JP5962036B2 - Magnetic detection system - Google Patents

Description

  The present invention relates to a magnetic detection system, and more particularly to a magnetic detection system that includes a magnetic sensor and detects a magnetic material.

  2. Description of the Related Art Conventionally, a magnetic detection system that includes a magnetic sensor and detects a magnetic substance is known (see, for example, Patent Document 1).

  Patent Document 1 discloses a magnetic detection system including a magnetic sensor, a likelihood ratio calculation circuit, a reference signal storage circuit, and a comparison circuit. Here, in the installation environment of the magnetic sensor, various noises (noise) due to geomagnetic fluctuations and the like exist. For this reason, in order to detect the magnetic material, the magnetic waveform measured by the magnetic sensor is a waveform (with a signal) in which a signal and noise caused by the magnetic material to be detected are mixed, or It is necessary to determine whether the waveform is composed only of noise (no signal). In this magnetic detection system, magnetic waveform data of a magnetic sensor and reference signal waveform (signal waveform when a magnetic material is detected) data stored in a reference signal storage circuit are input to a likelihood ratio calculation circuit. The likelihood ratio of whether or not a reference signal waveform (signal waveform when a magnetic material is detected) exists in the waveform data is calculated. In the magnetic detection system according to Patent Document 1, the calculated likelihood ratio is input to the comparison circuit, and when the likelihood ratio is larger than a predetermined threshold, it is determined that there is a signal (magnetic body is detected). When the likelihood ratio is equal to or less than a predetermined threshold value, it is determined that there is no signal (no magnetic material is detected).

JP-A-8-304556

  However, in a magnetic sensor installation environment, various noises (noise) constantly exist, and when this noise fluctuation occurs, it resembles a signal waveform (reference signal waveform) when a magnetic material is detected from the magnetic sensor. In some cases, a noise waveform (a waveform resulting from noise fluctuation) is output. In such a case, in Patent Document 1, the likelihood ratio exceeds the threshold value even when the magnetic waveform data of the magnetic sensor is only noise (a waveform resulting from noise fluctuation), and there is a signal (there is detection of a magnetic substance). ) May be erroneously detected.

  The present invention has been made to solve the above-described problems, and one object of the present invention is to provide a magnetic detection system capable of suppressing erroneous detection due to noise fluctuation. is there.

In order to achieve the above object, a magnetic detection system according to one aspect of the present invention includes a magnetic sensor and a calculation unit that performs a first calculation relating to a degree of approximation between a magnetic waveform measured by the magnetic sensor and a predictable noise fluctuation. And at least a determination means for making a determination related to detection of a magnetic signal based on the result of the first calculation. The calculation means is caused by the magnetic waveform and the magnetic material measured by the magnetic sensor in addition to the first calculation. Is configured to perform a second calculation regarding the degree of approximation with a theoretical standard waveform to be performed, and when performing a determination regarding detection of a magnetic signal, the determination means includes a magnetic signal based on the result of the second calculation. performing a first determination whether to, if it is determined that the magnetic signal by first determining the presence, based on the first calculation result, as to whether the measured magnetic waveform caused by noise variance 2 have line determination, in accordance with the second determination results, determining that detects a magnetic signal, or has been detected magnetic signals is determined to be likely due to noise fluctuations, the first determination When it is determined that there is no magnetic signal, it is determined that the magnetic signal is not detected without performing the second determination .

In the magnetic detection system according to one aspect of the present invention, as described above, the calculation means for performing the first calculation regarding the degree of approximation between the magnetic waveform measured by the magnetic sensor and the predictable noise fluctuation, and at least the first calculation Based on the result, it is possible to determine whether or not the measured magnetic waveform approximates a predictable noise fluctuation by providing a determination unit that performs determination regarding detection of the magnetic signal. As a result, even when a magnetic waveform that is determined to have a signal (magnetic material is detected) is measured, it is determined as a result of the first calculation that it approximates a predictable noise fluctuation. In this case, since it can be determined that the measured magnetic waveform is highly likely to be caused by noise fluctuation, erroneous detection caused by noise fluctuation can be suppressed. Further, from the result of the second calculation, it is determined whether or not the measured magnetic waveform approximates a theoretical standard waveform caused by the magnetic material (whether or not there is a signal (the magnetic material is detected)). It is possible to determine whether or not there is a high possibility of erroneous detection due to noise fluctuation from the result of the first calculation. Thereby, since the signal resulting from a magnetic body can be detected, suppressing the misdetection determination resulting from a noise fluctuation, the signal resulting from a magnetic body can be detected accurately.

  In this case, preferably, the first calculation includes a calculation related to a first likelihood ratio between the magnetic waveform measured by the magnetic sensor and a predictable noise fluctuation, and the second calculation is a magnetic waveform measured by the magnetic sensor. And a calculation related to the second likelihood ratio between the magnetic standard and the theoretical standard waveform, and the determination means is based on the result of the calculation related to the first likelihood ratio and the result of the calculation related to the second likelihood ratio. Thus, the determination regarding the detection of the magnetic signal is performed. If comprised in this way, the result of a 1st calculation and the result of a 2nd calculation can both be obtained by likelihood ratio calculation (calculation regarding a 1st likelihood ratio and a 2nd likelihood ratio). For this reason, compared with the case where a 1st calculation and a 2nd calculation are each performed by a different kind of calculation process, a calculation process can be simplified.

  In the configuration in which the determination unit performs the determination regarding the detection of the magnetic signal based on the result of the calculation regarding the first likelihood ratio and the result of the calculation regarding the second likelihood ratio, preferably the determination unit includes the second likelihood. It is configured to determine that a magnetic signal has been detected when the calculation result related to the ratio is equal to or greater than the first threshold value and the calculation result related to the first likelihood ratio is less than the second threshold value. ing. If comprised in this way, when the result of the calculation regarding a 2nd likelihood ratio is more than a 1st threshold value, and the result of the calculation regarding a 1st likelihood ratio is less than a 2nd threshold value, The measured magnetic waveform is approximated to a standard waveform caused by a magnetic material, and it is considered that there is no predictable noise fluctuation (not approximating predictable noise fluctuation). While confirming that there is no false detection due to noise fluctuation, it is possible to detect a signal due to the magnetic material.

  In the configuration in which the determination unit performs the determination regarding the detection of the magnetic signal based on the result of the calculation regarding the first likelihood ratio and the result of the calculation regarding the second likelihood ratio, preferably the determination unit includes the second likelihood. When the calculation result related to the ratio is equal to or greater than the first threshold value and the calculation result related to the first likelihood ratio is equal to or greater than the second threshold value, the magnetic signal is detected but may be caused by noise fluctuation It is comprised so that it may determine with the property. If comprised in this way, when the result of the calculation regarding a 2nd likelihood ratio is more than a 1st threshold value, and the result of the calculation regarding a 1st likelihood ratio is more than a 2nd threshold value, While the measured magnetic waveform approximates to the standard waveform due to the magnetic material, it is considered that the measured noise waveform also approximates the predictable noise fluctuation, so the detected signal can easily be attributed to noise fluctuation. It can be determined to be high. Thereby, the erroneous detection resulting from a noise fluctuation | variation can be suppressed easily.

  In the configuration in which the determination unit performs the determination regarding the detection of the magnetic signal based on the result of the calculation regarding the first likelihood ratio and the result of the calculation regarding the second likelihood ratio, preferably the determination unit includes the second likelihood. When the calculation result regarding the ratio is less than the first threshold value, it is determined that the magnetic signal is not detected. With this configuration, when the calculation result related to the second likelihood ratio is less than the first threshold value, the waveform caused by the magnetic material does not exist in the originally measured magnetic waveform (approximate to the standard waveform). Therefore, it can be easily determined that the magnetic signal is not detected.

  In the configuration in which the determination unit determines whether the result of the calculation related to the second likelihood ratio is equal to or greater than the first threshold value, preferably, a plurality of theoretical standard waveforms resulting from the magnetic material are set. Each of the theoretical standard waveforms resulting from a plurality of types of magnetic materials is weighted, and a first threshold value is individually set for each theoretical standard waveform in accordance with the weighting. If comprised in this way, even if the standard waveform suitable for the detection of a magnetic body changes with installation environments etc. of a magnetic sensor, a detection determination can be performed appropriately by using a some standard waveform. In addition, weighting is performed for each standard waveform, and the first threshold value corresponding to the weight is individually set for each standard waveform, so that the weight is appropriately set according to the appropriate degree of detection of the magnetic substance in each standard waveform. Since the first threshold value can be set, the detection accuracy of the magnetic material can be improved.

  In the configuration in which the determination unit performs the determination regarding the detection of the magnetic signal based on the result of the calculation regarding the first likelihood ratio and the result of the calculation regarding the second likelihood ratio, preferably, the determination unit includes the first likelihood In addition to the calculation result related to the ratio and the calculation result related to the second likelihood ratio, the determination regarding the detection of the magnetic signal is made based on the comparison result between the magnetic waveform data measured by the magnetic sensor and the third threshold value. Configured to do. If comprised in this way, in addition to likelihood ratio, the comparison result of measured magnetic waveform data and a 3rd threshold value will also be considered, and the determination of the signal detection resulting from a magnetic body from many aspects will be carried out. Therefore, the detection accuracy of the magnetic material can be further improved.

  In the magnetic detection system according to the above aspect, the predictable noise fluctuation preferably includes noise fluctuation when the magnetic sensor is shaken in the sea, noise fluctuation caused by power flow and swell, and noise fluctuation generated from the magnetic sensor. Including at least one of them. If configured in this way, noise fluctuations that occur when a magnetic sensor is installed in the sea, such as noise fluctuations when the magnetic sensor shakes in the sea, noise fluctuations caused by tidal currents and undulations (predictable noise fluctuations) Therefore, it is possible to effectively suppress false detection caused by noise fluctuation in the sea. In addition, erroneous detection due to noise fluctuations generated from the magnetic sensor itself can be suppressed.

  The magnetic detection system according to the above aspect preferably further includes a storage unit for storing predictable noise fluctuations in advance, and the calculation means uses the predictable noise fluctuations stored in the storage unit, It is configured to perform one operation. If comprised in this way, a 1st calculation can be easily performed by storing the noise fluctuation | variety which can be estimated beforehand in a memory | storage part. As a result, it is possible to easily determine whether or not the measured magnetic waveform is highly likely to be caused by noise fluctuation using the first calculation result.

  Preferably, the magnetic detection system according to the above aspect further includes a notifying unit for notifying a determination result related to the detection of the magnetic signal by the determination means, and detecting the magnetic signal as the determination regarding the detection of the magnetic signal, but due to noise fluctuation When it is determined that the possibility is high, it is possible to set whether to perform notification by the notification unit. If comprised in this way, a user will set whether to notify the judgment result as needed, when it is judged that a magnetic signal was detected but possibility that it originates in noise fluctuation is high. Therefore, the convenience of the magnetic detection system for the user can be improved.

  According to the present invention, as described above, erroneous detection due to noise fluctuation can be suppressed.

1 is a schematic diagram illustrating an overall configuration of a magnetic detection system according to an embodiment of the present invention. FIG. 2 is a block diagram of a magnetic sensing system according to the embodiment shown in FIG. 1. It is a figure which shows an example of the observation data (magnetic waveform data) of the magnetic detection system by one Embodiment shown in FIG. It is a figure which shows an example of the standard waveform used for the magnetic detection system by one Embodiment shown in FIG. It is a figure which shows an example of the standard noise waveform used for the magnetic detection system by one Embodiment shown in FIG. It is a flowchart for demonstrating the signal detection determination process of the magnetic detection system by one Embodiment of this invention.

  DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments embodying the present invention will be described below with reference to the drawings.

  First, with reference to FIGS. 1-5, the whole structure of the magnetic detection system 100 by one Embodiment of this invention is demonstrated.

  A magnetic detection system 100 according to the present embodiment includes a plurality of magnetic sensors 1 and a computer 2 as shown in FIG. In the present embodiment, an example of a magnetic detection system in which a plurality of magnetic sensors 1 are installed in the sea (such as the seabed) and detect a magnetic body (detection target) that passes through the vicinity of the magnetic sensor 1 will be described.

  The plurality of magnetic sensors 1 are installed in the sea (such as the seabed) apart from each other, and are wired to the computer 2. The magnetic waveform (observation data) (see FIG. 3) measured by each magnetic sensor 1 is configured to be output to a computer 2 installed on land. As shown in FIG. 2, the magnetic sensor 1 is formed of, for example, a fluxgate type sensor and includes a low-pass filter (LPF) 1a. The low-pass filter 1a has a function of removing high-frequency noise components. For this reason, the magnetic sensor 1 outputs data after passing through the low-pass filter 1a and removing high-frequency noise components to the computer 2 as observation data (see FIG. 3).

  The computer 2 includes a control unit 3 that performs detection determination of a magnetic body based on observation data acquired from each of the plurality of magnetic sensors 1, a memory 4, and a display unit 5 that displays determination results, observation waveforms, and the like by the control unit 3. And. The captured data is stored in the memory 4, and various data 4 a to 4 c (details will be described later), a signal detection determination program 4 d, and the like used for arithmetic processing of the control unit 3 are stored in advance. The control unit 3 is an example of the “calculation unit” and “determination unit” of the present invention. The memory 4 and the display unit 5 are examples of the “storage unit” and the “notification unit” of the present invention, respectively.

  In the present embodiment, the control unit 3 functions as a calculation unit that performs calculation processing to be described later on the observation data captured from each of the plurality of magnetic sensors 1 based on the signal detection determination program 4 d stored in the memory 4. In addition, the magnetic sensor 1 is configured to function as a determination unit that determines whether or not the magnetic body is detected by the magnetic sensor 1 based on the calculation processing result. The control unit 3 is configured to perform three types of detection determination on the observation data acquired from each magnetic sensor 1.

  First, as the first detection determination, FD determination is performed in which signal detection is performed by comparing the latest value (FD value) of measured observation data with the FD threshold value. In the FD determination, when the latest value (FD value) of the observation data having the signal level exceeding the FD threshold is acquired, it is determined that the signal is detected. The FD threshold value is an example of the “third threshold value” in the present invention.

  As the second detection determination, signal detection determination is performed based on the degree of approximation between the magnetic waveform (observation data) measured by the magnetic sensor 1 and the standard waveform that is a theoretical waveform of the magnetic signal caused by the magnetic material. Is called. Specifically, as the second detection determination, an LR determination is performed in which the calculation result (LR value) obtained by the likelihood ratio calculation process for the observation data is compared with the LR threshold value. The calculation result (LR value) of the likelihood ratio calculation process increases as the magnetic waveform of the observation data approximates the standard waveform. For this reason, when the LR value is equal to or greater than the LR threshold value, it is determined that a signal (magnetic signal due to the magnetic material) exists in the observation data. The LR threshold value is an example of the “first threshold value” in the present invention.

  In the present embodiment, as shown in FIG. 4, LR determination is performed using a plurality of types of standard waveforms 1 to 3. Here, the signal waveform (magnetic waveform) when the magnetic material passes in the vicinity of the magnetic sensor 1 shows a specific waveform such as a sine wave. Further, the period of the magnetic waveform measured when the magnetic material passes is not necessarily constant, and a waveform having a relatively short period (standard waveform 2 in FIG. 4) is measured as a signal caused by the magnetic material. In some cases, a waveform having a relatively long period (standard waveform 3 in FIG. 4) is measured. Therefore, a plurality of patterns of standard waveforms (standard waveform data 1 to x; x pieces (three pieces in the present embodiment)) having different periods are registered in advance and stored in the memory 4.

  When LR determination is performed using such a plurality of standard waveforms, there is a difference in the ease of detection of the magnetic material for each standard waveform due to the difference in the installation environment of the magnetic sensor 1. For this reason, in this embodiment, weighting is performed for each standard waveform according to the ease of detection of the magnetic material for each standard waveform, and the LR threshold value is set to a value according to the weighting of the standard waveform. Are set individually. Accordingly, x LR threshold values 1 to x are stored in the memory 4 corresponding to the standard waveform data 1 to x. As an example of weighting, for example, when there is a tendency that a relatively large number of short-period magnetic waveforms are measured in the sensor installation environment on the seabed in a certain area, a standard with a shorter period than a standard waveform with a long period is used. The waveform weight is increased and the LR threshold value is set larger.

  In the present embodiment, in addition to the first detection determination (FD determination) and the second detection determination (LR determination), the observation data (magnetic waveform) measured by the magnetic sensor 1 is used as the third detection determination. Based on the degree of approximation with the standard noise waveform, noise fluctuation detection determination is performed. Specifically, the LRn determination is performed by comparing the calculation result (LRn value) obtained by the likelihood ratio calculation process with respect to the observation data using the standard noise waveform and the LRn threshold value. The LRn threshold value is an example of the “second threshold value” in the present invention. Here, the standard noise waveform is a noise waveform resulting from noise fluctuation that can be predicted in consideration of the installation environment of each magnetic sensor 1 and the like.

  Standard noise waveforms include noise fluctuation waveforms that can be predicted experimentally and theoretically for physical fluctuations (position fluctuations) of the magnetic sensor 1, such as noise fluctuations when the magnetic sensor 1 shakes in the sea. In addition, noise fluctuation waveforms that can be empirically predicted from observation data over a long period of time, such as noise fluctuation due to the influence of undulation and noise fluctuation generated from the magnetic sensor 1, are included.

  An example of a standard noise waveform is shown in FIG. Noise fluctuation when the magnetic sensor 1 is shaken in the sea is generated when the position (posture) of the magnetic sensor 1 is changed due to the magnetic sensor 1 being shaken by an external force applied to the magnetic sensor 1 due to an ocean current or the like. The noise waveform observed due to the noise fluctuation during the oscillation of the magnetic sensor 1 in the sea is a relatively steep falling edge 101a as shown in the two standard noise waveforms (a) and (b) of FIG. And waveforms 101 and 102 with rising edge 102a and falling edge 101a and slow attenuation 101b and 102b after rising edge 102a, respectively.

  In addition, as shown in FIG. 5C, the noise waveform observed due to the noise fluctuation due to the influence of power flow and undulation is the noise (see FIG. 3) that is constantly observed and the standard noise waveform ( Unlike a) and (b), it has a sharp waveform with a very short period (high frequency) at a minute level. Note that such a high-frequency standard noise waveform (c) at such a minute level remains even after passing through the low-pass filter 1 a of the magnetic sensor 1. In addition, in the noise fluctuation due to the influence of the power flow and the swell, the amplitude of the noise waveform increases according to the strength of the swell effect.

  The noise fluctuation generated from the magnetic sensor 1 is a noise fluctuation rarely generated (observed) from the magnetic sensor 1 during observation over a long period of time. As shown in (d) and (e) of FIG. 5, the noise waveform observed due to the noise fluctuation generated from the magnetic sensor 1 has both a steep rise and a fall of the signal waveform and a relatively leading edge. It has pointed waveforms 201 and 202.

  Such a plurality (y (in this embodiment, 5)) of noise waveforms are acquired in advance as standard noise waveforms and stored in the memory 4 respectively. In these standard noise waveforms, separate LRn threshold values 1 to y are preset in accordance with each standard noise waveform.

  Here, in this embodiment, when it is determined in the third detection determination (LRn determination) that the degree of approximation between the observation data and the standard noise waveform is high, signal detection is performed in the second detection determination (LR determination). Even when the determination is made, it is determined that there is a high possibility that the detected signal is caused by noise fluctuation (high possibility of erroneous detection). In this case, the control unit 3 notifies the operator together with the detection result that the detected signal is likely to be caused by noise fluctuation based on the notification setting preset by the operator and recorded in the memory 4. Or the process of ending the detection determination without notifying is performed. The notification to the operator is performed by the screen display of the display unit 5.

  The memory 4 stores x standard waveforms used in the second detection determination (LR determination) as the standard waveform data (1 to x) 4a and the third detection determination (LRn determination). The y standard noise waveforms used are stored as standard noise waveform data (1 to y) 4b. Further, the memory 4 stores threshold data (FD threshold value, LR threshold value 1 to x, LRn threshold value 1 to y) 4c in each detection determination. These threshold data 4c are acquired theoretically or experimentally in advance.

  Next, arithmetic expressions and determination methods used for LR determination and LRn determination will be described in detail.

  First, the magnetic waveform FD (t) observed by the magnetic sensor 1 can be expressed by the following formula (1). That is, as shown in FIG. 3, the magnetic waveform observed by the magnetic sensor 1 includes a signal (a signal component indicated by a broken line in FIG. 3) caused by a magnetic body (detection target) that passes in the vicinity of the magnetic sensor 1, and It can be expressed as a sum with stationary noise.

ここで、Ｓ（ｔ）は磁気センサ１の近傍を通過する磁性体に起因する信号であり、Ｎｏｉｓｅ（ｔ）は雑音である。磁気センサ１の近傍を通過する磁性体が存在しなければ、信号Ｓ（ｔ）は０になる。

Here, S (t) is a signal caused by the magnetic material passing in the vicinity of the magnetic sensor 1, and Noise (t) is noise. If there is no magnetic material passing near the magnetic sensor 1, the signal S (t) becomes zero.

That is, when a signal S (k) due to a magnetic substance (detection target) is included in the magnetic waveform FD (k) at a certain time t = k, the magnetic waveform FD (k) is expressed by the following formula ( 2). This corresponds to the sum of the signal and noise in FIG.

On the other hand, when the signal S (k) due to the magnetic material (detection target) is not included in the magnetic waveform FD (k), the magnetic waveform FD (k) is expressed by the following equation (3). . This corresponds to the noise-only state of FIG.

  Therefore, in the LR determination, it is determined whether FD (k) at the time point k is a state expressed by Equation (2) or a state expressed by Equation (3). In the LR determination according to the present embodiment, a likelihood ratio Λ (the following equation (4)) which is a ratio between the probability density function of the state expressed by Equation (2) and the probability density function of the state expressed by Equation (3). )) Is used to determine the state of Expression (2) or Expression (3) based on the calculation result (LR value (see Expression (7) described later)) regarding the likelihood ratio Λ.

The likelihood ratio function Λ _k (likelihood ratio Λ at time k) obtained based on the expression (4) is expressed by the following expressions (5) and (6). Note that, in the equations (5) and (6), since it is assumed that the noise is white noise, the observation data (observation waveform FD) passes through a shaping filter for whitening the noise.

ここで、
β ：成形フィルタ定数
Ｔ ：標準波形の周期
ｈ_ｉ ：標準波形の成形フィルタ通過後の値
Ｚ_ｉ ：観測データの成形フィルタ通過後の値
Ｓ_ｉ ：標準波形データ
ＦＤ_ｉ ：観測データ
Δｔ ：サンプリングタイム
である。

here,
β : Molding filter constant T : Period of standard waveform h _i : value after passing through shaping filter of standard waveform Z _i : value after passing through shaping filter of observation data S _i : standard waveform data FD _i : observation data Δt : Sampling time.

Since the observation data affects only the first term on the right side at L _k in the above equation (6), the first term on the right side is set as the LR value. Since the second term on the right side of L _{k in} the above equation (6) is determined by the standard waveform data (known) for one period acquired in advance, it can be regarded as a constant. For this reason, it is possible to evaluate the likelihood ratio as to whether or not a signal (standard waveform) caused by the magnetic material is included in the observation data by the following equation (7) for obtaining the LR value. The calculation of the LR value according to the equation (7) is an example of the “second calculation” and the “calculation related to the second likelihood ratio” of the present invention.

ここで、ＬＲ_ｋは、時刻ｋにおけるＬＲ値である。

Here, LR _k is an LR value at time k.

  In the above equation (7), the LR value increases as the measured magnetic waveform (observation data) approximates the standard waveform used in the calculation. In this case, there is a high possibility (likelihood) that the signal S (standard waveform) represented by Expression (2) is included. On the other hand, when the measured magnetic waveform (observation data) does not approximate the standard waveform used in the calculation, the LR value becomes small and does not include the signal S (standard waveform) expressed by Equation (3). The possibility (likelihood) of being increased.

  Therefore, in the present embodiment, the LR values (LR1 to LRx) calculated using a plurality (x) of standard waveform data and the LR threshold values (1 to x) corresponding to the standard waveform data are obtained. In comparison, it is determined that a signal caused by the magnetic material has been detected when any one of the LR values (LR1 to LRx) is equal to or greater than the LR threshold value (1 to x). That is, it determines with it being the state of Formula (2).

  On the other hand, in the LRn determination (third detection determination), the likelihood ratio calculation process is performed on the observation data using the standard noise waveform (predictable noise fluctuation waveform) data, and the LRn value is calculated as the calculation result. To do. The formula for calculating the LRn value in this case is the following formula (8). This equation (8) is an equation in which the value relating to the standard waveform is replaced with the value relating to the standard noise waveform in the LR value calculation equation according to the above equation (7), and is basically the same as the equation (7) above. It is. The calculation of the LRn value according to the equation (8) is an example of the “first calculation” and the “calculation related to the first likelihood ratio” in the present invention.

ここで、
ＬＲｎ_ｋ ：時刻ｋにおけるＬＲｎ値
β ：成形フィルタ定数
Ｔｎ ：標準ノイズ波形の周期
ｈｎ_ｉ ：標準ノイズ波形の成形フィルタ通過後の値
Ｚ_ｉ ：観測データの成形フィルタ通過後の値
Ｓｎ_ｉ ：標準ノイズ波形データ
ＦＤ_ｉ ：観測データ
Δｔ ：サンプリングタイム
である。

here,
LRn _k : LRn value β at time k : Molding filter constant Tn : Period of standard noise waveform hn _i : value after passing through shaping filter of standard noise waveform Z _i : value after passing through shaping filter of observation data Sn _i : standard noise waveform data FD _i : observation data Δt : Sampling time.

  In the LRn determination, by using a standard noise waveform as the signal S in the equations (2) and (3), whether or not the standard noise waveform exists in the observation data (the waveform of the observation data is caused by noise fluctuation). The likelihood ratio of whether or not there is a high possibility of being present) is determined. For this reason, the LRn value increases as the measured magnetic waveform (observation data) approximates the standard noise waveform used in the calculation. In this case, there is a high possibility (likelihood) that the standard noise waveform is included. On the other hand, when the waveform of the observation data is not approximated with the standard noise waveform used in the calculation, the LRn value becomes small, and the possibility (likelihood) that the standard noise waveform is not included increases.

  Therefore, in the present embodiment, LRn values (LRn1 to LRny) calculated using a plurality (y) of standard noise waveform data, and LRn threshold values (1 to y) set for each standard noise waveform data. When one of the LRn values (LRn1 to LRny) is equal to or higher than the corresponding LRn threshold value (1 to y), there is a high possibility that the waveform of the observation data is caused by noise fluctuation. Is determined.

  Next, the signal detection determination process by the magnetic detection system 100 of this embodiment is demonstrated using the flowchart of FIG. In addition, in order to perform the same signal detection determination process for every some magnetic sensor 1, below, the signal detection determination process about one of the some magnetic sensors 1 is demonstrated. Further, the following signal detection determination process is executed by the control unit 3 based on the signal detection determination program 4 d stored in the memory 4.

  As shown in FIG. 6, first, in step S1, observation data from the magnetic sensor 1 is acquired. The acquired observation data is stored in the memory 4 in step S2. The memory 4 sequentially stores and accumulates observation data acquired every moment. Observation data for a certain period (the period T of the standard waveform data and the period Tn of the standard noise waveform data) stored in the memory 4 is used for calculating the LR value and the LRn value.

  In step S3, the observation data stored in the memory 4 is read, and the latest observation data is acquired as an FD value. Further, x standard waveform data (1 to x) and observation data for one period (T) of each standard waveform data (1 to x) are read from the memory 4 and each standard waveform data is used. Calculation processing of the LR values (LR1 to LRx) (see the above formula (7)) is executed. Thereby, the likelihood ratio calculation result (LR value) between the observation data and the standard waveform is acquired. The obtained FD values and x LR values (LR1 to LRx) are stored in the memory 4 in step S4.

  Next, in step S5, y standard noise waveform data (1 to y) and observation data for one period (Tn) of each standard noise waveform data (1 to x) are read from the memory 4, LRn values (LRn1 to LRny) are calculated using each standard noise waveform data (see the above equation (8)). Thereby, the likelihood ratio calculation result (LRn value) between the observation data and the standard noise waveform is acquired. The obtained y LRn values (LRn1 to LRny) are stored in the memory 4 in step S6.

  Next, in step S7, the FD value, the x LR values (LR1 to LRx), and the y LRn values (LRn1 to LRny) are read from the memory 4.

  In step S8, the control unit 3 reads the detection state setting (whether or not the “detecting” state of the signal is set) (step S15 and step S19) based on the signal detection determination result described later (step S15 and step S19) from the memory 4, and Check if it is set to “Detecting” status. If the signal detection state is set, the process proceeds to step S9 to determine whether or not a predetermined release condition is satisfied.

  The release condition for the “detecting” state is that a predetermined time has elapsed since the signal was detected, the FD value is less than the FD threshold value, and x LRs The value (LR1 to LRx) is less than the corresponding LR threshold value (1 to x). If this cancellation condition is not satisfied, the process returns to step S1 without performing the detection determination process described later, and the acquisition of observation data is continued. This prevents duplicate detection of the same signal. If it is determined in step S9 that the release condition is satisfied, the process proceeds to step S10, and the setting of the “under detection” state is released by the control unit 3.

  If the “detecting” state is not set in step S8, or if the “detecting” state setting is canceled in step S10 because the release condition is satisfied in step S9, the process proceeds to step S11. . In the subsequent processes, three types of detection determination processes based on the calculation results are performed.

  In step S11, FD determination and LR determination are performed. That is, it is determined whether or not the FD value is equal to or greater than the FD threshold value and any one of the x LR values (LR1 to LRx) is equal to or greater than the corresponding LR threshold value (1 to x). .

  When the FD value is less than the FD threshold, and when one or both of the x LR values (LR1 to LRx) are less than the corresponding LR threshold (1 to x) Advances to step S12, and the control unit 3 determines that no signal is detected (the signal resulting from the magnetic material does not exist in the observation data).

  On the other hand, if the FD value is greater than or equal to the FD threshold value and any one of the x LR values (LR1 to LRx) is greater than or equal to the corresponding LR threshold value (1 to x), the process proceeds to step S13. Advancing and LRn determination is performed.

  That is, in step S13, it is determined whether any one of the y LRn values (LRn1 to LRny) is greater than or equal to the corresponding LRn threshold value (1 to y).

  If all of the y LRn values (LRn1 to LRny) are less than the corresponding LRn threshold value (1 to y), the process proceeds to step S14. In this case, since the magnetic waveform of the observation data approximates the standard waveform and does not approximate the standard noise waveform, the control unit 3 determines that a signal caused by the magnetic material has been detected. In this case, the process proceeds to step S <b> 15, and the control unit 3 sets the signal detection state to the “detecting” state and stores it in the memory 4. The setting of the “being detected” state is held until it is canceled in step S10 described above. And it progresses to step S16 and the control part 3 alert | reports a detection to an operator by displaying on the display part 5 that the signal resulting from a magnetic body was detected.

  On the other hand, if any one of the y LRn values (LRn1 to LRny) is equal to or greater than the corresponding LRn threshold value (1 to y), the process proceeds to step S17. In this case, since the magnetic waveform of the observation data approximates the standard noise waveform, but does not approximate the standard waveform, the control unit 3 is caused by the magnetic material based on the LR determination (and FD determination). Although the signal is detected, as a result of the LRn determination, it is determined that the signal is highly likely to be caused by noise (noise fluctuation).

  Next, the process proceeds to step S18, and the control unit 3 reads out the notification setting when it is determined that the detected signal is highly likely to be caused by noise fluctuation from the memory 4, and if “notification setting is present”, the control unit 3 Proceed to S19. In step S <b> 19, the control unit 3 sets the signal detection state to the “detecting” state and stores it in the memory 4. The setting of the “being detected” state is held until it is canceled in step S10 described above.

  In step S20, the control unit 3 has detected that the signal has been detected based on the LR determination (and FD determination) and has determined that the signal is likely to be caused by noise (noise fluctuation) as a result of the LRn determination. Is displayed on the display unit 5 to notify the operator.

  If “no notification setting” is determined in step S18, the process proceeds to step S21. In this case, since the signal detected based on the LR determination (and FD determination) is determined to be highly likely to be caused by noise fluctuation (the possibility of erroneous detection is high), the signal is not notified to the operator. The detection determination process ends.

  As described above, the signal detection determination process is performed on the acquired observation data. In addition, since the observation data is measured by each of the plurality of magnetic sensors 1, in the magnetic detection system 100, the above-described signal detection determination process is performed on the observation data measured by each magnetic sensor 1. In addition, since the observation data is measured one after another as time elapses, the observation data stored in the memory 4 in step S2 is sequentially updated each time new observation data is acquired. And said signal detection determination process is implemented with respect to the newly acquired observation data.

  In the present embodiment, as described above, it functions as a calculation unit that calculates the LRn value related to the degree of approximation between the magnetic waveform measured by the magnetic sensor 1 and the standard noise waveform, and at least based on the LRn value, the magnetic signal By providing the control unit 3 that functions as a determination unit that performs LRn determination related to the detection of noise, it can be determined whether or not the measured magnetic waveform approximates a predictable noise fluctuation (standard noise waveform). As a result, even when a magnetic waveform that is determined as having a signal (with detection of a magnetic material) is measured, if it is determined from the LRn value that the standard noise waveform is approximated, the measurement is performed. Since it can be determined that there is a high possibility that the magnetic waveform generated is caused by noise fluctuation, it is possible to suppress erroneous detection caused by noise fluctuation.

  In the present embodiment, as described above, the control unit 3 calculates the LR value related to the degree of approximation between the magnetic waveform measured by the magnetic sensor 1 and the standard waveform in addition to the calculation of the LRn value. By configuring so as to make a determination related to detection of a magnetic signal based on the LRn value and the LR value, the measured magnetic waveform is approximated to a theoretical standard waveform caused by the magnetic material from the LR value. It is possible to determine whether or not there is a signal (whether or not a magnetic material is detected) and whether or not there is a high possibility of erroneous detection due to noise fluctuation from the LRn value. Thereby, since the signal resulting from a magnetic body can be detected, suppressing the misdetection determination resulting from a noise fluctuation, the signal resulting from a magnetic body can be detected accurately.

  In the present embodiment, as described above, the controller 3 causes the likelihood ratio calculation result (LRn value) regarding the likelihood ratio between the magnetic waveform measured by the magnetic sensor 1 and the standard noise waveform, and the magnetic sensor 1. The LRn value and the LR value are obtained by configuring the magnetic signal detection determination based on the likelihood ratio calculation result (LR value) related to the likelihood ratio between the magnetic waveform measured by the standard waveform and the standard waveform. Both can be obtained by likelihood ratio calculation. For this reason, arithmetic processing can be simplified.

  In the present embodiment, as described above, the controller 3 determines that the magnetic signal has been detected when the LR value is equal to or greater than the LR threshold value and the LRn value is less than the LRn threshold value. If the LR value is greater than or equal to the LR threshold value and the LRn value is less than the LRn threshold value, the measured magnetic waveform approximates the standard waveform, and Since it is considered that there is no standard noise waveform (it is not approximate to predictable noise fluctuation), it is easy to detect a signal caused by a magnetic substance while confirming that it is not a false detection due to noise fluctuation. be able to.

  In the present embodiment, as described above, the control unit 3 detects the magnetic signal when the LR value is equal to or higher than the LR threshold value and the LRn value is equal to or higher than the LRn threshold value. When the LR value is equal to or higher than the LR threshold value and the LRn value is equal to or higher than the LRn threshold value, the measured magnetic waveform is determined by determining that the possibility of being caused by the fluctuation is high. Can be easily determined that the detected signal is likely due to noise fluctuations. Thereby, the erroneous detection resulting from a noise fluctuation | variation can be suppressed easily.

  Further, in the present embodiment, as described above, the control unit 3 is configured to determine that the magnetic signal is not detected when the LR value is less than the LR threshold value. If it is less than the LR threshold value, it is considered that there is no waveform caused by the magnetic material in the measured magnetic waveform (it is not approximated with the standard waveform), so it is easy to detect the magnetic signal. It can be determined that it is not.

  Further, in the present embodiment, as described above, a plurality of types (x) of standard waveform data are set, weighted for each of the x standard waveform data (1 to x), and the standard waveform data ( By setting the LR threshold value (1 to x) individually for each of 1 to x), a plurality of (x) ) Can be used for appropriate detection determination. Further, weighting is performed for each standard waveform, and the LR threshold value (1 to x) corresponding to the weight is individually set for each standard waveform data (1 to x), thereby detecting the magnetic material in each standard waveform. Since an appropriate LR threshold value (1 to x) can be set by weighting according to the appropriate degree, the detection accuracy of the magnetic material can be improved.

  In the present embodiment, as described above, the control unit 3 adds the LRn value and the LR value to the comparison result between the magnetic waveform data (FD value) measured by the magnetic sensor 1 and the FD threshold value. Therefore, in addition to the likelihood ratio, the comparison result of the measured FD value and the FD threshold value is also taken into consideration, so that the magnetic signal can be detected in a multifaceted manner. Since the signal detection determination caused by the body can be performed, the detection accuracy of the magnetic body can be further improved.

  In the present embodiment, as described above, the standard noise waveform has a noise fluctuation due to the influence of noise fluctuation (see FIGS. 5A and 5B), tidal current, and swell when the magnetic sensor 1 is swung in the sea. (See (c) of FIG. 5) and noise fluctuations generated from the magnetic sensor 1 (see (d) and (f) of FIG. 5). As a result, noise fluctuations that occur when the magnetic sensor 1 is placed in the sea (the seabed), such as noise fluctuations caused by the vibration of the magnetic sensor 1 in the sea, noise fluctuations caused by tidal currents and undulations (predictable noise fluctuations). ) Can be detected by LRn determination, so that erroneous detection caused by noise fluctuation in the sea can be effectively suppressed. In addition, erroneous detection due to noise fluctuation generated from the magnetic sensor 1 itself can be suppressed by the LRn determination.

  Further, in the present embodiment, as described above, the control unit 3 is configured to perform the likelihood ratio calculation of the LRn value using the standard noise waveform stored in the memory 4, so that the standard noise waveform data By storing 4b in the memory 4 in advance, the LRn value can be easily calculated. As a result, it is possible to easily determine whether or not the measured magnetic waveform is highly likely to be caused by noise fluctuation using the obtained LRn value.

  In the present embodiment, as described above, the magnetic signal is detected as the determination related to the detection of the magnetic signal, but when it is determined that there is a high possibility of being caused by noise fluctuation (see step S17), the display unit 5 By configuring whether or not to perform notification, the operator can detect whether or not to notify the determination result when it is determined that the magnetic signal is detected but the possibility that it is caused by noise fluctuation is high. Since it can set as needed, the convenience of the magnetic detection system 100 with respect to an operator can be improved.

  The embodiment disclosed this time should be considered as illustrative in all points and not restrictive. The scope of the present invention is shown not by the above description of the embodiments but by the scope of claims for patent, and further includes all modifications within the meaning and scope equivalent to the scope of claims for patent.

  For example, in the above-described embodiment, an example in which the present invention is applied to a magnetic detection system that detects a magnetic substance by installing a magnetic sensor in the sea has been described, but the present invention is not limited thereto. The present invention may be applied to a magnetic detection system that detects a magnetic substance by installing a magnetic sensor on land or in the air (such as an aircraft).

  Moreover, in the said embodiment, although the example of the magnetic detection system provided with the several magnetic sensor was shown, this invention is not limited to this. There may be one magnetic sensor.

  In the above embodiment, an example of a magnetic detection system in which a plurality of magnetic sensors are wired to a computer is shown, but the present invention is not limited to this. In the present invention, a magnetic detection system may be configured by a magnetic sensor and a computer that are wirelessly connected.

  In the above embodiment, an example is shown in which the approximation degree between the observation data (measured magnetic waveform) and the standard noise waveform (and standard waveform) is obtained by likelihood ratio calculation, but the present invention is limited to this. Absent. In the present invention, the degree of approximation between observation data and a standard noise waveform (standard waveform) may be calculated by a method other than the likelihood ratio calculation. For example, a cross-correlation function between observation data and a standard noise waveform (standard waveform) may be used as a measure of the degree of approximation. Further, for example, a determination coefficient in regression analysis between observation data using a least square method and a standard noise waveform (standard waveform) may be used as a measure of the degree of approximation.

  Moreover, in the said embodiment, determination (LR determination) whether the magnetic signal resulting from a magnetic body was detected using the approximation degree (LR value) of observation data (measured magnetic waveform) and a standard waveform. Although the example which performs is shown, this invention is not limited to this. In the present invention, it is not necessary to use a degree of approximation with a theoretical standard waveform for determining whether or not a magnetic material has been detected. For example, it may be configured to determine whether or not a magnetic material has been detected only by FD determination that compares observation data (FD value) and an FD threshold value. Moreover, you may comprise so that determination whether the magnetic body was detected using determination methods other than FD determination and LR determination may be performed.

  In the above embodiment, the control unit 3 is configured to function as the “calculation unit” and the “determination unit” of the present invention by using software (signal detection determination program). The invention is not limited to this. In the present invention, the calculation unit (calculation circuit) that functions as the “calculation unit” of the present invention and the determination unit (determination circuit) that functions as the “determination unit” of the present invention may be provided individually in hardware. .

  Moreover, although the example which provided the control part which functions as a calculating means and a determination means in the computer was shown in the said embodiment, this invention is not limited to this. In the present invention, a control unit that functions as a calculation unit and a determination unit, or a calculation circuit and a determination circuit may be incorporated in the magnetic sensor without providing a computer.

  In the above-described embodiment, an example is shown in which three detection determinations of FD determination, LR determination, and LRn determination are performed as signal detection determination, but the present invention is not limited to this. In the present invention, the signal detection determination may be performed only by the LR determination and the LRn determination, or only by the FD determination and the LRn determination. Moreover, you may implement four or more detection determinations.

  In the above embodiment, in the signal detection determination, when the FD value is equal to or greater than the FD threshold value and the LR value is equal to or greater than the LR threshold value, it is determined that the signal is detected. Although shown, the present invention is not limited to this. In the present invention, even when the FD value is less than the FD threshold value, if the LR value is equal to or greater than the LR threshold value, it may be determined that a signal has been detected.

  In the above embodiment, an example in which a plurality (y) of standard noise waveform data is used has been described. However, the present invention is not limited to this. In the present invention, one standard noise waveform may be used. As many standard noise waveforms as are predictable in the installation environment of the magnetic sensor may be used.

  In the above embodiment, as an example of predictable noise fluctuation, noise fluctuation (figure 5 (a) and (b) in FIG. 5), noise fluctuation due to the influence of power flow and swell (Fig. 5) 5 (c)) and noise fluctuations generated from the magnetic sensor 1 ((d) and (e) in FIG. 5) are shown, but the present invention is not limited to this. The predictable noise fluctuation may be a noise fluctuation other than the above example. Since the predictable noise variation varies depending on the usage mode and installation environment of the magnetic sensor, the magnetic variation that can be predicted in the usage mode and installation environment of the magnetic sensor may be used as the standard noise waveform.

  Similarly, in the above-described embodiment, an example using a plurality (x) of standard waveform data is shown, but the present invention is not limited to this. In the present invention, the standard waveform data may be one.

  In the above embodiment, a plurality (x) of LR threshold values (1 to x) corresponding to a plurality (x) of standard waveform data are weighted for each of the plurality (x) of standard waveform data. Although the example which set is shown, this invention is not limited to this. In the present invention, a common LR threshold value (first threshold value) may be set for all standard waveform data. Further, for example, a plurality (x) of standard waveform data is divided into a plurality of groups (such as a relatively long wavelength group and a short wavelength group), and an LR threshold value (first threshold value) for each group. May be set.

  Further, in the above embodiment, when a magnetic signal is detected, but it is determined that there is a high possibility of being caused by noise fluctuation (see step S17 in FIG. 6), a notification setting for whether or not to notify the operator is set. Although an example of a possible configuration has been shown, the present invention is not limited to this. In this invention, you may comprise so that it may always alert | report without performing alerting | reporting setting, and you may comprise so that it may not always alert | report.

  Moreover, in the said embodiment, although the example which alert | reports to an operator by the screen display of the display part was shown, this invention is not limited to this. In the present invention, the operator may be notified by a method other than the screen display.

  Moreover, in the said embodiment, although the example using the fluxgate type | mold magnetic sensor 1 was shown, this invention is not limited to this. In the present invention, any type of magnetic sensor may be used.

DESCRIPTION OF SYMBOLS 1 Magnetic sensor 3 Control part (calculation means, determination means)
4 Memory (storage unit)
5 Display part (notification part)

Claims (10)

A magnetic sensor;
A calculation means for performing a first calculation related to a degree of approximation between a magnetic waveform measured by the magnetic sensor and a predictable noise fluctuation;
Determination means for making a determination on detection of a magnetic signal based on at least the result of the first calculation,
In addition to the first calculation, the calculation means is configured to perform a second calculation related to a degree of approximation between a magnetic waveform measured by the magnetic sensor and a theoretical standard waveform caused by a magnetic body,
When making a determination relating to detection of the magnetic signal, the determination means includes:
Performing a first determination as to whether a magnetic signal is present based on a result of the second operation;
If it is determined that the magnetic signal by the first judgment is present, on the basis of the first operation result, it has rows second determination as to whether the measured magnetic waveform caused by noise variance,
According to the result of the second determination, it is determined that the magnetic signal is detected, or the magnetic signal is detected, but it is determined that there is a high possibility of being caused by noise fluctuation,
A magnetic detection system that determines that a magnetic signal is not detected without performing the second determination when it is determined by the first determination that no magnetic signal is present . The first calculation includes a calculation related to a first likelihood ratio between a magnetic waveform measured by the magnetic sensor and a predictable noise fluctuation;
The second calculation includes a calculation related to a second likelihood ratio between a magnetic waveform measured by the magnetic sensor and a theoretical standard waveform caused by a magnetic body,
The determination means, the result of the operations on the first likelihood ratio, based on the results of operations on the second likelihood ratio, and is configured to make a determination regarding the detection of magnetic signals, according to claim 1 The magnetic detection system described in 1. If the result of the calculation related to the second likelihood ratio is greater than or equal to the first threshold and the result of the calculation related to the first likelihood ratio is less than the second threshold, The magnetic detection system of claim 2 , configured to determine that a signal has been detected. When the result of the calculation related to the second likelihood ratio is equal to or greater than the first threshold and the result of the calculation related to the first likelihood ratio is equal to or greater than the second threshold, was detected signal is configured to determine that there is likely due to noise fluctuations, magnetic detection system according to claim 2 or 3. Said determining means, if the result of operation on the second likelihood ratio is less than the first threshold value is configured to determine not to detect a magnetic signal, according to claim 2-4 The magnetic detection system according to any one of the above. A plurality of theoretical standard waveforms resulting from the magnetic material are set,
Weighting is performed for each theoretical standard waveform caused by the plurality of types of the magnetic bodies, and a first threshold is individually set for each theoretical standard waveform according to the weighting. Item 6. The magnetic detection system according to any one of Items 3 to 5 . In addition to the result of the calculation regarding the first likelihood ratio and the result of the calculation regarding the second likelihood ratio, the determination means compares the magnetic waveform data measured by the magnetic sensor with a third threshold value. The magnetic detection system according to any one of claims 2 to 6 , wherein the magnetic detection system is configured to make a determination on detection of a magnetic signal based on the above. The predictable noise fluctuation includes at least one of noise fluctuation when the magnetic sensor is shaken in the sea, noise fluctuation caused by tidal current and swell, and noise fluctuation generated from the magnetic sensor. The magnetic detection system according to any one of 1 to 7 . A storage unit for storing in advance the predictable noise fluctuation;
The calculating means uses the predictable noise variance stored in the storage unit, the first is configured to perform an operation, magnetic detection according to any one of claims 1-8 system. A notification unit that notifies a determination result related to detection of a magnetic signal by the determination unit;
The magnetic signal is detected as a determination relating to the detection of the magnetic signal, but when it is determined that there is a high possibility of being caused by noise fluctuation, it is possible to set whether or not to perform notification by the notification unit. The magnetic detection system according to any one of? 9 .

Images