SE543288C2 - Mining and mineral exploration system and method for performing time-accurate measurements in a mine - Google Patents

Abstract

The present invention relates to a mining and mineral exploration system and method, the system comprisinga local GPS unit (1) disciplined by an ultra- stable clock, configured to generate a simulated GPS signal,a remote unit (2), said remote unit (2) being operatively connected to the local GPS unit (1) for receiving the simulated GPS signal,at least one radiating cable (3) connected to the remote unit (2) and configured to extend from the remote unit (2) in a first direction at the remote site, the radiating cable (3) further being configured to transmit the simulated GPS signal in a vicinity (6) of the radiating cable (3), anda plurality of measuring units (4), each of the measuring units (4) comprising a receiver that is configured to receive the simulated GPS signal when the measuring unit (4) is in the vicinity (6) of the radiating cable (3) for the measuring unit to be able to perform time-accurate measurements based on the simulated GPS signal.

Description

MINING AND MINERAL EXPLORATION SYSTEM AND METHOD FORPERFORMING TIME-ACCURATE MEASUREMENTS IN A MINE TECHNICAL FIELD The present invention relates to a mining and mineral exploration system forperforming a temporary, independent and a distributed time-accuratemeasurements in a mine, the system comprising a plurality of measuringunits configured to receive a simulated GPS signal in order to perform time-synchronized measurements in deep mining and mineral explorationapplications. The invention also relates to a method for performing time-accurate measurements in underground spaces.

BACKGROUND A measuring system generally comprises a plurality of measuring units thatare each capable of performing measurements in a vicinity of the locationWhere they are placed. In order to synchronize measurements and record ineach measuring unit When particular measurements are taken, themeasuring units each comprise a receiver that is able to receive GPS signals.When performing measurements in GPS-denied environments, an outdoorexternal antenna connected to a central GPS unit can be used in order toreceive-or re-transmit the GPS signal to the measuring units by a smallerantenna placed on the central GPS unit inside the actual environment. Thisenables the measuring system to be adapted to the location Wheremeasurements are to be performed although the distance to the actualenvironment Will be the limiting factor. In an outdoor application themeasuring units can act independent of a central GPS unit and eachreceives the GPS signal from satellites: Within the field of mining and mineral exploration, measurements needtoday more and more to be performed in deep underground spaces. One ofthe main aims is to detect and quantify mineral deposit in terms of geometryand location as Well as their quality so that decisions for extending the minein relevant directions can be taken. Measuring units are of course not able todetect GPS signals from satellites When placed underground, but a centralGPS unit can still be used as long as it can be connected to an antenna atthe ground surface level. For deep mining and mineral explorationapplications and When mining infrastructures such as tunnels to be utilized,however due to long distance to surface, modifications to the GPS-timingsystem must be made.

There are some GPS-timing systems that comprise a highly accurate clockand a GPS unit that uses clock signals to generate simulated GPS signalsWithin a closed space. Even though this allows for simulated GPS signals to be created in the underground, environmental factors and the largedistances in the mine still make it difficult to connect to the measuring unitsand to synchronize an array of measuring units distanced from each other inorder to acquire reliable data. Especially Where measuring units need to beplaced in different tunnels or even on different levels or synchronized Withmeasuring units on the surface in order for measurements to cover therelevant area, there are no systems today that are able to provide accuratetime synchronization and thus measurements for these purposes.

There is therefore a need for an improved measuring system that enablesmeasurements in varying locations Within a deep mine in a time-synchronized manner. There is also a need for an easy and efficient Way ofmodifying an existing measuring system to make it suitable for such deepmining applications and at the same time avoiding costly modif1cations toeach commonly available measuring unit.

SUMMARY OF THE INVENTION The object of the present invention is to eliminate or at least to minimize theproblems mentioned above. This is achieved through a mining and mineralexploration system and a mining and mineral exploration method forperforming distributed time-accurate measurements in a mine according tothe appended independent claims.

The system and method according to the present invention allows for time-synchronized measurements being taken in deep mining applications so thata plurality of measuring units suitable for use in applications on groundsurface can also be used in deep mining applications.

Thus, mining and mineral exploration system comprises a local GPS unitconfigured to generate a simulated GPS signal, a remote unit for placing at aremote site, said remote unit being operatively connected to the local GPSunit for receiving the simulated GPS signal, at least one radiating cableconnected to the remote unit and configured to extend from the remote unitin a first direction at the remote site, the radiating cable further beingconfigured to transmit the simulated GPS signal in a vicinity of the radiatingcable for transmitting the simulated GPS signal to a plurality of measuringunits.

The system preferably also comprises a plurality of measuring units forperforming measurements in the mine, each of the measuring unitscomprising a GPS receiver that is configured to receive the simulated GPSsignal When the measuring unit is in the vicinity of the radiating cable forthe measuring unit to be able to perform time-accurate measurements andsynchronization based on the simulated GPS signal. Thereby, a simulated GPS signal can be generated in the mine and be transmitted to each of themeasuring units by the radiating cable. This allows for using existingmeasuring units configured for use on the ground surface withoutmodifications, resulting in an efficient and convenient measuring systemthat can be transported into the mine and be placed where measurementsare to be taken without requiring access or disturbance to local systemsalready in place inside the mine.

According to an aspect of the invention, the system further comprises atleast two radiating cables connected to the remote unit and configured toextend in different directions from the remote unit, and further comprising apower divider (preferably an RF-splitter) arranged to couple the simulatedGPS signal to each of the radiating cables. Thereby, measuring units can beplaced in two different vicinities eXtending from the remote unit, allowing fortime-synchronized measurements in at least two locations simultaneously.

According to another aspect of the invention, the at least one radiating cableis less than 200 m long, preferably less than 100 m long. Thereby, thesimulated GPS signals is amplified within certain limits, preferably also byusing a a line amplifier in the remote unit and transmitted through theradiating cable at a power that enables the measuring units to receive theGPS signals along the entire length of the radiating cable. This eliminatesthe need for line amplifiers along the radiating cable and thereby avoids theproblem of maintaining a sufficient signal to noise ratio despiteamplification. The vicinity is defined as an area surrounding the radiatingcable where the GPS signal is strong enough to be received by the measuringunits, i.e. where the GPS signal is within a dynamic range of an internal GPSreceiver of the measuring units. It is advantageous to have a large vicinity toallow spreading the measuring units over a larger area in order to increasethe quantity as well as quality of measuring data.

According to yet another aspect of the invention, the system comprises atleast one additional remote unit that is operatively connected to the remoteunit or to the local GPS unit, and also comprises at least one additionalradiating cable connected to the additional remote unit and configured toextend from the additional remote unit at the remote site, the additionalradiating cable further being configured to transmit the simulated GPSsignal in a vicinity of the radiating cable, and a plurality of additionalmeasuring units for performing measurements in the mine, each of theadditional measuring units comprising a receiver that is configured toreceive the simulated GPS signal when the additional measuring unit is inthe vicinity of the radiating cable for the additional measuring unit to be ableto perform time-accurate measurements based on the simulated GPS signal.Thereby, the measurements can be performed over a much larger area inside the mine, allowing for measuring units to be placed in different locations butstill operate in a time-synchronized manner.

According to a further aspect of the invention, the remote unit and theadditional remote unit are configured to be placed in different tunnels,preferably on different levels of a mine. Thereby, the area wheremeasurements can be performed is rendered even larger, and it is alsopossible for direct measurements to at the same level of the mine but fromdifferent directions, such as for detecting a presence and extent of amineralization from above the known mineralization as well as from below,or from either sides on the same level. This is advantageous since it providesgreater details and higher quality data for these purposes that are stillreliable. Since only the remote units need to be connected by cable to thelocal GPS unit and/ or to each other, it is also possible to perform costeffective measurements since the amount of cable needed to cover a verylarge area is greatly decreased compared to existing systems.

According to yet another aspect of the invention, the vicinity of the radiatingcable is defined as an area in which a power of a signal emitted from theradiating cable is at least a predetermined minimum signal power. Thepredetermined minimal signal power is preferably at a lower end of adynamic range of the measuring units or slightly above the lower end, toensure that each measuring unit placed anywhere in the vicinity is able toreceive the simulated GPS signals. Thereby, it can be ensured that the entirelength of the radiating cable gives rise to a vicinity along the radiating cableand that good quality measurements can be performed.

According to a further aspect of the invention, each remote unit furthercomprises an amplifier for amplifying the simulated GPS signal inserted intoeach radiating cable. Thereby, the simulated GPS signal can be amplif1ed toa preferred maximum signal power that is preferably selected as an upperend of the dynamic range of the measuring units or slightly below the upperend. This ensures that even measuring units placed directly adjacent to anend of the radiating cable that is connected to the remote unit are able toreceive the simulated GPS signal in the desired way. It is also highlyadvantageous that the amplif1cation is adjustable so that the maximumsignal power can be selected depending on the measuring units that are tobe used with the system. In some embodiments, it would also beadvantageous to set the maximum signal power to a limit above the dynamicrange of the measuring units to allow for the vicinity of the radiating cablewhere the signals can be received to be extended outwards so that themeasuring units can be placed further away, even if this means that an areaimmediately adjacent to the radiating cable near the remote unit will not be included in the vicinity since the signal power in that area Will be too large tobe received by the measuring units.

According to yet another aspect of the invention, the at least one radiatingcable comprises a plurality of radiating segments, said radiating segmentsbeing connected to each other to form the radiating cable, the radiatingsegments preferably being connected by coaxial cables for allowing thesimulated GPS signal to be transmitted along the radiating cable. Therebythe radiating segments can be stored and transported in an easy andconvenient way and be joined together by connectors such as coaxial cablesor other suitable connecting means that are able to transfer the simulatedGPS signal from one radiating segment to another. It also has the advantageof minimizing the risk of damage to the radiating cable when placed insidethe mine, since the connectors can be made more robust and also sincereplacing a damaged radiating segment or connector is far easier and morecost effective than repairing or replacing a radiating cable that does notcomprise segments.

According to the present invention, there is also provided a mining andmineral exploration method for performing distributed time-accuratemeasurements in a mine, the method comprising providing a simulated GPSsignal in a local GPS unit, a remote unit operationally connected to the localGPS unit, and a plurality of measuring units, transmitting the simulatedGPS signal from the local GPS unit to the remote unit; transmitting thesimulated GPS signal from the remote unit in at least one radiating cable,wherein the radiating cable is configured to transmit the simulated GPSsignal in a vicinity of the radiating cable, and receiving the simulated GPSsignal in each of the measuring units for performing time-accuratemeasurements, wherein the measuring units are each placed in the vicinityof the at least one radiating cable.

According to an aspect of the invention, the method further comprisestransmitting the simulated GPS signal from the remote unit in at least tworadiating cables, wherein the radiating cables extend in different directionsfrom the remote unit.

Preferably, the method also comprises transmitting the simulated GPS signalfrom the local GPS unit or from the remote unit to an additional remote unitthrough an optical fiber; transmitting the simulated GPS signal from theadditional remote unit in at least one additional radiating cable, wherein theadditional radiating cable is configured to transmit the simulated GPS signalin a vicinity of the additional radiating cable, receiving the simulated GPSsignal in each of a plurality of additional measuring units for performing time-accurate measurements, wherein the additional measuring units areeach placed in the vicinity of the at least one additional radiating cable.

Preferably, the method further comprises placing the remote unit and theadditional remote unit on different levels of a mine.

The present invention also provides a method for adapting a measuringsystem to enable distributed time-accurate measurements in a mine, themethod comprising providing a plurality of measuring units, wherein each ofthe measuring units comprises a receiver that is configured to receive a GPSsignal, providing a remote unit that is operatively connected to a local GPSunit for receiving a simulated GPS signal that is generated by the local GPSunit, providing a radiating cable that is operatively connected to the remoteunit and configured to transmit the simulated GPS signal in a vicinity of theradiating cable, and placing each of the measuring units in the vicinity of theradiating cable for receiving the simulated GPS signal. Thereby, a plurality ofmeasuring units configured for use above ground can be transported intothe mine and placed in the vicinity of a radiating cable that is able totransmit simulated GPS signals. This gives the significant advantage thatmeasuring units need no modif1cation to be able to be used with themeasuring system in the mine, resulting in time and cost savings while alsoproviding the time-synchronized measurements that are needed for themining and exploration applications.

Many additional benefits and advantages of the invention will become readilyapparent to the person skilled in the art in view of the detailed descriptionbelow.

DRAWINGS The invention will now be described in more detail with reference to the appended drawings, whereinFig. 1 discloses a schematic view of a mine; Fig. 2 discloses a schematic view of a system according to a preferredembodiment of the present invention; Fig. 3 discloses a schematic view of a system according to a secondembodiment of the present invention; Fig. 4 discloses a schematic view in more detail of the system accordingto the second embodiment; Fig. 5a discloses a schematic view of a vicinity of a radiating cableaccording to the preferred embodiment or the second embodiment; and Fig. 5b discloses a schematic view of another vicinity of a radiating cableaccording to the preferred embodiment or the second embodiment.

DETAILED DESCRIPTION A GPS signal as defined herein is a signal from a global navigation satellitesystem such as the Global Positioning System (GPS), the GLONASS or asimilar system in which signals are transmitted from a satellite andreceivable in a unit having a suitable receiver. When simulated GPS signalsare described in the following, these are to be understood as signals that aresimilar to those signals that are transmitted from any of the satellites thatform part of a global navigation satellite system.

For the present invention, the GPS signal or simulated GPS signal is usedmainly for ensuring time accuracy and synchronization of a plurality orarray of measuring units. There is also the possibility of using the GPSsignal for positioning and this may be contemplated in some embodimentswhere it is deemed suitable. However, in most embodiments the GPS signalwould be used only for timing and synchronization.

Fig. 1 discloses a schematic view of a mine 100 for exploiting amineralization 130 that extends below a ground level 140. A mineshaft 110extends essentially vertically into the subsurface and a plurality of tunnels150 are connected to the mineshaft 110 for exploration and mining and forextracting material removed from the mine 100. In some cases, access to themining tunnels can also be possible via spiral-shaped tunnel ramps.

Some of the tunnels 124, 125, 123, 122, 121, 129 extend in a generallyhorizontal direction while other tunnels 126, 120, 127, 128 extend toconnect the generally horizontal tunnels or to connect tunnels to themineshaft 110. The mineralization 130 has an extension that is only partlycovered by the tunnels for mining or exploration purposes and in order todetermine the quality and extension of the mineralization 130 measurementsneed to be performed. Generally, measuring units act by emitting forexample seismic signals that are transmitted through and/ or reflected fromthe mineralization and depending on the reflection traveltime and propertiesof the reflected signals (amplitude) conclusions can be drawn regardingcomposition, shape and location of the mineralization. This is well knownwithin the art and will not be described in detail herein, and it is also to benoted that what is said above regarding the mine is also general informationthat is aimed at an improved understanding of the present invention.

In order to perform the desired measurements, some measuring systemsexist that rely in most cases on a GPS antenna at ground level for receivingGPS signals from satellites and transferring the received GPS signals through cable to a desired location within the mine bearing in mind only alimited cabling can be done in this case. In other systems, relative timingcan be obtained using an accurate clock in deep mines and the measuringunits are modified to be able to obtain time information and synchronizationfrom this clock. This results in the need both to adapt the existingmeasuring units and to apply a large quantity of cables to provide the GPSsignal to each measuring unit.

However, mines are generally very large and complex in terms of shape andstructures and in order to accurately detect the presence and extension of amineralized body, measurements over a large area are needed, preferablyalso on separate levels of the mine or at least in different tunnels on thesame levels. Using a modified measuring system as outlined above isexpensive and cumbersome and can result in a low accuracy ofmeasurements. At the same time, building custom made measuring units formining applications is very expensive and time consuming sincemodif1cations depending on the precise circumstances of the location wherethe measuring units are to be placed are necessary.

Fig. 2 discloses a preferred embodiment of the present invention, having alocal GPS unit 1 that generates a simulated GPS signal for use with aplurality of measuring units 4. The local GPS unit 1 is operatively connectedto a remote unit 2, preferably through a fiber optic cable 5 but alternativelythrough a coaxial cable or by a transmitter at the local GPS unit 1,preferably an antenna, and a receiver at the remote unit 2 if they are closeenough that the simulated GPS signals can be received with a suff1cientquality by the remote unit 2. In the preferred embodiment, at least oneradiating cable 3 is operatively connected to the remote unit 2 fortransmitting the simulated GPS signal in a vicinity 6 of the radiating cable 3.Preferably, the radiating cable 3 is connected directly to an output of theremote unit 2 but there may also be intermediate components that transmitthe simulated GPS signal from the remote unit 2 to an input end of theradiating cable 3. The measuring units 4 each comprise an internal GPSreceiver for receiving the simulated GPS signal. Also, the measuring units 4are placed in the vicinity of the radiating cable 3 and therefore able to receivethe simulated GPS signal and to perform time-accurate and synchronizedmeasurements because each measuring unit 4 receives the same simulatedGPS signal at the same time.

The radiating cable 3 is also known as a leaky cable or leaky feeder andessentially comprises a coaxial cable that has gaps or slots in its outerconductor to allow a signal to leak out of the cable along its length. Thus,the radiating cable is essentially an extended antenna that is easy and convenient to handle and that is very suitable for the present application intransmitting a simulated GPS signal to a plurality of measuring units 4.

In the preferred embodiment disclosed in Fig. 2, two radiating cables 3 areconnected to the remote unit 2 and provide two different vicinities in whichmeasuring units 4 can be placed. There may be an overlap between thesetwo vicinities but it is advantageous to keep them separated in order to coveras large area as possible. The vicinity 6 is discussed in detail below withreference to Fig. 5a-5b.

Fig. 3 discloses a second embodiment of the invention that differs from thepreferred embodiment in that an additional remote unit 2' is connected tothe remote unit 2 and has at least one but preferably at least two additionalradiating cables 3' that each transmits the simulated GPS signal to aplurality of measuring units 4'. The additional remote unit 2' is in thissecond embodiment connected to the remote unit 2 by a fiber optic cable 5but here also a connection through an antenna and receiver is possible asdescribed above with reference to Fig. 2. Alternatively, the additional remoteunit 2' can be connected to the local GPS unit 1, and this is especiallyadvantageous when measurements are to be performed in a large area sincethe local GPS unit 1 can be placed in the middle and remote units 2, 2' canbe placed on either side of the local GPS unit 1. Of course, further remoteunits can also be connected in the same manner as the remote unit 2 andthe additional remote unit 2' so that the measuring system comprises anysuitable number of units that each comprises a remote unit 2, at least oneradiating cable 3 and a plurality of measuring units 4.

Due to the modular nature of the present invention, the local GPS unit 1 canbe placed at a central location such as the tunnel 121 shown in Fig. 1. Theremote unit 2 can be placed further along the same tunnel 121, whereas theadditional remote unit 2' can be placed in another part of that tunnel 121 orat a tunnel on a different level, such as tunnels 122 or 129. With a very largemeasuring system, remote units can be placed in any number of tunnels ortunnel portions on a plurality of levels and thereby enable time-accuratemeasurements over a very large area on multiple levels of the mine. Thisgives the opportunity for measurements of a much higher accuracy and dataquality than previously possible with very low cost of modifying existingmeasuring systems.

Fig. 4 discloses the mining and mineral exploration system in more detail,and although the second embodiment is shown in this Figure, it is to benoted that what is said of each component also applies to the preferredembodiment and to other embodiments of the present invention.

Thus, the local GPS unit 1 comprises a highly accurate clock 11 thatprovides clock signals to a GPS simulator 12 Where the simulated GPS signalis created as is Well known Within the art. The simulated GPS signal may betransmitted to a GPS master unit 13 before being transformed into anoptical signal by a converter 14. The GPS master unit 13 may be connectedto an antenna 15 that can be used Where a remote unit 2 is placed closeenough to receive the simulated GPS signal in this Way. In someembodiments, the GPS master unit 13 can be left out so that the GPSsimulator 12 is connected directly to the converter 14 and/ or the antenna 1 5.

A fiber optic cable 5 is connected to the converter 14 and transmits thesimulated GPS signals to the remote unit 2 Where they are received in anoptical splitter 21 that splits the signals so that they can also be transmittedto at least one additional remote unit 2'. Alternatively, the optical splitter 21can be left out if only one remote unit 2 is to be used in the system or if eachremote unit 2, 2' is to be connected directly to the local GPS unit, as hasbeen described briefly above.

A second converter 22 receives the simulated GPS signals from the opticalsplitter 21 or from the fiber optic cable 5 directly. In the second converter,the optical signals are converted into radio signals that are transmitted to aremote control unit 23 that controls operation of the remote unit 2. Anamplifier 24 is preferably connected to the remote control unit 23 foramplifying the simulated GPS signals before they are given as input to theradiating cable 3. If more than one radiating cable 3 is used, an RF splitter25 is provided for receiving the amplified simulated GPS signal and splittingit to provide input for the two radiating cables 3 as disclosed in Fig. 4. Thesimulated GPS signal is then transmitted in the radiating cable 3, and due tothe gaps or openings in the cover of the radiating cable 3 the radiating cable3 is able to act as an antenna and transmit the simulated GPS signal in thevicinity along its entire length.

The control unit 23 may be operated by manually controlling its operationbut may preferably be operated remotely, such as by including a mastercontrol unit (not shown) in the local GPS unit 1 that is configured to controloperation of each remote unit 2, 2' and that communicates With controlunits 23 of each remote unit 2, 2' through the same fiber optic cable 5 orWireless connection through an antenna and receiver as the simulated GPSsignals are transmitted. In some embodiments, the control units 23 mayfollow a predetermined mode of operation but in other embodiments theoperation of the control units 23 may instead be dynamically adjusted by aperson or by the master control unit. For example, the amplification of thesimulated GPS signal before input into each radiating cable 3 may be adjusted depending on the dynamic range of the measuring units 4 ordepending on a distance from the radiating cable 3 where it is desirable toplace the measuring units 4, so that the size and shape of the vicinity 6 areadjusted. There may also be a feedback function so that an informationregarding signal power or reception of the simulated GPS signal in themeasuring units 4 is transmitted back to the remote unit 2, 2' to allow forthe amplification being set depending on such information.

The control unit 23 may also be a distributed control unit whose functionsare distributed throughout the system.

The vicinity is defined as an area surrounding the radiating cable 3 wherethe simulated GPS signal is within a dynamic range of the measuring units4, i.e. where the measuring units 4 are able to receive the simulated GPSsignal. If the simulated GPS signal has a power that is above a maximum orbelow a minimum of the dynamic range of the measuring units 4, thesimulated GPS signal cannot be received and used by the measuring units 4which prevent them from performing the desired time-accuratemeasurements. It is therefore highly advantageous to be able to detect thepower of the simulated GPS signal at various distances from the radiatingcable and also to be able to select the amplif1cation of the simulated GPSsignal used as input to the radiating cables 3. It is therefore in someapplications highly advantageous to select the input power of the simulatedGPS signal to the maximum of the dynamic range of the measuring units 4,and in some applications advantageous instead to select the input power sothat the signal power at a far end of the radiating cable 3 is above theminimum of the dynamic range of the measuring units 4 since this allowsthe vicinity to be extended along to the end of the radiating cable. In someembodiments, a signal-to-noise ratio or power of the GPS signal can beperformed to determine if the GPS signal should be amplif1ed or otherwiseadjusted to be able to achieve a desired result of being received by themeasuring units 4.

It is advantageous therefore to limit a length of the radiating cable 3,preferably to a maximum of 200 m or less and more preferably to amaximum of 100 or less. Thereby, the vicinity of the radiating cable 3 can bemade to extend along the entire length of the radiating cable 3. It isadvantageous to avoid line amplifiers along the length of the radiating cable3, since the signal to noise ratio is signif1cantly decreased by amplif1cation sothat the signal quality is rendered too poor to be able to be received by themeasuring units 4.

In some parts of a mine 100, there may be radiating cables already in placefor use in communications systems. These radiating cables are highly 11 unsuitable for use as antennas in measuring systems such as that disclosedby the present invention, since the amplif1cations needed at intervals of 300-500 m render a simulated GPS signal useless for the measuring units 4. Ifonly a shorter length of such a radiating cable were to be used fortransmitting simulated GPS signals, this would also prevent the use of thecommunications system while measurements are being performed in orderto achieve suff1cient signal quality to reach at least some of the measuringunits 4. For security reasons and for reasons of practicality it is notpermitted to make such interruptions of the communications system and thepresence of other signals transmitted at the same time would interfere withthe operation of the measuring units. It would also be a problem to rely onradiating cables that form part of existing communications system in themine since exploration and assessment of mineralization quality is generallyperformed in parts of the mine and within a short period of time wheremining does not yet take place and where communications system aretherefore not necessarily available.

However, the present invention as set out herein provides a highlyadvantageous and suitable measurement system that overcomes all thesedrawbacks and challenges, and that provides time-accurate measurementsof high quality as outlined above.

Fig. 5a discloses the vicinity 6 of a radiating cable 3 that has simulated GPSsignal given as input from the remote unit 2. As shown in the Figure, thevicinity 6 has a shape that is wider at an input end where the signal isstronger and narrower at an output end where some of the power has beenlost along the length of the radiating cable 3. In most applications, it isadvantageous to provide a signal power at the output end that is at least atthe minimum of the dynamic range of the measuring units 4, preferablyabove the minimum so that measuring units 4 can be placed at a distancefrom the radiating cable 3 and still receive the simulated GPS signal.

Fig. 5b discloses the vicinity 6 of the radiating cable where the input powerof the simulated GPS signal is above the maximum of the dynamic range ofthe measuring units 4, so that the measuring units 4 have to be placed at adistance from the radiating cable 3. In this Figure, the vicinity 6 is wider atthe output end since the signal power at this end is larger than in Fig. 5a. Asis readily understood by the skilled person, it may be advantageous indifferent embodiments depending on the desired placement of the measuringunits 4 to select the input power to adapt the width and extension of thevicinity to what is suitable at a particular time.

In one embodiment, the local GPS unit 1 may also comprise at least oneradiating cable 3 and be configured to transmit the simulated GPS signal in 12 the radiating cable 3. A plurality of measuring units 4 may in thatembodiment be placed in the vicinity of the radiating cable 3 and thusreceive the simulated GPS signal in a similar manner as has already beendescribed With reference to other embodiments. This has the benefit ofcreating a vicinity of the local GPS unit 1 Where measuring units 4 can beplaced in order to perform measurements Without providing a remote unit 2adjacent to the local GPS unit 1.

The measuring units 4 preferably comprise seismic receivers along With dataacquisition systems, especially preferably in the form of Geophones (Velocity-meter) or accelerometers. These geophysical receivers detect very smallmotions in the ground from active-seismic sources (controlled) and passive-seismic sources, including direct, refracted, reflected, diffracted and RayleighWaves. A recording signal for a measuring unit for use With the presentinvention is a strength of vibration/motion, a so-called seismic amplitude, asa function of time (called a time-series signal). A time signal sampling isrecorded in various ranges but can be as small as O.25-2ms depending onthe application. The system according to the present invention is preferablyused to GPS time stamp a recorded signal With very high accuracy to be ableto synchronize an array of measuring units, i.e. the plurality of measuringunits 4 in a deep mine.

In some embodiments of the present invention, other types of measuringunits can alternatively be used such as those used for electromagneticsurveys. In such embodiments the measuring units can measure electricand magnetic fields as a function of time. When time-synchronizedmeasuring units are used according to the present invention, models ofresistivity or conductivity of subsurface materials can be provided.

In one embodiment, the radiating cable 3 comprises a plurality of radiatingsegments that are connected to each other by a plurality of connectors toform the radiating cable 3. Each radiating segment is then connected to asubsequent radiating segment by a connector that connects one end of afirst radiating segment to one end of a subsequent radiating segment so thatthe radiating segments are connected one after the other in an elongatedcable that forms the radiating cable 3. The radiating segments are shortersegments of radiating cable and the connectors are preferably coaxial cablesbut alternatively other connectors or connecting means that are able totransmit the simulated GPS signal from one radiating segment to the neXt.This is advantageous since the storage, transport and arrangement of theradiating cable 3 in the mine is significantly facilitated by avoiding very longradiating cables 3 that need to be stored and transported in a rolled-up formand that are very sensitive to damages, especially during arranging ormounting the radiating cable 3 in the inventive system before measurements 13 are to take place. During use, the risk of damages to the radiating cable 3 isalso signif1cantly lower than for other embodiments, since the radiatingsegments can more easily be protected by placing them where they are notsubjected to mechanical forces by persons, objects or vehicles in the mine.Also, if a radiating segment is damaged it can easily be replaced and a newradiating segment connected in its place, whereas a radiating cable that doesnot comprise segments would need to be replaced in its entirety or beremoved for repair. Using radiating segments is therefore especially robust,cost effective and reliable and also lowers the risk of measurements beinginterrupted or postponed. The same is of course true for the connectors thatcan also be individually replaced in an easy and cost effective way if theyshould be damaged or otherwise malfunction. The mining and mineralexploration method for performing distributed time-accurate measurementsin a mine according to the present invention will now be described in moredetail.

In order to transmit simulated GPS signals in a synchronized manner to themeasurement units 4, a simulated GPS signals is provided in a local GPSunit 1 and transmitted to the remote unit 2, preferably through an opticalfiber but alternatively by an antenna and receiver as described briefly above.From the remote unit 2, the simulated GPS signal is transmitted in at leastone radiating cable 3 so that a vicinity 6 of the radiating cable 3 is formed inwhich the simulated GPS signal is within a dynamic range of at least some ofthe plurality of measuring units 4. The dynamic range is defined herein as arange in which the simulated GPS signal is strong enough to be received bya measuring unit 4. If the signal is below the dynamic range, the measuringunit 4 cannot detect it and if the signal is above the dynamic range it canalso not be detected. For one suitable type of measuring units the dynamicrange has a maximum of -5dBm and a minimum of -144dBm.

Since each measuring unit 4 of the plurality of measuring units 4 is able toreceive the same simulated GPS signal at the same time, synchronized andtime-accurate measurements can be performed by the measuring units 4.

In embodiments where there are multiple remote units 2, 2', each remoteunit 2, 2' receives the simulated GPS signal from the local GPS unit 1 asdescribed above, preferably through an optical fiber 5 that is connected toboth the local GPS unit 1 and the remote unit 2, 2' or to the remote unit 2and the additional remote unit 2', but alternatively through transmission bymeans of antenna and receiver or through a combination of these means orthrough any other suitable way for transmitting signals.

When setting up a system for performing time-accurate measurements, theremote units 2, 2' may be placed in different tunnels or even on different 14 levels, and the radiating cables 3 may eXtend in different directions from theremote unit 2, 2' or alternatively may extend in one direction and be placedin parallel or at an angle towards each other. The deciding factor forselecting placement and extension of the remote units 2, 2' and the radiatingcables 3 and measuring units 4 is the requirements of a particularmeasurement or series of measurements that is to be performed. This isreadily understood by the skilled person and Will not be described in moredetail herein.

It is to be noted that features from the various embodiments describedherein may freely be combined, unless it is explicitly stated that such acombination Would be unsuitable.

Claims (14)

1. Mining and mineral exploration system for performing distributedtime-accurate measurements in a mine, the system comprising - a local GPS unit (1) conf1gured to generate a simulated GPS signal, - a remote unit (2) for placing at a remote site, said remote unit (2)being operatively connected to the local GPS unit (1) for receiving thesimulated GPS signal, - at least one radiating cable (3) connected to the remote unit (2) andconfigured to extend from the remote unit (2) in a first direction at theremote site, the radiating cable (3) further being configured to transmitthe simulated GPS signal in a vicinity of the radiating cable (3) fortransmitting the simulated GPS signal to a plurality of measuringunits. .

2. Mining and mineral exploration system according to claim 1, further comprising a plurality of measuring units (4) for performing measurements in themine, each of the measuring units (4) comprising a receiver that isconfigured to receive the simulated GPS signal When the measuringunit (4) is in the vicinity of the radiating cable for the measuring unit(4) to be able to perform time-accurate measurements based on thesimulated GPS signal. .

3. Mining and mineral exploration system according to claim 1 or 2, further comprising at least two radiating cables (3) connected to theremote unit (2) and configured to extend in different directions fromthe remote unit (2), and further comprising a power divider arrangedto couple the simulated GPS signal to each of the radiating cables (3).

4. Mining and mineral exploration system according to any of claims 1-3,Wherein the at least one radiating cable (3) is less than 200 m long,preferably less than 100 m long. .

5. Mining and mineral exploration system according to any of claims 1-4, further comprising at least one additional remote unit (2') that isoperatively connected to the remote unit (2) or to the local GPS unit(1), and also comprising - at least one additional radiating cable (3') connected to the additionalremote unit (2') and configured to extend from the additional remoteunit (2') at the remote site, the additional radiating cable (3') furtherbeing configured to transmit the simulated GPS signal in a vicinity ofthe radiating cable, and - a plurality of additional measuring units (4') for performingmeasurements in the mine, each of the additional measuring units (4')comprising a receiver that is configured to receive the simulated GPSsignal when the additional measuring unit (4') is in the vicinity of theradiating cable (3') for the additional measuring unit (4') to be able toperform time-accurate measurements based on the simulated GPSsignal.

6. Mining and mineral exploration system according to claim 5, wherein the remote unit (2) and the additional remote unit (2') are configured tobe placed in different tunnels, preferably on different levels of a mine.

7. Mining and mineral exploration system according to any previous claim, wherein the vicinity of the radiating cable (3, 3') is defined as anarea in which a power of a signal emitted from the radiating cable (3,3') is at least a predetermined minimum signal power.

8. Mining and mineral exploration system according to any previous claim, wherein each remote unit (2, 2') further comprises a lineamplifier (24) for amplifying the simulated GPS signal inserted intoeach radiating cable (3, 3').

9. Mining and mineral exploration system according to any previous claim, wherein the at least one radiating cable (3, 3') comprises aplurality of radiating segments, said radiating segments beingconnected to each other by a plurality of connectors to form theradiating cable (3, 3'), the connectors preferably being coaxial cablesfor allowing the simulated GPS signal to be transmitted along theradiating cable (3, 3').

10. Mining and mineral exploration method for performingdistributed time-accurate measurements in a mine, the methodcomprising- providing a simulated GPS signal in a local GPS unit (1), a remoteunit (2) operationally connected to the local GPS unit (1), and aplurality of measuring units (4) - transmitting the simulated GPS signal from the local GPS unit (1) tothe remote unit (2) ; - transmitting the simulated GPS signal from the remote unit (2) in atleast one radiating cable (3), wherein the radiating cable (3) isconfigured to transmit the simulated GPS signal in a vicinity (6) of theradiating cable (3), - receiving the simulated GPS signal in each of the measuring units (4)for performing time-accurate measurements, Wherein the measuringunits (4) are each placed in the vicinity (6) of the at least one radiatingcable (3).

11. Mining and mineral exploration method according to claim 10,further comprising transmitting the simulated GPS signal from theremote unit (2) in at least two radiating cables (3), Wherein theradiating cables (3) extend in different directions from the remote unit(2).

12. Mining and mineral exploration method according to claim 10 or 1 1, further comprising - transmitting the simulated GPS signal from the local GPS unit (1) orfrom the remote unit (2) to an additional remote unit (2'); - transmitting the simulated GPS signal from the additional remoteunit (2') in at least one additional radiating cable (3'), Wherein theadditional radiating cable (3') is configured to transmit the simulatedGPS signal in a vicinity (6) of the additional radiating cable, - receiving the simulated GPS signal in each of a plurality of additionalmeasuring units (4') for performing time-accurate measurements,Wherein the additional measuring units (4') are each placed in thevicinity (6) of the at least one additional radiating cable (3').

13. Mining and mineral exploration method according to claim 12,further comprising placing the remote unit (2) and the additionalremote unit (2') in different tunnels, preferably on different levels of amine.

14. Method for adapting a measuring system to enable distributedtime-accurate measurements in a mine, the method comprising- providing a plurality of measuring units (4), Wherein each of the measuring units (4) comprises a receiver that is configured toreceive a GPS signal, - providing a remote unit (2) that is operatively connected to a localGPS unit (1) for receiving a simulated GPS signal that is generatedby the local GPS unit (1), - providing a radiating cable (3) that is operatively connected to theremote unit (2) and configured to transmit the simulated GPSsignal in a vicinity (6) of the radiating cable (3), and - placing each of the measuring units (4) in the vicinity (6) of theradiating cable (3) for receiving the simulated GPS signal.