JP2021165669A - Cavity thickness estimation method and device thereof - Google Patents

Abstract

To provide a cavity thickness estimation method and a method thereof that can easily and accurately evaluate cavity thickness under a road in a nondestructive manner without traffic regulation.SOLUTION: While a vehicle 20 is running on a road 11, a plurality of transmission units 23 of a radar device 21 mounted on the vehicle 20 radiate electromagnetic waves toward the road 11 and a plurality of reception units 24 of the radar device 21 receive reflected waves. Reflected wave traces received by the respective reception units 24 are superposed by a common reflection point superposition method to generate a chart arranged in order of relative permittivity or velocity. Points where the reflected waves are emphasized by superposition are extracted at positions of the relative permittivity or reflected wave velocity between a medium on a starting end PS side of a cavity 12 under the road 11 in the chart and air in the cavity 12, and based on those positions, cavity thickness T under the road 11 is estimated.SELECTED DRAWING: Figure 1

Description

The present invention relates to a cavity thickness estimation method for estimating a cavity thickness under a road and an apparatus thereof.

Conventionally, cavities have been created due to aging of buried pipes under the road, causing the road to collapse. In recent years, the number of cavities has increased due to abnormal weather such as guerrilla rainstorms.

Due to the increase in the number of such cavities, it is necessary to add the priority of repair. The important information for determining the priority order for repairing cavities is the thickness of the cavities, that is, the thickness of the cavities.

In the case of an electromagnetic wave type ground penetrating radar device, it is only possible to measure the planar spread of a locally existing cavity such as a cavity under a road, and evaluating its thickness is the ground. It is not easy because the amount of information for the moving distance of the medium radar device is small. Therefore, generally, a method of visually confirming the inside of the cavity by boring the object at the predicted cavity position detected by the ground penetrating radar device is used (see, for example, Patent Document 1). ..

However, in the case of the above-mentioned method, traffic regulation of the road to be inspected is involved, and work such as backfilling after the inspection of the road is required.

It is also known that an antenna for transmitting and receiving electromagnetic waves is installed on the road and the cavity thickness is estimated by analyzing the reflected waves from the start and end of the cavity (see, for example, Patent Document 2). However, even in this case, traffic regulation of the road to be inspected is required.

Japanese Unexamined Patent Publication No. 5-87945 Japanese Patent No. 5062921

The present invention has been made in view of these points, and provides a cavity thickness estimation method and an apparatus thereof that can evaluate the cavity thickness under a road in a non-destructive manner easily and accurately without being accompanied by traffic regulation. With the goal.

The cavity thickness estimation method according to claim 1 radiates electromagnetic waves from a plurality of transmitting units of a radar device mounted on the vehicle toward the road while traveling on a road by a vehicle, and a plurality of receiving units of the radar device. A step of receiving the reflected wave at The points where the reflected wave is emphasized by the polymerization are extracted at the positions of the relative permittivity or the reflected wave velocity of the medium on the starting end side of the lower cavity and the air in the cavity, and based on those positions, under the road. It comprises a step of estimating the cavity thickness of.

The cavity thickness estimation method according to claim 2 is the cavity thickness estimation method according to claim 1. In the cavity thickness estimation method according to claim 1, the step of generating a chart is common to the reflected wave traces received by each receiving unit according to the start and end of the cavity. A step of generating an auxiliary chart in which those sharing a reflection point are arranged in the order of distance between the transmitting unit and the receiving unit, and a running correction of the auxiliary chart for each predetermined plurality of relative permittivity or for each speed are performed. It includes a step of generating a chart by arranging the layers in the order of the relative permittivity or the order of the speeds used for the run-time correction.

The cavity thickness estimation device according to claim 3 has a plurality of transmitters that emit electromagnetic waves and a plurality of receivers that receive reflected waves, a radar device mounted on a vehicle, and reflections received by each of the receivers. A chart generation means for generating a chart in which wave traces are polymerized by a common reflection point polymerization method and arranged in order of relative permittivity or velocity, and a medium on the starting end side of a cavity under the road in the chart generated by this chart generation means. With an estimation means that extracts the position where the reflected wave is emphasized by the polymerization at the position of each relative permittivity or reflected wave velocity with the air in the cavity, and estimates the cavity thickness under the road based on those positions. , Is provided.

The cavity thickness estimation device according to claim 4 is the cavity thickness estimation device according to claim 3, wherein the chart generating means is a common reflection point according to the start end and the end of the cavity among the reflected wave traces received by each receiving unit. Auxiliary charts are generated in which the shared ones are arranged in order of distance between the transmitting unit and the receiving unit, and the auxiliary charts corrected for running time for each of a plurality of predetermined relative permittivity or speeds are superimposed and run. The chart is generated by arranging them in the order of the relative permittivity or the speed used for the correction.

According to the cavity thickness estimation method according to claim 1, since the electromagnetic wave is transmitted and the reflected wave is received while the vehicle is traveling on the road, traffic regulation is not required and the reflected wave trace received by each receiving unit is not required. Since the cavity thickness under the road is estimated using the relative dielectric constant or reflected wave velocity of the known medium based on the chart in which noise is suppressed by polymerizing by the common reflection point polymerization method, the cavity thickness under the road is not destroyed. Can be evaluated easily and accurately.

According to the cavity thickness estimation method according to claim 2, in addition to the effect of the cavity thickness estimation method according to claim 1, noise can be effectively suppressed in the generated chart, and the position where the reflected wave is emphasized from the chart. Can be easily extracted, so that the accuracy of estimating the cavity thickness based on their positions can be improved.

According to the cavity thickness estimation device according to claim 3, since the electromagnetic wave is transmitted from the radar device and the reflected wave is received while the vehicle is traveling on the road, traffic regulation is not required and each receiving unit receives the electromagnetic wave. Since the cavity thickness under the road is estimated by the estimation means using the relative dielectric constant of the known medium or the velocity of the reflected wave based on the chart in which the noise is suppressed by superimposing the reflected wave trace by the common reflection point polymerization method. The thickness of the cavity under the road can be evaluated easily and accurately without destruction.

According to the cavity thickness estimation device according to claim 4, in addition to the effect of the cavity thickness estimation device according to claim 3, noise can be effectively suppressed in the generated chart, and the position where the reflected wave is emphasized from the chart. Can be easily extracted by the estimation means, so that the accuracy of estimating the cavity thickness based on their positions can be improved.

(A) is an external view showing a cavity thickness estimation device according to an embodiment of the present invention, (b) is a perspective view showing a part of the cavity thickness estimation device, and (c) is a model of a radar device of the cavity thickness estimation device. It is a cross-sectional view which shows. It is explanatory drawing which shows an example of the auxiliary chart generated by the cavity thickness estimation method of the same as above. It is explanatory drawing which shows the travel-time correction of the auxiliary chart shown in FIG. 2 for each relative permittivity by the same cavity thickness estimation method. It is explanatory drawing which shows an example of the chart generated by the cavity thickness estimation method of the same as above. It is explanatory drawing which shows the example which converted the chart shown in FIG. 4 into a gradation display by the same cavity thickness estimation method. It is explanatory drawing of the extraction method of the reflected wave corresponding to the position of the start end and the end end of the cavity from the chart by the cavity thickness estimation method of the same as above. It is a graph which shows the correlation between the estimated cavity thickness by the cavity thickness estimation method and the actual cavity thickness.

Hereinafter, an embodiment of the present invention will be described with reference to the drawings.

In FIGS. 1 (a), 1 (b), and 1 (c), 10 shows a cavity thickness estimation device. The cavity thickness estimation device 10 estimates the thickness of the cavity 12 generated in the lower part of the road 11 which is the inspection target, that is, the cavity thickness T. The road 11 is a paved road composed of a paved portion 15 such as asphalt or concrete and a roadbed portion 16 located below the paved portion 15. Hereinafter, the pavement portion 15 will be described as having a basically flat surface. Further, although the cavity 12 is described as being formed between the pavement portion 15 and the roadbed portion 16, it may be formed in the pavement portion 15.

The cavity thickness estimation device 10 includes a vehicle 20. A radar device 21 is arranged on the vehicle 20. The radar device 21 is mounted on the rear of the vehicle 20, for example. The radar device 21 is arranged longitudinally in the vehicle width direction of the vehicle 20, and is installed in the vehicle 20 so as to be parallel to a predetermined gap, for example, about 8 cm above the surface of the road 11, and is an obstacle. It goes up and down depending on the situation such as things.

The radar device 21 is a multi-channel radar device having a plurality of transmitting units 23 and receiving units 24. The transmitting unit 23 and the receiving unit 24 are arranged in the longitudinal direction of the radar device 21. That is, the transmitting unit 23 and the receiving unit 24 are sequentially arranged in the vehicle width direction, that is, in the crossing direction of the road 11. Further, the transmitting unit 23 and the receiving unit 24 are alternately arranged at equal intervals in the longitudinal direction of the radar device 21, for example. The transmitting unit 23 and the receiving unit 24 are arranged in a pair. That is, the same number of transmission units 23 and reception units 24 are arranged.

In the present embodiment, the radar device 21 generates a signal by the step frequency method. That is, while changing the transmitted wave from the transmitting unit 23 in a stepwise manner, the amplitude ratio and the phase difference between the transmitted wave at each frequency and the received wave reflected by the reflector and received by the receiving unit 24 are measured. Then measure the distance to the reflector. The signal generated by the radar device 21 in the step frequency system is transmitted to the computer 26. The computer 26 is connected to an input means 27 such as a keyboard and a mouse for an operator to input, and a monitor 28 which is a display means for displaying a chart and the like described later. The computer 26 includes an arithmetic unit such as a CPU, and has a function of a chart generation means that receives signals transmitted from the step frequency system and generates various charts based on the signals. Further, the computer 26 may include a storage means for storing data and the like. The computer 26, the input means 27, and the monitor 28 may be mounted on the vehicle 20 and operated by an operator on the vehicle 20, or may be installed in a remote location away from the vehicle 20 by a step frequency method. The generated signal may be received via a network such as the Internet.

Next, a method for estimating the cavity thickness by the above-mentioned cavity thickness estimation device 10 will be described.

First, while the vehicle 20 travels on the road 11 to be inspected at a predetermined speed, the radar device 21 radiates an electromagnetic wave from the transmitting unit 23 toward the road 11 and receives the reflected wave by the receiving unit 24. At this time, it is preferable that the vehicle 20 travels at a constant speed. The traveling speed may be a speed having little influence on traffic or no influence on traffic, such as 60 km / h in the case of a general road and 80 km / h in the case of an expressway.

Next, the computer 26 generates a chart in which the time change of the reflected wave received by the receiving unit 24, that is, the reflected wave trace is polymerized by the common reflection point polymerization method (CMP polymerization method) and arranged in order of relative permittivity or velocity.

When generating this chart, first, among the reflected wave traces received by each receiving unit 24, the one sharing the common reflection point CPS and CPE corresponding to the start PS and the end PE of the cavity 12 is shared with the transmitter 23. Auxiliary charts arranged in order of distance from the receiving unit 24 that received the reflected wave at the common reflection point CPS and CPE of the electromagnetic wave radiated from the transmitting unit 23, or in order of distance from the common reflection point CPS and CPE are arranged on the computer 26. Generated by. That is, the common reflection points CPS and CPE are the transmission unit 23 at the start PS and the end PE of the cavity 12, and the reception unit 24 that receives the reflected waves at the common reflection points CPS and CPE of the electromagnetic waves radiated from the transmission unit 23, respectively. It is the middle point of.

Auxiliary charts are also called CMP ensembles. As in the example shown in FIG. 1 (c), when there are five receiving units 24, the auxiliary chart is an arrangement of the reflected wave traces received by these five receiving units 24. FIG. 2 shows an example of the auxiliary chart C1. In the example shown in FIG. 2, one axis (horizontal axis) is the transmitting unit 23 and the receiving unit 24 that receives the reflected waves at the common reflection points CPS and CPE of the electromagnetic waves radiated from the transmitting unit 23 (FIG. 1 (FIG. 1 (FIG. 1)). c)) distance, the other axis (vertical axis) that intersects one axis is time. The adjacent reflected wave traces are appropriately complemented based on, for example, their average values.

In FIG. 2, L1 shows the reflected wave traveling at the starting end PS (FIG. 1 (c)) of the cavity 12, and L2 shows the reflected wave traveling at the ending PE (FIG. 1 (c)) of the cavity 12. Since a delay occurs depending on the distance between the transmitting unit 23 and the receiving unit 24 shown in FIG. 1C during the reflected wave traveling, the reflection wave travels approximately as a hyperbola. The auxiliary chart may be displayed on the monitor 28, or may be generated as data inside the computer 26 without being displayed on the monitor 28.

Next, in order to reduce the noise of the reflected wave trace received by each receiving unit 24 and improve the S / N ratio, the auxiliary chart is corrected for running time for each of a plurality of predetermined relative permittivity or for each speed. The computer 26 generates a chart obtained by polymerizing each of them and arranging them in order of relative permittivity or speed.

First, the delay during reflected wave running in the auxiliary chart is corrected for each of a plurality of predetermined relative permittivity or for each speed according to the relative permittivity (NMO correction). The velocity according to the relative permittivity is a velocity calculated by v = c / √ε _r, where c is the light velocity in vacuum and ε _{r is the relative permittivity of the medium.} That is, the relative permittivity and the speed according to the relative permittivity are inversely proportional to each other. The relative permittivity or velocity is predetermined within a predetermined range including at least the relative permittivity or reflected wave velocity of air and the relative permittivity or reflected wave velocity of the medium constituting the pavement portion 15 (FIG. 1 (c)). It is set at regular intervals.

FIG. 3 shows an example of _{auxiliary charts C1 1 to C1 24} in which the auxiliary charts C1 shown in FIG. 2 are corrected at each relative permittivity or each speed. In FIG. 3, they are arranged in ascending order of relative permittivity from the left side to the right side. In the example shown in FIG. 3, one axis (horizontal axis) is the relative permittivity and the other axis (vertical axis) intersecting one axis is time, but one axis may be velocity. When one axis is velocity, the magnitude is opposite to the relative permittivity. The corrected auxiliary chart may be displayed on the monitor 28, or may be generated as data inside the computer 26 without being displayed on the monitor 28 shown in FIG. 1 (b).

Then, each of these corrected auxiliary charts is polymerized (added). At this time, in the auxiliary chart corrected by a speed equal to or substantially equal to the reflected wave speed in the reflected wave trace, or a specific dielectric constant corresponding to the speed, the distance between each transmitting unit 23 and each receiving unit 24 is increased. The resulting time delay is just offset and the reflected wave traces received by all receivers 24 are corrected so that the distance between each transmitter 23 and each receiver 24 is the same (eg 0). The time of reflected wave running is converted to a substantially linear shape. In the example shown in FIG. 3, the reflected wave traveling time L1 is _{converted to the auxiliary chart C1 10} and the reflected wave traveling time L2 is _{converted to the auxiliary chart C1 14} in a substantially linear shape. That is, the reflected wave velocity of L1 during reflected wave traveling or the specific dielectric constant according to the reflected wave velocity is substantially equal to the velocity or specific dielectric constant used for the conversion of the _{auxiliary chart C1 10, and the reflection of L2 during reflected wave traveling is approximately equal.} The relative dielectric constant according to the wave velocity or its reflected wave velocity is approximately equal to the velocity or specific dielectric constant used for the conversion of _{auxiliary chart C1 14.} Therefore, by polymerization of the auxiliary chart C1 _10, C1 _14, so that the reflected wave of a medium having a respective auxiliary chart C1 _10, C1 ₁₄ dielectric constant corresponding speed or it is used to correct is highlighted ..

Then, the computer 26 generates a chart obtained by arranging each of these auxiliary charts in the order of relative permittivity or velocity used for each conversion. FIG. 4 shows an example of Chart C. In the example shown in FIG. 4, one axis (horizontal axis) is the relative permittivity and the other axis (vertical axis) intersecting one axis is time, but one axis may be velocity. When one axis is velocity, the magnitude is opposite to the relative permittivity. In this chart C, the intensity of the reflected wave is shown as the amplitude in the left-right direction. The traces between the auxiliary charts may be appropriately complemented based on, for example, these average values.

Further, in the present embodiment, the magnitude of the amplitude of the chart is converted into light and shade (contrast) by the computer 26 shown in FIG. 1 (b). An example of the chart C converted into FIG. 5 is shown. In the example shown in FIG. 5, as in FIG. 4, one axis (horizontal axis) is the relative permittivity, and the other axis (vertical axis) that intersects one axis is time, but one axis is also velocity. good. When one axis is velocity, the magnitude is opposite to the relative permittivity. In the chart C shown in FIG. 5, the larger the amplitude is in the positive or negative direction, the blacker it is, and the larger the amplitude is in the negative or positive direction, the whiter it is. Not limited to this, the chart may be represented by elements other than shading, such as color / saturation, light / darkness, and brightness, depending on the intensity of the reflected wave.

Then, from this chart, the position where the reflected wave is emphasized by the polymerization is extracted at the position of the relative permittivity or the reflected wave velocity between the medium on the PS side at the start end of the cavity 12 under the road 11 and the air in the cavity 12. The medium on the PS side at the starting end of the cavity 12 is a medium constituting the pavement portion 15 of the road 11, and generally has a relative permittivity of about 8 to 12. Further, the air in the cavity 12 has a relative permittivity of about 1. That is, since the medium of the pavement 15 and the air in the cavity 12 are known, the relative permittivity or the reflected wave velocity corresponding to these media is also known. In the present embodiment, using these known values, the reflected wave estimated to be reflected at the position where the reflected wave is emphasized by the polymerization, that is, the position of the starting point PS of the cavity 12, and the cavity 12 are used. The reflected wave that is presumed to be reflected at the position of the terminal PE of is extracted.

Specifically, on the chart, the lines of the known relative permittivity or reflected wave velocity of the medium on the starting PS side and the lines of the relative permittivity or reflected wave velocity of the air in the cavity 12 are overlapped with these lines. It is estimated that the emphasized points of the reflected waves extending in the orthogonal or substantially orthogonal directions are the desired positions. This is because, in the above-mentioned running time correction, when the speed is equal to or substantially equal to the reflected wave in the reflected wave trace, or the relative dielectric constant is corrected according to the speed, the reflected wave running time is converted into a substantially linear shape. Therefore, the position extending linearly in the direction orthogonal to or substantially orthogonal to the line of the specific dielectric constant or the reflected wave velocity corresponds to the position where the reflected wave is generated, that is, the position of the start PS and the position of the end PE of the cavity 12. This is because it is presumed to be the position to be used.

In the case of the example shown in this embodiment, _{the relative permittivity or velocity used for the conversion of the auxiliary chart C1 10} shown in FIG. 3 is the relative permittivity or the relative permittivity of the medium of the pavement portion 15 that generates the reflected wave at the starting point PS. The position of the reflected wave velocity by the medium, _{the relative permittivity or velocity used for the conversion of auxiliary chart C1 14} is the relative permittivity of the air in the cavity 12 that produces the reflected wave at the terminal PE or the reflected wave velocity by the air. Is presumed to be the position of.

For an example of chart C shown in FIG. 5, a line E1 showing the relative permittivity of air in the cavity 12 and a line E2 showing the relative permittivity of the medium on the starting end PS side of the cavity 12, that is, the medium of the pavement portion 15. Is shown in FIG. In the example shown in FIG. 6, as in FIGS. 4 and 5, one axis (horizontal axis) is the relative permittivity, and the other axis (vertical axis) that intersects one axis is time, but one axis. May be speed. When one axis is velocity, the magnitude is opposite to the relative permittivity. In the example of Chart C shown in FIG. 6, the position P1 at which the line E1 intersects with the black line or white line indicating the reflected wave that appears parallel to or substantially parallel to one axis is at the terminal PE of the cavity 12. It is presumed to be a reflected wave. Similarly, of the black or white lines indicating the reflected wave, the position P2 where the line appearing parallel to or substantially parallel to one axis and the line E2 intersect is presumed to be the reflected wave at the starting point PS of the cavity 12. NS. Not limited to this, positions P1 and P2 may be extracted in the same manner using the chart C shown in FIG.

Then, the cavity thickness T under the road 11 is estimated based on the reflected wave at the start PS and the reflected wave at the end PE of the cavity 12 extracted from the chart C. That is, the cavity thickness T is calculated by T = v · Δt / 2, where v is the speed of light in the medium, from the time difference Δt between the positions P1 and P2 extracted from the chart C. As described above, when the light velocity in vacuum is c and the relative permittivity of the medium is ε _r , the velocity v of the reflected wave from the medium is _{calculated by v = c / √ε r} , and the velocity v in the cavity 12 is calculated. Since the relative permittivity of air as a medium is about 1, T = c · Δt / 2 substantially.

Such an estimation may be performed by an analysis worker based on the displayed image, but can also be performed by image processing the chart, and therefore may be performed directly on the computer 26 using AI or the like. However, the analysis worker and the computer 26 may collaborate with each other. That is, the computer 26 may have the function of an estimation means. When it is estimated by the computer 26, it is preferable to output the estimation result.

In this way, the cavity thickness T in the transverse direction of the road 11 is estimated, and by arranging it along the longitudinal direction of the road 11, the three-dimensional shape such as the shape and the spread of the cavity 12 can be estimated.

FIG. 7 shows the correlation between the measured thickness of the cavity 12 and the estimated thickness estimated by the above estimation method. As shown in FIG. 7, it can be seen that the cavity thickness T can be estimated accurately by the cavity thickness estimation method of the present embodiment.

As described above, according to one embodiment, since the electromagnetic wave is transmitted and the reflected wave is received while the vehicle 20 is traveling on the road 11, traffic regulation is not required and the reflection received by each receiving unit 24 is not required. Since the cavity thickness T under the road 11 is estimated using the relative dielectric constant or the reflected wave velocity of the known medium based on the chart in which the noise is suppressed by polymerizing the wave trace by the common reflection point polymerization method, the cavity thickness T under the road 11 is estimated. The cavity thickness T can be evaluated easily and accurately in a non-destructive manner.

Also, among the reflected wave traces received by each receiving unit 24, those sharing the common reflection points CPS and CPE according to the start PS and end PE of the cavity 12 are arranged in order of the distance between the transmitting unit 23 and the receiving unit 24. Auxiliary charts are generated, and the auxiliary charts are superimposed for each of a plurality of predetermined relative permittivity or each speed, and arranged in order of relative permittivity or speed used for the running correction to generate a chart. Therefore, noise can be effectively suppressed in the generated chart, and the positions where the reflected wave is emphasized can be easily extracted from the chart, so that the estimation accuracy of the cavity thickness T based on those positions can be improved.

Then, since the cavity thickness T can be estimated accurately, it is possible to determine the priority order of repair of the cavity 12 based on the estimated cavity thickness T, for example, repairing the cavity 12 in order from the one having the largest cavity thickness T.

In the above embodiment, the cavity thickness estimation device 10 includes a dedicated vehicle 20, but the present invention is not limited to this, and a radar device 21 or the like may be mounted on a general-purpose vehicle for use. ..

10 Cavity thickness estimation device
11 road
12 cavities
20 vehicles
21 Radar device
23 Transmitter
24 Receiver
26 Computer C chart having the functions of chart generation means and estimation means
C1 auxiliary chart
CPE, CPS common reflection point
PE termination
PS Start T Cavity thickness

Claims (4)

While traveling on a road by a vehicle, a step of radiating electromagnetic waves from a plurality of transmitting units of a radar device mounted on the vehicle toward the road and receiving reflected waves by a plurality of receiving units of the radar device.
A step of polymerizing the reflected wave traces received by each of the receiving units by a common reflection point polymerization method to generate a chart arranged in order of relative permittivity or velocity.
The points where the reflected wave was emphasized by the polymerization were extracted at the positions of the relative permittivity or the reflected wave velocity of the medium on the starting end side of the cavity under the road and the air in the cavity in the chart, and those positions were extracted. The step of estimating the cavity thickness under the road based on
A cavity thickness estimation method comprising. The steps to generate a chart are
A step of generating an auxiliary chart in which among the reflected wave traces received by each receiving unit, those sharing a common reflection point according to the start and end of the cavity are arranged in the order of distance between the transmitting unit and the receiving unit, and
A step of superimposing the auxiliary charts corrected for each predetermined relative permittivity or for each speed and arranging them in the order of the relative permittivity or the speed used for the running correction to generate a chart. The cavity thickness estimation method according to claim 1, wherein the cavity thickness is estimated. A radar device that has a plurality of transmitters that radiate electromagnetic waves and a plurality of receivers that receive reflected waves and is mounted on a vehicle.
A chart generation means for generating a chart in which the reflected wave traces received by each of the receiving units are polymerized by a common reflection point polymerization method and arranged in order of relative permittivity or velocity.
The point at which the reflected wave was emphasized by the polymerization at the position of the relative permittivity or the reflected wave velocity of the medium on the starting end side of the cavity under the road and the air in the cavity in the chart generated by this chart generating means. An estimation means for extracting and estimating the cavity thickness under the road based on their positions, and
A cavity thickness estimation device comprising. The chart generation means generates an auxiliary chart in which among the reflected wave traces received by each receiving unit, those sharing a common reflection point according to the start and end of the cavity are arranged in order of the distance between the transmitting unit and the receiving unit. , This auxiliary chart is overlaid with a plurality of predetermined relative permittivity corrections or run time corrections for each speed, and the charts are generated by arranging them in the order of the relative permittivity or the speed used for the run time correction. The cavity thickness estimation device according to claim 3.

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