JP7036432B2 - Direction estimation system and method for planar exploration target using dipole array antenna - Google Patents

Description

The present invention estimates the direction in which an exploration target surface having a planar spread such as a crack, a fault, or a boundary surface existing in the ground faces the axis of a cylindrical well excavated in the ground. Regarding the direction estimation system and method to be performed.

Since the 1970s, a borehole radar that can measure the position and shape of exploration targets such as cracks, faults, and groundwater in the ground by placing an antenna for transmitting and receiving electromagnetic waves in a cylindrical well excavated in the ground. , Is being researched and developed internationally. The frequency of electromagnetic waves used for transmission and reception is about 10 to 400 MHz, and the wavelength in the ground is about 20 cm to several m. Rocks, sand and soil that do not contain water are electromagnetically close to air, and when water flows into cracks or faults, the water content increases and electromagnetic contrast occurs. That is, the borehole radar can estimate the positions of cracks and faults by estimating the spatial distribution of water content in the ground. In the borehole radar, a dipole antenna is usually used due to the limitation of the shape of the well, but in this case, it becomes omnidirectional in the circumferential direction of the well. Therefore, when the transmitting antenna and the receiving antenna are inserted into one well, the estimation is limited to the depth and distance at which the object exists.

Therefore, a dipole array antenna has been proposed in which a plurality of dipole antenna elements are arranged in an annular shape on a plane orthogonal to the axes of the antenna elements so that the axes of the antenna elements are parallel to each other (the following). (See Non-Patent Documents 1 and 2). Specifically, when an electromagnetic wave radiated into the ground and reflected by an exploration target is received by a dipole array antenna, the electromagnetic wave is received by each antenna element of the dipole array antenna with an arrival time difference depending on the position of the antenna element. Will be done. By using this arrival time difference, it is possible to estimate the arrival direction of the electromagnetic wave reflected by the exploration target.

As a method of feeding power to each antenna element of the dipole array antenna, a method of light feeding using an optical modulator to avoid electromagnetic interference between the coaxial feeder and the antenna element (see Non-Patent Document 1 below). , There is a method of coaxial feeding by covering the coaxial feeder with a conductor cylinder of an appropriate length to avoid interference (see Patent Document 1 below).

As a signal processing method used for estimating the arrival direction of an electromagnetic wave, assuming that each antenna element is in a homogeneous medium, the arrival time of the electromagnetic wave changes sinusically with a period of 360 ° with respect to the azimuth angle in which the antenna element exists. (See Patent Document 1 and Non-Patent Document 3 below).

Japanese Patent No. 5568237

S. Ebihara, "Directional borehole radar with dipole antenna array using optical modulators", IEEE Trans. Geoscience and Remote Sensing, January 2004, Vol. 42, No. 1, p. 45-58. M. Sato, 1 outside, "a Novel Directional Borehole Radar System Using Optical Electrical Field Sensors", IEEE Trans. Geoscience and Remote Sensing, August 2007, Vol. 45, No. 8, p. 2529-2535. S. Ebihara, Y. et al. Kimura, T.M. Shimamura, R.M. Uchimura, and H. Choshi, "Coaxial-fed Circular Dipole Array Antenna with Ferrite Loading for Thin Directional Borehole Radar Sonde," IEEE Trans. Geoscience and Remote Sensing, 2015, vol.53, no. 4, pp. 1842-1854.

When the wave vector of the incoming electromagnetic wave (vector pointing in the propagation direction of the electromagnetic wave) is orthogonal or almost orthogonal to the axis of the well, the dipole array antenna inserted in the well is used to estimate the arrival direction of the electromagnetic wave. It can be considered that the technology is established.

However, according to the diligent research of the inventor of the present application, in the signal processing method used for estimation when the angle formed by the wave vector and the axis of the well is 90 ° or its vicinity, the exploration target is planar and exists in the ground. In the case of an exploration target plane with an expanse, it may not be possible to accurately estimate the direction of arrival of electromagnetic waves over the entire range from 0 ° to 180 ° where the angle between the wave vector and the axis of the well is formed. I found.

Specifically, as described above, the incident electromagnetic wave incident from the exploration target surface toward the center of the dipole array antenna is received at each antenna element of the dipole array antenna with an arrival time difference depending on the position of the antenna element. However, when the arrival time difference between each antenna element does not appear large enough to accurately estimate the arrival direction of the electromagnetic wave, the incident elevation angle θ defined as the angle between the arrival direction of the incident electromagnetic wave and the axis of the well is , Occurs when approaching a specific incident elevation angle (θ ₀ or 180 ° −θ ₀ : hereinafter referred to as “critical incident elevation angle”). The incident elevation angle θ is synonymous with the angle formed by the wave vector and the axis of the well.

The present invention has been made in view of the above-mentioned problems, and an object thereof has a planar spread in consideration of the incident elevation angle (angle formed by the wave vector and the axis of the well) of the incident electromagnetic wave. It is an object of the present invention to provide a direction estimation system and a method capable of accurately estimating the direction in which the exploration target surface faces the axis of the well.

In the present invention, in order to solve the above-mentioned problems, the direction in which the exploration target surface having a planar spread existing in the ground faces the axis of the cylindrical well excavated in the ground is estimated. It is a direction estimation system that
The dipole array antenna used by being inserted into the well and the incident azimuth angle around the axis of the incident electromagnetic wave incident on the dipole array antenna inserted into the well from the exploration target surface are determined by the exploration target surface. The dipole array antenna is provided with three or more receiving dipole antenna elements extending in parallel with each other in a tubular container, and the dipole antenna element is provided. Are dispersed and arranged in the circumferential direction of the virtual cylindrical surface on the virtual cylindrical surface coaxial with the container.
The incident azimuth derivation unit is
When the dipole array antenna inserted into the well is an electromagnetic wave radiated toward the exploration target surface and receives the incident electromagnetic wave reflected and incident on the exploration target surface, the dipole antenna element is divided. The signal waveform of the received electromagnetic wave is analyzed, and the arrival time of the incident electromagnetic wave for each dipole antenna element is obtained.
Based on the arrival time of each dipole antenna element, the earliest arrival time or the earliest arrival time when the relationship between the position in the circumferential direction of the virtual cylindrical surface and the arrival time when the incident electromagnetic wave is received at the position is approximated by a sine function. The position in the circumferential direction of the virtual cylindrical surface indicating the latest arrival time is specified.
The incident elevation angle formed by the direction of arrival of the incident electromagnetic wave and the axis of the well is the first critical incident elevation angle existing between 0 ° and 90 ° and the second critical incident existing between 90 ° and 180 °. When it is within the range of the first incident elevation angle between the elevation angles, the position in the circumferential direction of the virtual cylindrical surface indicating the earliest arrival time is derived as the incident azimuth angle, and the incident elevation angle is from 0 ° to 180. When it is within the range of the second incident elevation angle outside the range of the first incident elevation angle within the range of °, the position in the circumferential direction of the virtual cylindrical surface indicating the latest arrival time is derived as the incident azimuth angle.
The first and second critical incident elevation angles are the circumferential direction in the electric field component parallel to the axial direction of the container of the incident electromagnetic wave when the incident elevation angle is changed within the range of 0 ° to 180 °. The electric field circumferential dependence index expressed by the ratio obtained by dividing the magnitude of the changing electric field by the magnitude of the electric field that does not change in the circumferential direction is given as the incident elevation angle that becomes the minimum value at -20 dB or less, and the first Provided is a direction estimation system whose first feature is that the sum of the first and second critical incident elevation angles is 180 °.

Further, in the present invention, in order to solve the above-mentioned problems, the direction in which the exploration target surface having a planar spread existing in the ground faces the axis of the cylindrical well excavated in the ground. It is a direction estimation method to estimate
Three or more dipole antenna elements for reception extending in parallel with each other are provided in a tubular container, and the dipole antenna elements are dispersed on a virtual cylindrical surface coaxial with the container in the circumferential direction of the virtual cylindrical surface. The first step of inserting the arranged dipole array antenna into the well, and
A second step of receiving an electromagnetic wave radiated toward the exploration target surface, which is reflected by the exploration target surface and is incident on the dipole array antenna inserted into the well.
A third step of analyzing the signal waveform of the incident electromagnetic wave received for each dipole antenna element and obtaining the arrival time of the incident electromagnetic wave for each dipole antenna element.
Based on the arrival time of each dipole antenna element, the earliest arrival time or the earliest arrival time when the relationship between the position in the circumferential direction of the virtual cylindrical surface and the arrival time when the incident electromagnetic wave is received at the position is approximated by a sine function. A fourth step of specifying the position in the circumferential direction of the virtual cylindrical surface indicating the latest arrival time and setting the incident directional angle of the incident electromagnetic wave incident on the dipole array antenna from the exploration target surface around the axis. , Equipped with
In the fourth step, the incident elevation angle formed by the arrival direction of the incident electromagnetic wave and the axis of the well is the first between the first and second critical incident elevation angles existing between 0 ° and 180 °. When it is within the incident elevation range, the exploration target surface faces the axis of the well with the incident azimuth corresponding to the position in the circumferential direction of the virtual cylindrical surface indicating the earliest arrival time. Derived as a direction, when the incident elevation angle is within the range of 0 ° to 180 ° and is within the second incident elevation angle range outside the first incident elevation angle range, the circumference of the virtual cylindrical surface indicating the latest arrival time. The incident azimuth corresponding to the position in the direction is derived as the direction in which the exploration target surface faces the axis of the well.
The first and second critical incident elevation angles are the circumferential direction in the electric field component parallel to the axial direction of the container of the incident electromagnetic wave when the incident elevation angle is changed within the range of 0 ° to 180 °. It is the first aspect that the electric field circumferential dependence index expressed by the ratio obtained by dividing the magnitude of the changing electric field by the magnitude of the electric field that does not change in the circumferential direction is given as the incident elevation angle which becomes the minimum value at -20 dB or less. The direction estimation method characterized by 1 is provided.

More preferably, the direction estimation system of the first feature includes a transmission dipole antenna element that emits electromagnetic waves toward the exploration target surface while being inserted together with the dipole array antenna in the well, and the transmission The second feature is that the credit dipole antenna element is arranged at a predetermined distance from the dipole array antenna in the axial direction of the well.

More preferably, in the method of estimating the direction of the first feature, in the first step, the transmission dipole antenna element is separated from the dipole array antenna by a predetermined distance in the axial direction of the well, and the inside of the well is separated. The second feature is that the electromagnetic wave is emitted from the transmission dipole antenna element toward the search target surface.

More preferably, in the direction estimation system of the second feature, the incident azimuth derivation unit has the transmission / reception antenna unit composed of the dipole array antenna and the transmission dipole antenna element, and the inside of the well is the axis of the well. The time difference between the earliest arrival time and the latest arrival time at each position when moving sequentially in the direction is derived.
When the position where the time difference is the minimum value of a predetermined value or less with respect to the change in the position in the axial direction of the well is specified as the singular position, the incident elevation angle is the first and the singular position at the specified singular position. It is approximately estimated that it coincides with any one of the second critical incident elevation angles, and the incident elevation angle is within the range of the first incident elevation angle on one side with respect to the singular position in the axial direction of the well. The third feature is to determine that the incident elevation angle is within the second incident elevation angle range on the other side with the singular position as a reference, and to derive the incident azimuth angle.

More preferably, in the method of estimating the direction of the second feature, in the first step, the transmission / reception antenna portion including the dipole array antenna and the transmission dipole antenna element is placed in the well with the axial center of the well. Move sequentially in the direction,
In the first step, each time the transmission / reception antenna unit sequentially moves in the well in the axial direction of the well, the second step to the fourth step are sequentially executed, or the fourth step is sequentially executed.
In the first step, each time the transmission / reception antenna unit sequentially moves in the well in the axial direction of the well, the second step and the third step are sequentially executed, and the first step is performed. After the step 1 to the third step is completed, the fourth step is executed.
In the fourth step, the transmission / reception antenna unit derives a time difference between the earliest arrival time and the latest arrival time at each position in which the well is sequentially moved in the axial direction of the well. When the position where the time difference is the minimum value of a predetermined value or less with respect to the change in the position in the axial direction of the well is specified as the singular position, the incident elevation angles are the first and the first at the specified singular position. It is estimated approximately that it coincides with any one of the two critical incident elevation angles, and the incident elevation angle is within the first incident elevation angle range on one side with respect to the singular position in the axial direction of the well. The third feature is to determine that the incident elevation angle is within the second incident elevation angle range on the other side with respect to the singular position and derive the incident azimuth angle.

Further, in the direction estimation system of the third feature, the incident azimuth derivation unit is used for transmission at each position when the transmission / reception antenna unit sequentially moves in the well in the axial direction of the well. The propagation time of the electromagnetic wave from the dipole antenna element to the dipole array antenna is measured, and based on the relationship between the position in the axial direction of the well and the propagation time, the well has a plane including the exploration target surface. Derived the tilt angle for the plane perpendicular to the axis,
When the inclination angle is larger than the first critical incident elevation angle,
The incident azimuth derivation unit
When the singular position is specified within the movement range of the transmission / reception antenna unit in the axial direction of the well, the plane including the search target surface is the well with reference to the singular position within the movement range. It is determined that the incident elevation angle is within the second incident elevation range on the intersection side intersecting the axis, and it is determined that the incident elevation angle is within the first incident elevation range on the side opposite to the intersection side. When the singular position is not specified within the movement range of the transmission / reception antenna unit in the axial direction of the well, it is determined that the incident elevation angle is within the first incident elevation angle range in the entire range of the movement range. This is the fourth feature.

Further, in the method of estimating the direction of the third feature, in the third step, the transmission dipole antenna element at each position where the transmission / reception antenna unit sequentially moves in the well in the axial direction of the well. The propagation time of the electromagnetic wave from the dipole array antenna to the dipole array antenna is measured, and as a pretreatment step of the fourth step, the exploration target surface is based on the relationship between the position in the axial direction of the well and the propagation time. Derived the tilt angle of the plane containing the above-mentioned well with respect to the plane orthogonal to the axis of the well.
When the inclination angle is larger than the first critical incident elevation angle,
In the fourth step,
When the singular position is specified within the movement range of the transmission / reception antenna unit in the axial direction of the well, the plane including the search target surface is the well with reference to the singular position within the movement range. It is determined that the incident elevation angle is within the second incident elevation range on the intersection side intersecting the axis, and it is determined that the incident elevation angle is within the first incident elevation range on the side opposite to the intersection side. When the singular position is not specified within the movement range of the transmission / reception antenna unit in the axial direction of the well, it is determined that the incident elevation angle is within the first incident elevation angle range in the entire range of the movement range. This is the fourth feature.

Further, in the direction estimation system of the fourth feature, in the dipole array antenna, the plane including the exploration target surface intersects the axis of the well from the transmission dipole antenna element in the well. The fifth feature is that it is located in.

Further, in the method of estimating the direction of the fourth feature, in the first step, the dipole array antenna is placed in the well, and the plane including the search target surface from the transmission dipole antenna element is the well. The fifth feature is to arrange it on the side of the intersection that intersects the axis.

According to the direction estimation system or method according to the present invention, the incident elevation angle formed by the arrival direction of the incident electromagnetic wave incident on the dipole array antenna and the axis of the well is within the first incident elevation angle range, or the first. 2 By determining whether it is within the incident elevation range, it is possible to derive an appropriate incident azimuth according to the incident elevation angle, and the incident elevation angle is the first and first over the entire range from 0 ° to 180 °. The incident azimuth around the axis of the well of the incident electromagnetic wave is set as the direction in which the surface to be explored faces the axis of the well, except when it coincides with or is near one of the two critical incident elevation angles. , Can be estimated accurately.

Here, the causes of the first and second critical incident elevation angles that make it difficult to estimate the incident azimuth will be described in detail with reference to FIGS. 1 and 2.

First, FIGS. 1 and 2 will be described. FIG. 1 shows a state in which a dipole array antenna configured with four dipole antenna elements D1 to D4 is inserted into a well, and accommodates the dipole antenna elements D1 to D4 and the dipole antenna elements D1 to D4. Schematic representation of the positional relationship between a tubular container (vessel) V, a cylindrical well B, and an incident electromagnetic wave Win that is reflected by an exploration target surface (not shown) and incident toward the center O of a dipole array antenna. FIG. 2 is a cross-sectional view (xy plane) which is orthogonal to the axis Z of the well B and passes through the center O of the dipole array antenna, showing the same positional relationship.

In each of the four dipole antenna elements D1 to D4, the axial centers of the dipole antenna elements D1 to D4 are separated from the axial center Z of the well by a predetermined distance b, parallel to the axial center Z, and 90 ° in the circumferential direction of the axial center Z. They are spaced apart and their respective feeding points are located on the same xy plane orthogonal to the axis Z. The container V is cylindrical and has inner and outer diameters of 2a ₁ and 2a ₂ , and the inner diameter of the well B is 2a ₃ (a ₁ <a ₂ <a ₃ ). Is coaxial and passes through the center O of the dipole array antenna. Therefore, the dipole antenna elements D1 to D4 are arranged on a virtual cylindrical surface having a radius b coaxial with the container V so as to be evenly dispersed in the circumferential direction of the virtual cylindrical surface.

The xyz Cartesian coordinate system is used to represent the surrounding space containing the dipole array antenna. The straight line connecting the center O of the dipole array antenna and the feeding points of the dipole antenna elements D1 and D3 is the x-axis (the element D1 side is in the + x direction from the center O), and the feeding points of the center O of the dipole array antenna and the dipole antenna elements D2 and D4. The straight line connecting the points is the y-axis (from the center O to the element D2 side in the + y direction), the axis Z of the well B is the z-axis, and the origin of the xyz orthogonal coordinate system is the center O of the dipole array antenna. There is. Hereinafter, the angle formed by the line segment connecting the origin O and a point on the circumference having an arbitrary radius centered on the origin O on the xy plane and the x-axis (+ x direction) is defined as "azimuth angle φ". Therefore, the azimuth angle φ in the + x direction is 0 °, and the azimuth angle φ in the + y direction is 90 °. Further, both the position of the "circumferential direction of the axis Z" and the position of the "circumferential direction of the virtual cylindrical surface" are specified by the "azimuth angle φ".

The incident electromagnetic wave Win is a plane wave, and the electric field vector E is included in the plane including the wave vector k of the incident electromagnetic wave Win and the axis Z of the well B, and the magnetic field vector H contains only the components perpendicular to the plane. It is assumed that the TM wave (Transverse Magic Wave) is possessed. In FIG. 1, the incident elevation angle θ of the incident electromagnetic wave Win is defined as an angle formed by the arrival direction of the incident electromagnetic wave Win (direction of the wave vector k) and the axis Z of the well B. In FIGS. 1 and 2, the incident azimuth angle φ ₀ around the axis Z of the well B of the incident electromagnetic wave Win is the angle (azimuth angle) formed by the component parallel to the xy plane of the wave vector k of the incident electromagnetic wave Win and the x-axis. Defined as φ). When the ρ-axis passing through the origin O and facing the exploration target plane is set in the xy plane, the angle (azimuth φ) formed by the ρ-axis and the _x -axis is the estimation target of the present invention and coincides with the incident azimuth angle φ0. If the line of intersection LF of the exploration target plane _F and the line of intersection xy plane is added with a broken line in FIG. 2, the ρ axis and the line of intersection _LF are orthogonal to each other.

Next, the electric field circumferential dependence index c (θ) (hereinafter, appropriately simply referred to as “exponent c (θ)”) used for defining the first and second critical incident elevation angles will be described.

The z component E _1z (φ) of the electric field E on the circumference of the radius ρ centered on the origin O on the xy plane set inside the container V is series-expanded by phasor display as shown in the following equation 1. Will be done. The n component of the electric field E _1z (φ) on the right side of the equation 1 indicates a component in which the electric field oscillates n times when the observed position of the electric field is changed in the circumferential direction on the circumference.

The term E _1z ⁽⁰⁾ of n = 0 on the right side of Equation 1 is a component in which the electric field strength is constant on the circumference regardless of the incident azimuth angle φ ₀ , and the term n ≠ 0 on the right side of Equation 1. exp (−jn (φ−φ ₀ )) E _1z ⁽ⁿ⁾ is a component in which the electric field strength is not constant on the circumference and fluctuates according to the incident azimuth angle φ ₀ . As shown in Equation 2 below, the exponent c (θ) is φ = φ ₀ in the term exp (-jn (φ-φ ₀ )) E _1z ⁽ⁿ⁾ of n ≠ 0 of the electric field E _1z (φ). It is defined as the ratio obtained by dividing the absolute value (magnitude of electric field) of the sum of the above by the absolute value (magnitude of electric field) of the term E _1z ⁽⁰⁾ of n = 0.

Of the electromagnetic fields on the cylindrical interface, which is the inner wall surface of the well B of the incident electromagnetic wave Win that is incident on TM, the electric field E _z of the z-direction component, the electric field E _φ of the φ-direction component, and the magnetic field H _φ of the φ-direction component. Contributes to the electromagnetic field in the well B. The incident electromagnetic wave Win enters the well B through the boundary conditions (electric field E _z , electric field E _φ , magnetic field H _φ ) on the cylindrical boundary surface, and the z component E ₁ z of the electric field in the well is generated. As shown in Equation 3, the z component E _1z ^can be decomposed _into E _1z ^Ez derived from the electric field E _z , E 1 z E _φ derived from the electric field E φ, and E ₁ ^z H _φ derived from the magnetic field H φ.

Here, E _1z ^Ez and E _1z ^Eφ are in opposite phase to each other. Further, E _1z ^Ez becomes maximum near θ = 90 ° and has both components of the numerator (n ≠ 0) and the denominator (n = 0) on the right side of Equation 2. On the other hand, E _1z ^Eφ becomes maximum near θ = 0 ° and 180 °, and has a component of the molecule (n ≠ 0) on the right side of Equation 2. Therefore, while the incident elevation angle θ is between 0 ° and 90 °, E _1z ^Ez and E _1z ^Eφ , which are components of n ≠ 0, are offset from each other because they are in opposite phase, and the sum of E _1z ^Ez and E _1z ^Eφ is 0. Alternatively, there is a critical incident elevation angle θ ₀ that is almost zero. Further, when θ = θ ₀ , E _{1z Hφ} ^of the n ≠ 0 component becomes 0 or almost 0. On the other hand, when θ = θ ₀ , E _1z ^Ez of n = 0 component exists and | E _1z ^Ez |> 0, and E _{1z Hφ} ^of n = 0 component is negligible as compared with E _1z ^Ez . small. Therefore, when θ = θ ₀ , the electric field of the n ≠ 0 component is almost eliminated, and the electric field changing in the φ direction at the z component E _1z (φ) of the electric field E on the circumference is almost eliminated, so that E _1z (φ). Does not change much on the circumference and becomes an almost constant value.

Even when the incident elevation angle θ is between 90 ° and 180 °, a phenomenon of vertical symmetry occurs across the xy plane passing through the origin O, so that the components E _1z ^Ez and E _1z ^Eφ of n ≠ 0 are in opposite phase to each other. Therefore, there is a critical incident elevation angle (180 ° −θ ₀ ) that is offset and the sum of E _1z ^Ez and E _1z ^Eφ is 0 or almost 0. Further, when θ = 180 ° −θ ₀ , E _{1z Hφ} ^of the n ≠ 0 component becomes 0 or almost 0. On the other hand, at θ = 180 ° −θ ₀ , E _1z ^Ez of the n = 0 component exists, | E _1z ^Ez |> 0, and E _{1z Hφ} ^of the n = 0 component is ignored as compared with E _1z ^Ez . As small as possible. Therefore, at θ = 180 ° −θ ₀ , the electric field of the n ≠ 0 component is almost eliminated, and the electric field that changes in the φ direction at the z component E _1z (φ) of the electric field E on the circumference is almost eliminated _. (Φ) hardly changes on the circumference and becomes a substantially constant value. In the following, for convenience, θ ₀ may be referred to as a first critical incident elevation angle, and (180 ° −θ ₀ ) may be referred to as a second critical incident elevation angle to distinguish between the two.

Further, as the incident elevation angle θ approaches the critical incident elevation angle θ ₀ or 180 ° −θ ₀ , the degree of cancellation of E _1z ^Ez and E _1z ^Eφ of the n ≠ 0 component increases, and the electric field of the n ≠ 0 component is asymptotic. It approaches 0, and the index c (θ) shown in Equation 2 also asymptotically approaches 0. Therefore, the critical incident elevation angles θ ₀ and 180 ° −θ ₀ can be defined as the incident elevation angles θ having the minimum value when the index c (θ) is −20 dB or less. Here, "-20 dB or less" is for excluding the case where the exponent c (θ) becomes a minimum value when the electric field of the n ≠ 0 component is 0 or almost 0.

The electric field E _1z (φ) is a phasor display of the electric field at a certain position on the circumference of the radius ρ _. Time domain waveform is obtained. When the incident elevation angle θ is the critical incident elevation angle θ ₀ or 180 ° −θ ₀ , E _1z (φ) does not vibrate even if the observation position is changed on the circumference, and is an almost constant value. The time domain waveform obtained in this way is the same at any position on the circumference. This means that when the time domain waveforms of each electromagnetic wave received by the dipole antenna elements distributed and arranged on the circumference of the radius ρ are superimposed, there is no deviation in the time axis direction, and there is no deviation between the antenna elements. The arrival time difference does not appear large enough to accurately estimate the arrival direction of the electromagnetic wave.

On the other hand, when the incident elevation angle θ deviates from the critical incident elevation angle θ ₀ or 180 ° −θ ₀ , E _1z (φ) vibrates when the observation position is changed on the circumference, so these are obtained by inverse Fourier transform. The time domain waveform to be generated changes according to the observation position on the circumference. This means that when the time domain waveforms of each electromagnetic wave received by the dipole antenna elements distributed and arranged on the circumference of the radius ρ are superimposed, a deviation occurs in the time axis direction, and the distance between the antenna elements occurs. It becomes possible to accurately estimate the arrival direction of electromagnetic waves by using the arrival time difference of.

Next, the simulation results of the time domain waveforms of the incident electromagnetic waves received by the dipole antenna elements D1 to D4 will be described using the models shown in FIGS. 1 and 2. The antenna characteristics are analyzed by the moment method using the green function considering the scattered electromagnetic field from the cylindrical boundary surface existing around the dipole array antenna, and the antenna characteristics are induced in the dipole antenna elements D1 to D4 via the incident electromagnetic wave. The received voltage can be calculated. FIG. 3A shows a time domain waveform of the electric field strength E (V / m) of the incident electromagnetic wave used in the simulation, and FIG. 3B shows the incident elevation angles θ of 20 °, 40 °, 60 °, and 80. The time domain waveforms of the received voltage induced in the dipole antenna elements D1 to D4 in the four ways of ° are shown in an superimposed manner. Although the vertical axis of the entire FIG. 3B is the incident elevation angle θ, the vertical axis of the time domain waveforms of the antenna elements D1 to D4 at each incident elevation angle θ is not specified, but is normalized reception. It is a voltage. In the simulation, the following conditions were assumed. The incident azimuth angle φ ₀ of the incident electromagnetic wave is 0 °, the dipole antenna elements D1 to D4 have a total length of 2h = 10 cm, and are on the circumference of the radius b (= 2 cm) on the xy plane in the circumferential direction with reference to the x axis. Arranged in order at 0 °, 90 °, 180 ° and 270 °, the inner diameter of the container V is 2a _1- = 4.7 cm, the outer diameter of the container V is 2a ₂ = 5.7 cm, and the diameter of the well B is 2a ₃ . = 6.7 cm. Further, the permittivity ε ₁ inside the container V, the permittivity ε ₂ at the wall of the container V, the permittivity ε ₃ between the outer wall of the container V and the inner wall of the well B, and the permittivity ε ₄ in the ground are in order. , Ε ₀ , 5ε ₀ , 81ε ₀ −j4.1 × 10 ^-3 / ω, 29ε ₀ −j6.4 × 10 ^-3 / ω. However, ε ₀ is the vacuum permittivity, and ω = 2π × 100 MHz.

Since the incident electromagnetic wave Win is a TM wave of a plane wave and the incident azimuth angle φ ₀ is 0 °, when the incident elevation angle θ is 90 °, the antenna element D1 receives first, and then the antenna element D2 and D4 receives at the same time, and finally the antenna element D3 receives. However, as shown in FIG. 3B, when the incident elevation angles θ are 60 ° and 80 °, the incident electromagnetic waves are in the order of the antenna elements D1, D2, D4, and D3, as in the case where the incident elevation angle θ is 90 °. However, when the incident elevation angle θ is 40 °, the incident electromagnetic waves reach the antenna elements D1 to D4 at the same time, and when the incident elevation angle θ is 20 °, the antenna elements D3, D2 and D4, The incident electromagnetic waves arrive in the order of D1, and the order of arrival is reversed from that when the incident elevation angles θ are 60 ° and 80 °.

When the incident elevation angle θ is 40 °, the incident electromagnetic waves reach the antenna elements D1 to D4 at the same time. Therefore, in this simulation result, it can be seen that the critical incident elevation angle θ ₀ is 40 °. Further, when the incident elevation angle θ is changed between 90 ° and 180 ° under the same conditions, the critical incident elevation angle 180 ° −θ ₀ becomes 140 °. Here, when the incident elevation angle θ is within the first incident elevation angle range (40 ° to 140 °) between the two critical incident elevation angles θ ₀ and 180 ° −θ ₀ , the antenna element D1 to which the incident electromagnetic wave first reaches is described above. The angle (0 °) corresponding to the position on the circumference coincides with the incident azimuth φ ₀ (0 °). However, the incident electromagnetic wave first arrived within the second incident elevation range (0 to 40 °, 140 ° to 180 °) outside the first incident elevation range in the entire range of the incident elevation angle θ from 0 ° to 180 °. The angle corresponding to the position on the circumference of the antenna element D1 finally reached by the incident electromagnetic wave (0 °) is not the angle corresponding to the position on the circumference of the antenna element D3 (180 °). Consistent with φ ₀ (0 °).

Next, when the incident elevation angle θ is within the second incident elevation angle range, the reason why the order of arrival of the incident electromagnetic waves to the antenna elements D1 to D4 is reversed from the case where the incident electromagnetic wave is within the first incident elevation angle range will be briefly described. ..

When the observation position is changed on the circumference due to the presence of the n ≠ 0 component of both E _1z ^Ez and E _1z ^Eφ shown in the above equation 3, the time domain waveform of the observed electric field changes. More specifically, when the observation position is changed on the circumference, the time domain waveform of the observed electric field shifts in the time direction with almost the same wave shape. E _1z ^Ez serves to shift to reach in the forward direction, and E _1z ^Eφ serves to shift to reach in the opposite direction. Here, the forward direction means that the direction in which the incident electromagnetic wave reaches each antenna element in order in the well B coincides with the propagation direction of the incident electromagnetic wave outside the well B. The reverse direction means that the direction in which the incident electromagnetic wave reaches each antenna element in order in the well B is opposite to the propagation direction of the incident electromagnetic wave outside the well B. In this way, the function of E _1z ^Ez and E _1z ^Eφ to shift the time domain waveforms of the electric field observed on the circumference in opposite directions is that E _1z ^Ez and E _1z ^Eφ are in opposite phase to each other. Due to that.

Therefore, as the incident elevation angle θ approaches 90 ° within the first incident elevation angle range, E _1z ^Ez becomes larger than E _1z ^Eφ , and E _1z ^Ez becomes dominant. The component of n ≠ 0 of E _1z ^Ez causes the time domain waveform of the incident electromagnetic wave to reach each antenna element in the forward direction in the well B, resulting in an arrival time difference. On the other hand, as the incident elevation angle θ approaches 0 ° or 180 ° within the second incident elevation angle range, E _1z ^Eφ becomes larger than E _1z ^Ez , and E _1z ^Eφ becomes dominant. Since the component of n ≠ 0 of E _1z ^{Eφ causes} an arrival time difference in the opposite direction with respect to each antenna element in the well B, when the incident elevation angle θ is within the second incident elevation angle range, the antenna elements D1 to The order of arrival of the incident electromagnetic wave to D4 is reversed from the case where the incident electromagnetic wave is within the first incident elevation angle range.

As is clear from the above description, according to the direction estimation system or method of the first to fifth features, whether the incident elevation angle is within the first incident elevation range or the second incident elevation range. Therefore, it is possible to derive an appropriate incident azimuth, and it is possible to accurately estimate the direction in which the exploration target surface faces the axis of the well.

A perspective view schematically showing the positional relationship between a well, a dipole array antenna composed of four dipole antenna elements inserted into the well, and incident electromagnetic waves. FIG. 3 is a cross-sectional view of a cross section in which the positional relationship shown in FIG. 1 is orthogonal to the axis of the well and passes through the center of the dipole array antenna. Using the models shown in FIGS. 1 and 2, the time domain waveform of the electric field strength of the incident electromagnetic wave used for simulating the time domain waveform of the incident electromagnetic wave received by the four dipole antenna elements, and induced in each antenna element. The figure which shows the time domain waveform of the received voltage. A block diagram schematically showing a schematic configuration example of a direction estimation system according to an embodiment of the present invention. Explanatory drawing explaining the relationship between the incident elevation angle and the center of a dipole array antenna. The figure which shows an example of the calculation result of the electric field circumferential dependence index c (θ) calculated under the condition corresponding to the structure of a field experiment. The figure which shows the time domain waveform of the received voltage induced in the four receiving antenna elements measured by the field experiment assumed in FIG. An explanatory diagram illustrating a model used for numerical calculation of the relationship between the incident elevation angle and the position of the feeding point of the dipole array antenna on the axis of the well. The figure which shows the result of having calculated the relationship between the incident elevation angle and the position of the feeding point of a dipole array antenna on the axis of a well by numerical calculation.

Hereinafter, the direction estimation system (hereinafter, appropriately referred to as “the present system”) and the direction estimation method (hereinafter, appropriately referred to as “the present method”) according to the embodiment of the present invention will be described with reference to the drawings. do.

<Outline configuration of this system>
FIG. 4 is a schematic configuration diagram of the system 10. As an example, the system 10 assumes a step frequency continuous wave (SFW) radar system that measures gain (amplitude) and phase at one frequency f and directly acquires data in the frequency domain by sweeping this frequency f. .. The system 10 includes an incident azimuth derivation unit 11, a transmission interface unit 12, a reception interface unit 13, a transmission antenna unit 14, and a reception antenna unit 15.

Here, the exploration target surface existing in the ground, which is the estimation target of the system 10 and the method, is actually a finite area, but is used for exploration in a finite-length well excavated in the ground for exploration. As long as the transmitting antenna and the receiving antenna of the above are scanned, it is assumed that the electromagnetic wave radiated from the transmitting antenna is reflected on the surface to be searched and has a sufficient planar spread that can reach the receiving antenna and be received. Further, in actual ground penetrating radar, a plurality of fragmentary fault planes existing in the ground are often approximated by one infinite flat plate, and such a case can also be an estimation target of the system 10 and the method. Therefore, in the present embodiment, the surface to be explored is treated as a part of the surface (plane) of the infinite flat plate.

The incident azimuth derivation unit 11 estimates the direction in which the surface to be explored in the ground faces the axis of the cylindrical well excavated in the ground, and the electromagnetic waves required for the processing. It is composed of an apparatus that performs processing related to transmission and reception, and in the present embodiment, it is configured to include a vector network analyzer 111 and a personal computer (personal computer) 112 as an example. The incident azimuth deriving unit 11 is used on the ground and is used for operator operation.

The vector network analyzer 111 applies a sinusoidal voltage X (complex number) having a frequency f to the feeding point of the dipole antenna element 141 provided in the transmitting antenna unit 14 via the transmitting interface unit 12 and the optical fiber cable 16. Power is supplied, and the reception voltage Y (complex number) at the feeding point of each antenna element of the dipole array antenna 151 provided in the receiving antenna unit 15 is measured and transmitted via the receiving interface unit 13 and the optical fiber cable 16. The characteristic G = Y / X (complex number) can be output.

The transmission interface unit 12 includes an amplifier 121 that amplifies the transmission wave signal output by the vector network analyzer 111, and an electric / optical conversion element 122 such as a laser diode that converts the transmission wave signal amplified by the amplifier 121 into an optical signal. It is configured and installed on the ground.

The transmitting antenna portion 14 is configured to include a dipole antenna element 141 in a cylindrical FRP (fiber reinforced plastic) vessel 142, and is used by being inserted into a cylindrical well B excavated in the ground. To. The transmission antenna unit 14 receives a transmission wave signal (optical signal) transmitted from the transmission interface unit 12 via the optical fiber cable 16 by an optical / electrical conversion element (not shown) such as a photodiode. It is converted into an electric signal, amplified by an amplifier (not shown) and supplied to the feeding point of the dipole antenna element 141, and electromagnetic waves are radiated from the dipole antenna element 141 from the inside of the well B toward the exploration target surface in the ground. do.

The receiving antenna unit 15 includes a dipole array antenna 151, an electric / optical conversion unit 153, and an azimuth meter 154 for knowing the orientation of the dipole array antenna 151 in the well B in a cylindrical FRP vessel 152. It is inserted into the same well B together with the transmitting antenna unit 14 and used. The electromagnetic waves radiated from the dipole antenna element 141 toward the exploration target surface are reflected by the exploration target surface, and the incident electromagnetic waves propagating toward the dipole array antenna 151 are the three or more dipoles constituting the dipole array antenna 151. It is received separately by the antenna element.

In the present embodiment, the dipole array antenna 151 is composed of four dipole antenna elements (reception antenna elements) having the same length, as in the configuration shown in FIG. 1, and each receiving antenna element has its own axis. However, they are arranged so as to be separated from the axis of the vessel 152 by the same distance, parallel to the axis, and separated by 90 ° in the circumferential direction of the axis. The feeding point of each receiving antenna element is located at the same position in the axial direction of the vessel 152, and is connected to one end of a coaxial cable having a characteristic impedance of 50Ω. It is bundled to form a feeder line, and the received wave signal is transmitted to the electric / optical conversion unit 153 via the feeder line. The electric / optical conversion unit 153 amplifies the received wave signal by an amplifier and converts it into an optical signal by an electric / optical conversion element such as a laser diode, thereby producing a received wave signal having an improved S / N ratio. It is transmitted to the receiving interface unit 13 via the optical fiber cable 16.

The receiving antenna unit 15 is provided with the above-mentioned electric / optical conversion unit 153, and is connected to the feeding point of each receiving antenna element by the feeding line of the coaxial cable (coaxial feeding configuration). By loading ferrite on the conductor column, it is possible to significantly reduce the influence of interference between each receiving antenna element and the central conductor column. Further, as a method of completely eliminating the influence of the interference, an optical modulator is connected to each feeding point of each receiving antenna element, and the received wave signal converted into an optical signal by each optical modulator is used as an optical fiber cable 16. It is also a preferable embodiment to adopt a configuration (optical power supply configuration) of transmitting to the receiving interface unit 13 via the above.

In the present embodiment, the vessel 142 of the transmitting antenna unit 14 and the vessel 152 of the receiving antenna unit 15 have the same inner diameter and outer diameter, and their respective axes are aligned and connected in series in the direction of the axis. And used. When the transmitting antenna unit 14 and the receiving antenna unit 15 are inserted into the well B and used, the axes of the vessels 142 and 152 and the axis Z of the well B coincide with each other, and the axes are coaxial. Align on top. Therefore, in the following description, the axis of the vessels 142 and 152 and the axis Z of the well B are used synonymously with each other. In a general borehole radar using a dipole antenna, the transmitting antenna unit 14 is generally arranged on the front side of the receiving antenna unit 15 (the insertion direction side when inserting into the well B). However, the receiving antenna unit 15 may be arranged on the front side of the transmitting antenna unit 14. Hereinafter, the transmitting antenna unit 14 and the receiving antenna unit 15 are collectively referred to as a “transmission / reception antenna unit” as appropriate.

The receiving interface unit 13 includes an optical / electric conversion element 132 such as a photodiode that converts a received wave signal (optical signal) separately output from each receiving antenna element of the dipole array antenna 151 into an electric signal, and optical / electric. It is configured to include an amplifier 131 that amplifies the received signal output by the conversion element 132, and is installed on the ground.

The optical fiber cable 16 includes an optical fiber that transmits a transmission wave signal (optical signal) between the optical / electrical conversion element of the transmission antenna unit 14 and the electric / optical conversion element 122 of the transmission interface unit 12, and a reception antenna. An optical fiber that separately transmits a received wave signal (optical signal) for each antenna element between the electric / optical conversion element in the electric / optical conversion unit 153 of the unit 15 and the optical / electric conversion element 132 of the receiving interface unit 13. It is composed by bundling and. As described above, when the transmitting antenna unit 14 is arranged on the front side of the receiving antenna unit 15, the optical fiber for the transmitted wave signal (optical signal) passes through the vessel 152 of the receiving antenna unit 15. (Not shown). On the other hand, when the receiving antenna unit 15 is arranged on the front side of the transmitting antenna unit 14, the optical fiber that separately transmits the received wave signal (optical signal) passes through the vessel 142 of the transmitting antenna unit 14. ..

In the present embodiment, in the incident azimuth angle deriving unit 11, the vector network analyzer 111 outputs a step frequency continuous wave (SFW) to the transmitting interface unit 12, and the receiving interface unit 13 outputs the step frequency continuous wave (SFW) for each antenna element of the dipole array antenna 151. The received wave data in the frequency region of the received received wave signal is generated and output to the personal computer 112 via the GPIB interface.

The personal computer 112 takes in the received wave data in the frequency domain, corrects the attenuation and delay time generated in the cable and the electronic circuit, and then performs the filter processing as necessary. At this time, there is a frequency band in which it is difficult to estimate the arrival direction of the received wave (incident electromagnetic wave) due to the interference between each receiving antenna element of the dipole array antenna 151 and the coaxial feeder or the influence of resonance between each antenna element. In this case, the filter processing is performed so that the frequency band is not passed and only the frequency band in which the arrival direction of the received wave can be estimated is passed. The personal computer 112 further obtains a received waveform in the time domain by performing an inverse Fourier transform on the received wave data in the frequency domain after the correction and filtering. By analyzing the received waveform for each receiving antenna element and obtaining the arrival time of the received wave for each receiving antenna element, the arrival direction (incident) around the axis Z of the well B of the incident electromagnetic wave incident on the dipole array antenna 151. The azimuth) can be estimated accurately as described later.

In the present embodiment, the electromagnetic wave radiated from the dipole antenna element 141 of the transmitting antenna unit 14 is radiated in all directions around the axis Z of the well B, and the electromagnetic wave radiated at a certain radiation azimuth angle ( (Radio electromagnetic wave) is reflected on the surface to be searched and is incident on the dipole array antenna 151 of the receiving antenna unit 15 as an incident electromagnetic wave at an incident azimuth angle _φ0 at the same angle as the radiation azimuth angle. The plane including the wave vector of the radiated electromagnetic wave, the wave vector of the incident electromagnetic wave, and the axis Z of the well B passes through the center O of the dipole array antenna 151 described with reference to FIGS. 1 and 2 and faces the exploration target surface. It coincides with the ρz plane containing the axis Z and the axis Z of the well B.

<Estimation processing of incident azimuth (1)>
Next, the content of the estimation process of the incident azimuth angle _φ0 performed by the incident azimuth derivation unit 11 will be described in detail. The system 10 and the method are characterized in the estimation process of the incident azimuth angle _φ0 . The estimation process is roughly classified into the following four steps.

(1) A step of sequentially moving and inserting the transmission / reception antenna portion into the well B, for example, by a fixed distance in the Z direction of the axis (first step). Here, the moving position (moving distance from the predetermined position) with respect to the predetermined position (for example, the entrance) in the well B of the center O of the dipole array antenna 151 is sequentially recorded by the personal computer 112. Hereinafter, for convenience, each movement position of the center O is referred to as Pr _j (j = 1 to N, where N is the number of movements).

(2) A step of radiating an electromagnetic wave from the dipole antenna element 141 toward the exploration target surface, and the dipole array antenna 151 receiving the incident electromagnetic wave reflected by the exploration target surface and propagating toward the receiving antenna unit 15 (second). Process). Here, the radiation of the electromagnetic wave is executed in the above manner by the vector network analyzer 111, the transmission interface unit 12, and the transmission antenna unit 14 under the control of the personal computer 112. Further, the reception of the incident electromagnetic wave is executed in the above manner by the receiving antenna unit 15, the receiving interface unit 13, and the vector network analyzer 111 for each receiving antenna element of the dipole array antenna 151 under the control of the personal computer 112. Will be done.

(3) A step of analyzing the signal waveform of the incident electromagnetic wave received for each receiving antenna element by the personal computer 112 and obtaining the arrival time of each receiving antenna element of the incident electromagnetic wave (third step). Here, the arrival time _Tij (i = 1 to M: where M is the number of receiving antenna elements and 3 or more (M = 4 in this embodiment)) at the moving position Pr _j for each receiving antenna element is set. From the time of a predetermined reference phase location (for example, when the electric field strength is maximum) in the time region waveform of the transmitted electromagnetic wave, the phase location corresponding to the reference phase location in each time region waveform for each receiving antenna element (for example, when the reception voltage is maximum). It is calculated as the delay time until the time of. The arrival time _Tij is sequentially recorded by the personal computer 112 together with the movement position Pr _j .

The second and third steps are sequentially executed each time the transmission / reception antenna unit moves sequentially in the first step.

(4) At the moving position Pr _j , based on the arrival time _Tij for each receiving antenna element obtained in the third step and the position (azimuth φi, i = 1 to M) around the axis Z of each receiving antenna element. The arrival time T _j (φ) when the same incident electromagnetic wave is received by the receiving antenna element located at an arbitrary azimuth angle φ is approximated by a sine function by the minimum square error method. Then, when the incident elevation angle θ at the moving position Pr _j is within the first incident elevation angle range, the azimuth angle φ _min at which the function T _j (φ) is the minimum value is calculated as the incident azimuth angle φ ₀ , and the moving position. When the incident elevation angle θ at Pr _j is within the second incident elevation angle range, the azimuth angle φ _max at which the function T (φ) is the maximum value is calculated as the incident azimuth angle φ ₀ (4th step). Hereinafter, for convenience, the estimation with φ ₀ = φ _min is referred to as “forward estimation”, and the estimation with φ ₀ = φ _max is referred to as “reverse direction estimation” to distinguish between the two.

It is preferable that the fourth step is collectively performed after the transmission / reception antenna portions have been sequentially moved, that is, after the first to third steps have been completed at all the moving positions Pr _j . However, as will be described later, if it is known in advance whether the incident elevation angle θ is within the first incident elevation angle range or the second incident elevation angle range at each movement position Pr _j , each time the transmission / reception antenna unit moves in sequence. It may be performed, and there are many embodiments of the implementation timing of the fourth step for each movement position Pr _j .

Here, as described above, the first incident elevation angle range is the range of the incident elevation angle θ between the two critical incident elevation angles θ ₀ and 180 ° − θ ₀ , and the second incident elevation angle range is from 0 ° to 180. The range of the incident elevation angle θ other than the first incident elevation angle range in the entire range up to ° (between 0 ° and θ ₀ and between 180 ° -θ ₀ and 180 °).

The processing content executed by the personal computer 112 in the first to fourth steps is a computer program for estimation processing of the incident azimuth angle _φ0 stored in advance in a predetermined storage area in the personal computer 112, and the CPU in the personal computer 112. It is carried out by sequentially reading and executing (central processing unit).

Next, the relationship between the incident elevation angle θ (the angle formed by the arrival direction of the incident electromagnetic wave and the axial center Z of the well B) and the moving position Pr _j (center O of the dipole array antenna 151) will be described with reference to FIG. .. FIG. 5 shows the dipole antenna element 141 in the _ρz plane including the ρ-axis and the z-axis (the axis Z of the well B) that pass through the intersection OF of the exploration target surface _F and the axis Z and face the incident azimuth angle φ0. The positional relationship between the center Pt _j , the center Pr _j of the dipole array antenna 151, and the exploration target plane F is shown. The ρ-axis shown in FIG. 5 and the ρ-axis passing through the center O (Pr _j ) of the dipole array antenna shown in FIG. 1 and facing the exploration target surface F are parallel to each other, and the ρz planes in both figures are the same. The exploration target plane F and the ρz plane are orthogonal to each other. The origin of the z-axis can be set to an arbitrary point on the axis Z of the well B, but in FIG. 5, as an example, the intersection OF of the exploration target surface _F and the axis Z is set to z = 0. Shows. Further, in FIG. 5, it is assumed that the dipole antenna element 141 is arranged below the dipole array antenna 151, and Pt _j and Pr _j are separated by a distance d.

The radiated electromagnetic wave (wave vector kt) radiated from the dipole antenna element 141 is reflected (mirror surface reflection) at the reflection point _Rj on the exploration target surface F, and is the center of the dipole array antenna 151 as an incident electromagnetic wave (wave vector kr). Reach Pr _j . The angle formed by the z-axis and the line segment Pr _j − R _j is the incident elevation angle θ corresponding to the moving position Pr _j .

_Arrival time for each receiving antenna element Ta _j (propagation time from Pt _j to Pr _j via R _j ) and the product of the propagation speed v of the electromagnetic wave (Ta _j · v) The total length L _j from Pt _j to Pr _j via R _j can be calculated. Here, when the transmission / reception antenna portion is moved in the axis Z direction by one step, the movement position Pr _j changes to Pr _{j + 1} , the z coordinate value changes by Δz, and the total length L _j is similarly L _{j + 1} (=). It changes to L _j + ΔL). The distance ρr _j (the length of the perpendicular line from the reflection point R _j to the axis Z) and the incident elevation angle θ of the reflection point R _j corresponding to the moving position Pr _j from the axis Z are obtained from these values and their changes. Can be calculated.

Further, a straight line obtained by linearly approximating the coordinate values (ρ _j , z _j ) of N reflection points R _j obtained by moving the transmission / reception antenna portion N times (in FIG. 5, on the exploration target plane F). The angle formed in the ρz plane of the ρ axis can be calculated as the inclination angle δ of the exploration target surface F.

As explained in the section of "Effects of the Invention", the critical incident elevation angle θ ₀ or (180 ° −θ ₀ ) is the incident elevation angle at which the electric field circumferential dependence index c (θ) becomes a minimum value at −20 dB or less. It can be defined as θ. The electric field E _1z (φ) shown in the above number 1 indicates the state around and inside the well B into which the transmission / reception antenna portion is actually inserted, and the boring core (excavation waste) is collected or the hole wall is used when the well B is excavated. Conditions necessary for calculation for the models shown in FIGS. 1 and 2 (boundary conditions, etc.), along with known information such as the inner diameter of the well B, the inner diameter and outer diameter of the FRP vessel 152, acquired by photography or the like. By setting, for example, an analytical solution using a cylinder function can be calculated on a personal computer. Therefore, the critical incident elevation angle θ ₀ or (180 ° −θ ₀ ) defined by the exponent c (θ) shown in Equation 2 can be theoretically calculated, and can be calculated in about a few seconds using a general personal computer. can. Therefore, the critical incident elevation angle θ ₀ or (180 ° −θ ₀ ) can be calculated in advance before carrying out the first to fourth steps. Hereinafter, for convenience, a method for deriving a critical incident elevation angle θ ₀ or (180 ° −θ ₀ ) by theoretical calculation will be referred to as a “theoretical calculation method”.

Therefore, for example, in the third step, if the incident elevation angle θ at the moving position Pr _j-1 one step before is calculated in the above manner in addition to the calculation of the arrival time _Tij , the critical incident calculated in advance is performed. Based on the elevation angle θ ₀ or (180 ° −θ ₀ ), in the fourth step, the incident elevation angle θ one step before is within either the first incident elevation angle range or the second incident elevation angle range. It is possible to specify whether or not there is, and the incident azimuth angle _φ0 can be appropriately estimated by either “forward direction estimation” or “reverse direction estimation” selected according to the incident elevation angle θ.

<Estimation processing of incident azimuth (2)>
Next, a modified example of the above-mentioned estimation process of the incident azimuth angle _φ0 will be described.

In the above description, it is assumed that the critical incident elevation angle θ ₀ or (180 ° −θ ₀ ) obtained in advance by theoretical calculation is used in the fourth step. However, as described with reference to FIG. 3B in the “Effect of the Invention” column, when the incident elevation angle θ is the critical incident elevation angle θ ₀ or (180 ° −θ ₀ ), each reception is performed. Since the time difference between the arrival times _Tij of the antenna element is 0 (or almost 0), the critical incident elevation angle θ ₀ or (180 ° −θ ₀ ) is not derived by the “theoretical calculation method” as described above. In the fourth step, the difference (maximum arrival time difference) between the maximum value (maximum arrival time Tmax _j ) and the minimum value (minimum arrival time Tmin _j ) of the function T _j (φ) derived for each movement position Pr _j in the same step. 2τj, _{2τj = Tmax j −Tmin j ) is calculated} , and the maximum arrival time difference _2τj is selected within a predetermined value (for example, within the range of 0.1 to 0.5 ns) within the entire movement range of the transmission / reception antenna section. If there is a moving position Pr _j that becomes a minimum value at 0.2 ns) or less, the Pr _j is set as the singular position P ₀ , and the incident elevation angle θ corresponding to the singular position P ₀ is critically incident. It can also be specified as an elevation angle θ ₀ or (180 ° −θ ₀ ). Hereinafter, for convenience, a method for deriving the critical incident elevation angle θ ₀ or (180 ° −θ ₀ ) based on the maximum arrival time difference _2τj is referred to as a “time difference method”.

Here, in the "time difference method", when the moving position Pr _j is changed as a computational process for searching for a singular position P ₀ in which the maximum arrival time difference _2τj is a predetermined value or less and becomes a minimum value, the change is made. The direction may be a direction in which the transmission / reception antenna portion is sequentially moved in the well B in the axial Z direction in the first step, that is, either in the same direction as the physical movement processing direction or in the opposite direction. ..

Here, the critical incident elevation angle θ ₀ or (180 ° −θ ₀ ) derived by the “theoretical calculation method” and the critical incident elevation angle θ ₀ or (180 ° −θ ₀ ) derived by the “time difference method” in the field experiment are The exact match will be described with reference to FIGS. 6 and 7.

In the field experiment, two wells B were excavated in the ground with their axes separated by 1 m, and a transmitting antenna portion 14 was inserted into one to fix the position at a predetermined depth, and the other. , The receiving antenna unit 15 is inserted so that the electromagnetic wave radiated from the dipole antenna element 141 is directly received by the dipole array antenna 151, and the incident elevation angle θ at the moving position Pr _j of the dipole array antenna 151 is accurate. I made it possible to calculate.

FIG. 6 shows the calculation results of the electric field circumferential dependence index c (θ) calculated under various conditions corresponding to the configuration of the field experiment on the graph with the incident elevation angle θ on the horizontal axis and the index c (θ) on the vertical axis. It is a figure plotted in. From FIG. 6, it can be seen that the critical incident elevation angle θ ₀ derived by the “theoretical calculation method” exists between 29 ° and 30 °.

In FIG. 7, the transmitting antenna portion 14 is sequentially moved in the well B on the other side in the axial Z direction, and is induced in four receiving antenna elements (D1 to D4) at each moving position Pr _j . The result of measuring the time domain waveform of the received voltage is shown. FIG. 7A shows the reception voltage waveforms of each receiving antenna element at 16 moving positions Pr _j superimposed and displayed, and FIG. 7B shows three of them (z = 0 cm, It is an enlarged view of the main part of what superposed and displayed the received voltage waveform of each receiving antenna element at the moving position Pr _j of (-180 cm, -280 cm). Note that z = 0 cm is equal to the depth of the feeding point of the dipole antenna element 141, and the incident elevation angles θ corresponding to z = 0 cm, −180 cm, and 280 cm are 90 °, 29 °, and 20 °. Therefore, from FIG. 7B, the received voltage waveforms of the four receiving antenna elements overlap at z = −180 cm (incident elevation angle θ = 29 °), and the maximum arrival time difference _2τj in the “time difference method” is. It is almost 0 ns, and it can be confirmed that it accurately matches the critical incident elevation angle θ ₀ derived by the “theoretical calculation method”. The vertical axis of each of FIGS. 7A and 7B is the z coordinate of the moving position Pr _j , but the vertical axis of the time domain waveform of each antenna element D1 to D4 of each moving position Pr _j is. Although not specified, it is a normalized reception voltage.

In the above "time difference method", if there is a moving position Pr _j that becomes a singular position P ₀ within the entire moving range of the transmitting / receiving antenna portion, the transmitting / receiving antenna portion is sequentially moved in the well B in the axial Z direction. The incident elevation angle θ is on either side of the first incident elevation angle range or the second incident elevation angle range up to the singular position P ₀ , and the incident elevation angle θ is after the singular position P ₀ is exceeded. It will be on either the other side of the first incident elevation range or the second incident elevation range.

On the other hand, if there is no moving position Pr _j that becomes a singular position P ₀ within the entire moving range of the transmitting / receiving antenna portion, the incident elevation angle θ is always the first incident elevation angle range within the entire moving range of the transmitting / receiving antenna portion. It will be on either side of the inside or within the second incident elevation range.

Therefore, if it can be assumed in advance whether the incident elevation angle θ is within the first incident elevation range or the second incident elevation range at the starting point where the transmission / reception antenna portion is sequentially moved in the axial Z direction in the well B. , It is omitted to calculate the critical incident elevation angle θ ₀ or (180 ° −θ ₀ ) in advance by the “theoretical calculation method” and to sequentially calculate the incident elevation angle θ at the moving position Pr _j in the third step. Then, at any moving position Pr _j , by determining only whether or not the singular position P ₀ has been reached by the above-mentioned "time difference method", based on either "forward estimation" or "reverse direction estimation". It can be determined whether the incident azimuth φ ₀ should be estimated.

Next, in the model shown in FIG. 8, the first arrangement configuration in which the transmitting antenna unit 14 is arranged on the front side of the receiving antenna unit 15 (the insertion direction side when inserting into the well B) and vice versa. Case A in which the transmitting / receiving antenna portion moves above the intersection OF of the axis Z of the well B in the ground and the exploration target surface _F (the entrance side of the well B) for both of the second arrangement configurations of the above. FIG. 9 shows the results obtained by numerically calculating the relationship between the incident elevation angle θ and the position of the feeding point of the dipole array antenna on the axis Z for the two cases of the case B moving below and the case B.

Normally, a well B is excavated so as to penetrate the exploration target surface F such as a fault to be measured in the ground, and a boring core (excavation debris) is collected or a hole wall is photographed (bore hole scanner). Information on the surface to be explored is acquired, and then information on a location away from well B is acquired using a borehole radar such as this system. Therefore, in most cases, the exploration target surface F and the well B intersect in the ground. Therefore, normally, the transmission / reception antenna portion is moved above the intersection _OF in the well B for measurement (case A). However, in the model shown in FIG. 8, the case B in which the well B is further _extended below the intersection OF and the transmission / reception antenna portion is moved below the intersection _OF in the well B for measurement is performed. In addition, we are trying to generalize the discussion of the incident elevation angle θ. Case B also includes a case where the ground surface is below the intersection _OF .

In FIG. 8, the z-axis is the axis _Z of the well B, the origin (z = 0) of the z-axis is the intersection OF, and the ρ-axis is the axis that passes through the intersection OF and faces the exploration target plane _F. , The exploration target surface F is orthogonal to the ρz plane. The + z direction is an upward direction (toward the entrance of well B) with _respect to the intersection OF. In both cases A and B, P1 (z = z1) is the feeding point of the antenna element arranged on the upper side, that is, the center (feeding point) of the dipole array antenna 151 in the first arrangement configuration, or the first. The center (feeding point) of the dipole antenna element 141 in the two-arranged configuration is shown, and P2 (z = z2) is the feeding point of the antenna element arranged on the lower side in both cases A and B, that is, the first. The center (feeding point) of the dipole antenna element 141 in the one arrangement configuration or the center (feeding point) of the dipole array antenna 151 in the second arrangement configuration is shown, z1> z2, and z1-z2 = d. R is a reflection point on the exploration target surface F when an electromagnetic wave radiated from one of P1 or P2 is specularly reflected by the exploration target surface F and is incident on the other of P1 or P2. δ is the inclination angle of the exploration target surface F, and is the angle formed by the exploration target surface F and the ρ axis on the ρz plane, and 0 ° <δ <90 °.

In both cases A and B, the incident elevation angle θ is the angle θ1 formed by the z-axis and the line segment P1-R in the first arrangement configuration, and the z-axis and the line segment P2-R in the second arrangement configuration. The angle θ2 is formed.

In FIG. 9, the first critical incident elevation angle θ ₀ and the second critical incident elevation angle (180 ° −θ ₀ ) are 30 ° and 150 °, and the inclination angle δ of the exploration target surface F is 70 ° (δ> θ ₀ ). ), For the case of d = 1.36 m, the result obtained by numerically calculating the relationship between the position P1 (z = z1) of the feeding point of the antenna element arranged on the upper side and the incident elevation angle θ (θ1 or θ2) is obtained. It is a plotted graph, the vertical axis shows the incident elevation angle θ (θ1 or θ2), and the horizontal axis shows the z coordinate (z1) of the position P1.

Case A is a range in which z1 ≧ d, Case B is a range in which z1 ≦ 0, and in the range of 0 <z1 <d, a solution can be obtained because the search target surface F exists between the transmitting and receiving antennas. However, it is difficult to obtain information even in actual measurement. Further, in FIG. 9, the incident elevation angle θ (= θ1) in the first arrangement configuration is shown by a solid line, and the incident elevation angle θ (= θ2) in the second arrangement configuration is shown by a broken line.

As shown in FIG. 9, in case A, when the position P1 moves in the + z direction, the incident elevation angle θ (θ1 or θ2) gradually approaches (180 ° −δ) in both the first and second arrangement configurations. (See the alternate long and short dash line in FIG. 9). At this time, θ1 decreases monotonically and θ2 increases monotonically. On the other hand, in Case B, when the position P1 moves in the −z direction, the incident elevation angle θ (θ1 or θ2) gradually approaches δ in both the first and second arrangement configurations (see the alternate long and short dash line in FIG. 9). .. At this time, θ1 decreases monotonically and θ2 increases monotonically.

Further, in the case A, when the position P1 is at the position where z1 = d (that is, the position P2 is on the intersection OF), the incident elevation angle θ (= _θ1 ) becomes 180 °, which is the upper limit value, in the first arrangement configuration. In the second arrangement configuration, the incident elevation angle θ (= θ2) is the lower limit value (180 ° -2δ). On the other hand, in case B, when the position P1 is at the position where z1 = 0 (that is, on the intersection OF), the incident elevation angle θ (= θ1) becomes the upper limit value _2δ in the first arrangement configuration, and the second arrangement configuration Then, the incident elevation angle θ (= θ2) becomes 0 °, which is the lower limit value. When the position P1 is z1 = 0 or d, the incident elevation angle θ can be calculated, including the case where it is in the vicinity thereof, but it is within the range where it is difficult to acquire information in actual measurement.

In the example shown in FIG. 9 (θ ₀ = 30 °, δ = 70 °), in the case of case A and the first arrangement configuration, the incident elevation angle θ (= θ 1) is the second critical incident elevation angle (180 ° −θ ₀ ). ), The position P1 (z1 ₌ z1 ₂ ) exists as the singular position P0, and when z1> z1 ₂ , the incident elevation angle θ (= θ1) is within the first incident elevation angle range, and the fourth step. In, "forward estimation" is selected, and when d ≦ z1 < _z12 , the incident elevation angle θ (= θ1) is within the second incident elevation angle range, and “reverse direction estimation” is selected in the fourth step.

Further, in the case A and in the case of the second arrangement configuration, the position P1 (z1 = z1 ₁ ) at which the incident elevation angle θ ( ₌ θ2) coincides with the first critical incident elevation angle θ ₀ exists as the singular position P0. However, the incident elevation angle θ (= θ2) is always within the first incident elevation angle range, and “forward estimation” is selected in the fourth step.

Further, in the case B and in the case of the first arrangement configuration, the position P1 (z1 = z1 ₂ ) where the incident elevation angle θ (= θ1) coincides with the second critical incident elevation angle (180 ° −θ ₀ ) is the above-mentioned singular position. It does not exist as P ₀ , the incident elevation angle θ (= θ1) is always within the first incident elevation angle range, and “forward estimation” is selected in the fourth step.

Further, in the case B and the second arrangement configuration, the position P1 (z1 = z1 ₁ ) where the incident elevation angle θ ( ₌ θ2) coincides with the first critical incident elevation angle θ ₀ exists as the singular position P0. , Z1 ₁ <z1 ≦ 0, the incident elevation angle θ (= θ2) is within the second incident elevation angle range, “reverse direction estimation” is selected in the fourth step, and z1 <z1 ₁ causes the incident elevation angle θ (= θ2). = Θ2) is within the range of the first incident elevation angle, and “forward estimation” is selected in the fourth step.

Next, an example shown in FIG. 9 (θ ₀ = 30 °, δ = 70 °) is further generalized, and an arbitrary first critical incident elevation angle θ ₀ (0 <θ ₀ <90 °) and an arbitrary exploration target surface. The relationship between the inclination angle δ (0 ° <δ <90 °) of F is examined. However, for the following reasons, the case of δ> θ ₀ is assumed. That is, in a borehole radar such as this system, the exploration target surface F such that the inclination angle δ is orthogonal to or close to the axial center Z of the well B, for example, is 20 ° or less, is actually This is because it is not the target of measurement. This is because it is difficult to radiate a large power electromagnetic wave in a direction close to parallel to the axis Z of the well B due to the directivity of the dipole antenna in the well B in the elevation direction, and further, from the same direction. The reason is that the sensitivity to receive electromagnetic waves is not high enough.

The inclination angle δ can be calculated and obtained in advance as the pretreatment of the fourth step as described above. If it is confirmed in the process of calculating the inclination angle δ that the intersection OF between the axis Z of the well B and the exploration target surface _F is in the ground, it is found in the well B of the transmission / reception antenna section. Whether the moving range of the case A or the case B is determined in advance. Further, when the intersection OF is on the ground (however, the intersection _OF is a plane including the exploration target surface F when the exploration target surface _F is extended to the ground, and the axis Z of the well B is on the ground. (This is the intersection with the case of extending to), the range of movement of the transmission / reception antenna portion in the well B is case B.

In case A and in the case of the first arrangement configuration, if δ> θ ₀ , the incident elevation angle θ (= θ1) always changes between the lower limit value (180 ° -δ) and the upper limit value 180 °. It passes through the second critical incident elevation angle (180 ° -θ ₀ ). That is, (180 ° -θ ₀ )> (180 ° -δ). Therefore, the treatment is the same as that of the example (θ ₀ = 30 °, δ = 70 °) shown in FIG. 9, and when z1> z1 ₂ , the incident elevation angle θ (= θ1) is within the first incident elevation angle range. “Forward estimation” is selected in the fourth step, and when d ≦ z1 < _z12 , the incident elevation angle θ (= θ1) is within the second incident elevation angle range, and “reverse direction estimation” is performed in the fourth step. Be selected.

In case A and the second arrangement configuration, the magnitude relationship between the lower limit value (180 ° -2δ) of the incident elevation angle θ (= θ2) and the first critical incident elevation angle θ ₀ becomes a problem. When (180 ° -2δ)> θ ₀ , the first critical incident occurs when the incident elevation angle θ (= θ2) changes between the lower limit value (180 ° -2δ) and the upper limit value (180 ° -δ). Since it does not pass through the elevation angle θ ₀ , the incident elevation angle θ (= θ 2) is always within the first incident elevation angle range as in the example (θ ₀ = 30 °, δ = 70 °) shown in FIG. "Forward estimation" is selected with.

On the other hand, when (180 ° -2δ) <θ ₀ , when the incident elevation angle θ (= θ2) changes between the lower limit value (180 ° -2δ) and the upper limit value (180 ° -δ), the first It passes through the critical incident elevation angle θ ₀ . Therefore, the position P1 (z1 = z1 ₁ ) where the incident elevation angle θ (= θ2) coincides with the first critical incident elevation angle θ ₀ exists as the singular position P0, and when z1 _> z1 ₁ , the incident elevation angle θ (=) θ2) is within the first incident elevation range, “forward estimation” is selected in the fourth step, and when d ≦ z1 <z1 ₁ , the incident elevation angle θ (= θ2) is within the second incident elevation range. , "Reverse direction estimation" is selected in the fourth step. Therefore, in the above-mentioned case A, the treatment is the same as in the case of the first arrangement configuration.

In case B and the first arrangement configuration, the magnitude relationship between the upper limit value 2δ of the incident elevation angle θ (= θ1) and the second critical incident elevation angle (180 ° −θ ₀ ) becomes a problem. When 2δ <(180 ° −θ ₀ ), the incident elevation angle θ (= θ1) passes through the second critical incident elevation angle (180 ° −θ ₀ ) when the incident elevation angle θ (= θ1) changes between the lower limit value δ and the upper limit value 2δ. Therefore, as in the example shown in FIG. 9 (θ ₀ = 30 °, δ = 70 °), the incident elevation angle θ (= θ1) is always within the first incident elevation angle range, and the “forward estimation” is performed in the fourth step. Is selected.

On the other hand, when 2δ> (180 ° −θ ₀ ), the second critical incident elevation angle (180 ° −θ ₀ ) when the incident elevation angle θ (= θ1) changes between the lower limit value δ and the upper limit value 2δ. Pass through. Therefore, the position P1 (z1 = z1 ₂ ) where the incident elevation angle θ (= θ1) coincides with the second critical incident elevation angle (180 ° −θ ₀ ) exists as the singular position P0, and in z1 _> z1 ₂ , The incident elevation angle θ (= θ2) is within the second incident elevation angle range, “reverse direction estimation” is selected in the fourth step, and when z1 <z1 ₂ , the incident elevation angle θ (= θ1) is the first incident elevation angle range. "Forward estimation" is selected in the fourth step. Therefore, in case B described later, the treatment is the same as in the case of the second arrangement configuration.

In case B and in the case of the second arrangement configuration, if δ> θ ₀ , when the incident elevation angle θ (= θ2) changes between the lower limit value 0 ° and the upper limit value δ, the first critical incident elevation angle is always present. Passes θ ₀ . Therefore, the treatment is the same as that of the example shown in FIG. 9 (θ ₀ = 30 °, δ = 70 °), and when z1 ₁ <z1 ≦ 0, the incident elevation angle θ (= θ2) is within the second incident elevation angle range. Yes, "reverse direction estimation" is selected in the fourth step, and when z1 < _z11 , the incident elevation angle θ (= θ2) is within the range of the first incident elevation angle, and in the fourth step, “forward direction estimation” is performed. Be selected.

It should be noted here that in case A and the second arrangement configuration, when (180 ° -2δ)> θ ₀ , the incident elevation angle θ (= θ2) is always within the first incident elevation angle range. There is a point that "forward estimation" is selected in the fourth step. In this case, since "forward estimation" can be used unconditionally in the fourth step, it is preferable in that the algorithm for the estimation process of the incident directivity angle φ0 can be simplified, and the incident elevation angle θ ( ₌ θ2) is further set. Since it changes across 90 °, it is preferable that the range of the incident elevation angle θ with high reception sensitivity of the dipole array antenna 151 can be used with respect to the directivity in the elevation angle direction of the dipole antenna in the well B.

Similarly, it should be noted that in the case of case B and the first arrangement configuration, when 2δ <(180 ° −θ ₀ ), the incident elevation angle θ (= θ1) is always within the first incident elevation angle range. There is a point that "forward estimation" is selected in the fourth step. In this case, since "forward estimation" can be used unconditionally in the fourth step, it is preferable in that the algorithm for the estimation process of the incident directivity angle φ0 can be simplified, and the incident elevation angle θ ( ₌ θ1) is further set. Since it changes across 90 °, it is preferable that the range of the incident elevation angle θ with high reception sensitivity of the dipole array antenna 151 can be used with respect to the directivity in the elevation angle direction of the dipole antenna in the well B.

As described above, in both the two cases to be noted, that is, the case A having the second arrangement configuration and the case B having the first arrangement configuration, the receiving antenna unit 15 is the transmitting antenna unit 14. It is common in that it is located closer to the intersection _OF .

As described above, the relationship between the first critical incident elevation angle θ ₀ and the inclination angle δ was examined assuming the case of δ> θ ₀ , but in the case of δ <θ ₀ , it is the case A and the first arrangement configuration. In the case of, the lower limit value (180 ° −δ) of the incident elevation angle θ (= θ1) becomes larger than the second critical incident elevation angle (180 ° −θ ₀ ), and in case A and the second arrangement configuration, The upper limit value (180 ° -δ) of the incident elevation angle θ (= θ2) is larger than the second critical incident elevation angle (180 ° -θ ₀ ), and in the case of case B and the first arrangement configuration, the incident elevation angle θ (180 ° −δ). = Θ1) The lower limit value δ is smaller than the first critical incident elevation angle θ ₀ , and in case B and the second arrangement configuration, the upper limit value δ of the incident elevation angle θ (= θ2) is the first critical incident elevation angle θ. Since it is different from the case of δ> θ ₀ in that it is smaller than ₀ , the incident elevation angle θ (θ1 or θ2) is either within the first incident elevation angle range or within the second incident elevation angle range in consideration of the difference. You just have to judge whether it belongs to.

[Another Embodiment]
Next, a modified example (another embodiment) of the above embodiment will be described.

<1> In the above embodiment, in the system 10, the dipole array antenna 151 receives the step frequency continuous wave generated by the vector network analyzer 111, and the personal computer 112 receives the received wave data in the frequency region obtained by the vector network analyzer 111. By analysis, we assumed a configuration to estimate the arrival direction (incident azimuth angle) around the axis Z of the well B of the incident electromagnetic wave incident on the dipole array antenna 151, but the transmission pulse with a predetermined frequency characteristic was transmitted by the dipole antenna. As a system configuration, the dipole array antenna 151 receives the incident electromagnetic wave radiated from the element 141 and reflected on the surface to be explored, and the time region waveform received by the personal computer 112 is analyzed to estimate the arrival direction of the incident electromagnetic wave. good. In this case, the incident azimuth angle deriving unit 11 does not necessarily have to include the vector network analyzer 111, and instead of the vector network analyzer 111, the pulse generator that generates the transmission pulse and the dipole array antenna 151 of the incident electromagnetic wave It can be configured to include a measuring instrument such as an oscilloscope capable of measuring the time region waveform of the received voltage at each receiving antenna element.

<2> In the above embodiment, the transmitting antenna unit 14 and the receiving antenna unit 15 maintain a constant distance between the feeding point of the dipole antenna element 141 and the feeding point of the dipole array antenna 151, and one shaft is provided. It is assumed that it is used by inserting it into the well B, but the depth in one of the well B of the transmitting antenna unit 14 and the receiving antenna unit 15 is fixed, and the other is the axial center in the well B. It may be an embodiment of moving in a direction. In this case, for example, two long and short wells B are excavated, the transmitting antenna portion 14 is inserted into the short side well B at a predetermined depth, and the receiving antenna portion 15 is inserted into the long side well B. May be configured to be inserted and moved in the axial Z direction of the well B on the long side to receive the incident electromagnetic wave each time.

<3> In the above embodiment, the incident azimuth angle deriving unit 11 is provided with a general-purpose personal computer 112, and the built-in computer program for estimating the incident azimuth angle _φ0 is executed to execute the first to fourth steps. Although the mode in which the processing content executed by the personal computer 112 in the above is executed has been described, the same processing content may be executed by dedicated hardware instead of the general-purpose personal computer 112.

The direction estimation system and method of the present invention relate to the axis of a cylindrical well in which an exploration target surface having a planar spread such as a crack, a fault, or a boundary surface existing in the ground is excavated in the ground. It can be used for the process of estimating the opposite direction.

10: Direction estimation system 11: Incident azimuth angle derivation unit 111: Vector network analyzer 112: Personal computer 12: Transmission interface unit 121: Amplifier 122: Electric / optical conversion element 13: Reception interface unit 131: Amplifier 132: Optical / electric Conversion element 14: Transmitting antenna part 141: Dipole antenna element 142: Vessel 15: Receiving antenna part 151: Dipole array antenna 152: Vessel 153: Electric / optical conversion unit 154: Direction meter 16: Optical fiber cable B: Well D1 to D4: Dipole antenna element F: Exploration target surface R: Reflection point V: Container (vessel)
Win: Incident electromagnetic wave Z: Axial center of the well

Claims (10)

It is a direction estimation system that estimates the direction in which the exploration target surface with a planar spread existing in the ground faces the axis of the cylindrical well excavated in the ground.
The dipole array antenna used by inserting it into the well,
An incident azimuth deriving unit that derives the incident azimuth around the axis of the incident electromagnetic wave incident on the dipole array antenna inserted into the well from the exploration target surface as a direction in which the exploration target surface faces. Be prepared
The dipole array antenna comprises three or more receiving dipole antenna elements extending parallel to each other in a tubular container.
The dipole antenna element is dispersed and arranged in the circumferential direction of the virtual cylindrical surface on a virtual cylindrical surface coaxial with the container.
The incident azimuth derivation unit is
When the dipole array antenna inserted into the well is an electromagnetic wave radiated toward the exploration target surface and receives the incident electromagnetic wave reflected and incident on the exploration target surface, the dipole antenna element is divided. The signal waveform of the received electromagnetic wave is analyzed, and the arrival time of the incident electromagnetic wave for each dipole antenna element is obtained.
Based on the arrival time of each dipole antenna element, the earliest arrival time or the earliest arrival time when the relationship between the position in the circumferential direction of the virtual cylindrical surface and the arrival time when the incident electromagnetic wave is received at the position is approximated by a sine function. The position in the circumferential direction of the virtual cylindrical surface indicating the latest arrival time is specified.
The incident elevation angle formed by the direction of arrival of the incident electromagnetic wave and the axis of the well is the first critical incident elevation angle existing between 0 ° and 90 ° and the second critical incident existing between 90 ° and 180 °. When it is within the range of the first incident elevation angle between the elevation angles, the position in the circumferential direction of the virtual cylindrical surface indicating the earliest arrival time is derived as the incident azimuth angle.
When the incident elevation angle is within the range of 0 ° to 180 ° and is within the range of the second incident elevation angle outside the range of the first incident elevation angle, the position in the circumferential direction of the virtual cylindrical surface indicating the latest arrival time is determined. , Derived as the incident azimuth
The first and second critical incident elevation angles are the circumferential direction in the electric field component parallel to the axial direction of the container of the incident electromagnetic wave when the incident elevation angle is changed within the range of 0 ° to 180 °. The electric field circumferential dependence index expressed by the ratio obtained by dividing the magnitude of the changing electric field by the magnitude of the electric field that does not change in the circumferential direction is given as the incident elevation angle that becomes the minimum value at -20 dB or less, and the first A directional estimation system characterized in that the sum of the first and second critical incident elevation angles is 180 °. A transmission dipole antenna element that radiates an electromagnetic wave toward the exploration target surface while being inserted into the well together with the dipole array antenna is provided.
The direction estimation system according to claim 1, wherein the transmission dipole antenna element is arranged at a predetermined distance from the dipole array antenna in the axial direction of the well. The incident azimuth derivation unit is the earliest at each position when the transmission / reception antenna unit including the dipole array antenna and the transmission dipole antenna element sequentially moves in the well in the axial direction of the well. Derived the time difference between the arrival time and the latest arrival time,
When the position where the time difference is the minimum value of a predetermined value or less with respect to the change in the position in the axial direction of the well is specified as the singular position, the incident elevation angle is the first and the singular position at the specified singular position. It is approximately estimated that it coincides with any one of the second critical incident elevation angles, and the incident elevation angle is within the first incident elevation angle range on one side with respect to the singular position in the axial direction of the well. The direction estimation system according to claim 2, wherein the incident elevation angle is determined to be within the second incident elevation angle range on the other side with the singular position as a reference, and the incident azimuth angle is derived. The incident azimuth derivation unit is
The propagation time of the electromagnetic wave from the transmission dipole antenna element to the dipole array antenna at each position when the transmission / reception antenna unit sequentially moves in the well in the axial direction of the well is measured, and the well is said. Based on the relationship between the position of the well in the axial direction and the propagation time, the inclination angle of the plane including the exploration target plane with respect to the plane orthogonal to the axis of the well is derived.
When the inclination angle is larger than the first critical incident elevation angle,
The incident azimuth derivation unit is
When the singular position is specified within the movement range of the transmission / reception antenna unit in the axial direction of the well, the plane including the search target surface is the well with reference to the singular position within the movement range. It is determined that the incident elevation angle is within the second incident elevation range on the intersection side intersecting the axis, and it is determined that the incident elevation angle is within the first incident elevation range on the side opposite to the intersection side. ,
When the singular position is not specified within the movement range of the transmission / reception antenna unit in the axial direction of the well, it is determined that the incident elevation angle is within the first incident elevation angle range in the entire range of the movement range. The direction estimation system according to claim 3. 2. The direction estimation system according to any one of 4 to 4. It is a direction estimation method that estimates the direction in which the exploration target surface having a planar spread existing in the ground faces the axis of the cylindrical well excavated in the ground.
Three or more dipole antenna elements for reception extending in parallel with each other are provided in a tubular container, and the dipole antenna elements are dispersed on a virtual cylindrical surface coaxial with the container in the circumferential direction of the virtual cylindrical surface. The first step of inserting the arranged dipole array antenna into the well, and
A second step of receiving an electromagnetic wave radiated toward the exploration target surface, which is reflected by the exploration target surface and is incident on the dipole array antenna inserted into the well.
A third step of analyzing the signal waveform of the incident electromagnetic wave received for each dipole antenna element and obtaining the arrival time of the incident electromagnetic wave for each dipole antenna element.
Based on the arrival time of each dipole antenna element, the earliest arrival time or the earliest arrival time when the relationship between the position in the circumferential direction of the virtual cylindrical surface and the arrival time when the incident electromagnetic wave is received at the position is approximated by a sine function. A fourth step of specifying the position in the circumferential direction of the virtual cylindrical surface indicating the latest arrival time and setting the incident directional angle of the incident electromagnetic wave incident on the dipole array antenna from the exploration target surface around the axis. , Equipped with
In the fourth step,
The incident elevation angle formed by the direction of arrival of the incident electromagnetic wave and the axis of the well is the first critical incident elevation angle existing between 0 ° and 90 ° and the second critical incident existing between 90 ° and 180 °. When it is within the range of the first incident elevation angle between the elevation angles, the incident azimuth corresponding to the position in the circumferential direction of the virtual cylindrical surface indicating the earliest arrival time is obtained, and the search target surface is the axis of the well. Derived as the direction facing the heart,
When the incident elevation angle is within the range of 0 ° to 180 ° and is within the range of the second incident elevation angle outside the range of the first incident elevation angle, the position in the circumferential direction of the virtual cylindrical surface indicating the latest arrival time is reached. The corresponding incident azimuth is derived as the direction in which the exploration target surface faces the axis of the well.
The first and second critical incident elevation angles are the circumferential direction in the electric field component parallel to the axial direction of the container of the incident electromagnetic wave when the incident elevation angle is changed within the range of 0 ° to 180 °. The electric field circumferential dependence index expressed by the ratio obtained by dividing the magnitude of the changing electric field by the magnitude of the electric field that does not change in the circumferential direction is given as the incident elevation angle that becomes the minimum value at -20 dB or less, and the first A direction estimation method characterized in that the sum of the first and second critical incident elevation angles is 180 °. In the first step, the transmitting dipole antenna element is inserted into the well at a predetermined distance from the dipole array antenna in the axial direction of the well, and the surface to be explored from the transmitting dipole antenna element. The direction estimation method according to claim 6, wherein the electromagnetic wave is radiated toward the antenna. In the first step, the transmission / reception antenna portion including the dipole array antenna and the transmission dipole antenna element is sequentially moved in the well in the axial direction of the well.
In the first step, each time the transmission / reception antenna unit sequentially moves in the well in the axial direction of the well, the second step to the fourth step are sequentially executed, or the fourth step is sequentially executed.
In the first step, each time the transmission / reception antenna unit sequentially moves in the well in the axial direction of the well, the second step and the third step are sequentially executed, and the first step is performed. After the step 1 to the third step is completed, the fourth step is executed.
In the fourth step,
The transmitting / receiving antenna unit derives the time difference between the earliest arrival time and the latest arrival time at each position where the well is sequentially moved in the axial direction of the well.
When the position where the time difference is the minimum value of a predetermined value or less with respect to the change in the position in the axial direction of the well is specified as the singular position, the incident elevation angle is the first and the singular position at the specified singular position. It is approximately estimated that it coincides with any one of the second critical incident elevation angles, and the incident elevation angle is within the first incident elevation angle range on one side with respect to the singular position in the axial direction of the well. The direction estimation method according to claim 7, wherein the incident elevation angle is determined to be within the second incident elevation angle range on the other side with the singular position as a reference, and the incident azimuth angle is derived. In the third step, the propagation time of the electromagnetic wave from the transmitting dipole antenna element to the dipole array antenna is set at each position where the transmitting / receiving antenna unit sequentially moves in the well in the axial direction of the well. Measure and
As the pretreatment step of the fourth step, the inclination of the plane including the exploration target plane with respect to the plane orthogonal to the axis of the well is based on the relationship between the position in the axial direction of the well and the propagation time. Derived the angle,
When the inclination angle is larger than the first critical incident elevation angle,
In the fourth step,
When the singular position is specified within the movement range of the transmission / reception antenna unit in the axial direction of the well, the plane including the search target surface is the well with reference to the singular position within the movement range. It is determined that the incident elevation angle is within the second incident elevation range on the intersection side intersecting the axis, and it is determined that the incident elevation angle is within the first incident elevation range on the side opposite to the intersection side. ,
When the singular position is not specified within the movement range of the transmission / reception antenna unit in the axial direction of the well, it is determined that the incident elevation angle is within the first incident elevation angle range in the entire range of the movement range. 8. The direction estimation method according to claim 8. The first step is characterized in that the dipole array antenna is arranged in the well on the intersection side of the transmission dipole antenna element so that the plane including the search target surface intersects the axis of the well. The direction estimation method according to any one of claims 7 to 9.

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