JP5804025B2 - Soil monitoring device and soil monitoring method - Google Patents

Description

  The present invention relates to a soil monitoring device and a soil monitoring method.

  In sloped areas such as mountains, landslides may occur due to rainfall, causing serious damage. There are two known modes of landslides: surface collapse and deep collapse. The magnitude of the damage is unclear, but deep layer collapse is often greater than surface collapse.

  Surface collapse occurs due to surface currents that flow over the surface of the earth when it rains so much that it cannot penetrate into the soil. That is, since water always flows to the lower side, even a slight unevenness on the ground surface concentrates (collects) on the concave side. At this time, the water flows while entraining soil and stones, and surface erosion occurs. The eroded groove gradually grows, erosion / collapse progresses, water and debris become debris flow, and finally surface collapse.

  On the other hand, deep collapse is likely to occur when precipitation time is long and precipitation is high. In other words, the rain fills the soil with water and loosens not only the soil grains but also the boundary between the rock and the soil. A layer of water is generated at the boundary between the rock and soil where it is difficult for water to penetrate, and the soil slides down with the rock, causing deep collapse.

  Therefore, development of a technique for monitoring the amount of moisture in the soil is desired, and Japanese Unexamined Patent Application Publication No. 2011-47676 proposes a soil moisture level detection device as described later.

  This soil moisture level detection apparatus is used by filling a tubular ultrasonic waveguide having one end sealed and the other end opened in the soil. And the detector and control part which have an ultrasonic transmission / reception element are provided in the sealing side of the ultrasonic waveguide. The control unit detects the moisture content in the soil based on the maximum amplitude of the reflected wave of the transmitted ultrasonic wave, and determines the position of the groundwater level surface based on the time required from the transmission of the ultrasonic wave to the reception of the reflected wave. To detect.

JP 2011-47676 A

  However, the direct cause of the disaster is often a landslide, and the main cause of the landslide is an increase in the amount of moisture in the soil. Therefore, a device for detecting the moisture level in the soil according to Japanese Patent Application Laid-Open No. 2011-47676 that detects them. Is useful, but it was insufficient from the viewpoint of minimizing (reducing) disasters.

  That is, when the amount of moisture in the soil increases, landslides do not always occur, and sometimes landslides do not occur. In addition, landslide may occur after a long time since the amount of water increased. Therefore, from the viewpoint of disaster prevention / reduction, it is necessary not only to monitor the increase in moisture content in the soil, but also to detect signs of landslides.

  Therefore, a main object of the present invention is to provide a soil monitoring device and a soil monitoring method capable of detecting not only a moisture content in the soil but also a sign of a landslide.

  In order to solve the above problems, the invention relating to the underground monitoring device includes a detection sound radiation unit that radiates a detection sound into the soil, a reverberation sound detection unit that detects a reverberation sound from the soil, and a signal level of the reverberation sound. A measurement judgment circuit that alternately repeats the moisture content monitoring process when the reverberant sound includes the detection sound reflection sound and the abnormal sound monitoring process when the reverberation sound does not include the detection sound reflection sound. The moisture content monitoring process obtains a difference value between the measurement data and the reference data stored in advance, determines whether the difference value exceeds a predetermined moisture content threshold value, and if it exceeds, It is a process of issuing a water content alarm and calculating the depth of the soil area exceeding the water content threshold value as the water content depth and outputting the water content depth along with the water content alarm, Abnormal sound monitoring processing is performed when the measured data is a predetermined abnormal sound threshold. It determines greater than or not, if large characterized in that it is a process of alarm the alarm abnormal sound.

  Further, the invention according to the soil monitoring method, the sound wave transmitter / receiver, the detection sound emission procedure for radiating the detection sound in the soil, the sound wave transmitter / receiver to detect the reverberation sound from the soil, The measurement judgment circuit that receives the signal from the sound wave transmitter / receiver measures the signal level of the reverberant sound as measurement data, and if the reverberant sound includes the reflected sound of the detection sound, the moisture content monitoring processing and the detection sound in the reverberant sound A measurement judgment procedure for performing a process of alternately repeating the abnormal sound monitoring process when the reflected sound is not included, and the water content monitoring process calculates a difference value between the measurement data and the reference data stored in advance. Determining whether or not the difference value exceeds a predetermined moisture content threshold value, and issuing a water content alarm when the difference value is exceeded, and determining the depth of the soil area exceeding the moisture content threshold value Calculated as the belt depth and the water content warning The abnormal sound monitoring process is a process for determining whether or not the measurement data is larger than a predetermined abnormal sound threshold value, and if it is larger, an abnormal sound alarm is issued. And

  According to the present invention, the moisture content monitoring process for detecting the moisture content in the soil and the abnormal sound monitoring process for detecting ground noise and the like are alternately repeated, so that not only the increase in the moisture content is monitored, but also a sign of landslide is detected. Can be detected.

It is a block diagram of an underground monitoring apparatus. It is the flowchart which showed the operation | movement procedure of the underground monitoring apparatus. It is a schematic diagram explaining the detection sound radiated | emitted from the underground monitoring apparatus. It is the figure which showed the envelope of the amplitude (signal level) in a detection sound and a reverberation sound, (a) is a reference data, (b) is a figure which shows measurement data. 5A and 5B are diagrams illustrating a comparison process between a difference value and a moisture content threshold value, in which FIG. 4A is a diagram illustrating reference data and measurement data in FIG. 4, and FIG. 5B is a diagram illustrating a difference value calculated from the reference data and measurement data; It is the figure which showed the relationship with a water quantity threshold value. It is a figure for demonstrating abnormal sound monitoring processing, (a) is the figure which showed the monitoring sequence of the measurement judgment circuit 15, (b) is abnormal because the difference value of reverberant sounds, such as a ground noise, exceeds an abnormal sound threshold value. It is a figure which shows a mode that a sound alarm signal is output.

  An embodiment of the present invention will be described. FIG. 1 is a block diagram of the underground monitoring device 2 according to the present embodiment. The underground monitoring device 2 includes a sound wave transmitter / receiver 11, a timing circuit 12, a transmission circuit 13, a signal processing circuit 14, a measurement determination circuit 15, a switching circuit 16, and an output unit 17 as main components. At this time, the sound wave transmitter / receiver 11, the timing circuit 12, the transmission circuit 13, and the switching circuit 16 constitute the detection sound radiation unit 6, and the sound wave transceiver 11, the switching circuit 16, and the signal processing circuit 14 constitute the reverberation sound detection unit 8. doing.

  In the following description, the soil monitoring device 2 will be described as an example of being embedded in a measurement location. However, it should be added in advance that it may be placed in the measurement location or in a semi-embedded state. To do.

  The sound wave transmitter / receiver 11 is configured by using, for example, a piezoelectric element, and emits sound such as ultrasonic waves (hereinafter referred to as detection sound) into the soil and detects sound from the soil (reverberation sound). The piezoelectric element is an element that converts an electric signal into a sound wave and a sound wave into an electric signal. In the present embodiment, the case where the sonic wave transmitter / receiver 11 is composed of one piezoelectric element will be described, but it is also possible to separately provide a wave transmitting means and a wave receiving means.

  The switching circuit 16 switches the circuit so that the signal (transmission signal G4) from the transmission circuit 13 is input to the sound wave transmitter / receiver 11 when transmitting the detection sound, and when detecting the reverberation sound, the switching circuit 16 Circuit switching is performed so that a signal from the transceiver 11 is input to the signal processing circuit 14. These switching operations are controlled based on a switching signal G1_b from the timing circuit 12.

  The timing circuit 12 outputs a timing signal G1 for transmitting the detection sound at regular intervals, and also outputs a recording instruction signal G3 for recording a signal (hereinafter referred to as a reception signal G9) input to the measurement judgment circuit 15. Output. The timing signal G1 is output to the transmission circuit 13, the switching circuit 16, and the measurement determination circuit 15. Hereinafter, for convenience of explanation, the timing signal G1 output to the transmission circuit 13 is the transmission permission signal G1_a, the timing signal G1 output to the switching circuit 16 is the switching signal G1_b, and the timing signal G1 output to the measurement determination circuit 15 is It is described as an analysis timing signal G1_c, and these are collectively referred to as a timing signal G1.

  The transmission permission signal G1_a is a signal that instructs the transmission circuit 13 to output a detection sound, the switching signal G1_b is a signal that causes the switching circuit 16 to perform circuit control, and the analysis timing signal G1_c is a measurement determination circuit. 15 is a signal for notifying the output timing of the detection sound when the analysis processing is performed at 15. The recording instruction signal G3 is a signal for instructing storage of reference data, and is a signal that is output only once when the underground monitoring device 2 is reset.

  The transmission circuit 13 outputs a high-power transmission signal G4 in synchronization with the transmission permission signal G1_a. At this time, the switching signal G1_b is input to the switching circuit 16, and the switching circuit 16 forms a circuit so that the transmission circuit 13 and the sound wave transmitter / receiver 11 are connected. Accordingly, the transmission signal G4 is input from the transmission circuit 13 to the sound wave transmitter / receiver 11 via the switching circuit 16. The sound wave transmitter / receiver 11 transmits a detection sound into the ground based on the transmission signal G4.

  When the detection sound is emitted, the timing circuit 12 outputs a switching signal G1_b to the switching circuit 16. The switching circuit 16 that has received the switching signal G1_b performs circuit switching so that the sound wave transmitter / receiver 11 and the signal processing circuit 14 are connected.

  The signal processing circuit 14 performs signal processing on a signal (hereinafter referred to as a received signal) G8 output from the sound wave transceiver 11. The signal level of the received signal G8 is weak, and the frequency component includes many components different from the frequency of the detection sound. Further, the received signal G8 includes various noises. Therefore, the signal processing circuit 14 adjusts the level of the received signal G8, limits the frequency band, performs signal processing to remove noise, and outputs the signal subjected to the signal processing to the measurement determination circuit 15 as the received signal G9. To do.

  The measurement judgment circuit 15 measures the signal level of the reception signal G9. Hereinafter, the signal level obtained by measurement is referred to as measurement data. The measurement determination circuit 15 performs three processes using the measurement data: a reference data storage process, a water content monitoring process, and an abnormal sound monitoring process. The reference data storage process is a process performed based on the recording instruction signal G3 output from the timing circuit 12 only when the underground monitoring device 2 is reset. In contrast, the water content monitoring process and the abnormal sound monitoring process are processes that are alternately repeated at predetermined time intervals. In other words, since the moisture content monitoring process is intermittently performed, the abnormal sound monitoring process is performed during the time.

  In the reference data storage process, the measurement data is stored as reference data in a storage unit (not shown) provided in the measurement determination circuit 15.

  In the water content monitoring process, a difference between the reference data and the measurement data is obtained, and it is monitored whether or not the difference value is larger than a preset water content threshold value. If it is determined by this monitoring that the difference value is greater than the water content threshold value, a water content abnormality signal is output to the output unit 17.

  Further, in the abnormal sound monitoring process, it is monitored whether or not the measurement data is larger than a preset abnormal sound threshold. If it is determined by this monitoring that the measurement data is larger than the abnormal sound threshold, an abnormal sound alarm signal is output to the output unit 17.

  When the output unit 17 receives the moisture content alarm signal or the abnormal sound alarm signal from the measurement determination circuit 15, the output unit 17 outputs these signals as an alarm signal G11 to a monitoring station (not shown) via wired or wireless means. The alarm signal G11 can include information indicating the measurement point, and the measurement point may be known using a known system such as a quasi-zenith satellite system or a global positioning system.

  Next, the detailed configuration of the above-described underground monitoring device 2 will be described with reference to FIG. FIG. 2 is a flowchart showing an operation procedure of the underground monitoring device 2.

  Step S1: The underground monitoring device 2 is activated and the underground monitoring device 2 is embedded. At this time, embedding is performed when the measurement site is dry. When it is dry, it does not mean that the amount of water is “zero”, but means so-called “dry soil”, which means a state in which no landslide is generated by moisture. When the time required for embedding has elapsed, the timing circuit 12 outputs a timing signal G1 (transmission permission signal G1_a, switching signal G1_b, analysis timing signal G1_c) and a recording instruction signal G3.

  Step S2: When the switching circuit 16 receives the switching signal G1_b, the switching circuit 16 performs circuit switching so that the sound wave transceiver 11 and the transmission circuit 13 are connected.

  Step S3: Upon receiving the transmission permission signal G1_a, the transmission circuit 13 outputs a transmission signal G4. At this time, since the switching circuit 16 connects the transmission circuit 13 and the sound wave transceiver 11, the transmission signal G 4 is input to the sound wave transceiver 11.

  The sound wave transmitter / receiver 11 converts the transmission signal G4 into a detection sound. Thereby, a detection sound is radiated toward the ground. FIG. 3 is a schematic diagram for explaining the detection sound radiated from the underground monitoring device 2. The detection sound is radiated in the underground direction D with the directivity width φ. Then, while propagating the particles in the ground, it is reflected by the particles and the like, returns to the sound wave transmitter / receiver 11 and is received as a reverberant sound.

  In the reference data storage process and the water content monitoring process, the reverberant sound is a reflected sound of the detection sound reflected by particles in the soil. On the other hand, in the abnormal sound monitoring process, it is a sound that is not related to the detection sound such as a ground noise or a collapsing sound.

  By the way, the reason why the detection sound is radiated with the directivity width φ is as follows. That is, there are rocks of various sizes in the soil, and there are strata with different hardness. It is very difficult to know in advance the existence of such rocks. In particular, in areas where landslides are a concern, there is a risk of causing landslides due to the effects of processing to confirm the presence of rocks (for example, vibrations), and leaving factors for landslides. It is difficult to know the existence.

  Therefore, in the soil moisture level detecting device including the ultrasonic waveguide as in Patent Document 1 (Japanese Patent Laid-Open No. 2011-47676), the directivity width of the detection sound is regulated by the ultrasonic waveguide. In some cases, the amount and position of moisture in the soil cannot be detected due to rocks. However, as described above, the underground monitoring device 2 according to the present embodiment is not provided with a member such as an ultrasonic waveguide that regulates the directivity width of the detection sound and the reverberation sound. There is an advantage that the influence can be reduced.

  Step S4: The timing circuit 12 determines the timing when the detection sound is radiated from the elapsed time or the like, and outputs the switching signal G1_b. Thereby, the switching circuit 16 performs circuit switching so that the sound wave transceiver 11 and the signal processing circuit 14 are connected.

  The time required for the detection sound to be emitted after the timing circuit 12 outputs the transmission permission signal G1_a (hereinafter referred to as detection sound emission time) is constant. Therefore, the switching circuit 16 performs circuit switching so that the sound wave transmitter / receiver 11 and the signal processing circuit 14 are automatically connected when the detection sound emission time has elapsed after receiving the switching signal G1_b in step S2. May be.

  Steps S5 and S6: Since the sound wave transmitter / receiver 11 and the signal processing circuit 14 are connected by the switching circuit 16, the reverberant sound is detected by the sound wave transmitter / receiver 11 and input to the signal processing circuit 14 as the received wave signal G8. The signal processing circuit 14 adjusts the level of the reception signal G8, limits the frequency band, performs signal processing to remove noise, and outputs the signal subjected to the signal processing to the measurement determination circuit 15 as the reception signal G9.

  Steps S7 to S9: The measurement determination circuit 15 acquires the measurement data by detecting the level of the reception signal G9. At this time, when the recording instruction signal G3 is received, the process proceeds to step S9. In step S9, the signal processing circuit 14 stores the measurement data as reference data and returns to step S2. On the other hand, when the recording instruction signal G3 is not received, the process proceeds to step S10.

  Steps S10 and S11: The signal processing circuit 14 obtains a difference between the reference data and the measurement data, and compares the difference value with a water content threshold value. In FIG. 3, the moisture band P is a diagram characteristically showing a moisture region caused by rainwater that has penetrated into the ground. When the moisture band P is generated in the ground due to rain, the sound velocity in the moisture band P increases and the sound attenuation decreases. This is because the density increases when water enters the gaps between the soil particles and the like, and when the water enters the gaps between the soil particles and the like, the amount of reflection (scattering amount) decreases and the sound is reduced. This is thought to be because the attenuation is reduced.

  FIG. 4 is a diagram showing an envelope of amplitude (signal level) in the detection sound and reverberation sound, where (a) shows reference data and (b) shows measurement data. Further, FIG. 5 is a diagram for explaining the comparison process between the difference value and the water content threshold value, (a) is a diagram showing the reference data and measurement data in FIG. 4, and (b) is the reference data and measurement data. It is the figure which showed the relationship between the calculated difference value and a moisture content threshold value.

  At this time, the analysis timing signal G1_c is used for positioning the measurement data and the reference data. This will be described with reference to FIG. If the analysis timing signal G1_c is input to the measurement determination circuit 15 at time T, the signal input after the detection time Δt has elapsed from this time T is determined as a reflected sound (reverberation sound) of the detection sound. Therefore, even if a signal is received before the detection time Δt elapses, it is ignored as a meaningless signal.

  Although it is the reception time of the reverberation sound, since the reverberation sound with respect to the detection sound is a reflection sound, the time on the horizontal axis in FIGS. 4 and 5 correlates with the reflection position. 4 and 5 show the relationship between the amount of moisture in the soil and its position. From this, FIG. 4 and FIG. 5 can be interpreted as moisture content distribution in the soil. However, the absolute value of the position and the density in the soil are unknown.

  In order to actively measure the moisture distribution in the soil, a method of gradually increasing the sound pressure of the detection sound is conceivable. Changing the sound pressure corresponds to changing the reach distance of the detection sound, so that a more accurate moisture content distribution can be measured.

  Now, from Fig.4 and Fig.5, the measurement data in the soil whose water content has increased due to rainfall is continued with respect to the reference data which is the measurement data in the dry soil (at least the soil that does not generate an alarm). It can be seen that the signal level increases with time.

  Therefore, the measurement determination circuit 15 calculates a difference value (= measurement data−reference data) between the reference data and the measurement data. The measurement determination circuit 15 determines whether or not the difference value exceeds a preset water content threshold value. When the difference value is exceeded (difference value ≧ water content threshold value), the process proceeds to step S12. When the difference value is not exceeded (difference value <water content threshold value), the process proceeds to step S13.

  In FIG. 5B, the time zone in which the difference value exceeds the water content threshold value (corresponding to the region of the water content zone exceeding the water content threshold value) is indicated by α, and the width of the water content zone P in FIG. 3 corresponds to α. This is the area.

  Step S12: The measurement judgment circuit 15 outputs a moisture content alarm signal to the output unit 17 together with the moisture zone depth, and the output unit 17 outputs an alarm signal G11 containing the moisture content alarm. The moisture zone depth can be obtained by multiplying the sound speed v by the time t1 from when the measurement of the reverberant sound starts until the difference value exceeds the moisture content threshold value. Note that the sound velocity v is obtained in advance through experiments or the like and stored in the measurement determination circuit 15.

  By the way, when calculating the moisture zone depth, it is possible to calculate the region (width) of the moisture zone depth. The calculation at this time is obtained by multiplying the difference between the time t2 and the time t1 when the difference value becomes smaller than the water content threshold by the speed v.

  Step S13: Although the reference data storage process and the water content monitoring process are completed as described above, the measurement determination circuit 15 continues to acquire the measurement data for the abnormal sound monitoring process. The measurement data at this time is data based on reverberant sound caused by ground noise or falling sound that is not related to the detection sound.

  Steps S <b> 14 and S <b> 15: Then, the measurement determination circuit 15 determines whether or not the measurement data exceeds the abnormal sound threshold, and if it exceeds, outputs an abnormal sound warning signal to the output unit 17. This abnormal sound warning signal is a signal notifying that a sign such as a landslide has been detected. Therefore, the abnormal sound threshold is set to a level at which no false alarm (error occurrence of an abnormal sound alarm signal) occurs due to environmental sounds generated in the surroundings, and is stored in the measurement determination circuit 15.

  6A and 6B are diagrams for explaining the abnormal sound monitoring process. FIG. 6A is a diagram illustrating a monitoring sequence of the measurement determination circuit 15, and FIG. It shows a state where an abnormal sound warning signal is output exceeding the threshold. At this time, the end of the water content monitoring section is the time when a sufficient time has elapsed from the end of the detection sound emission (at least the time when the reverberation sound composed of the reflected sound is not detected, the time indicated by β in FIG. 6A). ).

  Step S16: Then, the abnormal sound monitoring process is performed for a predetermined time, and the process returns to Step S1. Thereby, the timing circuit 12 outputs the transmission permission signal G1_a and the switching signal G1_b, and the next monitoring cycle (water content monitoring process and abnormal sound monitoring process) is repeated. At this time, since the reference data has already been acquired and stored, the recording instruction signal G3 is not output.

  In the above description, the reference data is acquired after the soil monitoring device 2 is embedded in the dry soil. However, if the reference data is acquired in advance, the reference data is written from the outside and stored. You may make it do.

  Moreover, although the radiation direction (direction D of FIG. 3) of the detection sound radiated | emitted from the sound wave transmitter / receiver 11 assumes the perpendicular direction, it is not limited to this direction. For example, when the mountain surface is inclined, it may be emitted in a direction perpendicular to the mountain surface. Further, the radiation direction can be controlled from the outside.

  As explained above, the detection sound is radiated into the soil, and it is judged from the reflected sound whether the moisture content in the soil exceeds the moisture content threshold, so the moisture content in the soil is wide and deep. Will be able to monitor.

  In addition, since the moisture content monitoring process and the abnormal sound monitoring process are repeated with the same configuration, it is possible to monitor disasters such as landslides at low cost.

DESCRIPTION OF SYMBOLS 2 Underground monitoring apparatus 6 Detection sound radiation unit 8 Reverberation detection unit 11 Sound wave transmitter / receiver 12 Timing circuit 13 Transmission circuit 14 Signal processing circuit 15 Measurement judgment circuit 16 Switching circuit 17 Output part

Claims (11)

A detection sound radiation unit that emits a detection sound having a directivity width in the soil;
A reverberation detection unit that detects reverberation from the soil,
The signal level of the reverberant sound is acquired as measurement data, a difference value between the measurement data and reference data stored in advance is obtained, and it is determined whether or not the difference value exceeds a predetermined water content threshold value. When the moisture content alarm is issued, the depth of the soil area exceeding the moisture content threshold is calculated as the moisture zone depth, and the moisture zone depth is output together with the moisture alert. A measurement determination circuit that alternately repeats moisture content monitoring processing and whether or not the measurement data is greater than a predetermined abnormal sound threshold, and abnormal sound monitoring processing that issues an abnormal sound alarm if large ,
Soil monitoring apparatus comprising: a. The soil monitoring device according to claim 1,
The underground monitoring apparatus, wherein the measurement data acquired immediately after the underground monitoring apparatus is activated is stored as the reference data. The soil monitoring device according to claim 1 or 2,
One sound wave transmitter / receiver shared by the detection sound radiation unit and the reverberation sound detection unit;
A switching circuit that causes the sound wave transmitter / receiver to function as a wave transmission unit when the detection sound is radiated, and that causes the sound wave transmitter / receiver to function as a wave reception unit when detecting the reverberation sound. Underground monitoring device characterized by. The soil monitoring device according to any one of claims 1 to 3,
The measurement judgment circuit obtains a product of a time when the difference value exceeds the moisture content threshold and a preset sound velocity in the soil, and outputs the value as a moisture zone depth. Underground monitoring device. The soil monitoring device according to any one of claims 1 to 4,
The measurement judgment circuit obtains a product of a time until the difference value becomes larger than the water content threshold value and thereafter becomes smaller than the water content threshold value and a preset sound speed in the soil, and this value. Is output as a width of the moisture zone depth. The soil monitoring device according to any one of claims 1 to 5,
The end of the water content monitoring process is a point in time that has continued for a predetermined time from the end of the reverberant sound. Detecting sound emission procedure to radiate detection sound with directivity width in the soil to the sound wave transmitter and receiver,
A reverberation sound detection procedure for causing the sound wave transceiver to detect a reverberation sound from the soil,
In the measurement judgment circuit that receives the signal from the sound wave transmitter / receiver, the signal level of the reverberant sound is obtained as measurement data,
Obtain a difference value between the measurement data and pre-stored reference data, determine whether the difference value exceeds a predetermined moisture content threshold, and if it exceeds, issue a moisture content alarm, and The water content monitoring process for calculating the depth of the soil area exceeding the water content threshold as the water content depth, and outputting the water content depth together with the water content alarm, and the measurement data is a predetermined abnormality determine greater or not than the sound threshold, the measurement determination procedures are alternately repeated and abnormal sound monitoring process to alarm an alarm abnormal sound is larger, the including,
A soil monitoring method characterized by that. The soil monitoring method according to claim 7,
A soil monitoring method, comprising: a step of storing the measurement data acquired immediately after the soil monitoring method is started as the reference data. The soil monitoring method according to any one of claims 7 to 8,
Including a procedure for obtaining a product of a time when the difference value exceeds the moisture content threshold value and a preset sound velocity in the soil, and outputting the value as a moisture zone depth in the measurement judgment circuit. Underground monitoring method characterized by The soil monitoring method according to any one of claims 7 to 9,
In the measurement judgment circuit, the product of the time when the difference value becomes larger than the water content threshold value and then becomes smaller than the water content threshold value and the preset sound speed in the soil is obtained, and this value is obtained. A soil monitoring method characterized by including a procedure for outputting as a width of a moisture zone depth. The soil monitoring method according to any one of claims 7 to 10,
The end of the water content monitoring process is a point in time that continues for a predetermined time from the end of the reverberant sound.

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