JPH09292350A - Nondestructive inspection method by radar image processing system - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable detecting the position and the magnitude of a target based on the direction and the position of the vector by obtaining the image to be measured in the ground or inside concrete by a radar, and obtaining the gradient vector having the high intensity from the measured image. SOLUTION: The electromagnetic waves are irradiated from a plurality of measuring positions on the strength line at the surface of, e.g. concrete layer, by a radar; the reflected waves are received and the measured image in the concrete layer is obtained. Then, the gradient vector having the high intensity in the signals from the target of the image to be measured is obtained. With the measured position as the reference, the lower intersecting point of the straight lines in the direction of the gradient vector located at the lower position of the circle whose radius is the vertical distance to the surface of the target is obtained. Thus, the shape or the position of the target can be obtained nondestructively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a non-destructive inspection by a radar image processing system for inspecting a target object having different permittivity in a medium such as concrete or reinforcing bars and voids in the ground.

[0002]

2. Description of the Related Art Conventionally, an underground exploration radar or a reinforcing bar exploration radar has been used to investigate targets such as voids in the ground and reinforcing bars in concrete without destruction.

However, the conventional method has the following problems. <a> Since the signal emitted from the radar spreads and propagates with a constant beam width, the image of the target object such as a gap is displayed as an image that spreads differently from the actual shape. When determining the presence or absence, it often depends on the experience of the engineer, and it is difficult to detect the size and shape. <B> In the case of reinforced concrete, since the reinforcing bars are arranged at narrow intervals in the concrete and the reflection from multiple reinforcing bars is strong, the leading edge of the reflected wave from each reinforcing bar due to scattering and interference of reflected waves. Becomes difficult to distinguish. Therefore, it was difficult to detect the position of the reinforcing bar.

[0004]

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method for easily inspecting the position and size (shape) of a target object in different media.

[0005]

SUMMARY OF THE INVENTION The present invention is a non-destructive inspection method by a radar image processing system for detecting a target existing in a medium, in which electromagnetic waves are emitted from a plurality of measurement positions on a straight line of the medium surface. Then, the reflected wave is received, the measurement image in the medium is obtained, the gradient vector with a large intensity is obtained in the signal from the target of the measurement image, the measurement position is set as a reference, and the gradient vector direction located below the measurement vector is determined. Non-destructive inspection method by a radar image processing system, characterized in that the shape or position of the target object is obtained by obtaining the lower measurement intersection of a circle whose radius is the vertical distance between the straight line and the surface of the target object, or In a non-destructive inspection method by a radar image processing system for inspecting a plurality of arranged reinforcing bars existing in a medium, electromagnetic waves are irradiated from a plurality of measurement positions on a straight line of the medium surface, The reflected wave is received, the measurement image in the medium is obtained, the diagram of the measurement image is obtained at each constant depth from the medium surface, the average line is obtained for each diagram, and the intensity above the average value is integrated, A nondestructive inspection method by a radar image processing system is characterized in that the depth of the reinforcing bar is obtained from the depth of the diagram which becomes the maximum integrated value.

[0006]

Embodiments of the present invention will be described below with reference to the drawings. <A> Outline of analysis method of nondestructive inspection A medium having a target such as a void, for example, a stratum having a concrete layer on a sand layer having a spherical void as shown in FIG. 1 is nondestructively inspected. Therefore, an exploration radar (UG-V33 underground exploration radar, Mitsui Shipbuilding Co., Ltd.) is moved along the measurement surface of the surface of the earth, and an electromagnetic wave is radiated from the exploration radar into the ground at each measurement position and its reflection is performed. The waves are received and image processing is performed to obtain the position and shape of the target such as voids and reinforcing bars. The exploration radar is, for example, a three-element dipole, three-polarization mode operation antenna system, and is a high resolution type with a wide band frequency of 20 MHz to 1 GHz.

Since the signal emitted from the radar spreads and propagates with a constant beam width, the signal image reflected and returned from the target differs from the actual shape of the target. Therefore, in the case of the right side of FIG. 1, the measurement result of the radar for the actual air gap as shown in FIG. 1 reflects from the target object of the spherical air gap as shown by the solid line and returns, so that on the radar screen,
It is assumed that the target is received from the vertical direction, and the target is displayed at the tip of the vertical dotted line.

As a result, on the radar screen, as shown in FIG. 2, the spherical void of the target appears as a curve B which is upwardly convex as shown by curve B. That is, the straight line (Y = tan θn (X−Xn)) of each signal obliquely incident is a locus ((X
It is displayed as the depth in the direction orthogonal to the measurement surface of the radar according to -Xn) ² + Y ² = Yn ² ).

The radar-measured image thus obtained is processed as shown in FIG. That is, in order to make the calculation efficient, a necessary or significant area is set (S1).
Next, the surface wave that becomes noise is removed, and the zero point of the time axis is adjusted to make the measurement position the origin (S2). Further, in order to suppress noise, the image is smoothed (S3). Next, in order to separate the target objects such as the reinforcing bars and the voids, the division of the detection target and the segmentation by target are blocked (S4). The voids and the reinforcing bars divided here are subjected to respective processings, and based on these results, image synthesis for each section is performed (S
5) Further, smoothing processing is performed (S6).

<B> Restoration of air gap shape The closer the position of the radar is to just above the air gap, the stronger the influence of a signal that is closer to a straight line, and the stronger the intensity of the reflected signal. That is, on the screen, the intensity of the reflected signal due to the change in the position between the moving radar and the fixed air gap is shown as the difference in light and shade of the image. Therefore, conversely, the direction in which the change in the grayscale of the image is the maximum is considered to indicate the direction of the signal from the radar, which is reflected by returning to the arbitrary surface of the air gap.

From this, the depth Y at arbitrary coordinates (Xn, Yn) of the radar image display obtained as shown in FIG.
A circle whose radius is n is drawn with the coordinate (Xn, 0) of the measurement position as the center. This is 0 to m which is half of the symmetrical section
Equation (1) is obtained for each image display coordinate in the section up to. Subsequently, the gradient vector G (Xn, Yn) of the grayscale intensity of the image at the coordinates (Xn, Yn) is obtained by the equation (2), and the vector direction (tilt) at that time
Is calculated by Equation (3) (however, in the tilt direction in this case, the sign of the reflected wave may need to be adjusted because the phase of the reflected wave may change depending on the signal processing method of the radar).

That is, the original shape of the void can be restored by obtaining a downward value (lower measured intersection) at the intersection where the circle of equation (1) and the straight line of equation (4) meet, This makes it possible to detect the shape and position of the void. Taking the case of the left side of Fig. 1 as an example, this is true when the radar image display position below the dotted line (the portion of the sine waveform of the reflected wave) is bent in the direction of the gradient vector (to the right) as shown by the solid line. It becomes the position of the surface of the void.

At this time, the analysis is performed on a signal having a certain image intensity or more. Further, in a multilayer structure such as a road, it may be necessary to consider the influence of the refraction of electromagnetic waves due to the difference in the dielectric constant of each layer. In order to take this effect into consideration, if the effect of refraction is corrected as in Expression (5), the degree of convergence of the restored image is further improved.

[0014]

(Equation 1)

[0015]

(Equation 2)

[0016]

(Equation 3)

[0017]

(Equation 4)

[0018]

(Equation 5)

The above points are shown in the flow chart of FIG. 4. Gradient vector processing of the void image is performed using a noise removal type differential filter (S10), and gradient vector coordinates of maximum intensity above a certain size are obtained. Is traced (S11), and the gradient (slope) is calculated for each coordinate according to Equation 3 (S12). Next, for each coordinate, the Y value (depth from the surface) is used as a radius to draw a circle centered on the measurement position (X, 0), and the circle is converted (S13). Step S1 of passing through the measurement position (X, 0) to restore the void shape
A downward intersection (lower measured intersection) between the straight line of the gradient of the gradient vector obtained in 2 and the circle obtained in step S13 is calculated (S14). When the restoration process is completed for the coordinates obtained in step S11 (S15), the influence of refraction is corrected when the strata are multiple (S16). Next, in order to remove the abnormal value, the restoration coordinate averaging process is performed (S
17) Further, in order to clarify the shape of the void, a weighting function in which the void is 1 and the others are 0 is used (S18). In addition,
In step S10, a gradient vector processing method for only corresponding coordinates by contour processing is also possible.
Further, in step S11, the stronger signal is selected from the first and second (the polarities are opposite to each other) reflected signals from the gap (depth correction is performed later).

<C> Identification of rebar position The gap is narrow like rebar in concrete. Especially in the case of double rebar, it is difficult to distinguish the focus of each rebar or the leading edge of the reflex signal due to scattering and interference of the reflex signal. Therefore, only the focal portion of the reinforcing bar is emphasized by the weighting coefficient (= 1), and the other portions are made the same as the background signal of the image by the weighting coefficient (= 0).

For example, FIG. 9 shows a radar image of a region in which a composite reinforcing bar is arranged near the surface and a rectangular void is formed below the reinforcing bar. When the peak signal (mountain apex) from the reinforcing bar is set as the position of the reinforcing bar in this image, this apex is difficult to recognize with the naked eye. Therefore, in the data of FIG. Depth for each array of image data (each row)
Drawing each line, the line diagram of the part where the reinforcing bar does not exist is as shown in FIG. 6, and the line diagram of the part where the maximum peak signal is obtained when the reinforcing bar exists is as shown in FIG. 7. . In addition,
6 to 7, the vertical axis represents the relative intensity (Relat).
iv Intensity), and the horizontal axis represents the distance (Distance (cm)) in the measurement direction.

In the line diagram drawn in this way, for example, as shown in FIG. 7, the coordinates when a series of peak points have the maximum strength indicate the position of each rebar. That is, the column coordinates in the horizontal direction of each peak (triangular display portion) indicate the pitch of the reinforcing bars (horizontal position), and the row coordinates at that time indicate the coating thickness (vertical position) of the reinforcing bars on the screen. To calculate this process by a computer, a straight line is drawn with the average value for each row (A1 in FIG. 7), and each section corresponding to a value equal to or higher than the average line (each portion forming a mountain on the average line) Is set for each section. At this time, two or more peaks may exist on the primary average line (A1 in FIG. 7) that are not independent but are connected to each other due to the difference in the reinforcing bar reinforcement depth. Second average line (A2)
When used as, the rebar position can be detected more accurately.

That is, by comparing the average values and selecting the maximum line, that line corresponds to the vertex of the reinforcing bar, that is, the vertical (depth) position of the reinforcing bar forming the maximum peak diagram in the array of row elements. Then, when the maximum value for each section in this line is calculated,
The horizontal position of the rebar.

The possibility that the multiple reflection signal from the reinforcing bar is selected as the peak can be avoided by selecting only a value above + on the average value for each row. Further, in the case of a double reinforcing bar, it is advisable to divide the existing section of both reinforcing bars into two blocks. Further, by performing visual confirmation and calculation in parallel, more accurate detection can be performed. If accurate depth information is required, consider the permittivity data and select only representative points to correct the actual depth of the reinforcing bar in the target medium and the depth of the reinforcing bar on the screen. And get accurate results.

When the above processing is shown in the flow of FIG. 5, first, the images from the respective reinforcing bars are displayed as hyperbolas. Therefore, in the case of a plurality of arranged reinforcing bars, an image in which a plurality of hyperbolas are combined is obtained ( S21). Next, a diagram for each row (constant depth) of this image is obtained as shown in FIG. 7 (S22). The primary average line and the secondary average line of each line diagram obtained in step S22 are obtained as shown by A1 and A2 in FIG. 7 (S2
3). Further, the integration of all the sections above the secondary average line is performed for each row (S24), the row of the maximum integrated value is selected, and the depth of the reinforcing bar is obtained (S25). The maximum value is calculated for each section above the secondary average line and the horizontal position of the reinforcing bar is calculated (S2).
6). To clarify the position of each rebar, set the rebar to 1,
A weighting function that sets the others to 0 is used (S27). In addition,
In steps S23, S24, and S25, the order in which the largest number of peaks is counted in the calculation by the primary and secondary averages is selected (the primary average may be good in some cases). In this case, the sign of the row value may be either positive or negative, but at the time of comparison, only one sign is used as a reference.

An embodiment of the present invention will be described below. <A> Example 1 As shown in FIG. 8, a rectangular void (40 cm wide, 10 vertical) in the sand.
cm of polyurethane material) and 3c from the sand surface
Five rebars each having a diameter of 22 cm are arranged at a depth of m at an interval of 20 cm, and further, rebars having the same diameter are arranged at a depth of 16 cm from the surface of the sand below the upper rebars. A 5 cm thick polyurethane layer is placed on the sand surface.

In order to measure the positions and sizes of the voids and the reinforcing bars, the radar is moved along a straight line on the surface of the polyurethane, and electromagnetic waves are radiated into the ground from a predetermined measuring position, and the ground such as the voids and the reinforcing bars is radiated. Receives reflected waves from inside.

<B> Measurement and Analysis Results of Example 1 The measurement results of Experiment 1 are shown in FIG. This measurement result is obtained by removing the surface wave and adjusting the surface to zero on the time axis. FIG. 9 is a plot of the intensity of the received reflected wave. The intensity distribution in FIG. 9 does not show the reflected waves from the material at the depth in the vertical direction but is a plot of the total of the reflected waves at various angles received at the measurement position, plotted below.
This vertical depth (Depth (cm)) roughly corresponds to the propagation distance of the reflected wave. The horizontal direction indicates the distance (Distance (cm)) in the measurement direction.

The void shape is restored from the measurement data of FIG.
FIG. 10 shows the positions of the reinforcing bars. FIG. 12 shows the gradient vector for the rectangular void of FIG. 9, which is obtained without removing noise. For practical application, narrow down the target, block it, remove noise, and use

FIG. 11 is a schematic representation of the process of restoring (converting) the shape of a rectangular void. This display is based on only the coordinates where the maximum gradient vector of a certain intensity or more in each measurement distance unit is obtained in the air gap reflection signal. Although some variation in the conversion result can be seen due to noise in the image, it can be seen that it is relatively close to the original shape.
In this conversion process, be careful to match the X and Y coordinates with the scale on the image display. In addition, in FIG. 11, the thick straight line in the center indicates the measurement surface, and the triangle mark indicates before conversion.
The square marks indicate the result after conversion.

By using the above results and method, it can be seen that the identification of the reinforcing bar position (white portion) and the shape of the rectangular void (black portion) are reproduced relatively clearly in FIG. Also, by displaying the polarity and magnitude of the electric field of the reflected wave in color, the characteristics of the material of each target can be clearly distinguished.

<C> Example 2 As shown in FIG. 13, a diameter 3 made of a polyurethane material in sand
An area in which a 0 cm spherical void is formed and a 10 cm thick layer of unreinforced concrete is placed on the sand is used. The void is arranged such that the upper part of the void is 30 cm above the concrete top surface. Concrete has W / C 55%, slump 5 cm, compressive strength 400 kg / cm ² , and sand from Fujikawa, Shizuoka Prefecture (specific gravity: 2.61, moisture content: 2-3%).
It was used.

<D> Measurement and Analysis Results of Example 2 The measurement results of Example 2 (FIG. 13) are shown in FIGS. 14 and 15. FIG. 14 shows the result when the surface wave and the reflected wave from the isotropic boundary are removed. This result is obtained by removing the surface wave and adjusting the surface to zero on the time axis.
FIG. 15 shows the result of restoration of the void shape from this measurement data. From the results shown in FIG. 15, it was found that although the perfectly spherical shape did not appear, the results close to the actual shape such as the size of the void were restored. 14 to 15, the vertical direction indicates the depth (Depth (cm)), and the horizontal direction indicates the distance in the measurement direction (Distance (c)).
m)) is shown.

[0034]

According to the present invention, the following effects can be obtained. <B> The shape and position of the target object can be obtained using the gradient vector of the image. <B> By obtaining the strength of the image in the row direction and averaging in the row direction, the depth of the reinforcing bar and the position in the lateral direction can be obtained.

[Brief description of drawings]

[Figure 1] Explanation of radar image display of air gap

FIG. 2 is an explanatory diagram of the restoration of the actual shape of the void.

FIG. 3 is an overall flowchart of measurement image processing.

FIG. 4 is a flow chart for determining the position and size of a void.

[Fig. 5] Flow chart for determining the position of the reinforcing bar

FIG. 6 is a lateral line diagram of a portion without a reinforcing bar.

FIG. 7 is a lateral line diagram of a portion having a reinforcing bar.

FIG. 8: Layout of rectangular voids under multiple rebar conditions

9 is a measurement image of the arrangement of FIG.

FIG. 10 is an analysis result of the arrangement of FIG.

FIG. 11 is an explanatory diagram of the restoration of the current state of the void.

FIG. 12 is an example of the gradient vector of FIG.

FIG. 13: Layout of spherical voids under non-rebar conditions

14 is a measurement image of the arrangement of FIG.

FIG. 15 is an analysis result of the arrangement of FIG.

Front Page Continuation (72) Inventor Park Suk-hyun 7-22-1, Roppongi, Minato-ku, Tokyo Inside Institute of Industrial Science, University of Tokyo (72) Inventor Masaru Yoshizawa 1-1-21 Toranomon, Minato-ku, Tokyo Metropolitan Expressway Inside the technical center

Claims (4)

[Claims] 1. A nondestructive inspection method using a radar image processing system for detecting a target existing in a medium, wherein electromagnetic waves are emitted from a plurality of measurement positions on a straight line of a medium surface and reflected waves are received. , Find the measurement image in the medium, find the gradient vector with high intensity in the signal from the target of the measurement image, and use the measurement position as the reference, and the straight line in the direction of the gradient vector below that and the surface of the target A non-destructive inspection method by a radar image processing system, characterized in that the shape or position of a target object is found by finding the lower intersection point of a circle whose radius is the vertical distance of. 2. A non-destructive inspection method by a radar image processing system for inspecting a plurality of arranged reinforcing bars existing in a medium, wherein electromagnetic waves are radiated from a plurality of measurement positions on a straight line of a medium surface, and reflected waves thereof are reflected. , The measurement image in the medium is obtained, the diagram of the measurement image is obtained at each constant depth from the medium surface, the average line is obtained for each diagram, and the intensity above the average value is integrated, and the maximum integrated value A nondestructive inspection method using a radar image processing system, characterized in that the depth of the reinforcing bar is obtained from the depth of the line diagram. 3. A nondestructive inspection method by a radar image processing system for inspecting a plurality of arranged reinforcing bars existing in a medium, wherein electromagnetic waves are radiated from a plurality of measurement positions on a straight line of the medium surface, and reflected waves thereof are reflected. To obtain a measurement image in the medium, obtain a diagram of the measurement image at each constant depth from the surface of the medium, obtain an average line for each diagram, and group by consecutive intensities above the average value, A non-destructive inspection method by a radar image processing system, characterized in that the position of the reinforcing bar in the medium surface direction is obtained from the maximum value of each group. 4. The non-destructive inspection method by the radar image processing system according to claim 1, wherein the measurement image near the target is divided into blocks. Non-destructive inspection method by system.