CH703352A1 - underground beacon positioning method. - Google Patents

Abstract

An underground beacon positioning method (10) comprising the steps of: installing on the surface of a plurality of beacons (20); exchanging first radio signals (200) between said beacons (20) to transmit data; moving a mobile beacon (100) into an underground cavity (1); sending second radio signals (100) between said mobile beacon (10) and said surface beacons (20) through the ground, at least one said beacon (10; 20) comprising three non-coplanar coils for transmitting and / or receiving said second radio signal (100); determining the position of said mobile beacon (10) by said second radio signals (100). The invention also relates to an underground beacon positioning system. According to an independent aspect of this invention, the method and system can be used for locating people in avalanches.

Description

Technical area

The present invention relates to a method and an underground beacon positioning system.

State of the art

The present invention relates to a method for locating people or objects in an underground cavity, for example in a cave, in a mine, etc..

Known underground location systems are based on a network of ZigBee transmitters or a fixed network of relays mounted inside the underground cavity and communicating with each other via an air interface through the cavity. For example, WO 09 118 762 describes a miners location system based on an ad hoc network of ZigBee devices worn by the miners and placed at strategic locations. Such systems require a complex prior installation and are only poorly adapted to the location of speleologists in a cave, for example.

EP 2 159 605 describes a method of locating a hidden object in a medium that uses a combination between the "Spread Spectrum" method and the "Sample-Hold" method.

[0005] The document WO 09 023 008 describes a system for locating minors based on acoustic signals.

US 2003 197 509 discloses a system for locating a cavity below the surface of the earth comprising a device for transmitting a magnetic dipole aligned with this cavity and a single receiver comprising two coils. The system is based on the detection of the phase of the signals induced in the coils by the magnetic field emitted when the axes of the two coils are in a particular position with respect to the axes of the magnetic field.

[0007] Known underground localization systems make it possible to locate an underground position at a short distance; the range is generally less than 40 m. The accuracy of this measurement is not always sufficient and can be disturbed by electrically conductive floors or by building foundations.

The most commonly used magnetic positioning system in underground cavity for example a borehole for catching an underground river uses a coil generating an alternating magnetic field, placed in the cavity, and a receiving coil on the surface. Such a system does not allow to map, but only to find the position of a point by successive iteration looking for the maximums or the minimums of the received signals.

In addition existing systems do not allow to use the knowledge of when a caver arrived on the spot to start a position measurement right away. It is necessary to wait until the speleologist arrives on the spot, for example in a cavity, places a beacon and then goes back to the surface to communicate the good positioning of the beacon before starting the measurement.

The underground location is also particularly used during drilling, for example to look for oil. This location, however, starts from the knowledge a priori of the position where the drilling is performed. Wires placed along the drill bit also make it possible to provide a communication channel for transmitting data on the surface and for connecting the beacon near the drill head with the module for calculating and displaying the position on the surface. . This wire also makes it possible to know the distance traveled in the borehole, and thus to advantageously use inertial sensors coupled to a magnetometer. Such devices are unsuitable for locating people or objects in a cave or mine, when a cable can not be pulled easily between the inside and the outside. The drilling head locating systems can not therefore be used to for example map a cavity or to locate a person buried by an avalanche, because it is not possible in this case to exploit a knowledge a priori of the position we want to measure.

There are also Search Devices Victims buried in Avalanches (ARVA) that use two frequencies, one working and the other for a more precise measurement. Some of these devices have three coils, one transmission and the other two receiving, to determine the position of a person buried by an avalanche. These devices only detect the presence of a person by following the magnetic field lines from a dipole. Therefore these devices do not directly give the person's position, which makes the search complicated and slow.

Brief summary of the invention

An object of the invention is to develop a method and a system for determining the position of an underground beacon with a greater range (for example more than 40 meters, preferably of the order of 200 meters ).

There is also a need for a method and a system that allow precise location of the beacon, even in the presence of conductive ground and / or ferromagnetic materials, for example building structures or metal pipes.

There is also a need for a system that allows to cover large areas and is flexible either in time, that is to say that can be easily reconfigured, or adapted to the nature of the field.

There is also a need for a system in which communication between the basement and the surface is improved.

There is also a need for an improved system for locating people in avalanches, which can directly give the position of buried persons, and not the direction of the magnetic field line (curvilinear towards the victim). Such a system would be much more efficient in locating than existing devices.

An object of the present invention is to provide a method and an underground beacon positioning system free from the limitations of known methods and devices.

According to the invention, these objects are achieved in particular by means of the underground beacon positioning method according to claim 1. These objects are achieved also by means of the underground beacon positioning system according to claim 20.

This solution has the advantage over the prior art of being able to determine the position of an underground beacon, that is to say the direction, distance and orientation of this beacon with respect to one of the surface markers, at significant depths, for example at depths greater than 40 m and an area of more than 10 hectares, depending on the transmit power and the size of the antennas. This increased range is achieved in particular by advantageously exploiting the redundancy of the surface beacons as well as the presence of three orthogonal coils, that is to say three coils with the orthogonal axes, in at least one of the beacons. More generally, it is sufficient for the coils to be non-coplanar, that is to say that the axes of the three coils are non-coplanar.

Advantageously, the method and the system according to the invention allow a precise location of the mobile beacon, even in the presence of conductive ground and / or ferromagnetic materials, using multilateration (trilateration over several distances) thanks to the data obtained. since several tags on the surface.

In another variant the system displays measurement quality indicators that take into account noise, eddy current absorption, magnetic deformation by magnetic bodies, and so on.

To improve the accuracy of the measurement it is possible to rotate at least one of the tags of a known angle, for example 90 ° or 180 °, between two measurement cycles to make a differential measurement. In another variant it is possible to measure the vertical direction for example with an accelerometer or an inclinometer, and then automatically turn the coil of the mobile beacon with a motor to align vertically. In another variant, it is possible to transmit simultaneously on several coils in order to emit a resulting field in predetermined vertical and horizontal directions.

Advantageously, each transmitting beacon has three orthogonal coils which emit in turn. In the case where each transmitting beacon comprises another number of orthogonal coils, or in general non-coplanar coils, they can also emit at any one time. The receiving beacon or beacons also comprise three orthogonal coils. By measuring the signals received during the three orthogonal transmissions of the transmitting beacon with the three receiver coils (nine information, from the three vectors received during each transmission), it is possible to determine the distance between the transmitting beacon and the receiving beacon, the angles between these two beacons (direction of the transmitter relative to the receiver), as well as the orientation of the transmitting beacon. It is therefore possible for each receiving beacon individually to determine the position as well as the orientation of the mobile beacon. In another variant it is possible to determine the position of the mobile beacon by multilateration from the distances measured by at least three beacons on the surface.

After having installed several beacons on the surface, they exchange first radio signals in order to transmit data, for example synchronization data or signals used to determine the position of each beacon at the surface by multilateration (UWB or other). or on the basis of other information drawn for example from a satellite receiver (GPS or other), inertial sensors (3D accelerometer used as a clinometer) and magnetic sensors (3D compass) or a position measurement by another method of positioning.

In this text, the expression "radio signal" indicates either a pure magnetic signal or an electromagnetic signal.

In another variant, the system automatically chooses the most appropriate algorithm (multilateration and / or weighted average of the positions calculated by each beacon individually) to find the position of the mobile beacon. Multilateration alone does not directly give its orientation, but only its position (direction and distance). However, a calculation unit can use the information available to calculate the orientation as well. The selection of the algorithm or algorithms used is done automatically according to one of the following parameters: number of tags available; nature of the terrain; quality of measurements from different tags; relative position of the different tags.

In a preferred embodiment, the mobile beacon is a transmitting beacon and the beacons on the surface are receivers.

Advantageously, the system according to the invention can be permuted so that the reception receiving beacons on the surface become emitting and the transmitting beacon under the ground becomes a receiver. In this way one can for example use the system for the navigation in the mines, obtaining directly underground the information on the position. The use of the mobile beacon as a reception beacon also makes it possible to reduce the energy consumption of the mobile beacon. The permutation can be decided by the user, for example by means of an option in the system controls, without replacing parts, each beacon can be transmitting or receiving.

In another variant it is possible to establish, from several measurements, a geological model of the field by highlighting the presence of ferromagnetic structures and / or more or less conductive. This model can be used either as a measurement result or to correct / compensate for position measurement errors in the same region. The system therefore can find the correct position of an underground beacon even in the presence of ferromagnetic or conductive layers.

In a preferred embodiment the system comprises a bidirectional data radio link between the beacons on the surface and the underground beacon; this bidirectional radio link can be advantageously used for: indicate to the surface beacons that the underground beacon is in position and that the measurement can be started; transmit other parameters useful for the measurement, for example parameters determined by a compass, a GPS on the surface, an inclinometer, etc .; transmitting to the mobile beacon the position calculated on the surface; transmit other data or voice.

The presence of this link also makes the method more efficient: once the speleologist arrived on site, he can press a button of the mobile beacon to communicate through this radio link beacons on the surface that the underground beacon is well placed and therefore it is possible to start making measurements. Alternatively, it can also use this bidirectional link to communicate messages or data orally.

In addition, the position calculated on the surface by an algorithm executed in a calculation unit can be transmitted always through this radio link to the mobile beacon which can display the result on a screen. The speleologist or miner can know immediately the calculated position.

In a preferred embodiment the bidirectional radio link uses the same coils as the location and does not need additional antenna or coil. In another variant this bidirectional radio link used different coils but which are wound around the same core of the coils already present, so each axis contains a pair of coils, for a total of six coils, that is to say three pairs of coils. In addition, it can use a modulation of the signal exchanged between the mobile beacon and the beacons on the surface. In a variant, another signal, possibly at another frequency, is used for this bidirectional communication.

Advantageously the underground beacon is "mobile" in the sense that it can be contained in a backpack carried by a walker, for example a minor or speleologist. In another variant it can be moved by vehicle or robot or also by a floating device or swimming in an underground river or a drowned gallery.

The mobile beacon can be coupled to a 2D scanner or a 3D scanner so that it is possible, for example, to map a cave. As will be discussed later, the 3D scanner allows faster measurements; however, it is larger, more expensive and more fragile than a 2D scanner.

The surface beacons may have a GPS to locate before the measurement. It is thus possible to know the precise distance between the surface beacons, which is for example greater than 50 m to be able to cover large areas. For precision questions, the use of a differential GPS technique is preferred, in order to obtain a local accuracy much better than a meter. In a variant, the relative position of the surface beacons is determined by multilateration from the signals exchanged directly between these beacons. With global and non-local coordinates, surface beacons can be located automatically in an official coordinate system: the underground points positioned by the system are then also located directly in the official (global) coordinate system.

The system can measure the depth of a cavity up to 400 m distance with an accuracy of about 1%. It can also measure the distance between two measurement points.

With a single beacon on the surface, which in a preferred embodiment is a receiving beacon, the system calculates two possible responses to the equations generated by the calculation algorithm. To eliminate the erroneous solution, the user can introduce an obvious condition, for example that the vertical coordinate Z is negative. When the two possible solutions to the system of equation can not be easily separated, for example if the two results are plausible, one can also perform a second measurement by moving the mobile beacon or the fixed beacon. The system displays instructions for this, then calculates the position of the moving beacon based on the two measurement cycles (before and after the move).

The calculation of the position is displayed graphically and numerically on a computing unit, for example a computer, connected to or integrated with the beacons on the surface or with the mobile beacon. If necessary, the information for displaying the position is transmitted by means of radio signals (101 or 300) to the computing unit.

According to an independent aspect of the invention, the system can also be used for locating people in avalanches, to determine the position of people at distances that can also exceed 30 meters. Thanks to the use of three orthogonal coils in the transmitting beacon or beacons and in the receiving beacon or beacons, this system is more accurate than the existing devices because it makes it possible to visualize the direction between a transmitting beacon and a receiving beacon and not the direction of field lines as in existing devices. Furthermore, the distance measurement does not depend on the orientation of the beacons and corresponds to the distance as the crow flies or the distance projected in a preferred plane of the beacon at the surface (for example the distance parallel to the ground) as well as the distance measured perpendicular to this same plane (for example the depth of burial). In a variant, the system used for locating people in avalanches only uses a surface beacon. Although the system can detect a person's position at distances greater than 30 m, normally the burial depths are in the order of magnitude of the meter. In addition in general there are no ferromagnetic structures that can disturb the measurement, but the person is buried under snow.

In a variant the surface beacons forming an ad hoc network, and the underground beacon positioning method comprises the automatic detection of the number of beacons on the surface.

In another variant, the mobile underground beacon positioning method comprises calculating two possible positions of said mobile beacon; eliminating one of said possible positions by mathematical conditions or by a second measurement performed after moving said mobile beacon or a beacon on the surface; displaying on a calculation unit instructions for performing said elimination.

In another variant, the underground beacon positioning method comprises computing the position of said moving beacon by said computing unit; transmitting said position to said mobile beacon; displaying said position on said computing unit and / or on said mobile beacon.

In another variant, the computing unit is integrated in a module with one of said surface tags.

Brief description of the figures

Examples of implementation of the invention are indicated in the description illustrated by the appended figures in which: <tb> Fig. 1 <sep> illustrates an underground beacon positioning system according to one aspect of the invention. <tb> Fig. 2 <sep> illustrates a block diagram of a transmitting beacon according to one aspect of the invention. <tb> Fig. 3 <sep> illustrates a block diagram of a receiving beacon as well as the computing unit according to one aspect of the invention.

Example (s) of embodiment of the invention

In most of the examples that follow, the surface beacons are receivers and the transmitting mobile beacons. Other examples may be constructed with an inverted system, i.e. with transmitting surface beacons and receiving mobile beacons.

An example of an underground beacon positioning system which is the subject of the invention is shown in FIG. 1. This system allows the measurement of the position of an underground mobile beacon 10 placed in a cavity 1, for the purpose for example to map this cavity or to determine the position of a person or an object, thanks to a or a plurality of surface tags 20 and a computing unit 30.

The surface beacons 20, unlike the mobile underground beacon 10, are in a fixed position. The word "fixed" in this invention indicates that their position does not change during the duration of the measurement. The duration of the measurement is between a few minutes and several hours. In cases of searching for the vertical of a point and buried person, the receiver is moved after each measurement. The system is therefore temporary: after having determined the necessary measures, for example after mapping a cavity, all the tags can be moved to, for example, make other measurements. Even fixed beacons are therefore preferably transportable and electrically autonomous.

According to an independent aspect of the invention, the system allows the location of people in avalanches. In this case the location is performed under a surface, for example a surface of snow, and not under the ground.

The system uses a magnetic measurement principle (induction) with one or more mobile beacons which in a preferred embodiment are emitting and one or more beacons on the surface which in a preferred embodiment are receivers each containing three coils. In a variant, the underground mobile beacon 10 emits second signals 100 that are received by the surface beacons 20. In another variant, the second signals 100 are emitted by the surface beacons 20 and are received by the underground mobile beacon 10. same system can be reconfigured automatically or following a command from the user to operate either according to the first variant, or according to the second variant.

In a variant, the system allows the determination of the position of an underground mobile beacon 10. In another variant, it also determines its orientation.

The word "underground" in this invention means under rock, earth, concrete, water, snow or any other solids or liquids.

The system is composed of three parts: A mobile underground beacon 10. In a preferred embodiment, the mobile beacon 10 emits second signals 100. The system thus makes it possible to determine its position. As will be seen below, this mobile beacon 10 may comprise three orthogonal coils that can successively generate three orthogonal magnetic moments. In one variant it is possible to use several mobile beacons 10 in the same system, and to determine the position of each of these mobile beacons, for example in order to locate several persons or objects in an underground cavity. One or more beacons placed at the surface 20. In a preferred variant, these surface beacons 20 measure the magnetic field emitted by the mobile underground beacon 10. As will be seen below, each surface beacon 20 may also comprise three orthogonal coils on which are measured successively the voltages induced by the second signals 100 emitted successively by the mobile beacon 10. A computing unit 30. This unit 30 allows the calculation of the position and the orientation of the mobile beacon 10, the digital and graphic display (plane, section and 3D) and the recording of the measurements from the data obtained by the receiving beacons which, in a preferred embodiment, are the beacons placed at the surface 20. In a variant this calculation unit 30 can be integrated with a beacon at the surface 20.

As discussed, in a preferred embodiment, the mobile beacon 10 is transmitting and the beacons 20 on the surface are receivers. In another variant it is possible to switch the transmitting and receiving beacons: the transmitting beacons are then on the surface and the receiver beacon underground. It is also possible to place all tags underground, all tags on the surface or any intermediate arrangements.

After installing several tags on the surface, they exchange first radio signals 200 in order to transmit data. The exchanged data may for example include the identifier of the receiving beacons and synchronization data in order to temporally synchronize the fixed beacons. It is also possible to exchange via this channel data making it possible to locate the fixed beacons, for example coordinates determined by a GPS in each fixed beacon, or introduced by an operator, or else signals making it possible to determine by multilateration or triangulation, measurement of flight time, etc., the relative position of each mobile beacon organized according to an ad hoc network. The data exchanged may also include signals useful to the operators, for example signals to indicate to different operators that the measurement is ready, maintenance signals such as the level of battery charge or alarm, etc. During measurement, this channel is used to communicate to the computing unit data from the signals received by each receiving beacon.

As discussed, in a preferred embodiment the mobile beacon 10 is a transmitting beacon. As illustrated in FIG. 2, a transmitting beacon may include: three orthogonal coils 11A, 11B and 11C, forming a 3D coil and making it possible successively to generate three orthogonal magnetic fields; three resonance capacitors 12A, 12B and 12C placed in series with the three coils 11A, 11B and 11C; three power amplifiers 13A, 13B and 13C; in a variant, these three amplifiers comprise power transistors placed in an H-bridge; a control electronics 14, preferably comprising a microcontroller 15; a frequency reference 17, which in one variant is constituted by a quartz oscillator; an energy source 18, for example a Pb battery or Liions; a pusher 16 for manually triggering the transmission.

The three coils 11A, 11B and 11C are, depending on the case, air coils or ferromagnetic cores. Air coils are used to make large coils of decimetric size. Conversely, ferromagnetic core coils are used for small coils. In a variant, a transmitting beacon comprises a combination of the two types of coils, that is to say two core coils and an air coil, to obtain a flattened shape. In a preferred embodiment the three coils are nested.

With the mobile beacon 10, composed of the three orthogonal coils 11A, 11B and 11C, three orthogonal dipoles are generated. By using at least two surface receiving beacons each having at least one coil, it is then possible to calculate the position and orientation of the mobile beacon, as well as the distance between the surface beacons and the mobile beacon. The same considerations are valid using several surface receiving beacons 20, composed of the three orthogonal coils 21A, 21B and 21C, and a mobile transmitting beacon having at least one coil. The same considerations are valid in the case of the inverted system, that is to say with a mobile receiver beacon and several transmitting beacons on the surface.

In a variant, each surface beacon allows the calucl unit to independently calculate the position of the mobile beacon, by means of second radio signals, with one of the following configurations: the mobile beacon comprises two orthogonal coils and the surface beacons three orthogonal coils; the mobile beacon comprises three orthogonal coils and the surface beacons at least two orthogonal coils.

If all the beacons are composed of three orthogonal coils 11A, 11B, 11C, 21A, 21B and 21C, each fixed beacon measures nine signals for calculating the position of the mobile beacon. This optimal configuration substantially improves the convergence of the algorithm for the extraction of the position executed in the computing unit 30, improves the accuracy and makes it independent of the orientation of the beacons.

The three orthogonal coils 11A, 11B and 11C are powered by a voltage reference, or current, modulated by a signal generated by the electronics. This signal is preferably a square or sinusoidal signal.

Each coil 11A, 11B and 11C is preferably connected to a capacitor 12A, 12B and 12C to form a series resonant circuit, whose resonant frequency is the working frequency. The working frequency is determined by the element 17, which may be a crystal oscillator, an LC oscillator (including the 3D coil), an RC circuit, for example an internal circuit to the microcontroller 15. It is imperative to know the phase between the three different emissions, so that during the demodulation, the signs (phase variant of 180 ° on receipt) magnetic moments can be obtained.

The magnetic moment generated by the 3D coil is alternating, preferably sinusoidal. In a variant, to save energy, this signal is not transmitted continuously but intermittently with a low duty cycle, and only for a limited time after the transmission request preferably introduced manually by means of the pusher, or at cyclic intervals. In addition to saving energy, it is preferable to transmit with a coil 11A for a short time before switching immediately on the other coils 11B and 11C to ensure that the transmitting coil remains stationary during the entire transmission cycle, especially if the beacon is not fixed, for example if it is in a backpack carried by a walker 8, or in a moving vehicle.

The transmitting beacon, for example the mobile beacon, is preferably provided with indicators, for example sound and / or light, for: Indicate how it works, for example indicate that it is in issue, or that it will be in issue. Indicate that she must remain motionless. Referencing the current program, for example with an emission counter. Indicate the reception of a signal coming from the reception beacons, for example the surface beacons 20, or the calculation unit 30. Indicate the level of the battery 18.

A transmitting beacon, for example a mobile beacon, can transmit either at predefined intervals, for example for one second every five seconds, either on request or after an event. In the latter case the event can be: Press button 16. In a variant this button 16 is a flexible device to avoid moving the beacon during the support and allowing the minor or speleologist 8 to move away to limit its exposure to the magnetic field . A voice command issued by the minor or speleologist 8. A command from another device coupled to the transmitting beacon, which in a variant is the mobile beacon, for example a robot that allows it to move autonomously, a scanner 2-D or 3-i D to reconstitute by for example the geometry of a cavity 1 or a computer coupled to the microprocessor 15. A signal transmitted through the radio link 101 by the receiving beacons, for example the surface beacons 20, or by another device. A change of position or orientation of the mobile beacon, detected for example by one or more accelerometers coupled to this beacon. A long period of immobility of the mobile beacon, detected for example by one or more accelerometers or by a vibration sensor, coupled to this beacon. An alarm triggered by one of the measuring means to be described later.

In a variant, the three magnetic signals generated by the three coils 11A, 11B and 11C in the three orthogonal directions are multiplexed temporally. In another variant, they can be multiplexed in frequency, feeding each coil 11A, 11B and 11C with a different frequency and separating the three signals by signal processing.

As discussed, in a preferred embodiment the transmitting beacon is the mobile beacon 10. It transmits second radio signals 100 to receiving beacons which, in this preferred embodiment, are the beacons at the surface 20. As shown in FIG. 1by the arrows 100 which are bidirectional, the communication between the mobile beacon 10 and the surface beacons 20 can be bidirectional. In order to allow this type of communication, the transmission coils 11A, 11B, and 11C can also be used as reception coils. This bidirectional communication can also make it possible to synchronize the transmitting beacons in the case where there are several.

The emission frequency depends on the environments of the applications: for underground applications in land containing limestone or granite, it is located in the ULF band (300 Hz - 3 kHz) or possibly at the beginning of the VLF (< 10 kHz). For applications in less conductive environments, such as snow, the emission frequency is preferably greater than 100 kHz. In the variant of the location of persons in avalanches, for reasons of compatibility, the emission can be carried out in a single direction at the normalized frequency of 457 kHz. The frequency changes can be made by adding or removing a capacity of the LC network (11A-12A, 11B-12B, 11C-12C), for example with one or more multiplexers, or with a switch, either analog or more simply a relay.

The transmission frequency can be modified depending on the type of terrain between the transmitting beacon, for example the mobile beacon 10, receiving beacons, for example the beacons at the surface 20. In the case of 'a clay-containing ground, since the terrain is rather conductive, the transmission frequency must be low, in any case <10 kHz, or even lower than 1 kHz. In the case of a rather insulating ground like granite, a higher frequency must be used, for example> 10 kHz. This modification of the transmission frequency can be automatic or manual.

In a variant it is possible to use several frequencies for the same measurement to highlight the limits from the ground or conductive objects interfering in the measure, such as marneux banks or clay very conductive indicated by the reference 3 in FIG. 1. In a variant, the mobile beacon, which in a variant is transmitting, transmits a magnetic signal containing harmonics because, for example, the emission coils 11A, 11B and 11C are fed with a triangular current, that is, ie a square voltage signal, or with a trapezoidal triangular current. The demodulation in the reception beacons is therefore performed either on the fundamental frequency or on the harmonics, to obtain the signals at the different frequencies. These multifrequency measurements can in particular be used to make geophysical measurements to determine the conductivity or other parameters of the terrain.

The transmission frequency is chosen between the harmonics of the electrical and rail networks, which are the integer multiples of 50 Hz, 60 Hz and 162/3 Hz. The ideal frequencies can therefore be 325 Hz, 625 Hz, 925 Hz, 1225 Hz, 1525 Hz, 1825 Hz, 2125 Hz, 2425 Hz or 2725 Hz.

For underground applications, the frequency of 1225 Hz is preferred because it represents a good compromise between the latency to measure the signal of a coil (typically 100 cycles), the signal absorption in the field and the magnetic noise of human origin.

The magnetic field generated by an emission beacon, for example a mobile beacon, is regulated in order to emit a precise magnetic moment. Two possibilities make it possible to realize this type of regulation: Measurement of the current flowing through the coils 11A, 11B and 11C by a Hall effect sensor or an inductive sensor. Measuring the field emitted by each coil 11A, 11B and 11C by a magnetometer which may consist of one or more Hall effect sensors, one or more magnetoresistive sensors or another coil.

In the case of a large emission tag, the use of a magnetometer is preferred, because it also makes it possible to compensate for couplings or parasitic effects. The use of a 3D magnetometer also makes it possible to compensate for the non-orthogonality of the emitted magnetic field, which is a combination of the three fields emitted simultaneously by the three transmitting coils 11A, 11B and 11C.

The reference value of the magnetic field generated by an emission beacon, for example by the mobile beacon, may be: Constant. Manually adjusted according to the distance between the transmit beacon and the reception beacon. Automatically adjusted according to the noise level measured by the transmit beacon itself or by the reception beacons.

In a variant, an emission beacon can be combined with: Inclination or motion sensors, for example accelerometers and gyroscopes. Electronic compasses (3D compasses), such as fluxgate, AMR, GMR, GMI or Hall effect sensors. Vibration sensors.

With accelerometers and / or compasses, it is possible to generate dipoles whose orientation is known and maintained identical. It is thus possible to superimpose the magnetic fields emitted by the three coils 11A, 11B and 11C of the transmit beacon to obtain a field which has a known orientation, for example a vertical field (Z direction in FIG. 1) or oriented magnetic north. In this way the number of degrees of freedom of the system is reduced and thus its accuracy is increased.

In a variant, once the vertical direction has been measured, for example with an accelerometer, the emission coils can then be rotated to obtain a vertically aligned magnetic field in the determined direction. This alignment can be automatic using a motor to rotate the beacon, or performed manually by a user preferably following visual or auditory instructions returned by the beacon. In another variant, once the vertical and horizontal directions have been measured, the emission of the three coils 11A, 11B and 11C can be carried out in known vertical and horizontal directions. In this way the accuracy of the measurement is increased.

The additional information from inclination or motion sensors, electronic compasses or vibration sensors may be used by the calculation algorithm executed in the computing unit 30 which determines the position of the beacon. program. This additional information is preferably transmitted in "real time", that is to say in a lapse of time less than 10 seconds. In a variant, this data useful for the measurement can be transmitted by using a third bidirectional radio link, indicated by the dotted arrows 101 in FIG. 1. In the case of a person location in avalanches, this information may also preferably be transmitted by radio frequency using an ISM frequency, for example the frequency of 433 MHz which passes through the snow being little or not absorbed.

As discussed, this additional information makes it possible to increase the accuracy of the calculations: for example the use of an inclination sensor and a compass makes it possible to eliminate the three degrees of freedom of rotation and in this way the calculation algorithm should no longer take into account these three degrees of freedom.

Some of this additional data can also be used to determine the transmission periods. For example, a broadcast can take place only after a movement of the mobile beacon or only during its periods of immobility. In this regard, the third bidirectional radio link 101 may be used to transmit the indication to the reception beacons, for example the surface beacons 20, that the transmitting beacon, for example the mobile beacon 10, is in position.

In another variant, this additional information can be stored in the transmit beacon for later transfer.

The third radio link 101 may use a modulation of the magnetic field generated by the coils 11A, 11B and 11C. It is possible to modulate: amplitude; the duration; frequency; the sentence; the delay between transmissions.

The third radio link 101 may be bidirectional. In this case, one or more coils of beacons are used as transmitting antenna and one or more coils as receiving antenna. In a preferred embodiment the third bidirectional radio link 101 uses the same coils as those used for the positioning of the mobile beacon and there is no need for an antenna or one or more additional coils. In a second variant, this bidirectional radio link uses different coils but which are wound around the same core of the coils already present, so each axis contains a pair of coils, for a total of six coils, that is to say three pairs of coils. In another variant of the electrodes placed in the ground several meters away, as for some radios used in the underground communications, can be used as surface emission antenna and one or more coils on the transmit beacon can be used as receiving antenna.

These two-way communication means are particularly useful for mapping applications. They can in particular allow the transmission of messages between the surface and the mobile beacon.

Measuring the position and orientation of the transmit beacon is a useful addition to many measurements. In a variant it is possible to combine the transmit beacon with measuring devices, a non-exhaustive list of which follows: A camera or a camera, for example to detect and position water leaks, landslides or plugs (each underground shot is then directly positioned and oriented). A 2-D scanner: each profile of a cavity or gallery 1 can thus be scanned and directly positioned and oriented, allowing the 3-D reconstitution of the galleries through a series of successive 2-D measurements. The 2D scanner captures a slice of a cavity or cave 1, then advances from a distance in the range 10 cm - 10 m, stops and captures another slice. This device allows efficient and fast 3-D reconstitution of cavities or galleries. A variant would be to measure with a 2-D scanner while advancing continuously. The profile would then become a helicoid. A 3-D scanner or a 3-D camera: in this case each shot is directly positioned and oriented allowing a 3-D reconstruction of cavities or underground galleries in single shot and with a reduced total measurement time compared to the scanner 2D. However a 3-D scanner is more expensive, bulkier and more fragile. In addition, for small galleries, the measurement performed by a 2-D scanner gives better results, given the shadows in out-of-profile measurements for a 3-D scanner. A hydrophone to listen to the sound of water, to detect noise from turbulence around an obstacle or that of water flowing into a crack. A pollution detector (toxic gases, hydrocarbons, radioactivity, etc.) to instantly know if and where there is pollution. A tracer detector used in hydrogeology (spectrofluorimeter), for example a fluorescent substance such as uranine, to find the position where a pipe joins a collector. The tag can also release this same plotter at a defined location. Sensors, for example pressure, radioactivity, hydrocarbon, turbidity, temperature or other sensors used in geophysics.

With the position and orientation information of the transmit beacon obtained by the system of FIG. 1, it is then possible to georeference the measurements obtained by the measuring devices above.

The mobile beacon can be moved by fixing it to: an unmanned vehicle, for example a robot for inspecting pipes or a submarine; an autonomous vehicle; a vehicle carried by water, for example by a river current, floating or of a density equal to water; a rope or cable.

The transmitting coils 11A, 11B and 11C are suspended as a pendulum. As a result, they naturally orient themselves according to the field of gravitation. To dampen the oscillations of this pendulum, a system for absorbing mechanical energy, for example an oil bath, can be used.

In one variant, several mobile transmit beacons can be used. In this case, to separate the signals from the different transmitting beacons, a multiplexing, either frequency (FDMA-Frequency Division Multiple Access), or time (TDMA - Time Division Multiple Access), or by orthogonal codes (CDMA - Division Multiple Access Code) ) can be used.

In the case of the TDMA, the multiplexing can be controlled by programming response delays with respect to the synchronization signal 17, or with the aid of a more evolved protocol allowing separate access to each beacon. tags, for example, being identified individually during production. In another variant, the synchronization signal 17 is not used and the beacons transmit at random time intervals. In the latter case there is the possibility of losing some data when there is superposition of emissions. A transmitting beacon, for example a mobile beacon, can also be synchronized (auto-synchronization) by analyzing the magnetic signals emitted by the other beacons and choosing the appropriate time for its own transmission.

As discussed, in a preferred embodiment the surface beacons 20 are receiving beacons. In a preferred embodiment the minimum distance between two receiving beacons is greater than 50 m, so that it is possible to cover a large area. In another variant a single reception beacon is used, for example to find the vertical of an underground point or to locate a person buried in an avalanche.

As illustrated in FIG. 3, a receiving beacon, for example a beacon on the surface, may include: three orthogonal coils 21A, 21B and 21C which make it possible to receive the magnetic signal emitted by inductive coupling; in a preferred variant the three coils 21A, 21B and 21C are interleaved; for these coils the considerations made for the coils 11A, 11B and 11C still remain valid; three capacitors 22A, 22B and 22C for forming with the coils 21A, 21B and 21C a parallel LC circuit; three low noise amplifiers (LNAs) 23A, 23B and 23C, one per coil; three demodulation circuits 25A, 25B and 25C, one per coil, for example rectifiers, in particular by lock-in detection; band-pass filters (24A, 24B, 24C) and low-pass filters (26A, 26B, 26C), these in particular to suppress the harmonics of the electrical and rail networks which, after demodulation, become 25 Hz, 35 Hz and 81 / 3 Hz; three analog-to-digital converters 27A, 27B and 27C, one per coil; a microcontroller having sufficient computing power for signal analysis (Digital Signal Processing) 28; a frequency reference 40 which is preferably a quartz oscillator; a power source 42, for example a Pb battery or Liions; a radio frequency transmission 29 for communicating with the computing unit 30; a switch not shown for startup.

In a variant, either the surface beacon or the mobile beacon contains only one coil. The positioning system, as illustrated in FIG. 1, will then include several beacons on the surface to increase the quality of the measurement, which in the case of a single coil per beacon is lower compared to the case of two or three coils.

The demodulation frequency is the same as that of the emission. It is generated from the frequency reference 40.

Correlations between the received signals and the ideal signals make it possible to synchronize the mobile beacon with those on the surface, and thus to measure the amplitude of the voltages of these signals for the successive ones according to X, Y and Z. These correlations are carried out preferably after demodulation (for example by synchronous detection or by using a PLL - Phase Locked Loop).

As discussed, the amplitudes of the voltages induced after demodulation are filtered with the filters 26A, 26B and 26C to suppress the harmonics of the 50 Hz and 60 Hz electrical networks and the 50 Hz, 60 Hz and 162/3 Hz electrical networks. digital filtering can be used, for example a moving average or a more elaborate FIR or IIR filter. The period of a moving average or a FIR or IIR filter is preferably: a multiple of 120 ms (for example 360 ms) to suppress the harmonics of 25 Hz and 81/3 Hz; a multiple of 1/35 s to suppress harmonics of 35 Hz.

A sampling frequency of 175 Hz or a multiple of 175 Hz is ideal because it makes it possible to filter both the harmonics of the frequencies of 35 Hz, 25 Hz and 81/3 Hz with a whole number of frequencies. samples. The preferred transmission frequency is still 1225 Hz, which is a multiple of the sampling frequency of 175 Hz.

The data obtained by the surface beacons, which are fixed in the direction defined above and which in a preferred variant are receivers, are transmitted to the calculation unit 30 by radio frequency (RF) transmission using fourth signals. radio 300. In a preferred embodiment, a reception beacon detecting a magnetic signal received by the transmitting beacon sends this information by RF to the computing unit 30, which then requests all the reception beacons to transmit to it the collected data, typically during the last 2 seconds. A signal is also regularly transmitted to the reception beacons to synchronize them.

If the transmitting beacon can be connected to receiving beacons for communicating information through a third bidirectional radio link 101, synchronization signals, such as in particular the modulation / demodulation signal, are transmitted using this link. radio. The radio connection 101 is particularly easy to implement in the case of a location of people in avalanches, because the snow is permeable to waves up to high frequencies such as 433 MHz or 868 MHz. In another variant, this connection can be made by wires or optical fibers.

In order to improve the measurement accuracy, an effective technique consists in rotating a beacon, for example a beacon on the surface, of a known angle, in particular 180 ° or 90 °, in order to combine the measurement before and after rotation. In the case of a 180 ° rotation in the horizontal plane, in order to measure with great precision it suffices to subtract the two measurements obtained by dividing them by two. This is particularly useful for searching the vertical of an underground point. With this technique, most measurement errors are removed once the surface beacon is positioned vertically to the desired point. This position is found by iteration, making measurements each time determining a more precise point.

This change of orientation is either manual, for example based on a protractor disposed on the plane where the rotation takes place, or possibly automated. In order to guarantee the horizontality of this plane of rotation, angular sensors may be installed in the surface beacons, in particular two orthogonal spirit levels. Preferably, the mobile beacon must rotate at the same angle, in order to obtain the maximum of symmetry during the measurement.

The surface beacons can be combined with a GPS or differential GPS receiver, which will transmit the position of these beacons to the computing unit 30. It is thus possible to locate the reception beacons before the measurement and also to move during the measurement without having to redo their positioning.

A reception beacon, for example a beacon on the surface, can be combined with: an inclination sensor, for example an accelerometer; an electronic compass, for example fluxgate sensors or Hall effect sensors. These sensors make it possible to automatically compensate the orientation of the receiving beacon.

Often the purpose of the measurement with this positioning system is to find a point on the surface, for example the vertical of the emission beacon. It is therefore necessary to be able to move the receiving beacons according to indications given by the system, in order to approach the point sought. In addition, this position in the vicinity is very advantageous from the point of view of precision, in particular in the case of a ground with a horizontal dip. In this configuration, the effects of eddy current absorption are minimal, even null.

Once the reception beacon is vertical to that of transmission, the depth is calculated by successively using the three transmitting coils 11A, 11B and 11C. So there is redundancy, because we use three pieces of information for one unknown. An indicator of accuracy is generated from these data.

A display can be on a surface beacon; it can indicate: The direction; the rectilinear distance to the moving beacon; the distance in the horizontal plane, that is to say the plane of the ground or the map of the display; the depth, that is, the vertical distance or distance measured from the ground.

In another variant, this display may be on the computing unit 30.

The reception beacons are positioned on the surface using the conventional techniques of a surveyor, such as the theodolite or the compass / clinometer or GPS described above. The orientation of the beacons is more delicate because it consists in measuring the two inclinations and the azimuth of each beacon constituted by the three coils 21A, 21B and 21C.

A preferred variant is to place the mobile beacon at known coordinate points, in order to calculate the orientation of the receiving beacons using the positioning system above; an algorithm executed in the computing unit 30 then gives these three orientation values (for example two slopes and an azimuth) instead of the coordinates. This orientation can also be measured using sensors such as inclinometers or an electronic compass. A rotation matrix can be calculated using the above measurements. It makes it possible to combine the signals received by the three reception coils 21A, 21B and 21C so as to obtain a rotation of the marker.

The positions that could be calculated precisely by multilateration can be used as a reference to calibrate the orientation of the receivers, which will be useful for other points. Indeed, the position obtained by multilateration is independent of the orientation of the receiving beacons, but requires at least three well positioned receivers. Note that using multilateration, it is not necessary to orient surface beacons to measure the position of the mobile beacon.

The distance measurement can be calibrated by calculating the ratio k between the distance indicated by the algorithm at the actual distance between the mobile beacon and a beacon on the surface. The magnetic moment or sensitivity can thus be multiplied by k high cube.

The ferromagnetic structures near the surface and mobile beacons, represented by the reference 3 in FIG. 1, can deviate the magnetic field lines and introduce an error of the position measurement. It is possible to compensate for this error by a calibration. The calibration consists in placing the surface beacons and the mobile beacon at known coordinate points: it is thus possible to compare the measured signals with the theoretical signals, and finally to calculate a compensation matrix.

The surface beacons may be provided with emission coils thus making it possible to use them as transmitting beacons and to measure their position. These transmitting coils may be the same as those of reception. In this case the beacons on the surface can be positioned mutually and automatically.

The automatic pendulum or motor orientation described for the mobile beacon is also valid for surface beacons.

As illustrated in FIG. 3, the computing unit 30 is preferably composed of: a communication module 304, preferably a radio frequency communication; a calculation module 302, for example a computer, a PDA, a mobile phone (smartphone) or an equivalent device with numerical calculation capabilities and with interfaces, for example a display screen, etc.

The computing unit 30 can be connected to the beacons at the surface 20. In this case it can include a touch screen. In another variant it is integrated in one of the tags 20.

For each orthogonal magnetic moment transmitted, the receiving beacons, for example the surface beacons, measure the magnetic induction field vector and calculate three pieces of information per magnetic moment, ie nine pieces of information in total. The calculation of the position and the orientation of the mobile beacon, which includes six degrees of freedom, is then made from these data by an algorithm executed in the calculation unit 30 and which is based on the model of the fields. magnetic data generated by three ideal orthogonal magnetic dipoles. This algorithm gives a solution, that is to say the position, the orientation and the distance between a mobile beacon and a surface beacon, but it also gives a virtual symmetrical solution, as already mentioned previously.

The position data thus collected make it possible to calculate and then display or record on the calculation unit 30: A 3-D representation, for example the projection of Monge. A 3-D representation superimposed with a digital terrain model. A 2-D superimposed representation with "ortho-photos" or cartography, for example 1: 25 000 national maps, cadastral maps, old plans or partially incomplete maps to complete and reference them in the same coordinate system as the surface. In particular, the position measurements obtained with the technique described are superimposed in real time on one of these cards. Photographs, 2D scans, 3D scans or any other measurements that have been georeferenced (position and orientation) by the system. A polar representation, with the radius displayed in a non-linear manner, for example according to a logarithm to graphically display both the position and the distance of near and far beacons in the case of locating people in avalanches. A list of points with compatible coordinates for geographic information systems, mapping software format or GPS format. The list of detected tags.

As discussed above, the algorithm gives as a result a first solution and a second symmetrical solution. In the case of the underground topography, as discussed to eliminate the calculated symmetric solution of the mathematical conditions are used: for example to find the "real" solution it is enough to place the mathematical condition Z <0, that is to say that the mobile beacon is under the surface beacon or under the ground.

In the case of the location of people in avalanches, with the or the receiving beacons that move, just observe if the distance between the beacons found by the algorithm increases or decreases: in the case of the real solution this distance decreases when approaching and increases while moving away. Based on this principle, the computing unit 30 can restore signals to ask the user 8 to move the beacon used for the search (on the surface), for example to advance a certain distance, for example a dozen steps , obtain a second measure and thus remove this ambiguity by taking into account the measurements before and after the displacement. This displacement can also be a rotation of the beacon. For other applications, these displacements can be known or easily measured, as in the case of a vehicle connected to the mobile beacon 10, thanks to accelerometers and measurements on its wheels.

With several receiving beacons whose position is known, the ambiguity on the symmetrical solution can be raised by comparing the positions obtained by the different receiving beacons. Indeed, the real solution will be the same for the different receiving beacons, while the virtual solutions will be different. In the case of localization of persons in avalanches, these positions may be communicated by radio, in particular using an ISM frequency such as 433 MHz or 868 MHz. If the position of the beacons on the surface is not known, emissions from several different positions (of the same or several mobile beacons) make it possible to find the real solutions by comparing the real and virtual positions obtained.

For example, in the case of locating people in avalanches, a surface beacon that is receiving is moved, in particular to find the vertical to the mobile beacon that is transmitting or the nearest point. The system will then have a display indicating: The directions of the transmitting beacons, or more particularly the selected beacon, from the receiving beacon. With current avalanche location systems (ARVA), the direction of the field line is indicated. The straight distances. With the current avalanche location systems (ARVA) that do not use this technology, the measured distance is very approximate because it depends on the orientation of the transmitter. The distance in the horizontal plane or in the plane of the ground. The depth (vertical distance). A 2-D or 3-D representation, preferably oriented so that what the user sees corresponds to what is indicated on the display, in the manner of a GPS equipped with a built-in compass. This representation is preferably polar with logarithmic radius, for the reasons indicated above.

When at least three surface beacons are used, the distances measured from these beacons make it possible to calculate the position of the mobile beacon by multilateration, the distances varying little in the presence of a conducting ground 3. The algorithm executed by the computing unit 30 thus calculates the position of the mobile beacon more precisely than that obtained by the algorithm used in the case of a single beacon at the surface, in particular if there is absorption of the field However, multilateration alone does not make it possible to directly determine the orientation of the mobile beacon. The computing unit 30 which uses multilateration to calculate the position (X, Y and Z), can use the information available to calculate the orientation as well.

In a variant, the algorithm executed in the most suitable calculation unit is chosen automatically according to one of the following parameters: number of tags available as explained above; nature of the terrain: in an urban environment and / or if there are many abundant ferromagnetic elements the algorithm based on multilateration is used, in other cases that which uses the direction of the detected magnetic field. Quality of the signals received by the different tags. The quality of the signals being in particular the range (magnetic noise), the absorption in conducting materials and the deformation by ferromagnetic materials

As discussed, the use of several transmission / demodulation frequencies for the same measurement is extremely interesting to highlight the limits from the field or conductive objects. Indeed, in the absence of eddy current absorption, the coordinates measured at different frequencies will be the same. In the contrary case, it is the proof of an absorption and also a measurement of the properties of the ground (geophysical measurement). A multi-frequency emission makes it possible in particular to extrapolate the measurement of the magnetic fields for a zero frequency, that is to say where there is no absorption. This is particularly interesting in the presence of ferromagnetic parts 3 such as building structures, or metal pipes. This extrapolation can for example be performed on each measurement of induced voltage as a function of frequency. It is also possible to use a trend line (regression) to obtain a retrospective forecast. The correct measure is then the intersection of this prediction with the ordinate of this curve, equivalent to a zero frequency.

Based on measurements on several known points, a mathematical transformation makes it possible to deform the space of the results, so that the coordinates of the measured points become the real coordinates. This transformation is preferably optimal from the point of view of least squares. This transformation can also be obtained with a mathematical model of the field including in particular the conductivity of the different materials. This model can for example be simulated by the finite element method or ideally by a correction according to a simplified model with a limited number of parameters.

In the case where several transmitters are used simultaneously, for example several minors or several people buried in an avalanche, a suitable device will allow the user to select a transmitting beacon. In a preferred embodiment the different tags are selected successively according to their distance to the receiver. This selection is preferably made through a touch screen or buttons. This makes it possible, for example, to optimize the routes for searching for victims buried under an avalanche.

As already mentioned, a surface beacon and the calculation unit 30 may form a single device, without the need for radio frequency transmission with fourth radio signals 300. The surface beacon then contains a processing unit allowing the calculation of the position with six degrees of freedom. Useful information is displayed on the beacon through a screen. An alternative is to transmit this data to a PDA or a mobile phone, for example using RF communication.

[0130] A surface beacon, a mobile beacon and the computing unit 30 may form a single device. This is particularly the case of the location of people in avalanches, because it allows the emission (transmitting beacon) and the search (receiver beacon and calculation unit).

As discussed, in a variant the receiving and transmitting beacons are permuted: the receiving beacons become the transmitters and the beacon transmitting the receiver, the same algorithm can be used for the calculation of the position. In particular, there is less magnetic noise underground, the parasites being absorbed by the eddy currents.

The variant described above, with several transmitting beacons at fixed locations and a mobile and underground receiving beacon, for example contained in a bag-to-back of a minor 8, can be advantageously exploited for carry out a navigation system in mines 1.

The algorithm that calculates the position is an iterative algorithm that solves a system of nonlinear equations based on the equation of an ideal dipole.

The system of FIG. 1 also allows to calculate indicators of quality or measurement accuracy based on: -The residue (error) after the convergence of the iterative algorithm executed in the calculation unit 30. The redundant data from the reception coils 21A, 21B and 21C, for example by comparing the measured magnetic signals with the theoretical signals. -Magnetic noise, preferably measured outside beacon emission periods or during emissions by measuring the variance with repeated transmissions. The measurement of the phase shift, caused by the eddy currents, between the signals received or preferably with the reference oscillator 40 of a receiving beacon, for example the beacon at the surface. This is, for example, the phase obtained by a lock-in amplifier having as input the reference oscillator 40 and the induced voltages of the reception coils 21A, 21B and 21C. The measurement of the position at different transmission frequencies, for example 1 kHz and 3 kHz, followed by the comparison of the signals obtained. -The position difference calculated by each of the different receivers.

Based on the above indicators, it is possible to obtain information on the measurement site, for example the presence of conductive materials 3 such as clay layers generating eddy currents, or magnetic field emitters. like electric cables. By positioning the surface beacons in known points and by orienting them, the nine received information can be used to make, for example, a geophysical measurement of the conductivity and / or permeability and / or permittivity of the terrain. With a matrix of beacons on the surface, it is possible to obtain the cartography of the electromagnetic properties of a terrain, which is particularly interesting if it is carried out at different frequencies.

It is therefore possible to establish from several measurements a geological model of the terrain to detect the presence of ferromagnetic and / or conductive structures. This model is used either as a measurement result or to correct / compensate positioning measurement errors in the same region.

The measurements made may be compared with simulations on a simplified terrain model, for example a horizontally dipping terrain consisting of a low-conducting layer (limestone) on a highly conductive layer (clay). This makes it possible, for example, to calculate the thickness of the insulating layer by modifying this parameter so that the measurements correspond best to the model.

According to these quality indicators, the emission is modified, for example by changing: The duration of remission or measurement to decrease the magnetic noise and increase the range of the system. The intensity of the magnetic moment to decrease the magnetic noise and increase the range of the system. The emission frequency to decrease the eddy current absorption.

In a variant, the computing unit 30 is provided with an audible or visual alarm. This alarm makes it possible to indicate in particular that: The distance between the mobile beacon and a surface beacon is too high and the surface beacon must be moved. The distance between the mobile beacon and the one on the surface is too small. The mobile beacon has reached or is too close to a prohibited point or a user-defined prohibited zone. The mobile beacon is vertical to the surface beacon or is on the axis perpendicular to its interface. This is particularly interesting for locating people in avalanches, as it is simply the place where you usually have to dig to find the victim (s). The transmitting beacon, for example the mobile beacon, has sent a particular signal, for example triggered by pressing a button, for example the same button used to trigger the measurements, but pressing for a long time. Inadequate measurement quality

The alarm can also be on a mobile beacon or on the surface. In this case, the information is either transmitted from the computing unit 30, magnetically or by radio, or thanks to a measurement made by the mobile beacon itself.

A beacon, either mobile or surface, consists of a housing with dimensions of approximately 25 cm x 45 cm in diameter and weighing 5 to 10 kg. The mobile beacon can be carried by a user 8 in a backpack. The typical distance between two surface beacons 20 is greater than 25 m. In a preferred embodiment, this distance is greater than 50 m.

[0142] Reference numbers used in the figures <Tb> 1 <September> Cavity <tb> 3 <sep> Ferromagnetic Materials <Tb> 8 <September> User <tb> 10 <sep> Mobile tag <tb> 20 <sep> Beacon on the surface <tb> 30 <sep> Calculation Unit <tb> 100 <sep> Second radio signal <tb> 200 <sep> First radio signal <tb> 300 <sep> Fourth radio signal <tb> 101 <sep> Third bidirectional radio link <tb> 11A <sep> First transmitting coil <tb> 11B <sep> Second transmitting coil <tb> 11C <sep> Third reel <Tb> 12A <September> Capacity <Tb> 12B <September> Capacity <Tb> 12C <September> Capacity <tb> 13A <sep> Power Amplifier <tb> 13B <sep> Power amplifier <tb> 13C <sep> Power amplifier <Tb> 14 <September> Processor <Tb> 15 <September> Microcontroller <Tb> 16 <September> Button <tb> 17 <sep> Frequency reference <Tb> 18 <September> Food <tb> 21A <sep> First receiving reel <tb> 21B <sep> Second receiving coil <tb> 21C <sep> Third Receiving Reel <Tb> 22A <September> Capacity <Tb> 22B <September> Capacity <Tb> 22C <September> Capacity <tb> 23A <sep> LNA Amplifier <tb> 23B <sep> LNA Amplifier <tb> 23C <sep> LNA Amplifier <tb> 24A <sep> Band Pass Filter <tb> 24B <sep> Band Pass Filter <tb> 24C <sep> Band Pass Filter <Tb> 25A <September> Rectifier <Tb> 25B <September> Rectifier <Tb> 25C <September> Rectifier <tb> 26A <sep> Low-pass filter <tb> 26B <sep> Low-pass filter <tb> 26C <sep> Low-pass filter <Tb> 27A <September> ADC <Tb> 27B <September> ADC <Tb> 27C <September> ADC <tb> 28 <sep> Microcontroller + DSP <tb> 29 <sep> RF Module <tb> 40 <sep> Frequency reference <tb> 302 <sep> Calculation module <tb> 304 <sep> RF Module

Claims (23)

An underground beacon positioning method (10) comprising the steps of: - installation on the surface of several tags (20); Exchanging first radio signals (200) between said beacons (20) in order to transmit data; Moving a mobile beacon (10) into an underground cavity (1); Sending second radio signals (100) between said mobile beacon (10) and said surface beacons (20) through the ground, At least one said beacon (10; 20) comprising three non-coplanar coils (11A, 11B, 11C, 21A, 21B, 21C) for transmitting and / or receiving said second radio signal (100); Determining the position of said mobile beacon (10) by means of said second radio signals (100). 2. The underground beacon positioning method according to claim 1, wherein said three non-coplanar coils (11A, 11B, 11C, 21A, 21B, 21C) are orthogonal. 3. The method of positioning an underground beacon according to one of claims 1 or 2, comprising the transmission of said second radio signals (100) by said surface beacons (20) and the reception of said second radio signals (100) by said mobile beacon (10) under the ground. 4. The underground beacon positioning method according to one of claims 1 or 2, comprising the transmission of said second radio signals (100) by said mobile beacon (10) under the ground and the reception of said second radio signals (100). by said surface beacons (20). 5. The underground beacon positioning method according to one of claims 3 to 4, wherein the emission of said second radio signals (100) is performed in turn by said non-coplanar coils (11A, 11B, 11C; 21A; , 21B, 21C). The underground beacon positioning method according to one of claims 1 to 5, wherein said determining of the position of said moving beacon (10) comprises determining the direction, distance and orientation of said beacon mobile beacon (10) with respect to one of said surface beacons (20), by means of said second radio signals (100). 7. The underground beacon positioning method according to one of claims 2 to 6, wherein each surface beacon (20) independently calculates the position of said mobile beacon, by means of said second radio signals (100), with one of the following configurations: The mobile beacon (10) comprises two orthogonal coils and the surface beacons (20) three orthogonal coils; The mobile beacon (10) comprises three orthogonal coils and the surface beacons (20) at least two orthogonal coils. 8. The underground beacon positioning method according to one of claims 1 to 7, comprising rotating a known angle of at least one beacon (10; 20) between two cycles of measurements. The method of locating an underground beacon according to claim 7, wherein the number of surface beacons (20) is at least three and comprising: Determining the position of said mobile beacon (10) by multilateration, Calibrating the orientation of said surface beacons (20) on the basis of said determination of the position of said mobile beacon (10) by multilateration. The method of positioning an underground beacon according to one of claims 7 to 9, comprising the automatic choice between the weighted average of the positions of said mobile beacon (10) calculated independently by each surface beacon (20) or said multilateration. according to one of the following parameters: - number of tags (10, 20) available; Relative position of the different beacons (10; 20); - nature of the terrain. The underground beacon positioning method according to one of claims 1 to 10, comprising a third bidirectional radio link (101) between said mobile beacon (10) and said surface beacons (20) for exchanging data or of the voice. The underground beacon positioning method according to claim 11, wherein said third radio link (101) uses the same orthogonal coils (11A, 11B, 11C, 21A, 21B, 21C) as those used for transmitting and / or receiving said second radio signals (100). The underground beacon positioning method according to one of claims 11 to 12, wherein said third radio link (101) uses a modulation of said second radio signals (100). The method of positioning an underground beacon according to one of claims 1 to 13, comprising - the establishment from several measurements of a geological model of the ground; The use of said geological model either as a measurement result or to correct and / or compensate for location measurement errors in the same region. The underground beacon positioning method according to one of claims 1 to 14, comprising displaying by a computing unit (30) measurement quality indicators. 16. The method of locating an underground beacon according to one of claims 1 to 15, comprising locating people under avalanches. 17. The method of locating an underground beacon according to one of claims 1 to 16, comprising moving said mobile beacon (10) in said underground cavity (1) by a walker (8) and / or a vehicle and / or a robot and / or by fluid streams. 18. The method of positioning an underground beacon according to one of claims 1 to 17, comprising the coupling of said mobile beacon (10) to a 2D laser scanner or a 3D laser scanner or a photogrammetric system. 19. The underground beacon positioning method according to one of claims 1 to 18, comprising locating at least several surface beacons (20) by a GPS or an inclinometer or by a compass in said surface beacons ( 20). 20. An underground beacon positioning system (10) comprising A mobile beacon (10); - several surface tags (20); - a computing unit (30); in which Said surface beacons (20) and said mobile beacon (10) are arranged to exchange first radio signals (200) in order to transmit data; Said surface beacons (20) and said mobile beacon (10) are arranged to exchange second radio signals (100) through the ground; At least one of said beacons (10; 20) comprises three non-coplanar coils (11A, 11B, 11C, 21A, 21B, 21C) for transmitting and / or receiving said second radio signals (100); Said computing unit (30) is arranged to determine the position of said mobile beacon (10) by means of said second signals (100). 21. The underground beacon positioning system of claim 20, wherein said three non-coplanar coils (11A, 11B, 11C, 21A, 21B, 21C) are orthogonal. 22. The underground beacon positioning system according to one of claims 20 or 21, wherein said mobile beacon (10) under the ground comprises means (11A, 12A, 13A, 11B, 12B, 13B, 11C, 12C, 13C, 14, 15, 16, 17, 18) for transmitting said second radio signals (100) and said surface beacons (20) comprise means (21A, 22A, 23A, 24A, 25A, 26A, 27A, 21B, 22B, 23B, 24B, 25B, 26B, 27B, 21C, 22C, 23C, 24C, 25C, 26C, 27C, 28, 29, 40, 42) for receiving said second radio signals (100). 23. The underground beacon positioning system according to one of claims 20 or 21, wherein said mobile beacon (10) under the ground comprises means (21A, 22A, 23A, 24A, 25A, 26A, 27A, 21B, 22B, 23B, 24B, 25B, 26B, 27B, 21C, 22C, 23C, 24C, 25C, 26C, 27C, 28, 29, 40, 42) for receiving said second radio signals (100) and said surface beacons (20). ) comprises means (11A, 12A, 13A, 11B, 12B, 13B, 11C, 12C, 13C, 14, 15, 16, 17, 18) for outputting said second radio signals (100).