also not subject to coupling problems and thus provide more accurate information than traditional geophones. For example, using multicomponent detection, all three components of the seismic pressure gradient can be detected.