Object detection device, object detection method, and program

Abstract

To provide an object detection device that can improve the accuracy of object detection. [Solution] The object detection device calculates an index value regarding the non-equivalence between the first and second regions based on the first offset function, which is obtained from the muon spectrum obtained from the measurement value of the first sensor and corresponds to the difference between the number of muons observed in the first direction and the number of muons observed in the second direction for a pair of directions including a first direction orthogonal to the zenith direction and a second direction opposite to the first direction, and the first and second muon spectra for the first region in the first direction and the second region in the second direction, respectively, which are set in a plane set to be orthogonal to the zenith axis of the second sensor within the field of view of the second sensor and are symmetrical with respect to the origin, which is the intersection point of the zenith axis and the plane, and determines whether or not a target object exists based on the index value.

Description

[Technical Field]

[0001] This disclosure relates to an object detection device, an object detection method, and a program. [Background technology]

[0002] A method for observing various structures, such as the interior of mountains, using muography with cosmic ray muons is known (Patent Documents 1 and 2). In these methods, the internal structure of a structure can be observed by detecting muons that have passed through the structure with a sensor and constructing a two-dimensional image.

[0003] In muography technology, various image processing techniques are applied to construct two-dimensional images (Patent Documents 1-3).

[0004] Muography technology allows for the observation of unknown structures, such as cavities with significant density changes within a mountain. In this case, a model (sometimes called a muon flux model) is constructed to predict the number of incoming muons (sometimes called muon flux) from the pixel values ​​of a two-dimensional image formed by detecting muons that have passed through the mountain. Then, by subtracting the pixel values ​​for cases where there are no unknown structures from the muon flux model, a two-dimensional image reflecting the internal structure of the mountain can be obtained. [Prior art documents] [Patent Documents]

[0005] [Patent Document 1] Japanese Patent Publication No. 2007-121202 [Patent Document 2] Japanese Patent Publication No. 2021-39000 [Patent Document 3] Japanese Patent Publication No. 2013-5840 [Overview of the project] [Problems that the invention aims to solve]

[0006] Incidentally, it is also possible to detect objects based on the difference between the predicted spectrum estimated from a muon flux model and the observed spectrum. However, it is difficult to accurately reflect statistical errors in the muon flux model, which may reduce the accuracy of object detection.

[0007] The purpose of this disclosure is to provide an object detection device, an object detection method, and a program that can improve the accuracy of object detection. It should be noted that this purpose is only one of several purposes that the various embodiments disclosed herein seek to achieve. Other purposes or problems and novel features will be revealed in the description herein or in the accompanying drawings. [Means for solving the problem]

[0008] The object detection device according to this disclosure is a first offset function obtained based on a muon spectrum showing the number of muons per muon energy obtained from a measurement of the first charged particle sensor among a first charged particle sensor and a second charged particle sensor arranged such that their zenith directions perpendicular to the sensor surface coincide, which includes a pair of directions including a first direction perpendicular to the zenith direction and a second direction opposite to the first direction, or obtained based on a prediction spectrum obtained from a muon flux model, which includes the number of muons observed in the first direction and the number of muons observed in the second direction The system comprises: a calculation unit that calculates an index value relating to the non-equivalence between the first and second regions based on both a second offset function and the first offset function corresponding to the difference with respect to the number of muons, and the first and second muon spectra for the first region and the second region, respectively, which are set in a plane that is set to be perpendicular to the zenith axis of the second charged particle sensor within the field of view of the second charged particle sensor, and which are mutually symmetric with respect to the origin, which is the intersection point of the zenith axis and the plane; and a determination unit that determines whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor based on the calculated index value.

[0009] The object detection method according to this disclosure is a method performed by an object detection device, and is obtained based on a muon spectrum showing the number of muons for each muon energy obtained from a measurement of the first charged particle sensor among a first charged particle sensor and a second charged particle sensor arranged such that their zenith directions orthogonal to the sensor surface coincide, which is a first offset function corresponding to the difference between the number of muons observed in the first direction and the number of muons observed in the second direction for a pair of directions including a first direction orthogonal to the zenith direction and a second direction opposite to the first direction, or obtained based on a prediction spectrum obtained from a muon flux model, which is the difference between the number of muons observed in the first direction and the second direction The method includes calculating an index value relating to the non-equivalence between the first and second regions based on both a second offset function and the first offset function, which correspond to the difference with respect to the observed number of muons, and the first muon spectrum and the second muon spectrum for each of the first region and the second region, which are set in a plane that is set within the field of view of the second charged particle sensor so as to be perpendicular to the zenith axis of the second charged particle sensor and are mutually originally symmetric with respect to the origin, which is the intersection point of the zenith axis and the plane, and determining whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor based on the calculated index value.

[0010] The program according to the present disclosure is based on a muon spectrum showing the number of muons for each muon energy obtained from the measurement values of the first charged particle sensor among the first charged particle sensor and the second charged particle sensor arranged such that the zenith directions orthogonal to the sensor surface coincide with each other. A first offset function corresponding to the difference between the number of muons observed in the first direction and the number of muons observed in the second direction for a direction pair including the first direction orthogonal to the zenith direction and the second direction opposite to the first direction, or a second offset function corresponding to the difference between the number of muons observed in the first direction and the number of muons observed in the second direction based on a predicted spectrum obtained from a muon flux model and both the first offset function, and a first muon spectrum and a second muon spectrum for each of a first region existing in the first direction and a second region existing in the second direction, which are symmetric with respect to the origin at the intersection of the zenith axis and the plane set in a plane set orthogonal to the zenith axis of the second charged particle sensor within the angular range of the second charged particle sensor. Based on these, calculating an index value regarding the non-equivalence between the first region and the second region, and determining whether a detection target object exists in the space between the first charged particle sensor and the second charged particle sensor based on the calculated index value, and causing an object detection device to execute a process including this.

Advantages of the Invention

[0011] According to the present disclosure, it is possible to provide an object detection device, an object detection method, and a program that can improve the accuracy of object detection.

Brief Description of the Drawings

[0012] [Figure 1] It is a diagram showing an example of the system of the present disclosure. [Figure 2] It is a diagram for explaining the zenith angle. [Figure 3] It is a diagram for explaining the azimuth angle. [Figure 4]A block diagram showing an example of an object detection device in this disclosure. [Figure 5] This diagram illustrates the relationship between the energy of a muon particle and the muon flux (number of particles). [Figure 6] This figure shows an example of a muon flux image generated from measurement data. [Figure 7] This flowchart shows an example of the processing operation of the object detection device disclosed herein. [Figure 8] This is a diagram used to explain the first offset function. [Figure 9] This is a diagram used to explain the first offset function. [Figure 10] This diagram illustrates pairs of azimuthal symmetric regions. [Figure 11] This diagram illustrates pairs of azimuthal symmetric regions. [Figure 12] This figure shows examples of the first and second muon spectra. [Figure 13] This figure shows an example of the first offset function. [Figure 14] A block list showing another example of an object detection device in this disclosure. [Figure 15] This is a diagram used to explain the second offset function. [Figure 16] This is a diagram used to explain the second offset function. [Figure 17] A block list showing another example of an object detection device in this disclosure. [Figure 18] This figure shows an example of a third muon spectrum. [Figure 19] This figure shows an example of the probability distribution of energy loss. [Figure 20] This figure shows an example of an expected muon spectrum. [Figure 21] This figure shows an example of a graph created by the creation department. [Figure 22] This flowchart shows another example of the processing operation of the object detection device disclosed herein. [Figure 23]This is a diagram showing an example of the configuration of an object detection device. [Modes for carrying out the invention]

[0013] The embodiments will be described below with reference to the drawings. In this disclosure, the drawings may be associated with one or more embodiments. Also, each element in the drawings may correspond to one or more embodiments. Furthermore, in the embodiments, the same or equivalent elements are denoted by the same reference numerals, and redundant descriptions are omitted.

[0014] <First Embodiment> <System Overview> Figure 1 shows an example of the system of this disclosure. In Figure 1, system 1 includes an object detection device 10 (not shown) and measuring instruments (charged particle sensors) 20-1 and 20-2. Hereinafter, unless otherwise distinguished, measuring instruments 20-1 and 20-2 may be collectively referred to as measuring instrument 20, or each of measuring instruments 20-1 and 20-2 may be simply referred to as measuring instrument 20. Here, the number of measuring instruments 20 included in system 1 is assumed to be two, but this is not limited to two, and there may be three or more.

[0015] Measuring instruments 20-1 and 20-2 are positioned in three-dimensional space such that their zenith directions, perpendicular to their sensor surfaces, coincide. The zenith angle is the angle θ from the zenith direction, as shown in Figure 2. The azimuth angle is, for example, the angle ψ from the reference direction in Figure 3. Figure 2 is a diagram illustrating the zenith angle. Figure 3 is a diagram illustrating the azimuth angle. The three-dimensional space in which measuring instruments 20-1 and 20-2 are installed may be in seawater, underground, or in the air. In Figure 1, it is assumed that measuring instruments 20-1 and 20-2 are installed below a uniform ground surface.

[0016] "The zenith directions perpendicular to the sensor surfaces coincide" means, for example, that the zenith axis of measuring instrument 20-1 and the zenith axis of measuring instrument 20-2 lie on a single straight line, or that the zenith axis of measuring instrument 20-1 and the zenith axis of measuring instrument 20-2 are parallel. "The zenith axis of measuring instrument 20-1 and the zenith axis of measuring instrument 20-2 are parallel" does not need to be strictly parallel.

[0017] The measuring instrument 20 measures the number of charged particles that have passed through three-dimensional space and reached the sensor surface of the measuring instrument 20, as well as the incident direction and the energy of each charged particle. The charged particles are not limited to these, but for example, muons.

[0018] The object detection device 10 acquires a first set of measurement values ​​for each measurement timing of the measuring instrument 20-1. The object detection device 10 also acquires a second set of measurement values ​​for each measurement timing of the measuring instrument 20-2.

[0019] Each first measurement set includes multiple measurement values ​​(hereinafter, each measurement value may be referred to as the "first measurement value") corresponding to multiple combinations of zenith angle candidates and azimuth angle candidates. Here, the zenith angle candidate is the angle relative to the direction perpendicular to the sensor surface of measuring instrument 20-1. The azimuth angle candidate is the angle from the reference point on the sensor surface of measuring instrument 20-1.

[0020] Furthermore, each second measurement set includes multiple measurement values ​​(hereinafter, each measurement value may be referred to as the "second measurement value") corresponding to multiple combinations of zenith angle candidates and azimuth angle candidates. Here, the zenith angle candidate is the angle relative to the direction perpendicular to the sensor surface of measuring instrument 20-2. The azimuth angle candidate is the angle from the reference point on the sensor surface of measuring instrument 20-2.

[0021] In other words, each first measurement and each second measurement represent the number of charged particles and the energy value of each charged particle for each combination of candidate zenith angle and candidate azimuth angle.

[0022] <Example of object detection device configuration> Figure 4 is a block diagram showing an example of an object detection device according to the present disclosure. In Figure 4, the object detection device 10 has a calculation unit 11 and a determination unit 12.

[0023] The calculation unit 11 calculates an "index value for non-equivalence" between the "first region" and the "second region" based on the offset function (which may hereafter be called the "first offset function"), the "first muon spectrum," and the "second muon spectrum." Hereafter, the first region and the second region described above may be called an "azimuthal symmetric region pair."

[0024] The first offset function is a function that represents the difference between the number of muons observed in the first direction and the number of muons observed in the second direction for a pair of directions, including a first direction orthogonal to the zenith direction and a second direction opposite to the first direction, obtained based on the muon spectrum showing the number of muons per muon energy obtained from the measurement of the measuring instrument 20-1. Multiple first offset functions corresponding to multiple zenith angles may be calculated by the calculation unit 11, and the calculation unit 11 may use the first offset functions corresponding to the zenith angles corresponding to the first and second regions to calculate an index value relating to the non-equivalence between the first and second regions.

[0025] The above-mentioned first muon spectrum is the muon spectrum of the first region of the second region, which is located in a setting plane set to be perpendicular to the zenith axis of the measuring instrument 20-2 within the field of view of the measuring instrument 20-2, and is set to be symmetrical with respect to the origin, which is the intersection point of the zenith axis and the setting plane.

[0026] Furthermore, the second muon spectrum shown above is the muon spectrum for the second region described above.

[0027] Here, we will explain the relationship between the energy of a muon particle and the muon flux (number of particles). Figure 5 is a diagram illustrating the relationship between the energy of a muon particle and the muon flux (number of particles). The horizontal axis represents the energy of the muon particle, and the vertical axis represents the muon flux. As shown in Figure 5, the minimum energy value E min The following muon particles are lost through interaction with matter. Therefore, the number of muon particles observed (measured) is the minimum value E. min That's all.

[0028] Here, the energy loss equation for a muon particle is empirically defined by the following equation (1).

number

number

[0029] The measurement results from the measuring instrument 20 can then be converted into a muon flux image (an example of a measured value) using known techniques. Figure 6 shows an example of a muon flux image generated from the measured value. The horizontal axis represents the tangent value of the azimuth angle (the tangent value of the 90 degrees around the sensor surface of the measuring instrument in the horizontal direction), and the vertical axis represents the tangent value of the zenith angle. The intensity of each pixel indicates the density of muon particles.

[0030] Returning to the explanation of Figure 4, the determination unit 12 determines, based on the calculated index value, whether or not a "target object" exists in the space between measuring instrument 20-1 and measuring instrument 20-2.

[0031] Here, the first offset function can be understood as a function that represents the "deviation from isotropy" for the muon spectrum of detector 20-1. This "deviation from isotropy" that appears for detector 20-1 is caused by the environment above detector 20-1, such as the Earth's magnetic field. Therefore, the "deviation from isotropy" that appears for detector 20-1 also appears in the "deviation from isotropy" for detector 20-2. Furthermore, if an object with a different density exists in the space between detector 20-1 and detector 20-2, a difference will occur between the first muon spectrum and the second muon spectrum described above. In this case, the "deviation from isotropy" will also appear for detector 20-2 due to the influence of this object. Therefore, by using the "deviation from azimuthal isotropy" obtained by eliminating the influence of the "deviation from azimuthal isotropy" obtained for measuring instrument 20-1 from the "deviation from azimuthal isotropy" obtained for measuring instrument 20-2, it is possible to determine whether or not an unknown object (i.e., the object to be detected) exists in the space between measuring instrument 20-1 and measuring instrument 20-2. That is, the calculation unit 11 can calculate an "index value regarding non-equivalence" between the "first region" and the "second region" based on the "first offset function", the "first muon spectrum", and the "second muon spectrum". Then, the determination unit 12 can determine whether or not the "object to be detected" exists in the space between measuring instrument 20-1 and measuring instrument 20-2 based on the calculated index value.

[0032] <Example of object detection device operation> Figure 7 is a flowchart showing an example of the processing operation of the object detection device of this disclosure.

[0033] The calculation unit 11 calculates an "index value for non-equivalence" between the "first region" and the "second region" of the azimuthal symmetric region pair based on the first offset function, the "first muon spectrum," and the "second muon spectrum" (step S11).

[0034] As described above, the first offset function is a function that represents the difference between the number of muons observed in the first direction and the number of muons observed in the second direction for a pair of directions including a first direction orthogonal to the zenith direction and a second direction opposite to the first direction, obtained based on the muon spectrum obtained from the measurement of instrument 20-1.

[0035] Figure 8 shows examples of muon spectra corresponding to the 0° azimuth angle and the 180° azimuth angle of the detector 20-1. The horizontal axis in Figure 8 represents energy, and the vertical axis represents the number of muons. Energy E i The difference between the muon spectral value corresponding to the azimuth angle of 0° and the muon spectral value corresponding to the azimuth angle of 180° is ΔN0(E i ) is shown. A graph plotting multiple differences corresponding to multiple energy values ​​is shown in Figure 9. Then, by fitting the points plotted in the graph in Figure 9 with a function, the first offset function is obtained. Figures 8 and 9 are diagrams used to explain the first offset function.

[0036] Next, we will describe the azimuthal symmetry region pairs. Figure 10 shows the field of view of the measuring instrument 20-2. Within the field of view of the measuring instrument 20-2, a plane PL1 is set at a predetermined distance from the sensor surface of the measuring instrument 20-2 in the zenith direction, perpendicular to the zenith axis of the measuring instrument 20-2. Figure 11 shows the plane PL1. In Figure 11, the x and y axes are set on the plane PL1. The origin O corresponds to the intersection point of the zenith axis of the measuring instrument 20-2 and the plane PL1. Also, each of the multiple concentric circles drawn in Figure 11 corresponds to a different zenith angle. Figure 11 shows the azimuthal symmetry region pairs PA1 and PA2. The azimuthal symmetry region pair PA1 includes regions AR11 and AR12. Region AR11 has, for example, a rectangular shape, with its longer side perpendicular to the x-axis (i.e., the azimuthal 0° direction). Furthermore, region AR12 has the same shape as region AR11, with its longer side perpendicular to the 180° azimuth direction. Also, regions AR11 and AR12 are each located at a distance d1 from the origin O. This distance d1 corresponds to a certain value of the zenith angle. That is, regions AR11 and AR12 are symmetric with respect to the origin O. Similarly, the azimuth-symmetric region pair PA2 includes regions AR21 and AR22. Region AR21 has, for example, a rectangular shape, with its longer side perpendicular to the 45° azimuth direction. Also, region AR22 has the same shape as region AR11, with its longer side perpendicular to the 225° azimuth direction. Also, regions AR21 and AR22 are each located at a distance d2 from the origin O. This distance d2 corresponds to a zenith angle of a different value than the zenith angle corresponding to distance d1. That is, regions AR21 and AR22 are symmetric with respect to the origin O. Figures 10 and 11 illustrate pairs of azimuthal symmetric regions.

[0037] FIG. 12 is a diagram showing an example of a first muon spectrum and a second muon spectrum. For example, it is assumed that spectrum 1 in FIG. 12 corresponds to the first muon spectrum and spectrum 2 corresponds to the second muon spectrum. For example, the first muon spectrum is a muon spectrum for region AR11, and the second muon spectrum is a muon spectrum for region AR12.

[0038] Here, a specific example of calculating the "index value regarding non-equivalence" will be described. FIG. 13 is a diagram showing an example of a first offset function. The E shown in FIG. 12 i and the E shown in FIG. 13 j indicate that when the muon with energy E j observed by the measuring instrument 20-1 is observed by the measuring instrument 20-2, it has energy E i .

[0039] The calculation unit 11 calculates the total number of muons corresponding to energy E i (i = 0 to n) for the first muon spectrum based on the following formula (3).

Equation

[0040] Also, the calculation unit 11 calculates the total number of muons corresponding to energy E i (i = 0 to n) for the second muon spectrum based on the following formula (4).

Equation

[0041] Then, the calculation unit 11 calculates Sum3 based on the following formula (5).

number

[0042] In equation (5), g[j] is the energy E in the first offset function. j The corresponding value (ΔN0(E j )) Also, in equation (5), (N1[i]-N2[i]+g[j]) has an energy E in the first muon spectrum. i The corresponding number of muons and the energy E in the second muon spectrum i This is the compensated value obtained by compensating for the difference with the corresponding number of muons based on the value of the first offset function g[j]. And in equation (5), the energy E i The sum of the compensation values ​​corresponding to (i=0 to n) is calculated. Note that in equations (3) to (5), the sum is calculated for i=0 to n, but if the size of the object to be detected is small, for example, the range of the sum may be limited to the low energy range (e.g., i=0 to 5).

[0043] The calculation unit 11 then calculates the Ratio based on the following formula (6). This Ratio corresponds to the "index value related to non-equivalence" mentioned above.

number

[0044] Returning to the explanation of Figure 7, the determination unit 12 determines, based on the calculated index value, whether or not a "target object" exists in the space between measuring instrument 20-1 and measuring instrument 20-2 (step S12).

[0045] For example, the determination unit 12 may determine whether or not a "target object" exists in the space between measuring instrument 20-1 and measuring instrument 20-2 based on the comparison result of the calculated index value with a threshold. For example, if the Ratio in the above formula (6) is used as an "index value related to non-equivalence", the determination unit 12 may determine that if the Ratio is greater than the threshold, an object with a lower density than the surrounding material of measuring instrument 20-2 exists in the space between measuring instrument 20-1 and measuring instrument 20-2.

[0046] As described above, according to the first embodiment, the calculation unit 11 in the object detection device 10 calculates an "index value for non-equivalence" between the "first region" and the "second region" based on the "first offset function", the "first muon spectrum", and the "second muon spectrum". The first offset function is a function obtained based on the muon spectrum showing the number of muons for each muon energy obtained from the measurement of the measuring instrument 20-1, and shows the difference between the number of muons observed in the first direction and the number of muons observed in the second direction for a pair of directions including a first direction orthogonal to the zenith direction and a second direction opposite to the first direction. The first muon spectrum is the muon spectrum of the first region, which exists in the first direction and the second region, which exists in the second direction, that are mutually originally symmetric with respect to the origin, which is the intersection point of the zenith axis and the setting plane, set in a setting plane set to be orthogonal to the zenith axis of the measuring instrument 20-2 within the field of view of the measuring instrument 20-2. The second muon spectrum is the muon spectrum of the second region. The determination unit 12 determines, based on the calculated index value, whether or not a "target object" exists in the space between measuring instrument 20-1 and measuring instrument 20-2.

[0047] The configuration of this object detection device 10 allows for the determination of whether or not a target object exists based on an index value relating to the non-equivalence between a first region existing in a first direction that is symmetrical with respect to the origin and a second region existing in a second direction, thereby improving the accuracy of object detection.

[0048] <Second Embodiment> In the second embodiment, in calculating the index value for the non-equivalence between the first and second regions, in addition to the first offset function, a second offset function is used that corresponds to the difference between the number of muons observed in the first direction and the number of muons observed in the second direction, obtained based on the predicted spectrum obtained from the muon flux model. The basic configuration of the system in the second embodiment is the same as system 1 in the first embodiment, so please refer to Figure 1. That is, system 1 in the second embodiment has an object detection device 30 instead of object detection device 10.

[0049] Figure 14 is a block diagram showing another example of the object detection device of this disclosure. In Figure 14, the object detection device 30 has a calculation unit 31 and a determination unit 32.

[0050] The calculation unit 31 calculates an "index value for non-equivalence" between the "first region" and the "second region" based on both the "first offset function" and the "second offset function," as well as the "first muon spectrum" and the "second muon spectrum." The first offset function, the first muon spectrum, the second muon spectrum, the first region, and the second region have been described in the first embodiment, so their description is omitted here.

[0051] The second offset function described above is a function that shows the difference between the number of muons observed in the first direction and the number of muons observed in the second direction, obtained based on the predicted spectrum from the muon flux model in instrument 20-1. The predicted spectrum may be calculated by incorporating factors whose time variations are almost negligible, such as surface non-uniformity or the static distribution of the geomagnetic field. For example, surface non-uniformity can be reflected in the spectrum by substituting the elevation and density of the surface into equations (1) and (2).

[0052] Figure 15 shows examples of predicted muon spectra corresponding to the 0° azimuth angle and the 180° azimuth angle, obtained from the muon flux model of detector 20-1. In Figure 15, the horizontal axis represents energy, and the vertical axis represents the number of muons. Energy E i The difference between the predicted muon spectrum value corresponding to the 0° azimuth direction and the predicted muon spectrum value corresponding to the 180° azimuth direction is ΔN m (E i ) is the case for N with respect to the energy value. m (E i The function of (i.e., the second offset function) is shown as a graph in Figure 16. Figures 15 and 16 are diagrams used to explain the second offset function.

[0053] Here, we will explain a specific example of calculating the "index value related to non-equivalence". E shown in Figure 12 i and E shown in Figure 16 j This is the energy E observed by detector 20-1. j If the muon is observed by detector 20-2, then its energy E i This indicates that it has such a characteristic.

[0054] The calculation unit 31, similar to the calculation unit 11, calculates the energy E for the first muon spectrum. i The sum of the muon numbers corresponding to (i=0 to n) is calculated based on equation (3).

[0055] Furthermore, the calculation unit 31, similar to the calculation unit 11, calculates the energy E for the second muon spectrum. i The sum of the muon numbers corresponding to (i=0~n) is calculated based on equation (4).

[0056] Then, the calculation unit 31 calculates Sum3 based on the following formula (7).

number

[0057] In equation (7), g[j] is the energy E in the first offset function. j The corresponding value (ΔN m (E j )) is the case. f[j] is the energy E in the second offset function. j The corresponding value (ΔN0(E j )) Also, in equation (7), (N1[i]-N2[i]+f[j]+g[j]) represents the energy E in the first muon spectrum. i The corresponding number of muons and the energy E in the second muon spectrum i This is the compensated value obtained by compensating for the difference with the corresponding number of muons based on the value of the second offset function f[j] and the value of the first offset function g[j]. And in equation (7), the energy E i The sum of the compensation values ​​corresponding to (i=0 to n) has been calculated.

[0058] Then, the calculation unit 31 calculates the Ratio based on equation (6). This Ratio corresponds to the "index value related to non-equivalence" mentioned above.

[0059] Returning to the explanation of Figure 14, the determination unit 32, similar to the determination unit 12, determines whether or not a "target object" exists in the space between measuring instrument 20-1 and measuring instrument 20-2 based on the calculated index value.

[0060] <Third Embodiment> <Example of object detection device configuration> Figure 17 is a block diagram showing another example of the object detection device of this disclosure. In Figure 17, the object detection device 50 includes a calculation unit 51, a identification unit 52, and a determination unit 53. The basic configuration of the system in the third embodiment is the same as that of system 1 in the first embodiment, so please refer to Figure 1. That is, system 1 in the third embodiment has an object detection device 50 instead of an object detection device 10.

[0061] The calculation unit 51 calculates the expected muon spectrum for a predetermined zenith angle associated with the measuring instrument 20-2 based on the muon spectrum obtained from past measurements of the measuring instrument 20-1 (which may hereafter be referred to as the "third muon spectrum") and the "probability distribution of energy loss". The calculation unit 51 may also calculate the expected muon spectrum for each of a plurality of candidate zenith angles.

[0062] The third muon spectrum is a muon spectrum that shows the number of muons per muon energy, obtained from past measurements taken by detector 20-1 for the predetermined zenith angle mentioned above.

[0063] The "probability distribution of energy loss" is the probability distribution of energy loss when a muon moves from the position of detector 20-1 to the position of detector 20-2.

[0064] Figure 18 shows an example of a third muon spectrum. Figure 19 shows an example of a probability distribution of energy loss. Figure 20 shows an example of an expected muon spectrum. The third muon spectrum in Figure 18 is the muon spectrum at a predetermined zenith angle. In Figure 20, the dashed line is the expected muon spectrum at a predetermined zenith angle, and the solid line is the muon spectrum obtained from the measurement of instrument 20-2 at a predetermined zenith angle (hereinafter sometimes referred to as the "fourth muon spectrum").

[0065] E in the third muon spectrum of Figure 18 min It is assumed that muons with the above energies can reach detector 20-2. For example, a muon with energy E1 in the third muon spectrum will lose energy based on the probability distribution of energy loss shown in Figure 19 and then be measured by detector 20-2. This muon is expected to be observed by detector 20-2 as a muon with energy E2 in the expected muon spectrum shown in Figure 20.

[0066] The identification unit 52 identifies "information regarding the direction" in which muons corresponding to muon energy values ​​where the fourth muon spectrum and the expected muon spectrum deviate by a predetermined level or more were observed. For example, the identification unit 52 identifies "information regarding the direction" in which muons corresponding to muon energy values ​​where the number of muons in the fourth muon spectrum differs by a predetermined number or more from the number of muons in the expected muon spectrum were observed. This "information regarding the direction" is, for example, a combination of the azimuth angle and a predetermined zenith angle in which muons corresponding to muon energy values ​​where the number of muons in the fourth muon spectrum differs by a predetermined number or more from the number of muons in the expected muon spectrum were observed. The identification unit 52 may also identify "information regarding the direction" for each of the above-mentioned multiple zenith angle candidates.

[0067] The determination unit 53 determines whether or not a target object exists in the space between measuring instrument 20-1 and measuring instrument 20-2, based on the "information regarding direction" identified by the identification unit 52.

[0068] For example, as shown in Figure 17, the determination unit 53 includes a creation unit 53A, a clustering unit 53B, and a determination processing unit 53C.

[0069] The clustering unit 53B clusters the combinations of azimuth angle and zenith angle candidate in the "direction information" identified for each of the multiple zenith angle candidates in a two-dimensional coordinate system in which the direction from the origin corresponds to the azimuth angle and the distance from the origin corresponds to the zenith angle. For example, the clustering unit 53B may perform clustering based on the graph created by the creation unit 53A.

[0070] The creation unit 53A creates a graph plotting the combinations of azimuth angle and zenith angle candidate from the "direction information" identified for each of the multiple zenith angle candidates mentioned above, on a two-dimensional coordinate system where the direction from the origin corresponds to the azimuth angle and the distance from the origin corresponds to the zenith angle. Figure 21 shows an example of a graph created by the creation unit. In Figure 21, the origin is the zenith direction of the measuring instrument 20-2. Also, each of the multiple concentric circles drawn in Figure 21 corresponds to a different zenith angle.

[0071] The plotting unit 53A differentiates the plotting format for combinations of muons corresponding to muon energy values ​​where the number of muons in the fourth muon spectrum is greater than the number of muons in the expected muon spectrum, and for combinations of muons corresponding to muon energy values ​​where the number of muons in the fourth muon spectrum is less than the number of muons in the expected muon spectrum. In Figure 21, circles indicate muons corresponding to muon energy values ​​where the number of muons in the fourth muon spectrum is greater than the number of muons in the expected muon spectrum. Triangles indicate muons corresponding to muons corresponding to muon energy values ​​where the number of muons in the fourth muon spectrum is less than the number of muons in the expected muon spectrum.

[0072] The determination processing unit 53C determines, for example, that if there are clusters containing a predetermined number or more combinations, the object to be detected is present in the space between measuring instrument 20-1 and measuring instrument 20-2. The dashed rectangle in Figure 21 is an example of a cluster. Based on the clusters in Figure 21, the determination processing unit 53C can determine that the space between measuring instrument 20-1 and measuring instrument 20-2 is occupied by an object with a density different from that of the surrounding material of measuring instrument 20-2.

[0073] <Example of object detection device operation> Figure 22 is a flowchart showing another example of the processing operation of the object detection device of this disclosure.

[0074] The calculation unit 51 calculates the expected muon spectrum for a predetermined zenith angle related to the measuring instrument 20-2 based on the third muon spectrum and the "probability distribution of energy loss" (step S21).

[0075] The identification unit 52 identifies "information regarding the direction" in which a muon corresponding to a muon energy value in which the fourth muon spectrum and the expected muon spectrum deviate by a predetermined level or more was observed (step S22).

[0076] The determination unit 53 determines whether or not a target object exists in the space between measuring instrument 20-1 and measuring instrument 20-2 based on the "information regarding direction" identified by the identification unit 52 (step S23).

[0077] As described above, according to the third embodiment, the calculation unit 51 in the object detection device 50 calculates an expected muon spectrum for a predetermined zenith angle related to the measuring instrument 20-2 based on a third muon spectrum obtained from past measurements of the measuring instrument 20-1 and the "probability distribution of energy loss". The third muon spectrum is a muon spectrum showing the number of muons for each muon energy obtained from past measurements measured by the measuring instrument 20-1 for the above predetermined zenith angle. The "probability distribution of energy loss" is the probability distribution of energy loss when a muon moves from the position of the measuring instrument 20-1 to the position of the measuring instrument 20-2. The identification unit 52 identifies "information regarding the direction" in which a muon corresponding to a muon energy value in which the fourth muon spectrum and the expected muon spectrum deviate by a predetermined level or more was observed. The determination unit 53 determines whether or not a target object exists in the space between the measuring instrument 20-1 and the measuring instrument 20-2 based on the "information regarding the direction" identified by the identification unit 52.

[0078] With the configuration of this object detection device 50, the expected muon spectrum for a predetermined zenith angle associated with the measuring instrument 20-2, calculated from the third muon spectrum which is unaffected by the object to be detected, is compared with the fourth muon spectrum obtained from the measurement value of the measuring instrument 20-2 at a predetermined zenith angle. The determination unit 53 can determine from this comparison result whether or not the object to be detected exists in the space between the measuring instrument 20-1 and the measuring instrument 20-2, thereby improving the accuracy of object detection.

[0079] <Other Embodiments> Figure 23 shows an example configuration of an object detection device. In Figure 23, the object detection device 100 includes a processor 101, a memory 102, and a communication circuit 103. The processor 101 may be, for example, a microprocessor, an MPU (Micro Processing Unit), or a CPU (Central Processing Unit). The processor 101 may include multiple processors. The memory 102 is composed of a combination of volatile memory and non-volatile memory. The memory 102 may include storage located away from the processor 101. In this case, the processor 101 may access the memory 102 via an I(Input) / O(Output) interface, which is not shown.

[0080] The object detection devices 10, 30, and 50 of the first to third embodiments can each have the configuration shown in Figure 23. The calculation units 11, 31, and 51, the determination units 12, 32, and 53, and the identification unit 52 of the object detection devices 10, 30, and 50 of the first to third embodiments may be realized by the processor 101 reading and executing a program stored in the memory 102. In other words, the object detection devices 10, 30, and 50 of the first to third embodiments can be realized by software. The program can be stored using various types of non-transitory computer-readable media and supplied to the object detection devices 10, 30, and 50. Examples of non-transitory computer-readable media include magnetic recording media (e.g., flexible disks, magnetic tapes, hard disk drives) and magneto-optical recording media (e.g., magneto-optical disks). Furthermore, examples of non-transitory computer-readable media include CD-ROMs (Read Only Memory), CD-Rs, and CD-R / Ws. Furthermore, examples of non-transitory computer-readable media include semiconductor memory. Semiconductor memory includes, for example, mask ROM, PROM (Programmable ROM), EPROM (Erasable PROM), flash ROM, and RAM (Random Access Memory). Programs may also be supplied to object detection devices 10, 30, and 50 by various types of transient computer-readable media. Examples of transient computer-readable media include electrical signals, optical signals, and electromagnetic waves. Transitory computer-readable media can supply programs to object detection devices 10, 30, and 50 via wired communication channels such as electric wires and optical fibers, or via wireless communication channels.

[0081] Alternatively, the object detection devices 10, 30, and 50 of the first to third embodiments may each have the configuration shown in Figure 23. The calculation units 11, 31, and 51, the determination units 12, 32, and 53, and the identification unit 52 of the object detection devices 10, 30, and 50 of the first to third embodiments may each be implemented with dedicated hardware. Furthermore, some or all of the components of each device may be implemented by general-purpose or dedicated circuits, processors, etc., or combinations thereof. These may be configured by a single chip or by multiple chips connected via a bus. Some or all of the components of each device may be implemented by a combination of the above-mentioned circuits, etc., and programs. Furthermore, a CPU (Central Processing Unit), GPU (Graphics Processing Unit), FPGA (field-programmable gate array), quantum processor (quantum computer control chip), etc., can be used as the processor.

[0082] Although the present invention has been described above with reference to embodiments, the present invention is not limited thereto. Various modifications to the structure and details of the present invention can be made within the scope of the invention as can be understood by those skilled in the art. Furthermore, each embodiment can be combined with other embodiments as appropriate.

[0083] Each drawing is merely illustrative to illustrate one or more embodiments. Each drawing may be associated with one or more other embodiments rather than with only one specific embodiment. As those skilled in the art will understand, various features or steps described with reference to any one drawing can be combined with features or steps shown in one or more other drawings, for example, to create embodiments not explicitly shown or described. Not all features or steps shown in any one drawing to illustrate an exemplary embodiment are necessarily required, and some features or steps may be omitted. The order of steps shown in any of the drawings may be changed as appropriate.

[0084] Some or all of the above embodiments may also be described as follows, but are not limited to the following: (Note 1) An object detection device, A first offset function obtained based on the muon spectrum showing the number of muons per muon energy obtained from the measurement of the first charged particle sensor among the first and second charged particle sensors arranged such that their zenith directions perpendicular to the sensor surface coincide, which includes a pair of directions including a first direction perpendicular to the zenith direction and a second direction opposite to the first direction, or a second offset function obtained based on the predicted spectrum obtained from a muon flux model, which corresponds to the difference between the number of muons observed in the first direction and the number of muons observed in the second direction, and both the first offset function and the second offset function, Based on the first muon spectrum and the second muon spectrum for each of the first region and the second region located in the second direction, which are mutually originally symmetric with respect to the origin, which is the intersection point of the zenith axis and the plane, set in a plane that is perpendicular to the zenith axis of the second charged particle sensor within the field of view of the second charged particle sensor, A calculation unit that calculates an index value relating to the non-equivalence between the first region and the second region, A determination unit that determines whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor based on the calculated index value, An object detection device equipped with the following. (Note 2) The calculation unit described above, If we take M (where M is an integer greater than or equal to 2) energy values ​​as the target energy values, In the first muon spectrum, the first sum of the number of first muons corresponding to each target energy value is calculated. In the second muon spectrum, the second sum of the number of second muons corresponding to each target energy value is calculated. A third sum of compensation values ​​is calculated by compensating for the difference between the first muon number and the second muon number for each target energy value based on the first offset function or based on both the first and second offset functions. The ratio of the third sum to the square root of the second sum is calculated as the index value. The object detection device described in Appendix 1. (Note 3) The determination unit determines, if the index value is greater than the threshold, that there is a target object with a density lower than the density of the surrounding material of the second charged particle sensor. The object detection device described in Appendix 2. (Note 4) An object detection device, A calculation unit calculates an expected muon spectrum for the predetermined zenith angle related to the second charged particle sensor, based on a third muon spectrum showing the number of muons per muon energy obtained from measurements taken by the first charged particle sensor at a predetermined zenith angle, among the first and second charged particle sensors arranged such that their zenith directions perpendicular to the sensor surface coincide, and a probability distribution of the amount of energy loss when a muon moves from the position of the first charged particle sensor to the position of the second charged particle sensor. A identifying unit identifies information regarding the direction in which muons corresponding to a muon energy value were observed, which differs by a predetermined number or more from the number of muons in the fourth muon spectrum obtained from measurements taken by the second charged particle sensor for a predetermined zenith angle, A determination unit that determines whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor based on the information regarding the identified direction, An object detection device equipped with the following. (Note 5) The information relating to the direction is a combination of the azimuth angle at which a muon corresponding to a muon energy value in which the number of muons in the fourth muon spectrum differs by a predetermined number or more from the number of muons in the expected muon spectrum is observed, and the predetermined zenith angle. The object detection device described in Appendix 4. (Note 6) The calculation unit calculates the expected muon spectrum for each of the multiple zenith angle candidates, The specified unit identifies information regarding the direction for each candidate zenith angle, The determination unit, A clustering unit that clusters the combinations of azimuth angle and zenith angle candidate information for each zenith angle candidate in a two-dimensional coordinate system in which the direction from the origin corresponds to the azimuth angle and the distance from the origin corresponds to the zenith angle. A determination processing unit determines that if a cluster containing a predetermined number or more of the above combinations exists, the object to be detected is present in the space between the first charged particle sensor and the second charged particle sensor. Equipped with, The object detection device described in Appendix 5. (Note 7) The determination unit includes a creation unit that creates a graph plotting the combinations in a two-dimensional coordinate system where the direction from the origin corresponds to the azimuth angle and the distance from the origin corresponds to the zenith angle. The clustering unit performs clustering based on the graph created. The object detection device described in Appendix 6. (Note 8) The creation unit makes the plot form corresponding to the combination for muons corresponding to muon energy values ​​where the number of muons in the fourth muon spectrum is greater than the number of muons in the expected muon spectrum different from the plot form corresponding to the combination for muons corresponding to muons where the number of muons in the fourth muon spectrum is less than the number of muons in the expected muon spectrum. The object detection device described in Appendix 7. (Note 9) A method performed by an object detection device, A first offset function obtained based on the muon spectrum showing the number of muons per muon energy obtained from the measurement of the first charged particle sensor among the first and second charged particle sensors arranged such that their zenith directions perpendicular to the sensor surface coincide, which includes a pair of directions including a first direction perpendicular to the zenith direction and a second direction opposite to the first direction, or a second offset function obtained based on the predicted spectrum obtained from a muon flux model, which corresponds to the difference between the number of muons observed in the first direction and the number of muons observed in the second direction, and both the first offset function and the second offset function, Based on the first muon spectrum and the second muon spectrum for each of the first region and the second region located in the second direction, which are mutually originally symmetric with respect to the origin, which is the intersection point of the zenith axis and the plane, set in a plane that is perpendicular to the zenith axis of the second charged particle sensor within the field of view of the second charged particle sensor, To calculate an index value relating to the non-equivalence between the first region and the second region, Based on the calculated index value, it is determined whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor. An object detection method that includes [a specific object]. (Note 10) The above calculation is, If we take M (where M is an integer greater than or equal to 2) energy values ​​as the target energy values, To calculate the first sum of the number of first muons corresponding to each target energy value in the first muon spectrum, To calculate the second sum of the number of second muons corresponding to each target energy value in the second muon spectrum, The third sum of compensation values ​​obtained by compensating for the difference between the first muon number and the second muon number for each target energy value based on the first offset function or based on both the first and second offset functions, The ratio of the third sum to the square root of the second sum is calculated as the index value, The object detection method described in Appendix 9, including the method described in Appendix 9. (Note 11) The determination includes determining that if the index value is greater than the threshold, there is a target object with a density lower than the density of the surrounding material of the second charged particle sensor. The object detection method described in Appendix 10. (Note 12) A method performed by an object detection device, Based on a third muon spectrum showing the number of muons per muon energy obtained from measurements taken by the first charged particle sensor at a predetermined zenith angle, among the first and second charged particle sensors arranged so that their zenith directions perpendicular to the sensor surface coincide, and a probability distribution of the amount of energy loss when a muon moves from the position of the first charged particle sensor to the position of the second charged particle sensor, the expected muon spectrum for the predetermined zenith angle related to the second charged particle sensor is calculated. To identify information regarding the direction in which muons corresponding to muons were observed were observed, based on the number of muons in the fourth muon spectrum obtained from the measurement values ​​measured by the second charged particle sensor for the predetermined zenith angle, where the number of muons differs by a predetermined number or more from the number of muons in the expected muon spectrum, Based on the information regarding the identified direction, it is determined whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor. An object detection method that includes [a specific object]. (Note 13) The information relating to the direction is a combination of the azimuth angle at which a muon corresponding to a muon energy value in which the number of muons in the fourth muon spectrum differs by a predetermined number or more from the number of muons in the expected muon spectrum is observed, and the predetermined zenith angle. The object detection method described in Appendix 12. (Note 14) The calculation described above includes calculating the expected muon spectrum for each of the multiple zenith angle candidates, The aforementioned identification includes identifying information regarding the direction for each candidate zenith angle, The object detection method includes clustering the combinations of azimuth angle and zenith angle candidate information related to the direction identified for each zenith angle candidate in a two-dimensional coordinate system in which the direction from the origin corresponds to the azimuth angle and the distance from the origin corresponds to the zenith angle. The determination includes determining that if there are clusters containing a predetermined number or more of the above combinations, the object to be detected is present in the space between the first charged particle sensor and the second charged particle sensor. The object detection method described in Appendix 13. (Note 15) This includes creating a graph by plotting the aforementioned combinations in a two-dimensional coordinate system where the direction from the origin corresponds to the azimuth angle and the distance from the origin corresponds to the zenith angle. The aforementioned clustering includes performing clustering based on the graph created. The object detection method described in Appendix 14. (Note 16) Creating the above involves differentiating the plot form for the combination of muons corresponding to muons where the number of muons in the fourth muon spectrum is greater than the number of muons in the expected muon spectrum, from the plot form for the combination of muons where the number of muons in the fourth muon spectrum is less than the number of muons in the expected muon spectrum. The object detection method described in Appendix 15. (Note 17) A first offset function obtained based on the muon spectrum showing the number of muons per muon energy obtained from the measurement of the first charged particle sensor among the first and second charged particle sensors arranged such that their zenith directions perpendicular to the sensor surface coincide, which includes a pair of directions including a first direction perpendicular to the zenith direction and a second direction opposite to the first direction, or a second offset function obtained based on the predicted spectrum obtained from a muon flux model, which corresponds to the difference between the number of muons observed in the first direction and the number of muons observed in the second direction, and both the first offset function and the second offset function, Based on the first muon spectrum and the second muon spectrum for each of the first region and the second region located in the second direction, which are mutually originally symmetric with respect to the origin, which is the intersection point of the zenith axis and the plane, set in a plane that is perpendicular to the zenith axis of the second charged particle sensor within the field of view of the second charged particle sensor, To calculate an index value relating to the non-equivalence between the first region and the second region, Based on the calculated index value, it is determined whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor. A program that causes an object detection device to perform a process that includes [specific actions]. (Note 18) The above calculation is, If we take M (where M is an integer greater than or equal to 2) energy values ​​as the target energy values, To calculate the first sum of the number of first muons corresponding to each target energy value in the first muon spectrum, To calculate the second sum of the number of second muons corresponding to each target energy value in the second muon spectrum, The third sum of compensation values ​​obtained by compensating for the difference between the first muon number and the second muon number for each target energy value based on the first offset function or based on both the first and second offset functions, The ratio of the third sum to the square root of the second sum is calculated as the index value, The programs listed in Appendix 17, including the program described therein. (Note 19) The determination includes determining that if the index value is greater than the threshold, there is a target object with a density lower than the density of the surrounding material of the second charged particle sensor. The program described in Appendix 18. (Note 20) Based on a third muon spectrum showing the number of muons per muon energy obtained from measurements taken by the first charged particle sensor at a predetermined zenith angle, among the first and second charged particle sensors arranged so that their zenith directions perpendicular to the sensor surface coincide, and a probability distribution of the amount of energy loss when a muon moves from the position of the first charged particle sensor to the position of the second charged particle sensor, the expected muon spectrum for the predetermined zenith angle related to the second charged particle sensor is calculated. To identify information regarding the direction in which muons corresponding to muons were observed were observed, based on the number of muons in the fourth muon spectrum obtained from the measurement values ​​measured by the second charged particle sensor for the predetermined zenith angle, where the number of muons differs by a predetermined number or more from the number of muons in the expected muon spectrum, Based on the information regarding the identified direction, it is determined whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor. A program that causes an object detection device to perform a process that includes [specific actions]. (Note 21) The information relating to the direction is a combination of the azimuth angle at which a muon corresponding to a muon energy value in which the number of muons in the fourth muon spectrum differs by a predetermined number or more from the number of muons in the expected muon spectrum is observed, and the predetermined zenith angle. The program described in Appendix 20. (Note 22) The calculation described above includes calculating the expected muon spectrum for each of the multiple zenith angle candidates, The aforementioned identification includes identifying information regarding the direction for each candidate zenith angle, The process includes clustering the combinations of azimuth angle and zenith angle candidate information for each zenith angle candidate in a two-dimensional coordinate system in which the direction from the origin corresponds to the azimuth angle and the distance from the origin corresponds to the zenith angle. The determination includes determining that if there are clusters containing a predetermined number or more of the above combinations, the object to be detected is present in the space between the first charged particle sensor and the second charged particle sensor. The program described in Appendix 21. (Note 23) The process described above includes creating a graph by plotting the combinations in a two-dimensional coordinate system in which the direction from the origin corresponds to the azimuth angle and the distance from the origin corresponds to the zenith angle. The aforementioned clustering includes performing clustering based on the graph created. The program described in Appendix 21. (Note 24) Creating the above involves differentiating the plot form for the combination of muons corresponding to muons where the number of muons in the fourth muon spectrum is greater than the number of muons in the expected muon spectrum, from the plot form for the combination of muons where the number of muons in the fourth muon spectrum is less than the number of muons in the expected muon spectrum. The program described in Appendix 23. [Explanation of symbols]

[0085] 1 System 10 Object detection device 11 Calculation Section 12 Judgment section 20 Measuring instruments 30 Object detection device 31 Calculation Section 32 Judgment section 50 Object detection device 51 Calculation Section 52 Specific part 53 Judgment section 53A Creation Section 53B Clustering section 53C Determination Processing Unit

Claims

1. An object detection device, A first offset function obtained based on the muon spectrum showing the number of muons per muon energy obtained from the measurement of the first charged particle sensor among the first and second charged particle sensors arranged such that their zenith directions perpendicular to the sensor surface coincide, which includes a pair of directions including a first direction perpendicular to the zenith direction and a second direction opposite to the first direction, or a second offset function obtained based on the predicted spectrum obtained from a muon flux model, which corresponds to the difference between the number of muons observed in the first direction and the number of muons observed in the second direction, and both the first and second offset functions, Based on the first muon spectrum and the second muon spectrum for each of the first region and the second region located in the second direction, which are mutually originally symmetric with respect to the origin, which is the intersection point of the zenith axis and the plane set in a plane perpendicular to the zenith axis of the second charged particle sensor within the field of view of the second charged particle sensor, A calculation unit that calculates an index value relating to the non-equivalence between the first region and the second region, A determination unit that determines whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor based on the calculated index value, An object detection device equipped with the following.

2. The calculation unit described above, When M (where M is an integer greater than or equal to 2) energy values ​​are taken as target energy values, In the first muon spectrum, the first sum of the number of first muons corresponding to each target energy value is calculated. In the second muon spectrum, the second sum of the number of second muons corresponding to each target energy value is calculated. A third sum of compensation values ​​is calculated by compensating for the difference between the first muon number and the second muon number for each target energy value based on the first offset function or based on both the first and second offset functions. The ratio of the third sum to the square root of the second sum is calculated as the index value. The object detection device according to claim 1.

3. The determination unit determines, if the index value is greater than the threshold, that there is a target object with a density lower than the density of the surrounding material of the second charged particle sensor. The object detection device according to claim 2.

4. An object detection device, A calculation unit calculates an expected muon spectrum for the predetermined zenith angle related to the second charged particle sensor, based on a third muon spectrum showing the number of muons for each muon energy obtained from a measurement taken by the first charged particle sensor at a predetermined zenith angle among a first and second charged particle sensor arranged such that their zenith directions perpendicular to the sensor surface coincide, and a probability distribution of the amount of energy loss when a muon moves from the position of the first charged particle sensor to the position of the second charged particle sensor. A identifying unit identifies information regarding the direction in which muons corresponding to a muon energy value were observed, which differs by a predetermined number or more from the number of muons in the fourth muon spectrum obtained from the measurement value measured by the second charged particle sensor for the predetermined zenith angle, A determination unit that determines whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor based on the information regarding the identified direction, An object detection device equipped with the following.

5. The information relating to the direction is a combination of the azimuth angle at which a muon corresponding to a muon energy value in which the number of muons in the fourth muon spectrum differs by a predetermined number or more from the number of muons in the expected muon spectrum is observed, and the predetermined zenith angle. The object detection device according to claim 4.

6. The calculation unit calculates the expected muon spectrum for each of the multiple zenith angle candidates, The specified unit identifies information regarding the direction for each candidate zenith angle, The determination unit, A clustering unit that clusters the combinations of azimuth angle and zenith angle candidate information for each zenith angle candidate in a two-dimensional coordinate system in which the direction from the origin corresponds to the azimuth angle and the distance from the origin corresponds to the zenith angle, A determination processing unit determines that if a cluster containing a predetermined number or more of the above combinations exists, the object to be detected is present in the space between the first charged particle sensor and the second charged particle sensor. Equipped with, The object detection device according to claim 5.

7. The determination unit includes a creation unit that creates a graph plotting the combinations in a two-dimensional coordinate system where the direction from the origin corresponds to the azimuth angle and the distance from the origin corresponds to the zenith angle. The clustering unit performs clustering based on the graph created. The object detection device according to claim 6.

8. The creation unit makes the plot form corresponding to the combination for muons corresponding to muon energy values ​​where the number of muons in the fourth muon spectrum is greater than the number of muons in the expected muon spectrum different from the plot form corresponding to the combination for muons corresponding to muons where the number of muons in the fourth muon spectrum is less than the number of muons in the expected muon spectrum. The object detection device according to claim 7.

9. A method performed by an object detection device, A first offset function obtained based on the muon spectrum showing the number of muons per muon energy obtained from the measurement of the first charged particle sensor among the first and second charged particle sensors arranged such that their zenith directions perpendicular to the sensor surface coincide, which includes a pair of directions including a first direction perpendicular to the zenith direction and a second direction opposite to the first direction, or a second offset function obtained based on the predicted spectrum obtained from a muon flux model, which corresponds to the difference between the number of muons observed in the first direction and the number of muons observed in the second direction, and both the first and second offset functions, Based on the first muon spectrum and the second muon spectrum for each of the first region and the second region located in the second direction, which are mutually originally symmetric with respect to the origin, which is the intersection point of the zenith axis and the plane set in a plane perpendicular to the zenith axis of the second charged particle sensor within the field of view of the second charged particle sensor, To calculate an index value relating to the non-equivalence between the first region and the second region, Based on the calculated index value, it is determined whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor. An object detection method that includes [a specific object].

10. A first offset function obtained based on the muon spectrum showing the number of muons per muon energy obtained from the measurement of the first charged particle sensor among the first and second charged particle sensors arranged such that their zenith directions perpendicular to the sensor surface coincide, which includes a pair of directions including a first direction perpendicular to the zenith direction and a second direction opposite to the first direction, or a second offset function obtained based on the predicted spectrum obtained from a muon flux model, which corresponds to the difference between the number of muons observed in the first direction and the number of muons observed in the second direction, and both the first and second offset functions, Based on the first muon spectrum and the second muon spectrum for each of the first region and the second region located in the second direction, which are mutually originally symmetric with respect to the origin, which is the intersection point of the zenith axis and the plane set in a plane perpendicular to the zenith axis of the second charged particle sensor within the field of view of the second charged particle sensor, To calculate an index value relating to the non-equivalence between the first region and the second region, Based on the calculated index value, it is determined whether or not a target object exists in the space between the first charged particle sensor and the second charged particle sensor. A program that causes an object detection device to perform a process that includes [specific actions].

Images