RU2771749C2 - Data collection device and method - Google Patents

Abstract

FIELD: information technologies.

SUBSTANCE: group of inventions relates to the collection of vector component data. A device for the collection of vector component data contains a spherical support mounted on a base node and a tool platform with at least one vector component sensor attached to it. The tool platform is mounted on the spherical support and supported by it. The spherical support connects the tool platform to the base node and allows for free angular rotation of the tool platform within the range of an inclination angle. The tool platform has a mass center located under a rotation center.

EFFECT: increase in the accuracy of collection of geophysical vector component data.

25 cl, 14 dwg

Description

FIELD OF TECHNOLOGY TO WHICH THE INVENTION RELATES

[0001] The present invention relates to the collection of vector component data. In particular, the invention relates to the collection of data from a mobile carrier.

BACKGROUND OF THE INVENTION

[0002] Electromagnetic (EM) survey systems detect electromagnetic fields scattered from the Earth and are widely used to map electrical properties, mainly changes in conductivity, as well as sensitivity to polarizability, permittivity, and magnetic permeability. Some electrical properties can be associated with different geological entities, so electromagnetic survey data can be used to determine the presence or likelihood of various raw materials such as oil, minerals, and groundwater.

[0003] An electromagnetic survey system typically responds to the presence of a quasi-static, time-varying electrical current in the ground. The electrical properties of the Earth can be determined by measuring the change over time in the magnetic field created by this current using a magnetic field sensor. Time-varying fields may be produced by a local transmitting antenna in the case of a controlled source, or by surrounding geomagnetic fields in the case of natural source systems.

[0004] The movable electromagnetic survey system may use a movable carrier to transport and hold the magnetic field sensor while collecting data. In a mobile electromagnetic survey system, the carrier may comprise a towed sensor (or probe) that may be suspended below the aircraft on a towline. Popular varieties of aeroelectromagnetic (AEM) imaging systems tow the sensor under a helicopter, typically on a towline that varies in length from 30 to 90 meters. An AEM survey typically covers an area using parallel flight paths separated by a fixed lateral separation.

[0005] To detect the presence of deep geological objects, the collection of low-frequency EM data is preferred. At present, AEM systems are usually limited to collecting data at 20-25 Hz and above. Data collection in the range below 25 Hz would allow detection of geological objects that cannot be detected using existing AEM systems. In the frequency band below 25 Hz, the magnetic field strength due to conduction changes detected by EM systems is generally proportional to frequency. As the collection frequency of an electromagnetic system decreases, the magnetic fields dissipated due to these changes in conductivity become weaker. To detect changes in conductivity due to the deep structures of the Earth, a magnetic field sensitivity of the order of picoTesla may be required.

[0006] Electromagnetic survey systems typically detect EM fields using vector component sensors. Many types of magnetic (EM) vector component sensors can be used to measure the electromagnetic field, including search coils, feedback coils, superconducting magnetometers, fiber optics, and fluxgate magnetometers. When a magnetic field is detected by a coil, according to Faraday's Law, the EMF output from the coil is attenuated in proportion to the decrease in frequency, so more powerful coils may be required to compensate for the desensitization at low frequencies. Electromagnetic sensors can be "DC coupled", having sensitivity to a steady field, or "AC coupled", having no sensitivity to a steady field.

[0007] EM survey systems are different from magnetic survey systems that measure the Earth's static magnetic field. The latter is usually associated with the measurement of changes in the Earth's static magnetic field, which are usually due to changes in magnetic permeability. The time-varying field can be an order of magnitude smaller than the static field, often millions of times. Therefore, for a high-quality electromagnetic measurement, it is necessary to limit the rotational movement of the EM vector sensor in a static magnetic field during the entire measurement. When collecting low-frequency electromagnetic data, the duration of the limitation of this rotational movement is increased. At low frequencies, the rotational stability of an EM vector encoder is often critical. Noise in the electromagnetic dimension, caused by the rotation of the magnetic sensor vector components in the background static magnetic field of the Earth, may be referred to as motion noise.

[0008] The static magnetic field of the Earth has a magnitude on the order of 50,000,000 pT. To limit motion noise to 1 pT, it may be necessary to limit rotational change to about 1/50,000,000 radians during the entire measurement. To limit motion noise to 10 pT, it may be necessary to limit rotational change to about 1/5,000,000 radians. A field can be considered essentially static if it changes at a frequency below the acquisition bandwidth used to measure the detected vector field data.

[0009] Rotary motion noise can be calculated from the following motion noise equations. For a coil vector encoder pointing in the direction described by the unit vector m, the rotational noise Nc can be written as:

Nc=m⋅(ω×B),

[0010] where ω is the angular velocity of the coil sensor relative to the static field B of the Earth. This dependency is described in WO2013/170340A1 to Dodds. For a vector magnetometer with a dipole moment m, the rotational noise Nm can be written as follows:

Nm=m⋅(ΔΘ×B),

[0011] where ΔΘ is the angular change in the orientation of the magnetometer relative to the Earth's static magnetic field during the measurement.

[0012] For convenience, the angular change in orientation or angular velocity may be referred to as "angular motion", and the resulting signal due to the angular motion of the vector component sensor in the presence of the Earth's background field is referred to as "motion noise". Motion noise can be similarly defined for other fields in addition to the magnetic field, and similar motion noise equations can be applied to vector component sensors that probe small time-varying fields in the presence of a relatively large background field in which the sensor is moving. Motion noise can occur when a background vector field is superimposed on a smaller time-varying vector field that is the object of measurement, when both vector fields are probed by a conventional vector component sensor mounted on a moving platform subject to angular motion, and when the detection axis of the sensor is specified by the orientation of the instrument platform on which it is installed. Then, as a rule, the motion noise N due to the angular motion A of the vector component sensor in the background field F can be written in the following form:

N=m⋅(A×F).

[0013] Motion noise is different from pointing error effects. Pointing error effects typically occur when radiating fields from a source are detected in a certain direction through an aperture that is pointed at it. The aperture typically picks up a signal from a particular location and boosts the power of the signal from the source compared to the background field in the same frequency band. In the case of motion noise, the sensor is generally insensitive to the direction of the source, and apertures are generally useless.

[0014] Motion noise can occur, for example, when measuring quasi-static or potential fields or their gradients with a vector component sensor. In these cases, the motion noise is insensitive to the direction of the source. In quasi-static EM and gravimetric measurements, a vector sensor can be used to detect a signal from a source in the presence of a much larger static or substantially static background field. It is the angular motion of the vector component sensor in the background field that causes the sensitivity of the vector measurement to the background field, and it is this that is the source of motion noise. Thus, motion noise is different from pointing error, which is sensitive to the direction of the source.

[0015] Decisions associated with the effects of pointing error are generally different from those associated with the effects of motion noise. Pointing error is typically associated with the acquisition of focused radiant fields in frequency bands that are different and separable from the motion of the instrument platform, in the presence or absence of a significant background field. Decisions related to motion noise involve collecting vector component fields that overlap the frequency band in which the instrument is moving, in which case a background field is necessarily present. Thus, pointing error is related to maintaining heading during data acquisition and may be present in scalar (amplitude) measurements. Motion noise is associated with a limitation of angular motion in the acquisition bandwidth of the desired vector measurement and by definition cannot be present when performing scalar (amplitude) measurements.

[0016] The problem of driving noise control is not unique to aeroelectromagnetic systems and also arises in the field of airborne gravimetric measurements. As with aeroelectromagnetic measurements, very small, time-varying changes in the probed vector field can be measured in the presence of a much larger, essentially static, background field. In a gravitational field, small time-varying changes are subject to gravitational acceleration due to changes in the density of the earth's crust, which are measured as the gravimetric system moves from place to place. Similarly, motion noise may be present in a gradiometric measurement in the presence of a background gradient field.

[0017] Other designs of rotationally isolated instrument platforms, such as those commonly used in camera, inertial systems, or gravity gradiometer applications, do not address the operational requirements of an electromagnetic sensing system and are not suitable for high resolution electromagnetic data acquisition. Requirements for electromagnetic measurements may include an environment with low electromagnetic noise. In EM data acquisition systems, highly resistive components with low magnetic permeability and exceptionally low vibration noise are preferred.

[0018] US Patent Application Publication No. 2011/0175604 (Polzer et al.), which is incorporated herein by reference, describes a method for collecting low frequency EM data from a mobile carrier. This document describes EM sensors on a centrally balanced instrument platform supported on a spherical air support.

[0019] PCT International Patent Application Publication No. WO 2015/103608 A1 (to Meyer et al.) entitled "Gravity Gradiometer System with Spherical Air Bearing Based Platform", which is incorporated herein by reference, describes a center-balanced tool platform mounted on an air support. This document describes the addition of a centrally balanced tool platform with actuators and springs to control the platform's range of motion. However, while these attitude stabilization devices may have the advantage of limiting the range of motion, they may be vectors along which motion noise can be transmitted from the wearer to sensors mounted on the tool platform.

[0020] Such conventional attitude stabilization devices can generate vibrational noise or torque, which can degrade data quality. The motion noise caused by such attitude stabilization systems can degrade the quality of high-precision electromagnetic measurements, and is difficult to predict and eliminate. Thus, orientation stabilization can negate the kinematic advantages achieved by balancing in the center of the tool platform.

[0021] Thus, there is a need for improved methods and systems for acquiring low-noise vector component geophysical data in a wide bandwidth, and in particular magnetic field vector component data ("EM survey data") from a mobile carrier, in particular in frequency band below 25 Hz.

SUMMARY OF THE INVENTION

[0022] The present invention provides methods and apparatus for collecting electromagnetic survey data from a moving medium. Some embodiments disclosed herein may provide electromagnetic survey data collection with low motion noise. The device disclosed herein can be used on mobile or stationary media to collect EM data in the air, on land, and at sea or underwater. Stationary media may move due to vibrations. Embodiments are not limited to collecting electromagnetic survey data. The methods and apparatuses described herein are also suitable for implementation in other applications where it is necessary to reduce angular motion or motion noise in vector component field sensors.

[0023] Some aspects of the present invention provide low motion noise electromagnetic data collection by mounting one or more vector component EM sensors on a lower weighted instrument platform. The tool platform can balance on a spherical support that supports its weight. Thus, the instrument platform may be substantially unrelated to carrier movements within the bandwidth.

[0024] In accordance with one aspect, a vector component data acquisition device is provided, comprising: a base node; a spherical support mounted on the base assembly; a tool platform having at least one vector component sensor attached thereto, wherein the tool platform is mounted on and supported by a spherical support, whereby the spherical support connects the tool platform to the base assembly and allows free angular rotation of the tool platform within a tilt angle range around a spherical support so that the tool platform has a center of rotation; moreover, the tool platform has a center of mass located under the center of rotation.

[0025] In some embodiments, the instrument platform is configured to pendulum around a center of rotation such that motion noise within the acquisition bandwidth of at least one vector component sensor is suppressed.

[0026] In some embodiments, the instrument platform has a natural pendulum frequency that is below the lowest frequency of the acquisition bandwidth of at least one vector component sensor.

[0027] In some embodiments, the tool platform is rigid.

[0028] In some embodiments, the device further comprises a carrier, wherein the base assembly is connected to the carrier.

[0029] In some embodiments, the carrier includes a towing frame and a coupling mechanism connecting the base assembly to the towing frame.

[0030] In some embodiments, the carrier is an air carrier capable of being towed by an air vehicle.

[0031] In some embodiments, the spherical bearing is an air bearing.

[0032] In some embodiments, the spherical support includes a single mechanical connection between the base assembly and the tool platform.

[0033] In some embodiments, at least one vector component sensor comprises three independently oriented vector component sensors.

[0034] In some embodiments, the device further comprises a controller, the controller comprising a processor and memory, the controller receiving data from said at least one sensor.

[0035] In some embodiments, the controller stores the received data.

[0036] In some embodiments, the device further comprises a wireless communication means, wherein the controller causes the wireless communication means to transmit received data for storage in a database.

[0037] In some embodiments, the base assembly includes a support post, with the spherical support mounted on the support post.

[0038] In some embodiments, the support leg includes a post extending upward from the base assembly.

[0039] In some embodiments, at least one vector component sensor comprises at least one of the following: at least one electromagnetic sensor; at least one gravimetric sensor.

[0040] In some embodiments, at least one vector component sensor comprises at least one gradiometer sensor.

[0041] In some embodiments, the tool platform comprises a downward-facing skirt, wherein the downward-facing skirt provides clearance around the spherical support and the base assembly to provide a range of tilt rotation of the tool platform within the tilt angle range.

[0042] In some embodiments, the device further comprises: an alignment system; and an angular motion measuring system, wherein the alignment system, depending on the angular motion measured by the angular motion measuring system, applies equalizing torques to the tool platform, causing it to rotate around the spherical support.

[0043] In some embodiments, the alignment system comprises one of the following: a plurality of propulsors located on the tool platform, the propulsors generating said alignment torques; and a plurality of movable mass assemblies disposed on the tool platform, the movable mass assemblies producing said equalizing torques.

[0044] In some embodiments, alignment torques are generated for at least one of the following: orienting the bottom-weighted tool platform such that its major axis is substantially vertical; and decrease in angular velocity.

[0045] In some embodiments, the device further comprises an accelerometer located on the tool platform, wherein the accelerometer measures acceleration data, and the controller is configured to: receive acceleration data; beat noise estimates depending on acceleration data; and removing beat noise from the data received from the at least one vector component sensor.

[0046] In accordance with another aspect, there is provided a method for collecting vector component data from a movable instrument platform having at least one vector component sensor attached thereto, the method comprising: moving a device comprising: a base assembly; a spherical support mounted on the base assembly; and a tool platform, wherein the tool platform is mounted on and supported by the spherical support, whereby the spherical support connects the tool platform to the base assembly and allows free angular rotation of the tool platform within a range of inclination around the spherical support, so that the tool platform has a center of rotation, moreover, the tool platform has a center of mass located under the center of rotation; and during movement of the device, vector component data is collected using at least one vector component sensor.

[0047] In some embodiments, the device further comprises a carrier, wherein the base assembly is connected to the carrier, and movement of the device comprises towing the carrier.

[0048] In some embodiments, the instrument platform is configured to pendulum around a center of rotation so that motion noise within the acquisition bandwidth of at least one vector component sensor is suppressed.

[0049] Other aspects and features of the present invention will become apparent to a person skilled in the art upon examination of the following description of specific embodiments.

BRIEF DESCRIPTION OF THE DRAWINGS

[0050] Aspects and embodiments of the invention will be described in more detail below with reference to the accompanying drawings, in which:

[0051] Figure 1A is a perspective view of a data acquisition device in accordance with some embodiments, with the carrier shell shown in partial section;

[0052] Figure 1B is a front sectional view of the device shown in Figure 1A;

[0053] Figure 1C is a partially exploded sectional view of the tool platform, spherical support, and base assembly of the device shown in Figures 1A and 1B;

[0054] Figure 1D is a perspective view of the device shown in Figures 1A and 1B;

[0055] Figure 2 is a block diagram of device components in accordance with some embodiments;

[0056] Figure 3 is a schematic illustration of a bottom-weighted tool platform, in accordance with some embodiments;

[0057] Figure 4A is a graph illustrating the occurrence of beat noise;

[0058] Figure 4B is a graph illustrating the effect of beat noise on measurement;

[0059] Figures 5A-5D illustrate various exemplary spherical support configurations in accordance with some embodiments;

[0060] Figure 6A is a perspective view of an exemplary alignment system in accordance with some embodiments;

[0061] Figure 6B is a perspective view of another exemplary alignment system in accordance with some embodiments;

[0062] Figure 7 is a schematic side sectional view of a data acquisition device in accordance with some embodiments;

[0063] Figure 8 is a partial sectional side view of an exemplary tool platform mounted on a pole via a spherical support, in accordance with another embodiment;

[0064] Figure 9 is a side view of the tool platform and post shown in Figure 8;

[0065] Figure 10 is an exploded perspective view of the spherical support and pillar shown in Figure 8;

[0066] Figure 11 is a graph illustrating traffic noise and geomagnetic spectrum versus frequency for one exemplary embodiment;

[0067] Figure 12 is a block diagram of a sensor and controller system in accordance with some embodiments;

[0068] Figure 13 is a flowchart of a method for collecting data from a movable instrument platform having at least one vector component sensor attached thereto, in accordance with some embodiments; and

[0069] Figure 14 is a flowchart of an exemplary method for correcting beat noise, in accordance with some embodiments.

DETAILED DESCRIPTION

[0070] To control motion noise, it is necessary to isolate the angular motion of the sensor from the angular motions and vibrations of the carrier. In traditional aeroelectromagnetic systems, cable suspensions are usually used for this purpose. However, as a rule, they are not able to provide the high degree of stability necessary to reduce traffic noise to acceptable levels at frequencies below 20-25 Hz. The methods and systems disclosed herein are particularly suitable for airborne electromagnetic surveys in the 1-25 Hz range.

[0071] In accordance with various embodiments of the present invention, an electromagnetic survey apparatus for collecting electromagnetic data is disclosed that can reduce traffic noise. The device disclosed herein may be towed or otherwise moved by a vehicle to collect geophysical survey data. The specific embodiments described herein relate to aircraft that can be towed by an aircraft. However, it should be understood that embodiments of the invention are not limited to mobile carriers for use in air. The concepts discussed in this document can be applied to other environments where traffic noise reduction is required. For example, the vehicle moving the device may be a car, a truck, a train, a boat, and so on. In other applications, the device is not actively moved by the vehicle and may be substantially stationary.

[0072] In accordance with some aspects, an apparatus is provided that includes a base assembly supporting a spherical support, which in turn supports a tool platform. The instrument platform is weighted at the bottom and supports the vector component sensor. In other words, the center of mass of the instrument platform for at least one vector component sensor is under the center of rotation provided by the spherical support. Due to this arrangement, the tool platform can perform a pendulum movement relative to the spherical support. This pendulum motion may have a frequency below the lowest frequency of the acquisition bandwidth of at least one EM sensor, or at least below a portion of the acquisition bandwidth. If the pendulum motion has a frequency below at least a portion of the acquisition bandwidth, motion noise can be at least partially suppressed or attenuated in that bandwidth. By properly selecting the inertial parameters of the instrument platform, motion noise can be significantly reduced in the acquisition bandwidth of the sensors.

[0073] In some embodiments, the natural frequency of the pendulum movement of the tool platform may have a period of more than 1 second and less than 1000 seconds. An aeroelectromagnetic survey may include this device, having a tool platform weighted at the bottom and a base assembly supported by a towing frame inside the hull. However, as noted above, the device may also be configured for use in non-airborne data acquisition systems.

[0074] Figure 1A is a perspective view of an AEM data acquisition device 100, in accordance with some embodiments. The exemplary device 100 is configured to collect data from the air, although embodiments are not limited to airborne systems. The exemplary apparatus 100 includes: a carrier 101 comprising a carrier shell 102 and a towing frame 104 mounted within the carrier shell 102; a base assembly 106 connected to the towing frame 104 via a coupling mechanism 105 (in this example comprising a cable damper system 123, shown in more detail in Figure 1B); a spherical support 110 (shown in Figure 1B) on the base assembly; and a tool platform 108 mounted on a spherical support 110. In this example, vector component EM sensors 146 are attached to the tool platform 108.

[0075] In some embodiments, the carrier 101 includes a carrier shell 102 and a tow frame 104, and the coupling mechanism 105 is omitted. In other embodiments, the device may include a base assembly and a tool platform connected to the base assembly by a spherical support. The device may be used with other media or may be used on its own. For example, the device can be towed on a trailer. In other embodiments, the device may be mounted or suspended on the vehicle itself. In other embodiments, the device may be mounted in a substantially stationary position (eg, on a platform or building) that is still subject to slight and/or slow movement over time.

[0076] The carrier 101 shown in Figure 1A is a movable carrier that is capable of being towed by an aircraft or other air vehicle. The term "movable medium" in this document does not mean that the medium is always movable, but rather means that the medium can be configured to collect data on the move. For example, in other embodiments, other movable carriers may be used, such as trailers, towed platforms, or other means of connecting the carrier to the vehicle.

[0077] Embodiments are not limited to a device that is actively moved by a vehicle. In some cases, natural movements of the earth's surface, structure, or building may cause motion noise in the acquisition band, even if the device is substantially stationary. In such cases, a tool platform weighted at the bottom on a spherical support can reduce such driving noise.

[0078] When used in an air environment, the carrier shell 102 (or gondola shell) may be generally teardrop shaped with a rounded bulbous front end 114 and a tapered tail 116 as illustrated. The carrier shell 102 may be weather resistant. The teardrop shape is suitable for aerial sensing, although other shapes may be used. In the figure, carrier shell 102 has been partially removed to expose tow frame 104, base assembly 106, and instrument platform 108. Keels 151 near tail end 116 may provide some stability in flight. The carrier shell 102 is provided by way of example, and it should be understood that other shell shapes and designs may be used for air carriers. In the case of using a carrier, the embodiments are not limited to the particular shape of the carrier shell 102 .

[0079] The towing frame 104 shown in Figure 1A includes a main support ring 118 and an upper support ring 120. Extending from the main support ring in opposite directions are split tow axles 122a (Figure 1B) and 122b that extend outward through the shell 102 carrier. A cable 103 (shown in Figure 1B) can be attached to axles 122a and 122b of device 100 and to an aircraft (not shown). Upper support ring 120 may, for example, have a diameter that is approximately half the diameter of main support ring 118. In this example, upper support ring 120 is offset upward from main support ring 118 by a distance approximately equal to its diameter. The upper and main support rings 120 and 118 are connected in common by a hemispherical carrier shell 119. Axles 122a and 122b are rotatably connected to the carrier shell 102, and the towing frame 104 is sized and shaped to allow relative rotation of the towing frame 104 in the carrier about the horizontal axis 121, which passes through the divided towing axles. The towing frame 104 is provided by way of example, and it should be understood that other designs may be used to connect the base assembly (eg, base assembly 106) to the carrier (eg, carrier 101). For example, in another embodiment, the base assembly may be suspended by one or more cables from an anchor or bracket located at or near the top of the carrier shell. In other embodiments, the base assembly 106 may be directly connected to the axles 122a and 122b. Embodiments are not limited to the exemplary design of the towing frame 104.

[0080] Although not shown in Figure 1A, in this exemplary embodiment, the rope damper system 123 (shown in Figure 1B) forms a coupling mechanism 105 between the base assembly 106 and the tow frame 104. The structure of the tow frame 104 is shown by way of example, and in in other embodiments, towing frames or assemblies of other designs may be used. For example, other suitable tow frame designs are disclosed in US Patent Application Publication Nos. 2015/0034795 and 2011/0175604 to Polzer et al., which are incorporated herein by reference.

[0081] In this example, the base assembly 106 includes an upper annular rim 126 and a lower base 128 with spaced apart ribs 130 extending therebetween. The ribs 130 connect the base 128 and the top rim 126. Each rib 130 is attached to the top rim 126. The ribs 130 continue down first outward and then fold inward, intersecting with the base 128. In this example, six ribs 130 are evenly spaced around the top rim 126. Thus thus, adjacent ribs 130 are at an angle of approximately 60 degrees relative to each other. In other embodiments, a different base assembly design may be used and more or fewer ribs may be provided.

[0082] Figure 1B is a front sectional view of the device 100 shown in Figure 1A. In this example, the connecting mechanism 105 between the towing frame 104 and the base unit 106 is a cable damper system 123, but this is only one of the possible options. However, it should be understood that other designs of the coupling mechanism may also be used. See, for example, the anti-vibration damper system described in US Patent Publication No. 2011/0175604 to Polzer et al., which is incorporated herein by reference.

[0083] Cable damper system 123 includes a plurality of pneumatic cable dampers 132a and 132b, one for each rib 130. Each cable damper 132a and 132b is attached to the interior of the tow frame 104 and aligned with the corresponding rib 130 of the base assembly 106. In this example, six cable dampers 132a and 132b are provided (one for each rib 130). Each cable damper 132a and 132b is an aerostatically supported pneumatic cylinder as disclosed in U.S. Patent Application Publication No. 2015/0034795 to Polzer et al. cassette 134a or 134b. In this example, the ends of the pneumatic pistons terminate on a common cross member (not shown). Each cable damper 132a and 132b further includes a respective pulley 136a or 136b and cable 138a or 138b. Each cable 138a and 138b is attached to a respective cassette 134a or 134b and draped over a respective pulley 136a or 136b to support the weight of the base assembly 106. Each cable 138a and 138b terminates at a respective anchorage 140 at the end 142 of a respective rib 130.

[0084] In this example, the three cable dampers 132a are provided with a cable 138a extending from the lower end 143 of the cassette 134a so that the cable 138a extends in a partially transverse direction to the corresponding rib 130. The other three cable dampers 132b are provided with a cable 138b extending from the upper end 145 cassette 134b so that cable 138b continues down in a substantially vertical direction to the corresponding rib 130 as shown.

[0085] The annular rim 126 shown in Figure 1A is indicated by dotted lines in Figure 1B so that the spherical support 110 is visible. aligned cable 138b is adjacent to two ribs 130 connected to a partially transverse cable 138a, and vice versa. Dashed lines illustrating the position of cables 138a and 138b are also shown in Figure 1A. The pneumatic pistons of the cassettes 134a and 134b can dampen vibrations of the carrier 101 on the base assembly 106. In this embodiment, each vertically supporting cable damper 132b is equidistant in the horizontal direction from adjacent transversely supporting cable dampers 132a. Thus, the cable dampers 132a and 132b can dampen the vertical and horizontal vibrations of the carrier shell 102 and the towing frame 104.

[0086] Referring to Figure 1B, the base assembly 106 includes a support post 144 that extends upward from the base 128 supporting the tool platform 108 through the spherical support 110. The ribs 130 support the support post 144 that protrudes vertically from the point where the ribs 130 intersect, supporting the spherical a support 110 on which the tool platform 108 is mounted. In this embodiment, the support column is in the form of a pole, however, other designs of the support column may be used in other embodiments. The expression "support post" as used herein does not necessarily mean a support post extending upward from the base structure. For example, the support leg may include one or more sections that extend at least partially horizontally or at an angle. The support column may be of any design suitable for supporting the spherical support and tool platform.

[0087] Together, the plurality of ribs 130 form a cavity partially receiving the tool platform 108 and allowing the tool platform 108 to rotate around the spherical support 110 without colliding with the sides of the cavity, as best shown in Figure 1B. In this example, the ribs 130 are structurally supported by additional panels 131.

[0088] In this example, the instrument platform 108 is rigid and holds a plurality of vector component sensors 146. The tool platform 108 may be "stiff" in the sense that motion noise associated with tool platform 108 deformations is not as significant as other motion noise. Sensors 146 may be electromagnetic (EM) vector component sensors. In some embodiments, sensors 146 may include three or more sensors. For example, vector component sensors 146 may include three independently oriented vector component sensors. Some embodiments may include four or more sensors. Embodiments are not limited to a specific number or design of vector component sensors. The tool platform 108 is weighted at the bottom so that its center of gravity is under the center of rotation around the spherical support.

[0089] In an alternative embodiment, the spherical support may be attached directly to the wearer or may be supported directly by the wearer 101. In some embodiments, the base assembly may be part of the wearer or may be built into the wearer. For example, in some embodiments, a spherical support may be mounted on a carrier, whereby a portion of the carrier serves as a base assembly.

[0090] In some embodiments, mounting the spherical support 110 on a carrier may include the features disclosed in US Patent Application Publication No. 2011/0175604 (to Polzer et al.).

[0091] In some embodiments, the connection mechanism between carrier 101 and base assembly 106 is not a cable damper system. In some embodiments, the coupling mechanism may include a pneumatic vibration damping system and associated systems disclosed in US Patent Application Publication No. 2013/0200248 (A1) to Polzer et al., the contents of which are incorporated herein by reference. Compressed air can be supplied from the air supply pump mounted on the towline to the carrier through the air supply pipe mounted on the towline.

[0092] The carrier 101 can be stabilized for air towing by distributing the weight such that the weight of the carrier and its contents below the axle 121 is greater than the weight above the axle.

[0093] As carrier 101 is lifted by an air vehicle, axles 122a and 122b support its weight. The carrier shell 102 is rotatable about axis 121 and cannot transmit torque to the internal systems, which may maintain their approximately vertical orientation. As the aircraft moves forward, the airflow around the carrier shell 102 may cause the carrier shell to rotate about the horizontal axis 121. Because the carrier shell is rotatably coupled to the axes 122a and 122b, any such rotation is substantially unrelated to the towing frame 104 and hence the tool platform. 108, which she supports.

[0094] Figure 1C is an exploded sectional view of base assembly 106, spherical air support 110, and tool platform 108 individually, in accordance with some embodiments. The annular rim 126 shown in Figure 1A is indicated by dotted lines in Figure 1C so that the spherical support 110 is visible. In this example, the tool platform 108 has a lower portion 152 containing a hollow cone 157 (which may be a truncated cone) with an upper inner vertex 153 that is engaged and supported on a spherical air support 110. The tool platform 108 also has an upper portion 154 containing a cylindrical portion or stem 159 that extends upward from the cone 157, over the top 153 and into the downwardly facing hemispherical cavity formed by the towing frame. 104 (shown in Figures 1A and 1B). The main axis 156 of the instrument platform passes through the cone 157 and the stem 159. The spherical bearing 110 provides low-friction or virtually frictionless rotation about the main axis 156 of the instrument platform, called "rotation rotation" or "roll and pitch", as well as rotation of the platform around the main axis 156, which is called either "rotation" or "yaw". In some embodiments, the spherical support 110 is the only mechanical connection between the base assembly 106 and the tool platform 108.

[0095] The base assembly 106 includes a main base section 155 (comprising ribs 130, a base 128, and a rim 126) and a pillar-shaped support leg 144 that is securely attached to and extends upwardly from the main base section 155. The ribs 130 of the base assembly 106 are sized and angled to provide a range of roll and pitch of the instrument platform 108 on the spherical air support 110 by 10-30 degrees.

[0096] Embodiments are not limited to the particular design of the base assembly 106 shown in Figures 1A and 1B. For example, in another embodiment, the base assembly may comprise a block with a support leg on it to support the spherical support and tool platform. Any suitable structure may be used to support the spherical support and tool platform.

[0097] In this embodiment, the spherical seat 110 includes a raised, rounded portion 158 attached to the tool platform 108 and a seat 160 attached to the support post 144. The raised portion 158 cooperates with the seat 160 to provide low friction or substantially frictionless rotation.

[0098] An additional alignment system 650 is also provided on the tool platform 108 shown in Figure 1B (discussed in more detail below with reference to Figure 6C).

[0099] Figure 1C also shows a shielded electronics bay 170 that can accommodate a high-precision 3-way accelerometer 164 or, in some embodiments, interfering electrical components.

[00100] Figure 1D is a perspective view of a carrier 101 and a tether 103. The carrier 101 is suspended on both sides from a tow tether 103 that is attached to an aircraft (not shown). The towline 103 can be bifurcated to form a pair of inverted "Y" shaped towlines, with the bifurcated sections of the inverted "Y" attached to opposite sides of the carrier 101. In this embodiment, the ends of the towline 103 are attached to rigid towbars 125 that rigidly transmit supporting forces through axles 122a and 122b onto tow frame 104 (shown in Figures 1A and 1B) and carrier shell 102. In other embodiments, the towline 103 may be directly attached to or otherwise support the tow frame and carrier shell. Any suitable method may be used to connect the carrier 101 to the vehicle.

[00101] Upon landing on the ground, the weight of the carrier is supported by the landing legs 150. After landing, the towline 103 sags and can be placed on the ground. Figure 1B illustrates the configuration of the tow line when the carrier is in the air and supported by the tow lines.

[00102] In the device 100 shown in Figures 1A-1D, the center of rotation provided by the spherical support 110 is above the center of mass of the tool platform 108, making the tool platform "heavy at the bottom".

[00103] Figure 2 is a block diagram illustrating the structural layout of the device 100 shown in Figures 1A-1D. Arrows 202a-202f shown in Figure 2 indicate the direction of the supporting forces. The carrier 101, which includes the carrier shell 102 and the towing frame 104 shown in Figure 1A, may be towed by a vehicle (not shown) on a towline 103. The carrier 101 supports the base assembly 106 with the coupling mechanism 105. Specifically, in the example, shown in Figures 1A-1D, the towing frame 104 of the carrier 101 supports the base assembly with a coupling mechanism 105. In the apparatus 100 shown in Figures 1A-1D, the coupling mechanism 105 comprises the cable damper system 123 shown in Figure 1B. However, other connection systems may be used. The base assembly 106 supports a spherical support 110 which in turn supports a lower weighted tool platform 108.

[00104] In some embodiments (for example, in gravimetric systems), the base assembly may comprise a three-axis platform with motion compensation. For example, such systems may be installed on an aircraft.

[00105] The tool platform 108 may include a grid or truss, sheet or plate surfaces, or a combination thereof.

[00106] As noted above, at least one vector component sensor 146 is attached to the tool platform 108. In this embodiment, at least one sensor 146 includes one or more vector component EM sensors. The EM sensors may be gradiometric or other type of EM sensors. Although the examples described herein refer to EM sensors, it should be understood that the embodiments are not limited to the use of EM sensors, and other types of vector component sensors may be installed on the instrumentation platform in other embodiments. In other embodiments, sensors 146 may include one or more gravimetric sensors, which may also be gradiometric or other type of gravimetric sensors. Other types of gradiometric vector component sensors may also be used. The implementation options are not limited to collecting a particular type of data.

[00107] Embodiments are not limited to the specific design shown in Figures 1A-1C. For example, a tool platform may take many different forms. In some embodiments, the tool platform is substantially flattened. For example, the tool platform may be approximately disc-shaped. In the case of a flattened instrument platform, the distal portions of the instrument platform may extend transversely from the spherical support. In other embodiments, the tool platform is substantially elongated. In this case, the distal portions of the instrument platform may lie substantially above and below the spherical support.

[00108] The instrumentation platform may include a structure for mounting one or more EM sensors used to collect EM survey data and may support the electronics and auxiliary sensors required for data acquisition and post-processing. In some embodiments, the tool platform is rigid. The tool platform may have a high moment of inertia. The spherical support may be the only point of contact between the base assembly and the tool platform. The tool platform rotates on a spherical support around one point, namely the "center of rotation".

[00109] EM sensor data can be collected continuously provided that the limits of the tool platform's angular movement around the spherical support are not reached. Thus, at least one EM sensor mounted on the instrument platform may be substantially unrelated to the vibratory motion of the carrier, which may pitch and roll around it.

[00110] Figure 3 is a schematic side view of an exemplary tool platform 300, in accordance with some embodiments. The rectangular profile shown in Figure 3 does not necessarily represent the actual shape of the tool platform 300. Rather, Figure 3 simply illustrates the bottom-heavy nature of the tool platform 300. For example, the tool platform 300 shown in Figure 3 may have the design and shape of the tool platform 108 shown in Figures 1A-1C.

[00111] The tool platform 300 has a center of mass 304 and a center of rotation 306. Center of rotation 306 is the point at which the tool platform 300, when assembled, will rotate around a spherical support (eg, spherical support 110 shown in Figure 1C). Figure 3 shows the relationship between the center of mass 304 and the center of rotation 306 of the tool platform 300. In particular, the tool platform 300 is weighted at the bottom. In the lower-weighted tool platform 300, the center of mass 304 is located under the center of rotation 306, with support provided by a spherical support (not shown). The main axis 308 of the tool platform 300 can be defined as an axis passing through the center of rotation 306 and the center 304 of mass. In accordance with some embodiments, the tool platform 300 includes an upper portion 310 located above the center of rotation 306 and a lower portion 312 located below the center of rotation 306 .

[00112] The schematic view shown in Figure 3 is not intended to represent the actual shape of the tool platform 300, but rather to illustrate the relationship of the center of mass 304 and the center of rotation 306. The actual shape of the tool platform 300 may vary. For example, the top portion 310 may be rod-shaped and the bottom portion may be generally tapered. Other shapes (flattened, elongated, etc.) are also possible. The weighting of the tool platform in the lower part can be implemented in various ways. For example, the dimensions, materials, and shape of the bottom and top portions 312 and 310 can be adjusted to provide weight at the bottom. For example, compared to a centrally weighted tool platform (where the center of mass and center of rotation are aligned), the lower portion 312 of the tool platform 300 may be larger, may be made of a heavier material, may be thicker, or may be otherwise weighted to provide more low center of gravity of the tool platform 300. Embodiments are not limited to any particular method of weighting the lower part of the tool platform.

[00113] The tool platform 300 at rest can be vertically balanced with its main axis 308.

[00114] Forces acting on the lower weighted tool platform 300 can create an unbalancing torque because the center of mass 304 is offset from the center of rotation 306 . The unbalancing torque may include gravitational restoring torque as well as "moving torques" due to vibrations of the spherical support caused by motions of the wearer. Due to the periodic movement of the tool platform due to the gravitational restoring torque, pendulum motion noise may occur. Due to the accelerations of the spherical bearing due to the carrier vibrations, beat noise can occur. When these accelerations are perpendicular to the main axis 308, a torque may be applied to the tool platform 300 causing it to rotate and causing an angular motion. Together, the pendulum noise and the beat noise are called unbalance noise. Although the heaviness at the bottom may cause unbalance noise, a significant amount of the unbalance noise may be removed from the EM data or may be of such low amplitude as to be unimportant.

[00115] When the tool platform 300 is in a vertical position with the center of mass 304 located just below the center of rotation 306, gravitational forces will act through the center of rotation and there will be no gravitational restoring torque.

[00116] If the tool platform is tilted, the gravitational restoring torque may prevent rotational movement when tilted or rotated from a vertical position. The gravitational restoring torque may prevent or delay the tool platform from reaching the limits of the range of rotation around the center of rotation.

[00117] Balancing at the bottom can extend the data acquisition time compared to the time that can be obtained with a centrally balanced instrument platform, possibly without tethers, actuators or other active attitude control systems, and eliminate the noise caused by these systems.

[00118] The characteristics of pendulum noise and beat noise can be predicted based on the inertial properties of the tool platform 300. The tool platform 300 can be characterized by moments of inertia Ih and Iz about the horizontal axis and the main (or vertical) axis 308, the mass m and the distance L between the center 304 mass and the center of rotation 306 around which it rotates. Since the center of mass is located under the center of rotation, the tool platform can perform free pendulum movement on a spherical support with a natural frequency F=1/(2×pi)× sq. root((m×g×L)/Ih). Using a sufficiently low degree of unbalance (m×L) and a high moment of inertia Ih, the natural frequency of the pendulum noise can be well below the acquisition bandwidth of the EM sensors. Thus, the instrument platform may have a pendulum frequency that suppresses motion noise in the acquisition bandwidth of the vector component sensor(s) on the instrument platform. In this context, the verb "suppress" does not mean that the movement noise is necessarily eliminated or negligible, but rather that the movement noise of the bottom-weighted tool platform is reduced by the bottom-weighted platform.

[00119] Figures 4A and 4B are plots 400 and 410, respectively, which illustrate the occurrence of beat noise and its manifestation. For harmonic accelerations of amplitude a0 perpendicular to the principal axis (eg, principal axis 308 shown in Figure 3) and frequency f, the time dependence can be defined as a0×sin(2×pi×f×t). The harmonic beat noise may be given by multiplying the acceleration a0 and the transfer function W of the beat noise, and may be written as W=a0×Wt, where Wt=m×L/(4×Ih×pi ² ×f ² ). Plot 400 shown in Figure 4A illustrates the beat noise as the product of acceleration and the transfer function of the beat noise. The shape of the acceleration spectrum, which is typical for an air carrier, is shown. The beat noise shown in Figure 4A has a much steeper slope with increasing frequency compared to the acceleration itself.

[00120] Plot 410 shown in Figure 4B illustrates the effect of beat noise and pendulum motion on measured EM data. The desired EM data is in a specific measurement bandwidth, which is shown in light gray. Even in a stationary, vibration-free environment, an EM system has a minimum noise level due to electronics and other sources. This noise floor typically slopes slightly to the right on a log-log plot, as shown by the dotted line. The pendulum frequency can be chosen such that the pendulum noise (dotted line) is much less than the noise floor in the measurement bandwidth. The beat noise (dashed line) has a much steeper slope than the system noise floor, which it crosses at the "beat noise cutoff frequency" (solid vertical line). For frequencies above this cutoff frequency, the system noise can dominate the measurement noise and the beat noise has no significant effect. If the cutoff frequency is above the lower limit of the measurement bandwidth, there will be a signal bandwidth in between where the signal is contaminated with beat noise. If such in-band beat noise is present, it can be predicted by measuring the accelerations of the spherical bearing. The predicted beat noise can then be subtracted or otherwise removed from the measured data to obtain an improved estimate of the EM data without beat noise.

[00121] In practice, EM sensors may be sensitive to signals at frequencies below their measurement bandwidth. In such cases, low-frequency unbalance noise can be superimposed on the signal to which the EM sensor responds. For example, data acquired over periods longer than the natural pendulum period of the instrument platform may contain a slowly varying sinusoidal signal due to the changing orientation of the EM sensors in the Earth's magnetic field. Low frequency noise can be separated from the in-band signal in several ways. For example, such low frequency noise can be removed using the compensation techniques disclosed in WO2014/146184 (A1) to West et al. Filtering techniques known in the art can also be used to separate out-of-band low-frequency noise from the in-band EM signal.

[00122] The following characteristics can guarantee the collection of high quality electromagnetic data with low unbalance noise:

i. the amplitude of the pendulum noise is small enough to be covered by the dynamic range of the EM sensor,

ii. the frequency of the pendulum noise is low enough to be outside the required acquisition bandwidth, allowing the unbalance noise caused by the pendulum to be removed by filtering,

iii. the beat noise signals due to torques on the bottom-weighted tool platform, which can be caused by lateral accelerations of the spherical support, are sufficiently low, and

iv. beat noise signals can be computed and removed from the EM sensor signal.

[00123] Referring again to Figure 2, beat noise can be further reduced if the coupling mechanism 105 that connects the base assembly 106 to the carrier 101 includes vibration damping components such as shock absorbers, cables, dampers, springs, or pneumatic elements. Such a vibration-dampening coupling mechanism 105 can reduce vibrations transmitted through it from the carrier 101, and therefore can dampen the vibrations of the spherical support 110. Thus, the driving torques acting on the tool platform 108 can be reduced, and the noise is correspondingly reduced. imbalances. The function of the vibration damping coupling mechanism 206 may be to attenuate the acceleration spectrum shown in Figure 4A, resulting in reduced beat noise. In addition to noise reduction in the EM measurement, beat noise reduction advantageously reduces the beat noise cutoff frequency shown in Figure 4B.

[00124] The unbalance noise is due to the displacement of the center of mass from the center of rotation provided by the spherical support. The function of the spherical support 110, in accordance with some embodiments, is to transfer the weight of the tool platform 108 to the base assembly 106 while allowing low friction or substantially frictionless rotation of the tool platform in any angular direction. The expression "spherical" is not intended to describe or limit the shape of the support, but describes the range of angular movement provided by the support. Spherical bearings, such as spherical air bearings, or sharp or slightly rounded tips can provide the desired range of rotational movement. The spherical support provides a single center of rotation for the tool platform. The spherical support can rotationally separate the movement of the base assembly from the tool platform along three independent axes. The spherical support may allow unlimited rotation about the main axis of the tool platform 108, while also allowing rotation within a limiting angle of inclination about axes orthogonal to the main axis, taking into account the angular location and limitations of the tool platform and the limitations of the spherical support itself.

[00125] Figures 5A-5D illustrate four examples of possible spherical bearing configurations that can be used as spherical bearing 110 in the apparatus 100 shown in Figures 1A-1D.

[00126] Figure 5A is a sectional side view of a spherical air support 500a according to one embodiment. The spherical support 500a includes a first part 502a and a second part 504a. The first part 502a may be attached to the base assembly (eg, to the support leg 144 of the base assembly 106 shown in Figure 1C). The second part 504a may be attached to a tool platform (eg, tool platform 108 or 300 shown in Figures 1A-1C and 3). In this embodiment, the first part 502a contains the seat 506a. The second part 504a contains a protruding part 508a that interacts with the seat 506a. In this embodiment, the seat 506a is a concave spherical seat, and the projection 508a is spherical in shape and fits into the concave spherical seat 506a. Arrows 510a indicate the direction of the upward airflow from the base assembly to the spherical air support 500a. The spherical protrusion 508a can rotate in a corresponding spherical seat 506a separated from it by an air cushion. This type of spherical air support may be preferred to support the mass of the tool platform. However, the embodiments are not limited to any particular type of support.

[00127] Figure 5B is a sectional side view of a spherical air support 500b according to another embodiment. The spherical support 500b includes a first part 502b and a second part 504b. The first part 502b may be attached to a tool platform (eg, tool platform 108 or 300 shown in Figures 1A-1C and 3). This spherical air bearing 500b is similar in design to the spherical bearing 500a shown in Figure 5A, but vertically inverted. Arrows 510b indicate the direction of the upward airflow from the base assembly to the spherical air support 500b.

[00128] Figure 5C is a sectional side view of a spherical support 500c according to another embodiment. The spherical support 500c includes a first part 502c that can be attached to the base assembly and a second part 504c that can be attached to the tool platform. In this embodiment, the first portion 502c includes an anvil seat 506c. The second part 504c includes a rigid tip-like protrusion 508c that engages with an anvil seat 506c. The protruding portion 508c in the form of a tip can rotate in the saddle 506c in the form of an anvil.

[00129] Figure 5D is a side sectional view of a spherical support 500d according to another embodiment. The spherical support 500d includes a first part 502d that can be attached to the tool platform and a second part 504d that can be attached to the base assembly. This spherical support 500d is similar in design to the spherical support 500c shown in Figure 5C, but is vertically inverted. The examples shown in Figures 5C and 5D can be used, for example, on smaller and lighter instrument platforms, such as an instrument platform containing one or more MEMS sensors. However, the examples shown in Figures 5C and 5D are not limited to such use.

[00130] Those skilled in the art will appreciate that the cases illustrated in Figures 5A-5D should be considered exemplary and not limiting, and that many spherical bearing configurations are possible that provide a similar effect while still providing the desired range of low friction or almost frictionless rotary motion.

[00131] Because aspects of the present invention may be used to collect electromagnetic or other survey data from a moving carrier, the instrument platform may be fixed or otherwise tethered to the carrier or base assembly for transport or delivery to the survey site. Accordingly, some embodiments may include a locking system for holding the tool platform in a fixed position relative to the base assembly during transport. If it is necessary to collect survey data, the instrument platform can be released or untied from the carrier for independent rotation. When the tool platform is released, it can maintain the angular velocity acquired in a fixed or tied state. In such cases, the tool platform must be leveled so that its major axis is substantially vertical and is positioned at little or no angular velocity.

[00132] Some embodiments may also include an alignment system to adjust the orientation as well as the angular velocity of the tool platform. At the start of data collection, it is preferable to place the instrument platform (for example, instrument platform 108 and 300 shown in Figures 1A-1C and 3) in such an orientation that its main axis (for example, axis 308 shown in Figure 3) is substantially vertical, as this ensures that the instrument platform is oriented as far as possible from the limits of angular motion without gravitational potential energy. Thus, it is possible to maximize the duration of data collection before reaching the limits of angular motion. It may also be preferable that the instrument platform has little or no angular velocity, as this can also maximize the duration of data collection before reaching the limits of angular motion. When the alignment system positions the tool platform with little or no angular velocity and a substantially vertical major axis, EM or other vector component data can be collected with minimal motion noise for maximum time.

[00133] The leveling system may be located on the tool platform and may include propellers or a movable mass that can control the gravitational torque acting on the platform. The leveling system can place the tool platform in a substantially vertical position with substantially zero angular velocity. The leveling system may also operate intermittently to level the tool platform if the tilt angle movement limit is reached. The leveling system can also brake the rotation of the tool platform to reduce its angular velocity.

[00134] As noted earlier, since the tool platform can be mounted on a single spherical support with the center of mass offset from the center of rotation, vibrations of the spherical support can create a torque on the tool platform. This torque may cause the tool platform to rotate, and this rotation may cause beat noise. Knowing the accelerations of the spherical support and the inertial properties of the tool platform, it is possible to calculate the rotation and hence the beat noise. You can then remove beat noise from the measured EM data to obtain EM data corrected for the effects of beat noise.

[00135] Figure 6A is a perspective view of an exemplary alignment system 600, in accordance with some embodiments. The alignment system 600 is shown on a disc-shaped cover 602 that contains the upper side of the cylindrical top of the tool platform (eg, the stem 159 of the upper portion 154 of the tool platform 108 shown in Figure 1C). In this example, the alignment system 600 includes first, second, and third moving mass assemblies 604a, 604b, and 604c. In other embodiments, more or fewer moving mass assemblies may be used. Each moving mass assembly 604a, 604b, and 604c consists of a respective linear motor 611, rail 612, and mass 613. In this exemplary embodiment, top cover 602 includes an additional electronics compartment 616 and an access cover 614 that covers electronics compartment 616. The first and second moving mass assemblies 604a and 604b are configured to move the masses 613 in the generally horizontal x and y directions, respectively, to adjust the leveling torques in the y and x directions. The third movable mass assembly 604c provides for adjusting the amount of weight at the bottom and hence the natural frequency of the tool platform.

[00136] Figure 6B is a perspective view of another exemplary alignment system 650, in accordance with some embodiments. In this example, the alignment system 650 includes first, second, third, and fourth movers 654a, 654b, 654c, and 654d. In other embodiments, more or fewer movers may be used. In this example, the propellers 654a, 654b, 654c and 654d are reversible fans. In this embodiment, the propulsors 654a, 654b, 654c, and 654d are mounted on a disc-shaped cover 652 that contains the upper side of the cylindrical upper part of the tool platform (for example, the stem 159 of the upper section 154 of the tool platform 108 shown in Figure 1C). In this embodiment, the first and second reversible fans 654a and 654b are configured to transmit torque around a respective horizontal axis of rotation through a spherical support. The third and fourth reversible fans 654c and 654d are configured to transmit torque through a spherical support around the main axis of the tool platform (eg, axis 308 shown in Figure 3). In this exemplary embodiment, the top cover 602 includes an additional electronics compartment 665 and an access cover 664 that covers the electronics compartment 665.

[00137] In some embodiments, the accelerations of the spherical bearing are measured by one or more accelerometers. For example, acceleration can be measured by the high precision three-component accelerometer 164 shown in Figure 1C. One or more accelerometers may be located on the instrument platform (for example, on the instrument platform 108 shown in Figures 1A-1C) proximate a spherical bearing (for example, spherical bearing 110 shown in Figures 1A-1C) such that any Coriolis or centripetal rotational the forces that they can take due to the rotation of the tool platform around the spherical support are negligible. Between the acceleration input measured by the three-component accelerometer and the angular movement of the instrument platform caused by the resulting torques, a direct mathematical relationship can be determined, such as the transfer function Wt. The transfer function Wt can be written as follows:

i. Wt=m×L/(4×Ih×pi ² ×f ² ).

[00138] In some embodiments, other mathematical relationships between acceleration and angular motion are also known and can be implemented, for example, using neural networks, fuzzy logic, lookup tables, predictive filtering, least squares, or other model fitting techniques.

[00139] A vector component fluxgate magnetometer, gyroscopes, GPS, and other related devices may be used on the instrument platform. These instruments can measure the Earth's static magnetic field within the instrument platform and can determine the orientation, movement, and location of the instrument platform within the Earth. The sensor data may be stored in a controller located on the instrument platform, or it may be transmitted wirelessly to a controller or data recorder located near the instrument platform, such as on a carrier. Input from these tools and sensors can also be used to control the operation of the fixation and/or alignment systems.

[00140] Some embodiments include or are connected to compressed air systems for supplying compressed air to one or more pneumatic components. As noted above, the spherical bearing may be an air bearing and compressed air systems may supply air to the bearing. The coupling mechanism between the carrier and the base assembly may also include vibration dampening pneumatic elements that receive compressed air from the compressed air system. Other pneumatic elements may also be included. The compressed air system may include an air pump or air supply tanks, air supply lines, valves, regulators, and accumulators or buffer tanks. Embodiments are not limited to any particular compressed air system design, and some embodiments may operate without a compressed air system.

[00141] In some embodiments, the device (comprising at least a base assembly, a spherical support, a bottom-weighted tool platform, and sensors) is carried by a carrier capable of aerial photography. The carrier may be a "nacelle" or "probe" towed by an aircraft, typically a helicopter, using a towline which may be in the range of 30 to 90 meters. The carrier may be shaped to minimize drag at towing speeds of 25-30 meters per second. The towed nacelle may include a cavity in which the base assembly, spherical support, and tool platform described herein can be installed.

[00142] Figure 7 is a schematic sectional view of a data acquisition device 700, in accordance with some embodiments. The apparatus 700 includes a base assembly 702, a spherical support 704, and a tool platform 706. The spherical support 704 is mounted on the base assembly 702, and the tool platform 706 is mounted on and supported by the spherical support 704. The spherical support 704 allows free angular rotation of the tool platform 706 within a range of inclination around the spherical support 704. The tool platform 706 is weighted at the bottom similar to the tool platform 300 shown in Figure 3 (i.e., the center of mass 723 of the tool platform 706 is located under rotation center 720).

[00143] In this embodiment, the base assembly 702 includes a main base section 708 and a pole support 710 that is securely attached to and extends upward from the main base section 708. Post 710 continues upward along the axis 712 of the post. The spherical seat 704 includes a seat 714 attached to the top surface of the post 710. The spherical seat 704 is an air seat with a projection 716 attached to the tool platform 706 (similar to the air seat 500a shown in Figure 5A).

[00144] Tool platform 706, shown in Figure 7, is a housing containing a lower part 717, located generally under the center 720 of rotation. The lower portion 717 is in the form of a tapered downward skirt 718 that forms a downwardly facing open bell with a spherical support 704 located at its apex 721. The center of gravity of the tool platform 706 is located at a distance below the apex 721. This arrangement of the conical skirt 718 and column 710 may to allow rotation of the main axis 722 of the tool platform 706 on the spherical support 704 relative to the axis 712 of the column in the range of the limit angle α of inclination shown in Figure 7. oblique rotation of the tool platform within the tilt angle range. The allowable rotation in directions orthogonal to the major axis 722 may be greater than or less than the limit angle α shown in Figure 7 according to the opening angle of the conical skirt 718 and/or the angular range of motion provided by the spherical support 704. Embodiments are not limited to a specific range rotation.

[00145] In some embodiments, a single vector component EM sensor (eg, sensor 146 shown in Figures 1A-1C) is securely attached to the bottom-weighted tool platform 706. In another embodiment, three EM sensors are securely attached to the bottom-weighted instrument platform 706, arranged in independent probing orientations.

[00146] In some embodiments, the tool platform described herein is made from a rigid and/or resistive composite material.

[00147] Figures 8 and 9 illustrate an exemplary aerial data acquisition instrument platform 800 in accordance with another embodiment. In Figure 8, the tool platform 800 is shown in partial section, so that a pole support column 810 and a spherical support 804 are visible. The tool platform 800 is mounted on the specified column 810 through a spherical support 804 in a manner similar to other embodiments described herein. The tool platform 800 includes a platform body 806 comprising a lower portion 817 including a tapered skirt 818 that forms a downwardly facing open conical bell and an upper portion 819 including a cylindrical stem 820. In this embodiment, the spherical bearing 804 is a spherical a support with a saddle 814 and a projection 816. Post 810 may extend upward from the main portion of the base assembly (eg, base assembly 106 shown in Figures 1A-1C or base assembly 702 shown in Figure 7). The projection 816 of the air support 814 is attached to and faces down from the top 821 of the conical skirt 818, and the saddle 814 is securely attached to the top surface of the column 810. platform 800 and spherical support 804.

[00148] In this embodiment, the instrument platform 800 resembles an inverted funnel supported by an air support from the top 821 of the conical funnel skirt 818, with a cylindrical stem 820 extending upward from the top. The center of mass of the tool platform 800 is located at a distance below the vertex 821 and below the center of rotation around the cylindrical support (not shown in Figure 8). Along the periphery of the tool platform, as viewed from above, are three pairs of longitudinal rib support members 830 and 832 that reinforce the tool platform along the longitudinal portions where vector component EM sensors 840 are installed in this embodiment. Paired members 830 and 832 may be longitudinally attached along the outer sides of the instrument platform 800. To reduce platform deformations, additional longitudinal support members 834 are located midway between the paired longitudinal members 830 and 832. The members 834 contribute to the rigidity of the instrument platform, maintaining stable relative direction cosines between the probing directions of the EM sensors, and therefore limiting the movement noise that is associated with platform deformations. These support elements 830, 832 and 834 extend from the distal end 835 of the tapered skirt 818 to the distal end 836 of the stem 820. Together, the longitudinal support elements 830, 832 and 834 can reduce the bending deformation associated with the bending of the instrument platform around the apex 821. In this example, the instrument platform platform 800 also includes transverse support members 838 that extend horizontally between longitudinal support members 830, 832, and 834. The transverse members 838 are vertically spaced from the sides of tool platform 800 and may provide transverse support to longitudinal members 830, 832, and 834. The embodiments are not limited to the specific shape and design of this exemplary tool platform 800.

[00149] In this embodiment, the tool platform is rigid. Due to this rigidity, the motion noise due to the angular movements of the vector component sensors caused by the deformations of the instrument platform in response to the acceleration of the air bearing can be acceptably low.

[00150] In one embodiment, the tool platform 800 has a mass of 75 kg, and a mL weight at the bottom of 0.035 kg/m. The instrument platform 800 may have a natural period of about 1 minute and may support three independently oriented EM sensors with a 1 Hz acquisition rate lower limit. The motion noise associated with the pendulum movement of the instrument platform 800 for 1 minute may have an inverse square frequency dependence above the 1 Hz sampling rate limit of the EM sensors and may be easily removed by standard techniques known in the art, which may include high pass filtering. . In this embodiment, the movement noise of the carrier can be effectively suppressed by the inertial properties of the tool platform 800, leaving the residual movement noise with favorable frequency dependence.

[00151] Figure 10 is a partial perspective view of the pillar 810 and spherical support 804 shown in Figure 8. In this example, the spherical support 804 is an air support, although other spherical supports may be used in other embodiments. Seat 814 has a concave spherical shape and is attached to the top surface of column 810 as illustrated in Figure 10. Compressed air can be supplied upward through small holes (not shown) in seat 814 into a small gap between it and convex spherical projection 816 (shown in Figure 10). nine). The resulting air cushion that is formed between the seat 814 and the projection 816 of the spherical air support 804 can provide a substantially low friction or near frictionless support and connection on which the tool platform 800 (shown in Figure 9) can freely rotate relative to the column 810.

[00152] In some embodiments, particularly where the vector component sensors are EM sensors, the spherical air bearing 804 is made of a metal with poor conductivity and low magnetic permeability, such as titanium. In other embodiments, the spherical air bearing is made of ceramic or other resistive and mechanically strong material. In other embodiments, such as where the vector component sensors are not EM sensors (eg, gravimetric sensors), the magnetic permeability and conductivity of the air bearing may have little effect on the measured field data. The embodiments are not limited to any particular material. If the spherical support 804 and the carrier coupling mechanism (not shown) contain pneumatic elements, a common pneumatic system can be used to supply air to the spherical support 800 and the pneumatic elements that comprise the connecting mechanism.

[00153] Figure 11 is a graph 1100 illustrating traffic noise and geomagnetic spectrum versus frequency f for an embodiment having a mass of 75 kg and a bottom weight of 0.035 kg/m. When collecting EM data, the geomagnetic spectrum is an important reference because it shows the noise floor in the case of controlled source EM measurements, and it shows the source signal in the case of natural source EM measurements. The geomagnetic spectrum generally responds inversely to frequency between 1 Hz and 500 Hz, with beat noise being able to respond inversely to the square of the frequency in the same range.

[00154] The imbalance noise shown in Figure 11 is for a lateral acceleration signal that is spectrally flat using observed accelerations in the 6-15 Hz range in one embodiment for airborne electromagnetic surveying. The unbalance noise can be further reduced by adjusting the frequency response of the coupling mechanism between the carrier and the base assembly to reduce the accelerations of the base assembly, or by further adjusting the natural frequency of the pendulum movement of the platform in the downward direction.

[00155] Unbalance noise aspects can be adjusted by changing the weighting at the bottom according to the shooting purpose. In EM surveys of natural fields, EM data may be collected at frequencies that exceed the lowest Schumann resonance by approximately 8 Hz. For such a survey, the motion noise shown in Figure 11 is low enough to provide useful estimates of the Earth's conductivity structure. In a controlled source survey where the EM survey device contains a transmitter that induces a time-varying current in the ground, geomagnetic noise forms a useful measurement noise floor, and the motion noise illustrated in Figure 11 is low enough to collect useful data up to 2 or 3 Hz.

[00156] Referring again to Figures 8 and 9, in an embodiment, three EM sensors 840 are mounted on the platform body 806 between a respective pair of longitudinal support members 830 and 832 on the conical skirt 818 of the instrument platform. In this example, the EM sensors 840 are electromagnetic vector component sensors, although other types of sensors may be used. The mass of the EM sensors 840 can be offset by the mass of the accessories and batteries located in the cylindrical rod 820 to provide an instrument platform 800 (including sensors and accessories) slightly weighted at the bottom when balanced on the spherical support 804.

[00157] Each of the EM sensors 840 may be a feedback magnetometer with a data acquisition bandwidth extending from 1 Hz to 25 kHz and a noise power spectral density of 1 pT/sq. root of Hz per 1 Hz. In this embodiment, the EM sensors 840 are rigidly attached to the instrument platform. In this example, the EM sensors 840 are evenly spaced around the periphery of the conical skirt 818 of the tool platform 800. However, it should be understood that in other embodiments, the number, type, and placement of sensors may differ. Some embodiments may include four or more sensors. Some sensors can be independently oriented. In addition, in some embodiments, one or more sensors may be swapped. In embodiments suitable for electromagnetic surveying of natural fields, the EM sensor may, for example, operate in a data collection frequency band of 8 to 700 Hz. In an embodiment suitable for controlled source electromagnetic surveying, the EM sensor may, for example, operate over a data acquisition bandwidth of 1 to 25,000 Hz and may have a noise floor on the order of less than a picoTesla at 1 Hz. In some embodiments, the EM sensor may be a vector component magnetometer.

[00158] Figure 12 is a block diagram of an exemplary sensor system 1200 that may be implemented using an instrument platform 1201. The instrument platform 1201 may be similar to the instrument platforms 108, 300, 706, or 800 shown in Figures 1A-1C, 3, 8 and 9. In this example, system 1200 includes one or more EM sensors 1202, one or more additional auxiliary sensors and systems 1204, an alignment system 1206, a fixation system 1208, first and second controllers 1210 and 1214, a wireless communication means 1212, and device 1216 data recorder. In this example, the EM sensor(s) 1202, auxiliary sensor(s) and systems 1204, the alignment system 1206, the first controller 1210, and the wireless communication means 1212 are mounted on the instrument platform 1201. One or more components may also be located outside the instrument platform. . For example, in this embodiment, the second controller 1214, the fixation system 1208, and the data recorder 1216 are installed outside of the tool platform. The wireless communication means 1212 may include a wireless communication means such as a wireless transmitter, receiver, transceiver, or any suitable combination thereof for wireless communication between the first and second controllers 1210 and 1214. In some embodiments, the wireless communication means may be installed directly between the first controller 1210 and the device 1216 data recorder.

[00159] The EM sensor(s) 1202 and auxiliary sensor(s) and systems 1204 may be mounted on the tool platform 1201 in various positions. Auxiliary sensor(s) and systems 1204 may be designed to collect electromagnetic survey data. Auxiliary sensors and systems 1204 may also include a means of determining the attitude, for example, a three-component static field vector magnetometer, accelerometer, gyroscopes, tilt and rotation sensors. Auxiliary sensors 1204 may further comprise GPS, Glonass, or equivalent sensors.

[00160] The tool platform attitude information allows the transfer of collected electromagnetic vector data or other sensor vector data from the local coordinate system of the tool platform to the global coordinate system.

[00161] As shown in Figure 12, EM sensor(s) 1202, auxiliary sensor(s) and systems and alignment system 1206 are connected to and controlled by the first controller 1210. The first and second controllers 1210 and 1214 may include one or more processors and memory. For example, Figure 12 shows a first controller including processor 1211 and memory 1213. Memory 1213 may store instructions to cause processor 1211 to perform the functions discussed herein. Other combinations of hardware and software may be used to implement controllers 1210 and 1214. The fixation system 1208 and the data recorder are connected to and controlled by the second controller 1214. The first and second controllers 1210 and 1214 are in wireless communication via the wireless communication means 1212. The instrument platform can be equipped with additional power supplies and batteries required for the operation of System 1200 components.

[00162] The data collected by sensors 1202 and/or 1204 may be stored in a database. The database may contain memory for storing and retrieving data. For example, the first and/or second controllers 1210 and 1214 may cause the received data to be transmitted (eg, via the wireless communication means 1212) to be stored in a database. In the specific example shown in Figure 12, the data recorder 1216 contains the specified database. Thus, the data collected by the sensors 1202 and/or 1204 can be downloaded by the second controller 1214 and/or the data recorder 1216 using the wireless communication means 1212. The data may be retrieved from the data recorder 1216 for further processing. In other embodiments, the first controller 1210 may include a database implemented in memory 1213 to store said data.

[00163] Using means 1212 for wireless communication between the first controller 1210 and the second controller 1214, the instrument platform can be freed from any mechanical links or connecting cables connecting it to the base assembly or carrier when collecting EM data, with the exception of contact on spherical support. In the embodiment, there are no connecting cables or restrictive devices that can impede the free movement of the tool platform relative to the base assembly. Means 1212 wireless may include a wireless transmitter. Alternatively, the transmitting portion of the wireless communication means 1212 may be part of the controller 1210, and the controller may provide a wireless communication function. Embodiments are not limited to a particular hardware layout.

[00164] Components on the tool platform 1201 may be powered by a battery or an equivalent power source such as a fuel cell or a large capacitor. The supply wires to the 1202 and/or 1204 sensors may be twisted to minimize stray magnetic fields from supply currents. All elements mounted on the tool platform 1201 can be securely fastened to minimize or eliminate random vibrations caused by relative movement of the element relative to the tool platform 1201.

[00165] Some of the components mounted on the tool platform 1201 may be placed in an electromagnetically shielded electronics compartment (eg, compartment 170 shown in Figure 1C). The shielded electronics bay and the components contained therein can form an offset weight for the vector component sensors so that the instrument platform including the sensors and ancillary equipment can only be slightly weighted at the bottom. In an embodiment, a shielded electronics bay may be mounted at the top cylindrical portion of the tool platform, and vector component sensors (eg, sensors 146 or 840 shown in Figures 1B and 9) may be mounted at the bottom of the tool platform.

[00166] The auxiliary sensor(s) and systems 1204 shown in Figure 12 may also include a three-component static field vector magnetometer. The three-component static field vector magnetometer can probe the Earth's static magnetic field. The three-component static field vector magnetometer may be a DC coupled vector magnetometer and may be a magnetometer other than an EM sensor, which may be an AC coupled sensor. For example, an EM sensor may comprise an induction magnetometer with a 1 Hz low-frequency cutoff and a noise floor of 1 pT/sq. root of Hz per 1 Hz. The three-component static field vector magnetometer may be a fluxgate magnetometer configured to probe a static magnetic field with a noise floor of 10 pT/sq. root of Hz per 1 Hz.

[00167] Auxiliary sensor(s) and system 1204 may include a highly accurate three-component accelerometer located proximate the air bearing, such as the accelerometer 164 illustrated in Figure 1C.

[00168] The locking system 1208 is optional and can be used to lock the tool platform in a fixed position relative to the base assembly (and/or the support column on which the spherical support is mounted) while electromagnetic data is not being collected. The locking system 1208 can be actuated by compressed air and can receive commands to lock and release the tool platform from the first controller 1210. The locking system 1208 can be installed on the top surface of a support column (for example, a pillar 144, 710, or 810 shown in Figures 1B, 7 , 8 and 9). The locking system 1208 may include pneumatic clamps that protrude upward from the column to engage the tool platform 1201 and lock it in position.

[00169] Embodiments are not limited to the particular configuration of system 1200 shown in Figure 12. For example, in some embodiments, a single controller may be used to control all elements of the system. One or more auxiliary sensors and systems 1204, alignment system 1206, and fixation system 1208 may be omitted. Similarly, data recorder 1216 may be removed from system 1200 and data may be transferred to an external database for storage. Other changes are also possible.

[00170] The alignment system 1206 shown in Figure 12 can be used to transmit torque to the tool platform, which causes it to rotate around a center of rotation. The alignment system may include its own controller (not shown), which may include a processor and/or memory. In other embodiments, the alignment system may be controlled by the first controller 1210.

[00171] The transmitted torque may change the orientation of the tool platform or its angular velocity. In this embodiment, the alignment system 1206 is located on the tool platform 1201 and receives commands from the first controller 1210. However, other locations are also possible.

[00172] The alignment system 1206 may include fans or other means of propelling air to create thrust. The air propulsion may generate a torque about the center of rotation, causing the tool platform 1201 to rotate. The alignment system 1206 may include means for propelling the air in three independent angular directions, and may include means for providing forward or reverse thrust in each of these directions. Leveling system 1206 may include three independently oriented reversible fans (eg, 654a, 654b, and 654c shown in Figure 6B), or it may include a fan that can be rotated to direct thrust in a particular direction. The leveling system 1206 may include a fan attached to the tool platform, which may direct air through movable channels, louvers, or vanes so that the direction of its draft may change.

[00173] In addition or alternatively, the alignment system 1206 may comprise a movable mass. The position of the moving mass can be adjusted to change the gravitational torque acting on the tool platform. The gravitational torque may vary to counteract the pendulum movement of the tool platform. In an embodiment, the gravitational torques can be continuously adjusted while collecting data to reduce the pendulum movement of the tool platform.

[00174] In one embodiment, the leveling system 1206 includes fans positioned at the top of the tool platform to provide thrust in three independent angular orientations. The alignment system may be operated intermittently when the instrument platform is tilted close enough to the tilt limit (e.g., the angle α shown in Figure 7) and/or before EM or other vector data is collected to place the instrument platform vertically and at low angular velocity.

[00175] In some embodiments, the system described herein is used for airborne electromagnetic surveying. The instrument platform 1201 can freely oscillate relative to the pole on which the spherical support is mounted long enough to complete one EM survey flight path. During the transition from route to route when surveying or when the tool platform is tilted excessively close to the pole, the tool platform 1201 may return to the vertical position by the leveling system 1206. When leveling the tool platform 1201, the main axis of the tool platform 1201 can move to a spatial position that is approximately parallel to the column axis at an angular velocity close to zero. During the rotation of the tool platform 1201 by the alignment system 1206, electromagnetic data collection may be suspended because the operation of the alignment system may cause excessively high electromagnetic or vibrational movement noise.

[00176] The alignment system 1206 may include an angular motion measurement system. The angular motion measuring system may include a controller and an angular measuring means for detecting the angular motion of the tool platform 1201. The angular motion measuring system can track the angular location of the tool platform in relation to its tilt angle and/or track its angular velocity. An angle measurement means for detecting the tool platform's angular motion may include a DC coupled vector magnetometer, tilt sensors, accelerometers, rate of rotation gyroscopes, and/or rotation speed sensors attached to the tool platform 1201. In an embodiment, the leveling system controller 1206 can receive signals from means of angular measurement. The controller may calculate the slope of the tool platform 1201 and control the leveling system 1206. The controller may instruct the alignment system 1206 to reorient the tool platform 1201 or significantly reduce its angular movement. In an alternative embodiment, the angular motion measurement system may be included in the auxiliary sensors and systems 1204, and not in the alignment system 1206.

[00177] In some embodiments, one or more components of the device described herein may be made from highly resistive and magnetically impervious materials to reduce electromagnetic noise that can occur due to eddy current induction and magnetization. Electronic components can be shielded with mu-metal or other highly permeable or conductive materials to suppress electromagnetic noise, preventing it from interfering with EM data measurements. Highly resistive and magnetically impermeable materials that may be used include, but are not limited to, carbon fiber, glass fiber or natural fiber composites, aramids, plastics, wood, rubber, ceramics, and glass.

[00178] Figure 13 is a flowchart of a method for collecting data from a movable instrument platform having at least one vector component sensor attached thereto, in accordance with some embodiments.

[00179] At 1302, the device containing the instrument platform (including the vector component sensor) is moved. The device may be similar to any of the exemplary embodiments described above, comprising: a base assembly; a spherical support mounted on the base assembly; and a tool platform mounted on a spherical support. The tool platform is weighted at the bottom in the sense that it has a center of mass located below the center of rotation. The device may also include a carrier (eg, carrier 101 shown in Figures 1A, 1B and 1D).

[00180] Moving the device may include towing the device with a vehicle, mounting the device on a moving vehicle or other moving body, or transporting the device, to name a few.

[00181] In step 1304, during device movement, vector component data is collected using at least one vector component sensor.

[00182] In some embodiments, a high-precision three-component accelerometer (eg, accelerometer 164 shown in Figure 1C) is mounted on the instrument platform adjacent to the spherical support. A transfer function can be used as a mathematical relationship to calculate the angular motion during a beat based on the measured acceleration. The beat noise can then be calculated based on the motion noise equations.

[00183] Figure 14 is a flowchart of an exemplary method implemented in the apparatus described above for correcting beat noise, in accordance with some embodiments. The method may be performed by a controller, such as the first controller 1210 shown in Figure 12, or any other suitable processing means.

[00184] In step 1402, acceleration data is received from the accelerometer.

[00185] In step 1404, the beat noise is estimated as a function of the acceleration data. This estimate may comprise calculating rotational motion based on input from a high precision three component accelerometer. Thus, the beat noise can be estimated based on the motion noise equations using the computed angular change and the measured static earth magnetic field. The Earth's static magnetic field can, for example, be obtained from a three-component DC coupled vector magnetometer attached to the instrument platform.

[00186] At 1406, the estimated beat noise is removed from the vector component sensor data, which may provide improved measurement with reduced motion noise.

[00187] In some embodiments, motion noise can be further reduced by measuring the angular movements of the instrument platform and adjusting the EM data of the sensor accordingly. The device may contain a magnetometer of the vector components of the static field and a sensor for measuring the angular motion installed on the tool platform. One way that can be used is to first calculate the motion noise using the rotational motion noise equations,

Nc=m⋅(ω×B),

Nm=m⋅(ΔΘ×B), or

N=m⋅(A×F).

[00188] And then removing the calculated noise from the data. The device controller may, for example, estimate the motion noise based on the data received from the attitude determination means and the angular motion measurement sensor. However, in practice, in the case of EM data, direct angle measurements are not accurate enough to accurately estimate the noise at least to resolve the order of picoTesla in the frequency band below 20 Hertz using currently available instrumentation and the transfer function approach, or other mathematical means, and instead of using a direct angular measurement, it may be necessary to calculate the angular motion from the acceleration measurements.

[00189] It should be understood that in some embodiments, a combination of more than one of the above approaches may be implemented. Embodiments are not limited to any particular one or more of the approaches, methods, or devices disclosed herein. Those skilled in the art will appreciate that changes to the embodiments described herein may be made in various implementations without departing from the scope of the invention. In this regard, it should be understood that within the scope of the appended claims, the invention may be practiced otherwise than specifically described.

[00190] The above description simply illustrates the application of the principles of the invention. Other designs and methods can be implemented by those skilled in the art without departing from the scope of the present invention.

Claims (44)

1. A device for collecting data of vector components, containing: base node; a spherical support mounted on the base assembly; a tool platform having at least one vector component sensor attached thereto, wherein the tool platform is mounted on and supported by a spherical support, whereby the spherical support connects the tool platform to the base assembly and allows free angular rotation of the tool platform, within a range of angle tilt, around a spherical support, so that the tool platform has a center of rotation; moreover, the tool platform has a center of mass located under the center of rotation. 2. The apparatus of claim 1, wherein the instrument platform is configured to oscillate about a center of rotation so that motion noise within the acquisition bandwidth of at least one vector component sensor is suppressed. 3. The apparatus of claim 1, wherein the instrument platform has a natural pendulum frequency that is below the lowest frequency of the acquisition bandwidth of at least one vector component sensor. 4. The device according to any one of paragraphs. 1-3, in which the tool platform is rigid. 5. The device according to any one of paragraphs. 1-4 further comprising a carrier, the base assembly being connected to the carrier. 6. The apparatus of claim 5, wherein the carrier comprises a towing frame and a coupling mechanism connecting the base assembly to the towing frame. 7. An apparatus according to claim 5 or 6, wherein the carrier is an air carrier capable of being towed by an air vehicle. 8. The device according to any one of paragraphs. 1-7, in which the spherical support is an air support. 9. The device according to any one of paragraphs. 1-8, in which the spherical support contains a single mechanical connection between the base assembly and the tool platform. 10. The device according to any one of paragraphs. 1-9, wherein said at least one vector component sensor includes three independently oriented vector component sensors. 11. The device according to any one of paragraphs. 1-10 further comprising a controller comprising a processor and memory, the controller receiving data from said at least one sensor. 12. The apparatus of claim. 11, in which the controller stores the received data. 13. The apparatus of claim 11 or 12, further comprising wireless communication means, wherein the controller causes the wireless communication means to transmit received data for storage in a database. 14. The device according to any one of paragraphs. 1-13, wherein the base assembly comprises a support post, the spherical support being mounted on the support post. 15. The apparatus of claim 14, wherein the support post includes a post extending upward from the base assembly. 16. The device according to any one of paragraphs. 1-15, wherein said at least one vector component sensor includes at least one of the following: at least one electromagnetic sensor; at least one gravimetric sensor. 17. The device according to any one of paragraphs. 1-16, wherein said at least one vector component sensor comprises at least one gradiometric sensor. 18. The device according to any one of paragraphs. 1-17, wherein the tool platform comprises a downwardly facing skirt, the downwardly facing skirt providing clearance around the spherical support and the base assembly to provide a range of tool platform oblique rotation within the tilt angle range. 19. The device according to any one of paragraphs. 1-18, additionally containing: leveling system; and angular motion measuring system, moreover, the alignment system, depending on the angular movement measured by the angular movement measurement system, applies leveling torques to the tool platform, causing it to rotate around the spherical support. 20. The apparatus of claim 19, wherein the alignment system comprises one of the following: a plurality of propulsors located on the tool platform, the propulsors producing said equalizing torques; and a plurality of movable mass assemblies disposed on the tool platform, wherein the movable mass assemblies generate said equalizing torques. 21. The device according to claim 19 or 20, in which the equalizing torques are generated for at least one of the following: orienting the lower-weighted tool platform such that its major axis is substantially vertical; and decrease in angular velocity. 22. The device according to any one of paragraphs. 1-21, further comprising an accelerometer located on the tool platform, wherein the accelerometer measures acceleration data, and the controller is configured to: receiving acceleration data; beat noise estimates depending on acceleration data; and removing beat noise from data received from said at least one vector component sensor. 23. A method for collecting vector component data from a movable instrument platform having at least one vector component sensor attached thereto, the method comprising: move the device, containing: the site of the base; a spherical support mounted on the base assembly; and a tool platform, wherein the tool platform is mounted on and supported by the spherical support, whereby the spherical support connects the tool platform to the base assembly and allows free angular rotation of the tool platform, within a range of inclination angle, about the spherical support, so that the tool platform has a center rotation, and the tool platform has a center of mass located under the center of rotation; and while the device is moving, vector component data is collected using said at least one vector component sensor. 24. The method of claim 23, wherein the device further comprises a carrier, the base assembly being connected to the carrier, and the step of moving the device includes towing the carrier. 25. The method of claim 23 or 24, wherein the instrument platform is operable to pendulum about a center of rotation so that motion noise within the acquisition bandwidth of said at least one vector component sensor is suppressed.

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