JP2006105907A - Exploration system - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a exploring technique capable of enhancing exploring accuracy. <P>SOLUTION: The present aerial towed object 7 with a receiving sensor receiving the signal including information of exploratory objects is towed by flight vehicles such as a helicopter in air. The aerial towed object 7 is configured with a stilliform main body 71 slenderizing toward opposite direction to the towed direction 200 and a cylindrical stabilizing wing 90 slenderizing toward opposite direction to the towed direction 200, encompassing the tail 71b of main body concerned 71. <P>COPYRIGHT: (C)2006,JPO&NCIPI

Description

  The present invention relates to a search system that acquires information related to a search target based on a received signal received by an air towed towed by a flying object such as a helicopter.

  As methods for exploring underground structures using electromagnetic waves, there are conventionally known a method of installing a transmitter and a receiver on the ground surface and a method of installing a transmitter and a receiver on a flying object.

  The former is a CSAMMT (Control Source Audio Magneto Telluric) method for exploring the crustal structure by receiving and measuring induced electromagnetic waves generated in the crust by electromagnetic waves transmitted from a transmitter installed on the ground surface by a receiver installed on the ground surface. Or TDEM (Time Domain ElectroMagnetic) method.

  The latter is an aerial electromagnetic exploration method in which a transmitter and a receiver are installed on a flying object such as a helicopter, and the induced electromagnetic field generated in the crust by the electromagnetic wave transmitted from the transmitter is received and measured by the receiver to explore the crustal structure. It is a method called.

  In the former method of installing a transmitter and a receiver on the ground surface, when measuring over a wide area, it is necessary to move and install the receiver for each measurement point, which requires enormous effort and time for measurement. .

  In addition, the latter method of installing a transmitter and receiver on a flying object and transmitting and receiving from the air is easy to measure, but the size and weight of a transmitter or receiver that can be mounted on a flying object such as a helicopter. Is limited. Since the distance between the transmitter and the receiver is short, a strong electromagnetic wave cannot be transmitted and the depth of the crust that can be explored is limited.

  Therefore, in order to solve such problems, a method called a ground source type aerial electromagnetic exploration method in which a transmitter is installed on the ground surface and a receiver is mounted on a flying object to explore an underground structure using electromagnetic waves. Has been proposed. This exploration method is disclosed in, for example, Patent Documents 1 and 2 and Non-Patent Document 1.

JP-A-9-304547 International Publication No. 92/19989 Pamphlet R. A. Bosschart et al., “Advances in Deep Penetration Airborne Electromagnetic Methods”, Exploration Geophysics, 24th IGC, section 9, 1972, p37-48

  Now, in the airborne electromagnetic exploration method, a receiving sensor that receives the induced electromagnetic field generated in the crust is mounted in an aerial towed vehicle called “bird” suspended from a flying object, so that the receiving sensor is being towed. It was easy to shake, and it was difficult to obtain sufficient exploration accuracy because of the noise signal generated by the shaking of the receiving sensor.

  Therefore, the present invention has been made in view of the above-described problems, and an object thereof is to provide a search technique capable of improving the search accuracy.

  An exploration system according to claim 1 of the present invention is an exploration system including a receiving sensor that receives a signal including information related to an exploration target, and an aerial towed body that is towed by the flying object in the air, The aerial towed body has a water drop type main body that narrows in a direction opposite to the towing direction, and a cylindrical stabilizing wing that surrounds the tail of the main body and narrows in the direction opposite to the towing direction. Prepare.

  Moreover, the exploration system according to claim 2 of the present invention is the exploration system according to claim 1, wherein the main body portion of the aerial towed body has a spindle-shaped cross section along a direction perpendicular to the towing direction. It is.

  Moreover, the exploration system according to claim 3 of the present invention is the exploration system according to any one of claim 1 and claim 2, wherein the head of the main body portion of the aerial towed body The receiving sensor is mounted, and a sensor base having a gimbal structure for suppressing the shaking is provided.

  The exploration system according to claim 4 of the present invention is the exploration system according to claim 3, wherein an attitude meter for detecting the attitude of the reception sensor is provided in the head, The attitude meter is attached to the upper surface of the gimbal structure, and the reception sensor is attached to the lower surface of the gimbal structure.

  Moreover, the exploration system according to claim 5 of the present invention is the exploration system according to any one of claims 1 to 3, wherein the head of the main body portion of the aerial towed vehicle is An attitude meter that measures the attitude of the reception sensor is provided, and a predicted value of a noise signal included in a reception signal at the reception sensor due to the shaking of the reception sensor is obtained based on a measurement result of the attitude sensor. The apparatus further includes a vibration noise prediction unit and a search information acquisition unit that acquires information on the search target based on a signal obtained by subtracting the prediction value from the reception signal.

  The exploration system according to claim 6 of the present invention is the exploration system according to claim 5, further comprising a frequency characteristic correction unit that corrects the frequency characteristic of the predicted value to the frequency characteristic of the reception sensor. The search information acquisition unit acquires information related to the search target based on a signal obtained by subtracting the predicted value corrected by the frequency characteristic correction unit from the reception signal.

  Further, the exploration system according to claim 7 of the present invention is the exploration system according to claim 6, wherein the frequency characteristic correction unit is configured to calculate the predicted value and the noise signal measured by the reception sensor. Based on the transfer function indicating the relationship, the predicted value is corrected to a frequency characteristic at the receiving sensor.

  An exploration system according to an eighth aspect of the present invention is the exploration system according to the sixth aspect, wherein the frequency characteristic correcting unit uses an adaptive filter to convert the predicted value into a frequency characteristic at the reception sensor. to correct.

  According to the exploration system according to claim 1 of the present invention, the main body portion of the aerial towed body is a water droplet type that becomes narrower in the direction opposite to the towing direction, so that the main body portion is moved when the flying object is moving. Air vortices are less likely to occur behind Therefore, the shake of the air towed body can be suppressed.

  Furthermore, since the cylindrical stabilizer wings narrow in the direction opposite to the towing direction, the wind passing through the cylindrical stabilizer wings collides with the tail and moves backward while the flying object is moving. It becomes easy to flow. Therefore, a force in the direction opposite to the towing direction is likely to be generated at the tail, and the tail is pulled backward. Therefore, the aerial towed body can be easily oriented in the towing direction, and the aerial towed body can be further prevented from shaking. As a result, noise generated in the received signal due to the shaking of the reception sensor can be reliably reduced, high-accuracy search is possible, and the search depth is improved.

  According to the exploration system according to claim 2 of the present invention, the main body of the aerial towed body has a spindle shape in cross section along the direction perpendicular to the towed direction, so that the vibration of the aerial towed body can be further reduced. . As a result, more accurate exploration is possible and the exploration depth is improved.

  In the exploration system according to claim 3 of the present invention, since the gimbal structure is adopted for the sensor base, the shaking of the receiving sensor is further reduced and the exploration accuracy is further improved.

  Further, according to the exploration system according to claim 4 of the present invention, when receiving a weak signal, the receiving sensor is usually heavier than the attitude meter, so that the heavy receiving sensor is provided on the lower surface of the gimbal structure. In addition, unnecessary shaking of the gimbal structure can be reduced, and the exploration accuracy is further improved.

  Further, according to the exploration system according to claim 5 of the present invention, since the predicted value of the noise signal caused by the fluctuation of the receiving sensor is acquired, necessary processing such as measurement noise removal can be executed only on the predicted value. . Therefore, the noise signal included in the received signal can be reliably removed, and the search accuracy is improved.

  In the exploration system according to claims 6 to 8 of the present invention, the frequency characteristic of the predicted value of the noise signal caused by the fluctuation of the reception sensor is corrected to the frequency characteristic of the reception sensor. Therefore, the noise signal included in the received signal can be reliably removed.

<Overall configuration>
FIG. 1 is a diagram showing a configuration of an exploration system according to an embodiment of the present invention. The exploration system according to the present embodiment is an exploration system that performs underground exploration using, for example, a ground source type airborne electromagnetic exploration method. As shown in FIG. 1, two transmission lines are linearly connected to a transmitter 11 installed on the ground surface, and electrodes 8 and 9 are provided at respective ends. A part of the electrodes 8 and 9 is buried in the ground. In the air, the helicopter 1 is flying in a state where an air towed body 7 called “bird” is suspended. Therefore, the air towed body 7 is towed in the air by the helicopter 1. In the present embodiment, a receiving sensor 25 described later is mounted on the air towed body 7, and the receiving sensor 25 receives an induced electromagnetic field generated in the earth's crust by the electromagnetic wave transmitted from the transmitter 11.

  In FIG. 1, coordinate axes X and Y are coordinate axes orthogonal to each other in a plane parallel to the ground surface, and the Z axis indicates a position in a direction perpendicular to the ground surface (that is, a height from the ground surface). Here, the position of the transmitter 11 installed on the ground surface can be measured in advance. On the other hand, since the helicopter 1 towing the air towed vehicle 7 equipped with the receiving sensor 25 moves in the air, it is necessary to always acquire position information. Therefore, the helicopter 1 is equipped with a GPS (Global Positioning System) receiver 21 that can receive information from an artificial satellite and recognize an absolute position in real time. Since the GPS receiver 21 can recognize the planar position (position on the XY plane), information on the height (Z axis) is obtained by the altimeter 22 mounted on the helicopter 1. It is possible. The relative positional relationship between the helicopter 1 and the transmitter 11 is obtained from the position of the helicopter 1 thus obtained and the position of the transmitter 11.

<Aerial towed vehicle structure>
The air towed body 7 according to the present embodiment includes a main body portion 71 and a cylindrical stabilizing wing 90 surrounding the tail portion 71b. 2 is a side view showing the structure of the main body 71 of the aerial towed body 7, and FIG. 3 is a sectional view taken along the line AA in FIG. FIG. 4 is a plan view when the main body 71 of the air towed body 7 is viewed from above. As shown in FIGS. 2 to 4, the shape of the main body 71 according to the present embodiment narrows toward the rear, that is, in the direction opposite to the towing direction (traveling direction) 200 of the air towing body 7. Water drop type. As shown in FIG. 3, in the main body 71, the cross-sectional shape along the vertical direction perpendicular to the towing direction 200 is a spindle shape that is long in the left-right direction. In the present embodiment, the direction obtained by rotating the towing direction 200 by 90 ° clockwise when viewed from above is the right direction, and the direction obtained by rotating 90 ° counterclockwise is the left direction.

  The main body 71 is composed of a head 71a and a tail 71b. The head 71a is composed of a substantially hemispherical portion 71aa that has a spindle-shaped cross section and protrudes forward, and a substantially truncated cone-shaped portion 71ab that has a spindle-shaped cross section and narrows toward the rear. A sensor base 100 on which the receiving sensor 25 and the like are mounted is accommodated. The tail portion 71b has a spindle shape in cross section, and its outer shape is a substantially conical shape that narrows toward the rear.

  At the rear end of the tail 71b, a vertical tail 72 projecting upward, a vertical tail 73 projecting downward, a horizontal tail 74 projecting right, and a horizontal tail 75 projecting left are provided. ing. A vertical wing 76 protruding upward is provided on the upper surface of the tail portion 71b, and a vertical wing 77 protruding downward is provided on the lower surface, and the vertical wings 76 and 77 are arranged side by side in the vertical direction in a side view. Has been. Further, on the lower surface of the tail portion 71b, a mounting portion 83 of a belt-like lifting device 95a used when the air towed body 7 is suspended by the helicopter 1 is provided slightly ahead of the vertical wing 77. In addition, attachment portions 80 and 81 of the suspension 95a are also provided on the right side surface and the left side surface of the tail portion 71b, respectively. The attachment portions 80, 81, 83 are provided with insertion holes 80a, 81a, 83a, respectively, into which the hanger 95a is inserted. As shown in FIG. 4, the insertion holes 80a and 81a are arranged side by side in the left-right direction when viewed from above. In addition, when viewed from the side, the insertion holes 80a and 81a and the insertion hole 83a are arranged side by side in the vertical direction.

  On the upper surface of the head 71a, there is provided a lead hole 84 for drawing out a cable for transmitting the output signal of the reception sensor 25 in the aerial towed body 7 to the equipment in the helicopter 1. Attachment portions 78, 79, 82 of a lifting device 95b different from the suspension device 95a are provided on the right side surface, the left side surface, and the lower surface of the head portion 71a, respectively. Insertion holes 78a, 79a, and 82a for inserting the hanger 95b are provided, respectively. As shown in FIG. 4, when viewed from above, the insertion holes 78a and 79a are arranged on a virtual straight line 300 extending in the left-right direction through the center O of a semicircle formed by the outer shape of the substantially hemispherical portion 71aa. . In addition, when viewed from the side, the insertion holes 78a and 79a and the insertion hole 82a are arranged side by side in the vertical direction.

  The extraction hole 84 is disposed slightly rearward of the insertion holes 78a and 79a in a top view. In the top view, the vertical tail 72, the vertical wing 76, the extraction hole 84, and the center O are linearly arranged along the towing direction 200. Further, in the bottom view, the vertical tail 73, the vertical wing 77, the attachment portions 82 and 83, and the center O are linearly disposed along the towing direction 200.

  FIG. 5 is a perspective view showing the structure of the stabilizer wing 90 of the air towed body 7. As shown in FIG. 5, the stabilizer blade 90 has, for example, a cylindrical shape and narrows toward one end. FIG. 6 is a side view showing the state of the air towed body 7 in the towing state. As shown in FIG. 6, the cylindrical stabilizer wing 90 uses the vertical tails 72, 73, the horizontal tails 74, 75, and the like to surround the tail part 71 b of the main body 71 with wires or the like. And narrows in the direction opposite to the towing direction 200. The GPS antenna 21 a is attached to the rear end of the tail portion 71 b of the main body 71 via an attachment jig 121. The belt-like hanger 95a is attached to the attachment portions 80, 81, 83 so as to surround a part of the tail portion 71b, and the belt-like hanger 95b is similarly attached to the attachment portions 78, 79, 79, so as to surround a part of the head 71a. 82 is attached. A main rope 96 is attached to each of the suspension tools 95 a and 95 b, and the air towed body 7 is suspended from the helicopter 1 by the main rope 96.

<The structure of the sensor base and the structure of the sensor attached to it>
FIG. 7 is a perspective view showing the structure of the sensor base 100 attached to the main body 71, and FIG. 8 is a view showing the configuration of the sensor attached to the sensor base 100. The upper half of the housing forming the head 71a can be removed from the main body 71, and FIG. 7 shows the main body 71 with the housing removed.

  As shown in FIG. 7, the sensor base 100 according to the present embodiment is a sensor base having a gimbal structure, and an attachment frame 101 for attaching the sensor base 100 to the lower half housing forming the head portion 71a. The frame 102 and a mounting plate 103 to which various sensors are attached are provided. Each of the mounting frame 101, the frame body 102, and the mounting plate 103 is circular, and the radius decreases in this order. The frame 102 is arranged so that the center coincides with the inside of the mounting frame 101, and the mounting frame 101 is rotated by the mounting jig 104 so as to rotate about the axis along the towing direction 200 passing through these centers. Is attached. Further, the mounting plate 103 is disposed so that the center coincides with the inside of the frame body 102, and is attached by the mounting jig 105 so as to rotate about the axis along the left-right direction passing through the center. It is attached to the frame body 102.

  As shown in FIG. 8, a receiving sensor 25 for detecting an induced electromagnetic field including information related to a search target (hereinafter referred to as “search information”) is attached to the lower surface of the mounting plate 103. An attitude meter 23 that measures the attitude of the reception sensor 25 and an orientation meter 24 that detects the geomagnetic field and measures the orientation of the reception sensor 25 are attached. The reception sensor 25 is, for example, an induction type three-axis magnetic field sensor. The attitude meter 23 detects the pitch angle α, the roll angle β, and the rotation angle γ around the Z axis of the reception sensor 25 and outputs these as attitude information of the reception sensor 25. The azimuth meter 24 includes three MI (Magnetic-Impedance) sensors. The MI sensor detects each component of the earth's magnetic field and outputs azimuth information of the reception sensor 25.

  Since the sensor base 100 according to the present embodiment has the gimbal structure as described above, the mounting plate 103 to which various sensors are attached has an axis extending in the left-right direction passing through the center thereof. Since it can rotate and the frame body 102 also rotates, it can rotate using the axis along the towing direction 200 passing through the center as a rotation axis. Therefore, when the aerial towed body 7 is shaken so as to rotate about the towing direction 200, or when it is shaken such that it rotates about the left-right direction, the mounting plate 103 is moved. By rotating relatively, various sensors are difficult to shake.

<Configuration of equipment mounted on flying objects>
FIG. 9 is a configuration diagram of equipment mounted on the flying object of the present invention. An amplifier 2 is mounted in the helicopter 1, and outputs from the reception sensor 25, the attitude meter 23 and the azimuth meter 24 are amplified by the amplifier 2. Since the output of the amplifier 2 is an analog signal, it is converted into a digital signal by the A / D converter 3. Each digitized signal is input to the computer 4 for recording and analysis. The computer 4 is connected to a receiving side quartz clock 5 in order to synchronize with the transmitter 11 installed on the ground surface. The GPS receiver 21 and altimeter 22 described above are also mounted on the helicopter 1 and connected to the computer 4 as necessary.

<Configuration of equipment installed on the ground>
FIG. 10 is a block diagram of equipment installed on the ground surface in the present invention. Two transmission lines 10 are connected to the transmitter 11, and electrodes 8 and 9 are provided at the other end. As shown in the figure, parts of the electrodes 8 and 9 are buried in the ground. Further, a step-up transformer 13 is connected to the transmitter 11, and a generator 14 is connected to the step-up transformer 13, which serves as a power supply source. That is, the electricity generated by the generator 14 is changed to a high voltage by the step-up transformer 13. An electromagnetic wave reaching far can be generated by flowing a high-voltage current to the ground through the transmission line 10 and the electrodes 8 and 9. Further, the transmitter 11 is connected to a transmitter-side quartz clock 12 for obtaining synchronization with a device installed on the flying object. In order to synchronize the transmitting side (ground surface) and the receiving side (flying object), the respective quartz clocks are set in advance in advance.

<Configuration of A / D converter>
In the present embodiment, the A / D converter 3 includes a plurality of A / D converters, and by alternately using them, the entire waveform of the analog input signal can be converted into a digital signal. . For example, when the A / D conversion apparatus 3 includes two A / D converters, the computer 4 can convert the other A / D converter while the other A / D converter performs A / D conversion on the input signal. Digital data output from the A / D converter is stored in the memory, and output from one A / D converter while the other A / D converter is A / D converting the input signal. Store digital data in memory. As a result, the A / D conversion process can be performed on the input signal without interruption. Accordingly, the computer 4 can perform an analysis process using all the waveform information about the signals received by the reception sensor 25 and the signals of the pitch angle α, roll angle β, and rotation angle γ output from the attitude meter 23. it can.

<Exploration method of underground structure>
An electromagnetic wave is transmitted from the transmitter 11 and an induced electromagnetic field is generated by the crust inside the basement. The reception sensor 25 in the air towed body 7 suspended from the helicopter 1 observes the X-axis direction and the Y-axis direction. And three magnetic field components in the Z-axis direction. Among these, for analysis, a magnetic field component in the Z-axis direction, that is, a vertical magnetic field is used to derive an underground structure as shown in FIG. FIG. 11 is an underground cross-sectional view when the underground structure is a horizontal layer structure, but the observation target is not limited to the horizontal layer structure. In FIG. 11, ρ ₁ , ρ ₂ , and ρ ₃ are specific resistances of the A layer, the B layer, and the C layer, respectively, and the unit is [Ωm]. H ₁ , H ₂ , and H ₃ indicate the thicknesses (depths) of the A layer, the B layer, and the C layer, respectively. If the vertical magnetic field observed at time t is H _Z (t), the vertical magnetic field H _Z (t) is generally expressed by the following equation (1).

  Here, x, y, and z indicate coordinates at which the receiving sensor 25 is located, and f (a) indicates a function for a.

  Therefore, the underground structure is clarified by collecting the necessary number of data and substituting them into the equation (1) and numerically solving the simultaneous equations obtained thereby.

  A signal actually transmitted from the transmitter 11 is shown in FIG. FIG. 12 is a diagram showing a waveform of a current flowing through the electrodes 8 and 9 through the transmission line 10 and the timing of the transmission-side quartz clock 12. T in the figure indicates a current signal, and CLK indicates a timing signal. At the same time as the timing signal is input from the transmission side quartz clock 12, the transmitter 11 causes a large current to flow through the electrodes 8 and 9. Then, when a current is supplied for several seconds and then a timing signal is input from the transmission side quartz clock 12, the current stops flowing. That is, when a rectangular wave current as shown in FIG. 12 is passed, two transmission lines arranged in a straight line function as a dipole antenna, and electromagnetic waves are instantaneously generated or extinguished. Here, the time during which no current flows takes about several seconds in consideration of the response on the receiving side. In such a device installed on the ground surface, a rectangular wave operation (ON / OFF operation) as shown in FIG. 12 is repeatedly performed. Moreover, the polarity may be reversed for each pulse, and the current may be passed.

  Then, an induced electromagnetic field is generated by the crust inside the underground, and the vertical magnetic field is observed by the receiving sensor 25 in the air towed body 7 suspended from the helicopter 1 as described above.

  FIG. 13 is a diagram illustrating a reception signal at the reception sensor 25 and the timing of the reception-side quartz clock 5. In the figure, R is a signal obtained by amplifying the reception signal received by the reception sensor 25 by the amplifier 2, and CLK is a timing signal of the reception side quartz clock 5. The timing of CLK in FIG. 12 and the timing of CLK in FIG. 13 are the same time.

  The reception signal R output from the amplifier 2 includes a noise signal due to the shaking of the reception sensor 25. That is, when the reception sensor 25 moves in the earth's magnetic field, the reception sensor 25 captures the fluctuation as a magnetic field fluctuation, and the fluctuation magnetic field appears in the reception signal R as a noise signal. Hereinafter, this noise signal is referred to as a “swing noise signal”. Therefore, even if the received signal R is processed as it is, an accurate underground structure cannot be grasped. Therefore, the measurement result data of the attitude meter 23 mounted on the air towed body 7 is read into the computer 4, and the computer 4 is obtained from the digitized signal of the received signal R shown in FIG. 13 and the attitude meter 23. The received vertical magnetic field signal is corrected from the data. The information obtained as a result is as shown in FIG. FIG. 14 is a diagram showing the relationship between time and the corrected vertical magnetic field. In the relationship of FIG. 14, the important part for the analysis of the underground structure is the part showing the transient response of B in the figure. If the underground structure is different, the waveform indicating this transient response is also different. However, in other steady states, it is the same regardless of the underground structure, so it is not important for the analysis of the underground structure. Therefore, after correction is performed as shown in FIG. 14, only a portion showing a transient response, such as a portion B, is set as an analysis target.

  In the portion B of FIG. 14, when the initial time t = 0 and sampling is performed every Δt, the following equations (2) to (4) are obtained from the above equation (1).

Here, the coordinates (x ₀ , y ₀ , z ₀ ), (x ₁ , y ₁ , z ₁ ), (x ₂ , y ₂ , z ₂ ) are the GPS receiver 21 and altimeter 22 mounted on the helicopter 1. Therefore, the exploration information can be acquired by numerically solving the simultaneous equations composed of the equations (2) to (4). That is, the specific resistance and thickness of each layer shown in FIG. 11 are obtained. Note that the number of samplings is three in the above case, but this is for ease of explanation. In the case of actual analysis, the necessary number of samplings may be performed and substituted into equation (1).

<Coordinate value calculation method>
In the above processing, an example of a method for calculating coordinate values x _i , y _i , z _i (i = 0, 1,...) Using the GPS receiver 21 and the altimeter 22 will be described.

In the coordinate calculation, a predetermined position on the ground surface is set as the origin, and the coordinate axis Z is taken in the height direction. For the horizontal coordinate axis, for example, the direction of the line segment connecting the electrodes 8 and 9 can be the Y axis, and the direction perpendicular to the horizontal plane can be the X axis. The coordinate values (x _T , y _T , z _T ) on the transmission side are, for example, the coordinate values of the intermediate points of the electrodes 8 and 9, which can be observed in advance on the ground surface or can be known from the topographic map.

Then, the latitude and longitude observed by the GPS receiver 21 of the helicopter 1 are converted into the XY directions to obtain the current coordinate values x _Hi and y _Hi of the helicopter 1 at time (i · Δt), and from the output of the altimeter 22 The coordinate value z _Hi is obtained.

  Once these coordinate values have been determined in this way, the difference between them is calculated:

Thus, the coordinate values (x _i , y _i , z _i ) of the equations (2) to (4) can be known for each time of (i · Δt).

<Reception signal correction method>
In Patent Document 1 described above, in order to remove the shaking noise signal, the received signal is corrected based on the tilt information of the receiving sensor obtained by the inclinometer. For example, when the inclination of the receiving sensor detected by the inclinometer is expressed by the inclination θ from the horizontal plane, the received vertical magnetic field signal is corrected by dividing it by cos θ. However, in this method, when filtering processing is performed on the corrected vertical magnetic field signal in order to remove measurement noise in the inclinometer, the waveform of the signal including the exploration information included in the vertical magnetic field signal is changed. It may be distorted and the exploration accuracy may deteriorate.

  Therefore, in the present invention, the fluctuation noise signal included in the received signal is predicted and the received signal is corrected by subtracting the predicted value from the received signal. As a result, necessary processing such as measurement noise removal can be performed only on the predicted value, so that the shaking noise signal can be reliably removed without distorting the waveform of the signal including the search information included in the received signal. The correction method according to the present invention will be described in detail below.

  FIG. 15 is a flowchart showing a received signal correction method. As shown in FIG. 15, in step s 1, the computer 4 acquires and stores the pitch angle α, roll angle β, and rotation angle γ output from the attitude meter 23. In step s2, the computer 4 obtains a predicted value of the shaking noise signal included in the received signal based on the acquired pitch angle α, roll angle β, and rotation angle γ.

  Next, in step s3, the computer 4 corrects the frequency characteristic of the predicted value of the shaking noise signal to the frequency characteristic of the reception sensor 25, and subtracts the corrected predicted value from the received signal in step s4. Then, the computer 4 acquires exploration information such as resistivity based on the vertical magnetic field component of the received signal from which the corrected predicted value is subtracted using the above equation (1).

  Usually, since the frequency characteristic of the attitude meter 23 and the frequency characteristic of the reception sensor 25 are different, even if the predicted value of the shaking noise signal obtained from the measurement result of the attitude meter 23 is subtracted from the received signal as it is, it is included in the received signal. The shaking noise signal may not be sufficiently removed. Therefore, as in step s3, the predicted value obtained in step s2 is corrected to the frequency characteristics of the reception sensor 25, and in step s4, the corrected predicted value is subtracted from the received signal, thereby being included in the received signal R. The shaking noise signal can be reliably removed.

  As described above, the computer 4 functions as a fluctuation noise prediction unit that obtains a predicted value of a fluctuation noise signal included in the received signal, and also functions as a frequency characteristic correction unit that corrects the frequency characteristic of the predicted value. The computer 4 also functions as a search information acquisition unit that acquires search information based on the received signal from which the corrected predicted value has been subtracted.

  Note that each piece of data handled in the processes from the above steps s1 to s4 is digital data after A / D conversion processing by the A / D conversion device 3.

<Calculation method of predicted value of shaking noise signal>
Next, the calculation method of the predicted value of the shaking noise signal in step s2 will be described in detail. FIG. 16 is a diagram for explaining a method for calculating a predicted value of a shaking noise signal. In FIG. 16, an orthogonal coordinate system represented by coordinate axes Xo, Yo, and Zo is a reference fixed coordinate system (hereinafter referred to as “reference coordinate system”), and orthogonal coordinates represented by coordinate axes Xt, Yt, and Zt. The system is a coordinate system (hereinafter referred to as “reception sensor coordinate system”) representing each component of the reception magnetic field at the reception sensor 25 at time t.

  The shaking noise signal can be considered to be generated when the receiving sensor coordinate system is changed from the reference coordinate system due to the shaking of the receiving sensor 25. Therefore, the shake noise signal can be predicted by converting the value of the geomagnetic field He in the reference coordinate system into the value in the reception sensor coordinate system.

The value of the geomagnetic field He that will be included in the reception signal at the reception sensor 25, that is, the values of the Xt-axis component, the Yt-axis component, and the Zt-axis component of the shaking noise signal at time t are haxn (t) and hayn ( t), hazn (t), pitch angle α, roll angle β, and rotation angle γ output from attitude meter 23 at time t are α (t), β (t), and γ (t), respectively, and reference coordinates If the Xo-axis component, Yo-axis component, and Zo-axis component of the geomagnetic field He in the system are hxm (t ₀ ), hym (t ₀ ), and hzm (t ₀ ), respectively, haxn (t), hayn (t) and hazn (t) is expressed by the following equations (5) to (7) using coordinate transformation equations.

  Here, each of fx (a), fy (a), and fz (a) indicates a function for a. Also, as shown in FIG. 16, the pitch angle α (t) is the Xt-axis tilt angle from the XoYo plane, and the roll angle β (t) is the Yt-axis tilt angle from the XoYo plane. . The rotation angle γ (t) is an angle formed by the Xo axis and the axis obtained by projecting the Xt axis onto the XoYo plane.

In the present embodiment, as the values of hxm (t ₀ ), hym (t ₀ ), and hzm (t ₀ ), the values of the XYZ components of the geomagnetic field He obtained by the three MI sensors in the compass 24 are used. To do.

  When the aerial towed body 7 reaches the sky above the exploration area and the transmission signal as shown in FIG. 17 is output from the transmitter 11, the computer 4 outputs the period S1 during which the pulse signal is output. The non-period S2 is defined as a measurement cycle CYC, and the pitch angle α (t), roll angle β (t), and rotation angle γ (t) output from the attitude meter 23 during the measurement cycle CYC are acquired and stored. At the same time, the computer 4 acquires and stores the value of each component of the geomagnetic field He output from the bearing meter 24 in the period S2 during which no pulse signal is output during the measurement cycle CYC.

Next, the computer 4 substitutes the values of the components of the earth's magnetic field He from the azimuth meter 24 into the equations (5) to (7) as hxm (t ₀ ), hym (t ₀ ), and hzm (t ₀ ). . Then, the computer 4 substitutes the acquired pitch angle α (t), roll angle β (t), and rotation angle γ (t) into the expressions (5) to (7), and haxn (t), hayn (t ) And hazn (t). Thereby, the XYZ component of the predicted value of the shaking noise signal at each time in the measurement cycle CYC is obtained. The computer 4 repeats this operation every measurement cycle CYC. Therefore, hxm (t ₀ ), hym (t ₀ ), and hzm (t ₀ ) are updated every measurement cycle CYC.

<Frequency characteristics correction method for predicted value of shaking noise signal>
Next, the frequency characteristic correction method in step s3 in FIG. 15 will be described. When the aerial towed object 7 reaches the sky above the exploration area, the computer 4 uses the equations (5) to (7) before starting the underground exploration in a state where no pulse signal is output from the transmitter 11. Haxn (t), hayn (t), and hazn (t) are obtained. At the same time, the reception signal from the reception sensor 25 is acquired in this state. The XYZ components of the received signal at this time are assumed to be hrx (t), hry (t), and hrz (t), respectively.

  Next, the computer 4 transfers the transfer function Hcx (ω) indicating the relationship between haxn (t) and hrx (t), the transfer function Hcy (ω) indicating the relationship between hayn (t) and hry (t), A transfer function Hcz (ω) indicating the relationship between hazn (t) and hrz (t) is obtained. First, the computer 4 performs FFT (fast Fourier transform) on haxn (t), hayn (t), and hazn (t), and converts them from a time domain signal to a frequency domain signal Haxn (ω). , Hayn (ω) and Hazn (ω), respectively. The computer 4 also performs FFT on hrx (t), hry (t), and hrz (t), and outputs them to frequency domain signals Hrx (ω), Hry (ω), and Hrz (ω). Respectively. Then, the computer 4 sets the value obtained by dividing Hrx (ω) by Haxn (ω) as Hcx (ω), the value obtained by dividing Hry (ω) by Hayn (ω) as Hcy (ω), and Hrz (ω). Is a value obtained by dividing Hzn (t) by Hcz (ω).

  Since hrx (t), hry (t), and hrz (t) are received signals when no pulse signal is transmitted from the transmitter 11, these signals include an induced electromagnetic field including exploration information. Not. Therefore, these signals contain only the shaking noise signal. Therefore, Hcx (ω), Hcy (ω) and Hcz (ω) are the predicted value of the shaking noise signal calculated based on the measurement result of the attitude meter 23, and the shaking noise signal actually measured by the receiving sensor 25. It is a transfer function which shows the relationship.

  When the transmission signal as shown in FIG. 17 is output from the transmitter 11 and the underground exploration starts, the computer 4 executes the above-described step s2, and haxn (t), hayn (t), and hazn (t) Ask for. Then, FFT is performed on the obtained haxn (t), hayn (t), and hazn (t) to obtain Haxn (ω), Hayn (ω), and Hazn (ω).

  Next, the computer 4 obtains the acquired Haxn (ω), Hayn (ω), and Hazn (ω) and the transfer functions Hcx (ω), Hcy (ω), and Hcz (ω) obtained in advance as Substituting into (8) to (10), Hbx (ω), Hby (ω) and Hbz (ω) are obtained.

  Then, the computer 4 performs inverse FFT on the obtained Hbx (ω), Hby (ω), and Hbz (ω), and performs them on the time domain signals hbxn (t), hbyn (t), and hbzn ( respectively converted to t). At this time, the inverse FFT is performed by removing high frequency components of 30 Hz or more that are considered as measurement noise in the attitude meter 23 from Hbx (ω), Hby (ω), and Hbz (ω).

  In this way, the frequency characteristics of haxn (t), hayn (t), and hazn (t), which are predicted values of the shaking noise signal, are corrected to the frequency characteristics at the reception sensor 25, and these corrected signals are These are hbxn (t), hbyn (t) and hbzn (t), respectively.

  Assuming that the XYZ components of the received signal at the receiving sensor 25 in the state where the underground exploration is being performed are hx (t), hy (t) and hz (t), the computer 4 obtains the hx acquired from the receiving sensor 25 Substituting (t), hy (t) and hz (t) and hbxn (t), hbyn (t) and hbzn (t) into the following equations (11) to (13), hxs (t) , Hys (t) and hzs (t).

Then, by using hzs (t) among them as H _Z (t) in the above formula (1), the search information can be acquired based on the vertical magnetic field signal from which the shaking noise signal has been removed.

<Modification>
So far, the case where the flying object is a helicopter has been described. However, the present invention is not limited to this, and other flying objects capable of flying with the equipment necessary for the above-described reception may be used. Preferably, a helicopter or an airship capable of low speed flight or air suspension is used. A drone can also be used.

  In the analysis of the underground structure, in addition to the method of solving the simultaneous equations (5) to (7) as described above, the frequency component included in the received signal R is derived using Fourier transform. Thus, a method of obtaining an underground structure may be employed.

  Further, the altitude value of the reception sensor 25 may be obtained using a reading of a flight altimeter mounted on the helicopter 1 itself. In the crustal survey, a slight difference in altitude between the helicopter 1 main body and the reception sensor 25 has little influence on the survey results.

  Further, when the horizontal position and altitude for observation are set in advance, the output of the receiving sensor 25 can be captured when the position and altitude are reached.

  Further, the frequency characteristic of the predicted value of the shaking noise signal has been corrected in the frequency domain using a transfer function, but it can also be corrected in the time domain using an adaptive filter. This modification will be described below.

When the adaptive filter is composed of a transversal filter, the filter order is N, A _{i, j} (i = 0, 1, 2,..., N) is the sampling time jT of the input signal (T: sampling period) ), The relationship between the filter input signal X _j and the output signal Y _j is generally expressed by the following equation (14).

  The computer 4 according to the modification of the present embodiment corrects the frequency characteristic of the predicted value of the shaking noise signal to the frequency characteristic of the reception sensor 25 using Expression (14).

  When the air towed body 7 reaches the sky above the exploration area and the transmission signal as shown in FIG. 17 is output from the transmitter 11, the computer 4 is output from the attitude meter 23 during the measurement cycle CYC. The pitch angle α (t), roll angle β (t), and rotation angle γ (t) are acquired and stored, and the reception signal at the reception sensor 25 in the measurement cycle CYC is acquired and stored. At the same time, the computer 4 acquires and stores the value of each component of the geomagnetic field He output from the bearing meter 24 in the period S2 during which no pulse signal is output during the measurement cycle CYC.

Next, the computer 4 sets the values of each component of the geomagnetic field He from the direction meter 24 as hxm (t ₀ ), hym (t ₀ ), and hzm (t ₀ ) in the equations (5) to (7). And substituting the acquired pitch angle α (t), roll angle β (t), and rotation angle γ (t) into equations (5) to (7), and haxn (t) in the measurement cycle CYC, Hayn (t) and hazn (t) are obtained.

Next, the computer 4 calculates the filter coefficient A _{i, j} using haxn (t), hayn (t), and hazn (t) in the period S2 during which no pulse signal is output, and the received signal in the period S2. decide. First, the computer 4 substitutes haxn (t) in the obtained period S2 as the input signal X _{j into the} expression (14), and uses the acquired X component of the received signal in the period S2 as the output signal Y _j in the expression (14). substitute. Then, the filter coefficient A _{i, j} for the X component is determined from the obtained relational expression between the input signal X _j and the output signal Y _j at each time. The filter coefficient A _{i, j} can be determined using, for example, the least square method. Similarly, the filter coefficient A _{i, j} of the Y component can be determined from the equation obtained by substituting the Hayn (t) in the period S2 and the Y component of the received signal in the period S2 into the equation (14). The filter coefficient A _{i, j} of the Z component can be determined from an equation obtained by substituting hazn (t) in the period S2 and the Z component of the received signal in the period S2 into the equation (14).

Next, the computer 4 substitutes the obtained filter coefficient A _{i, j} of the X component into the equation (14), and substitutes haxn (t) in the measurement cycle CYC into the equation (14) as the input signal X _j. The X component output signal Y _j at each time in the measurement cycle CYC is obtained. In this way, the frequency characteristic of haxn (t), which is the predicted value of the shaking noise signal, is corrected to the frequency characteristic of the reception sensor 25.

Similarly, the obtained Y-component filter coefficient A _{i, j} is substituted into the equation (14), and Hayn (t) in the measurement cycle CYC is substituted into the equation (14) as the input signal X _j. The output signal Y _j of the Y component at each time in CYC is obtained. Further, the obtained filter coefficient A _{i, j} of the Z component is substituted into the equation (14), and hazn (t) in the measurement cycle CYC is substituted into the equation (14) as the input signal X _j , and the measurement cycle CYC The output signal Y _j of the Z component at each time is obtained. Then, the computer 4 uses the output signal Y _j of the Z component of the output signal Y _j obtained as H _Z (t) in Equation (1).

  The computer 4 executes the above operation for each measurement cycle, and executes correction processing for the frequency characteristic of the predicted value of the shaking noise signal in the time domain using an adaptive filter.

  As described above, in the exploration system according to the present embodiment, since the main body 71 of the aerial towed body 7 is a water droplet type that becomes narrower in the direction opposite to the towing direction 200, the helicopter 1 is moving. In addition, air vortices are less likely to occur behind the main body 71. Therefore, the shaking of the air towed body 7 can be suppressed.

  Further, since the cylindrical stabilizer wing 90 is narrowed in the direction opposite to the towing direction 200, the wind passing through the cylindrical stabilizer wing 90 collides with the tail portion 71b when the helicopter 1 is moving. However, it becomes easy to flow backward. Therefore, a force in the direction opposite to the towing direction 200 is easily generated in the tail portion 71b, and the tail portion 71b is pulled backward. Therefore, the air towed body 7 can easily be directed in the towing direction 200, and the air towed body 7 can be further prevented from shaking. As a result, the noise signal generated in the reception signal due to the shaking of the reception sensor 25 can be reliably reduced, high-accuracy search is possible, and the search depth is improved.

  Further, in the main body portion 71 of the air towed body 7, the cross-sectional shape along the direction perpendicular to the towing direction 200 is a spindle shape, so that the shaking of the air towed body 7 can be further reduced. As a result, more accurate exploration is possible and the exploration depth is improved.

  In this embodiment, since the gimbal structure is adopted for the sensor base 100, the shaking of the reception sensor 25 is further reduced, and the search accuracy is further improved.

  Further, when receiving a weak signal such as an induction electromagnetic field, the receiving sensor 25 is usually heavier than the attitude meter 23. Therefore, as in this embodiment, the heavy receiving sensor 25 is provided on the lower surface of the gimbal structure. Therefore, unnecessary shaking of the gimbal structure can be reduced, and search accuracy is further improved.

  Moreover, in this Embodiment, since the predicted value of a shake noise signal is acquired, required processes, such as measurement noise removal, can be performed only to the said predicted value. Therefore, the shaking noise signal contained in the received signal can be reliably removed, and the search accuracy is improved.

  In addition, since the frequency characteristic of the predicted value of the vibration noise signal is corrected to the frequency characteristic of the reception sensor 25, the vibration noise signal included in the reception signal can be reliably removed.

It is a figure which shows the structure of the search system which concerns on embodiment of this invention. It is a side view which shows the structure of the main-body part of the air towed body which concerns on embodiment of this invention. It is sectional drawing which shows the structure of the main-body part of the air towed body which concerns on embodiment of this invention. It is a top view which shows the structure of the main-body part of the air towed body which concerns on embodiment of this invention. It is a perspective view which shows the structure of the stable wing | blade of the air towed body which concerns on embodiment of this invention. It is a side view which shows the towing state of the air towed body which concerns on embodiment of this invention. It is a perspective view which shows the structure of the sensor stand which concerns on embodiment of this invention. It is a side view showing composition of a sensor attached to a sensor stand concerning an embodiment of the invention. It is a figure which shows the structure of the apparatus mounted in the flying object which concerns on embodiment of this invention. It is a figure which shows the structure of the apparatus installed in the earth surface in the exploration system which concerns on embodiment of this invention. It is an underground sectional view in case an underground structure is a horizontal layer structure. It is a figure which shows the timing of the electric current waveform sent to an electrode via a transmission line, and a transmission side quartz timepiece. It is a figure which shows the timing of the received signal obtained with an amplifier, and the receiving side crystal clock. It is a figure which shows the relationship between time and the perpendicular magnetic field of the induction electromagnetic field which generate | occur | produces with a crust. It is a flowchart which shows operation | movement of the search system which concerns on embodiment of this invention. It is a figure for demonstrating operation | movement of the search system which concerns on embodiment of this invention. It is a figure which shows the electric current waveform sent to an electrode via a transmission line.

Explanation of symbols

1 helicopter, 4 computer, 7 aerial towed vehicle, 23 attitude meter, 25 receiving sensor, 71 main body, 71a head, 71b tail, 90 stabilizer, 100 sensor base, 200 towing direction.

Claims (8)

Flying objects,
An exploration system having a receiving sensor for receiving a signal including information related to an exploration target, and an aerial towed body towed in the air by the flying object,
The air towed vehicle is
A drop-shaped body that narrows in the direction opposite to the towing direction;
An exploration system comprising a cylindrical stabilizing wing that surrounds the tail of the main body and narrows in a direction opposite to the towing direction. The exploration system according to claim 1,
In the main body part of the aerial towed body, a cross-sectional shape along a direction perpendicular to the towing direction is a spindle system. The exploration system according to any one of claims 1 and 2,
In the head of the main body in the aerial towed body,
An exploration system in which the receiving sensor is mounted and a sensor base having a gimbal structure for suppressing the shaking is provided. The exploration system according to claim 3,
In the head, an attitude meter for detecting the attitude of the receiving sensor is provided,
The attitude meter is attached to the upper surface of the gimbal structure,
The exploration system, wherein the reception sensor is attached to a lower surface of the gimbal structure. The exploration system according to any one of claims 1 to 3,
An attitude meter that measures the attitude of the reception sensor is provided in the head of the main body in the aerial towed vehicle,
A fluctuation noise prediction unit for obtaining a predicted value of a noise signal included in a reception signal at the reception sensor due to a fluctuation of the reception sensor based on a measurement result of the posture meter;
A search system further comprising a search information acquisition unit that acquires information related to the search target based on a signal obtained by subtracting the predicted value from the received signal. The exploration system according to claim 5,
A frequency characteristic correction unit that corrects the frequency characteristic of the predicted value to the frequency characteristic of the reception sensor is further provided.
The exploration information acquisition unit acquires information on the exploration target based on a signal obtained by subtracting the predicted value corrected by the frequency characteristic correction unit from the received signal. The exploration system according to claim 6,
The frequency characteristic correcting unit corrects the predicted value to a frequency characteristic at the receiving sensor based on a transfer function indicating a relationship between the predicted value and the noise signal measured by the receiving sensor. . The exploration system according to claim 6,
The frequency characteristic correction unit corrects the predicted value to a frequency characteristic at the reception sensor using an adaptive filter.

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