JP6088165B2 - Detection device, detection method, and detection program - Google Patents

Description

  The present invention relates to a detection device for detecting a target using an arrival direction estimation device for estimating the arrival direction of an incoming wave received by a receiving element array, and a detection method for detecting a target by estimating the arrival direction of the incoming wave. And a detection program therefor.

  The arrival direction estimation apparatus is used for estimation of the arrival direction of the ultrasonic wave reflected by the target, for example, in an underwater detection apparatus that detects the target using ultrasonic waves. For example, as a conventional underwater detection apparatus, there is an apparatus that transmits and receives ultrasonic waves using a transducer configured by an ultrasonic transducer array. FIG. 13 is a conceptual diagram showing an example of an underwater detection device using an ultrasonic transducer array. The transmitting beam 151 is irradiated from the ship 100 toward the seabed (FIG. 13A), and the seabed is viewed through the receiving beam 152 (FIG. 13B). As a result, the seabed where the transmission beam range and the reception beam range overlap is examined.

  A multi-beam method (beam former method) is conventionally known as a method for detecting a target by applying it to an underwater detection device using such an ultrasonic transducer array. In the multi-beam method, the intensity of the ultrasonic echo for each direction can be estimated by forming a reception beam having a predetermined beam pattern in which the main beam is directed to the direction for each direction.

  In the multi-beam method, since the main beam width of the reception beam is determined by the aperture length of the ultrasonic transducer array, the azimuth resolution is also limited by the aperture length of the ultrasonic transducer array. Therefore, in order to acquire a fine underwater cross-sectional image, it is necessary to widen the aperture length of the ultrasonic transducer array and improve the azimuth resolution. In order to realize this, it is generally necessary to increase the number of array elements. In addition, beam formation using Chebyshev weight or the like is generally performed in order to suppress a virtual image due to a side lobe of the received beam. However, the main beam width is increased accordingly, and the azimuth resolution tends to deteriorate.

  As a method for improving the azimuth resolution and the sidelobe virtual image without increasing the number of array elements, for example, a sum-difference method or an adaptive beamforming method is known. The sum / difference method, for example, divides the output of the linear array type transducer into the output of the ultrasonic transducer on the right half and that of the left half, and subtracts the difference between the two outputs from the sum of both outputs, as if the main beam of the received beam. This is a technique to obtain a video image that looks as if the width is reduced and the sidelobe virtual image is suppressed. However, the sum-difference method has a drawback that detection of a plurality of targets at the same distance becomes inaccurate.

  Unlike the multi-beam method, the adaptive beam forming method is a method of forming a reception beam having a different beam pattern according to a reception signal even in the same direction. As an adaptive beam forming method, for example, there is a Capon method described in Non-Patent Document 1. The Capon method realizes improvement in azimuth resolution and suppression of virtual images due to side lobes by forming a reception beam having a beam pattern that does not receive incoming waves from other than the scanning direction as much as possible.

Nobuyoshi Kikuma, “Adaptive signal processing by array antenna”, Science and Technology Publishing, November 25, 1998.

  However, if the adaptive beamforming method such as the Capon method that estimates the incoming wave on the assumption that the incoming incoming wave has no correlation is applied to an underwater detection device such as active sonar as it is, due to the correlation of the reflected wave, The target image such as the seabed becomes inaccurate. Therefore, it is difficult to put an underwater detection device using the Capon method into practical use.

  An object of the present invention is to provide a detection device, a detection method, and a detection program that can accurately capture a target when the direction of arrival is estimated by an adaptive beamforming method.

  The detection device according to the present invention includes a transmission element array including a first transmission element and a second transmission element that are arranged apart from each other, and a second transmission with respect to a first pulse wave transmitted from the first transmission element. A transmitter that delays the second pulse wave transmitted from the element and outputs a transmission signal to the transmitting element array so that the second pulse wave is transmitted following the first pulse wave; A receiving element array including a plurality of receiving elements arranged so as to receive a first reflected wave generated and a second reflected wave generated by the second pulse wave, and a first received continuously by the receiving element array And a receiver having an arrival direction estimation device that performs an operation on an incoming wave by applying an adaptive beamforming method to a synthesized echo signal obtained from a synthesized reflected wave including the reflected wave and the second reflected wave.

  In the detection device of the present invention, since the first transmission element and the second transmission element are spaced apart from each other, the distance from the first transmission element to the reflector and the distance from the second transmission element change depending on the direction. Depending on the direction when the combined reflected wave returns to the receiving element array, the waveform of the combined reflected wave including the first reflected wave and the second reflected wave that are mutually continuous changes variously. Therefore, the mutual correlation between combined reflected waves received at different orientations of the receiving element array can be weakened, and the intensity of the combined reflected waves detected when the adaptive beamforming method is applied depends on the mutual correlation. It can suppress that it falls.

  The detection method according to the present invention transmits a first pulse wave from a first transmission element and a second delay delayed from the first pulse wave by a second transmission element arranged separately from the first transmission element. A pulse wave transmission step in which a pulse wave is transmitted following the first pulse wave, and a first reflected wave generated by the first pulse wave and a second reflected wave generated by the second pulse wave are composed of a plurality of receiving elements. Adaptive beam forming method for a synthesized echo signal obtained from a synthesized reflected wave including a reflected wave receiving step received by the receiving element array and a first reflected wave and a second reflected wave successively received by the receiving element array And a direction-of-arrival estimation step of performing calculation related to the incoming wave by applying the above.

  In the detection method of the present invention, since the first transmission element and the second transmission element are spaced apart from each other, the distance from the first transmission element to the reflector and the distance from the second transmission element change depending on the direction. In the reflected wave receiving step, the waveform of the combined reflected wave including the first reflected wave and the second reflected wave that are continuous with each other varies depending on the direction in which the combined reflected wave returns. Therefore, the correlation between the combined reflected waves received in different directions can be weakened, and the intensity of the combined reflected waves detected when the adaptive beamforming method is applied in the direction of arrival estimation step is correlated with each other. It can suppress that it falls by.

  According to the present invention, since the intensity of the reflected wave is suppressed from decreasing due to the correlation between signals, the reflected wave can be detected accurately, so that the accuracy of capturing a target is increased.

The block diagram which shows the outline | summary of the underwater detection apparatus which concerns on one Embodiment of this invention. The conceptual diagram for demonstrating the concept of the pulse wave which the transducer for transmission transmits. (A) The wave form diagram for demonstrating the pulse wave transmitted to the direction of azimuth | direction 0 degree | times. (B) A waveform diagram for explaining a pulse wave transmitted in the direction of azimuth −90 degrees. (A) The conceptual diagram for demonstrating an example of a structure of the transducer for transmission using a subarray. (B) The conceptual diagram for demonstrating the other example of a structure of the transducer for transmission using a subarray. The graph for demonstrating the transmission beam pattern of the pulse wave of the subarray multiplied by the weight. The graph for demonstrating the phase characteristic of the pulse wave of the subarray multiplied by the weight. The graph which shows the correlation of the incoming wave from two different directions received by the underwater detection apparatus of this embodiment. The conceptual diagram for demonstrating the adaptive array which forms a receiving beam. The flowchart for demonstrating the arrival direction estimation procedure in the case of detecting the condition of a seabed. The conceptual diagram which shows the condition of the seabed detection using the transducer for transmission and reception. The graph for demonstrating the effect at the time of using the underwater detection apparatus of this embodiment. The conceptual diagram for demonstrating the other concept of the pulse wave which the transducer for transmission transmits. (A) The conceptual diagram for demonstrating the transmission beam in the seabed observation of the conventional multibeam method. (B) The conceptual diagram for demonstrating the receiving beam in the seabed observation of the conventional multibeam method. The block diagram which shows the outline | summary of the other underwater detection apparatus which concerns on one Embodiment of this invention.

  Hereinafter, an underwater detection device according to an embodiment of the present invention will be described with reference to FIG. FIG. 1 is a block diagram illustrating an outline of a configuration of an underwater detection device including an arrival direction estimation device.

(1) Outline of Configuration of Underwater Detection Device As shown in FIG. 1, the underwater detection device 10 includes a transmitter 20, a transmission transducer 30, a reception transducer 40, a receiver 50, And a display device 60. The transmission transducer 30 and the reception transducer 40 are, for example, linear array type transducers in which ultrasonic transducers 31 and 41 are arranged in a straight line at equal intervals of a half wavelength at the carrier frequency. In order to receive the reflected wave generated by the pulse wave transmitted by the transmitting transducer 30 by the receiving transducer 40, the transmitting transducer 30 and the receiving transducer 40 are, for example, mounted on the ship bottom and exposed to the sea.

(1-1) Transmitter and Transmitting Transducer The transmitting transducer 30 is connected to the transmitter 20. The transmitter 20 generates a transmission signal based on conditions set by an operation / display device 60 described later. When transmitting, the transmitter 20 outputs a transmission signal so that a large number of ultrasonic transducers 31 of the transmitting transducer 30 transmit a pulse wave described later.

The concept of the pulse wave transmitted by the transmitting transducer will be described with reference to FIG. The transmitting transducer 30A shown in FIG. 2 includes three ultrasonic transducers 31 ₁ , 31 ₂ , and 31 ₃ that are adjacent to each other by a half of the carrier wavelength λ. Assuming that the pulse length of the pulse wave transmitted from the transmitting transducer 30A is 0.3 ms, for example, pulse waves P1, P2, P3 having a pulse length of 0.1 ms from the ultrasonic transducers 31 ₁ , 31 ₂ , 31 ₃ are obtained. Each wave is transmitted. When these three pulse waves are added together, a pulse wave having a pulse length of approximately 0.3 ms is obtained. Regarding the azimuths of these three pulse waves P1, P2, and P3, the azimuth perpendicular to the direction in which the ultrasonic transducers 31 ₁ , 31 ₂ , and 31 ₃ are arranged is 0 degrees, and θ toward the ultrasonic transducer 31 ₁ It is assumed that the angle when tilted only by -θ degrees and the angle when tilted by θ toward the ultrasonic transducer 31 ₃ are expressed by θ degrees.

For example, when θ is 90 degrees, the pulse wave is radiated toward the ultrasonic transducer 31 ₃ along the direction in which the ultrasonic transducers 31 ₁ , 31 ₂ , 31 ₃ are arranged. Therefore, when the reference ultrasonic transducer 31 _2, pulse wave P1 of the ultrasonic transducer 31 _1, the ultrasonic transducer 31 _{and second} ultrasonic transducers 31 ₁ and 31 ₂ intervals than the pulse wave P2 (lambda / 2) advances the phase. In other words, pulse wave P1 of the ultrasonic transducer 31 ₁ at theta = -90 degrees, phase than the ultrasonic transducer 31 _second pulse wave P2 is advanced by π radians. Conversely, when theta = 90 degrees, a pulse wave P3 of the ultrasonic transducer 31 ₃ phase than the ultrasonic transducer 31 _second pulse wave P2 is delayed by π radians. Therefore, the synthesized pulse wave transmitted in the direction of 0 degree azimuth has the pulse waves P1, P2, P3 of the ultrasonic transducers 31 ₁ , 31 ₂ , 31 ₃ as shown in FIG. The waveform is continuous and uninterrupted. On the other hand, the synthesized pulse wave transmitted in the direction of −90 degrees is the pulse waves P1, P2, P3 of the ultrasonic transducers 31 ₁ , 31 ₂ , 31 ₃ as shown in FIG. Is a waveform that continues intermittently at a half wavelength λ / 2. Since the pulse wave of FIG. 3A and the pulse wave of FIG. 3B do not overlap each other even if the phase is shifted, the correlation is weak.

Next, the concept of the configuration of a transmitting transducer using a subarray will be described with reference to FIG. The operation of transmitting a pulse wave from the transmitting transducer 30A described with reference to FIGS. 2 and 3 includes three pulse waves P1, radiated from the ultrasonic transducers 31 ₁ , 31 ₂ , 31 ₃ of the transmitting transducer 30A. P2 and P3 are sequentially transmitted at each timing. On the other hand, the transmitting transducer 30B shown in FIG. 4 has h + 2 ultrasonic transducers 31 _{1 to} 31 _{h + 2} , and three ultrasonic transducers form one set (subarray). It is composed. For example, sub-array Sua ₁ is constituted by the ultrasonic oscillator 31 _{1-31 3,} sub-arrays Sua _h is constituted by the ultrasonic oscillator 31 _h ~31 _{h + 2.} In this way, the transmitting transducer 30B in FIG. 4 (a), h subarrays Sua ₁ ~Sua _h is formed. The pulse wave emitted from each sub-array Sua ₁ ~Sua _h is sequentially transmitting at different timing for each subarray Sua ₁ ~Sua _h. Therefore, the transmission signal is transmitted based on the timing and weight of each of the ultrasonic transducers 31 _{1 to} 31 _{h + 2} set in the transmission signal generation unit 21 of the transmitter 20 or calculated by the transmission signal generation unit 21. From the machine 20 to the ultrasonic transducers 31 _{1 to} 31 _{h + 2} .

Here, a transmission transducer using a sub-array will be described with a specific example having _eight ultrasonic transducers 31 _{1 to} 318. The transmitting transducer 30C shown in FIG. 4B is a linear array in which _eight ultrasonic transducers 31 _{1 to} 318 are linearly arranged at a λ / 2 pitch, and three subarrays Sua _{11 to} Sua. ₁₃ is composed.

Each of the sub-arrays Sua _{11 to} Sua ₁₃ applies the weight shown in Table 1 to each ultrasonic transducer and causes the six ultrasonic transducers to transmit pulse waves. Element numbers in Table 1, for example, represents the order when arranged in order of ascending order or argument of the sign of the argument of the ultrasonic transducer 31 _{1-31 8.} The weights shown in Table 1 are complex numbers.

When transmission is performed with such weights, the pulse waves of the sub-arrays Sua _{11 to} Sua ₁₃ each have the transmission beam pattern shown in FIG. The reason why the depression (the portion where the sound pressure is reduced) is provided near the center of the transmission beam pattern in FIG. 5 is to suppress the virtual image of the seabed just below the transmission transducer 30C.

The weights in Table 1 are asymmetrical with different weights for element numbers 1 and 6, 2 and 5, 3 and 4. Therefore, if the weights of the element numbers 1 and 6, 2 and 5, 3 and 4 are interchanged and the left and right weights are turned over and transmitted, transmission beams having the same transmission beam pattern and different phases may be transmitted. it can. When these two types of weighting methods are applied to the three sub-arrays Sua _{11 to} Sua ₁₃ , the weights shown in Table 2 are obtained, and six transmission beams having the same amplitude characteristics but different phase characteristics are obtained. Can be generated. In Table 2, the description of the imaginary part of the complex number is omitted. Since all six transmission beams have different phase characteristics as shown in FIG. 6, if a pulse wave is transmitted using the six transmission beams in the three subarrays Sua _{11 to} Sua ₁₃ , 3 The effect of suppressing the correlation is greater than when three subarrays Sua _{11 to} Sua ₁₃ transmit a pulse wave using three transmission beams.

FIG. 7 is a graph showing the correlation between an incoming wave from an orientation of 0 degrees and an incoming wave from an orientation other than 0 degrees. In FIG. 7, the graph connecting the black circles shows the correlation of the reflected waves (arrival waves) generated from the pulse waves of a predetermined pulse length simultaneously transmitted from the _eight ultrasonic transducers 31 _{1 to} 318 as in the prior art. The graph with white circles is a reflection generated from a pulse wave formed by sequentially delaying six types of transmission beams multiplied by the weights shown in Table 2 and transmitting each one-sixth of the predetermined pulse length. It shows the correlation of waves (arrival waves). When the same pulse wave is transmitted simultaneously from the _eight ultrasonic transducers 31 _{1 to} 318, for example, the correlation between the incoming wave with the 0 ° azimuth and the incoming wave with the 15 ° azimuth becomes 1. On the other hand, when six transmission beams are sequentially transmitted from the _eight ultrasonic transducers 31 _{1 to} 318 by applying the weights shown in Table 2, for example, an incoming wave with a 0 degree azimuth and a 15 degree azimuth The correlation of the incoming waves becomes 0.4.

(1-2) Reception Transducer and Receiver The reception transducer 40 is connected to the receiver 50. The receiving transducer 40 outputs an echo signal corresponding to the received reflected wave to the receiver 50. The receiver 50 processes the received echo signal, converts it into a video signal, and outputs the video signal to the operation / display device 60. The operation / display device 60 displays a video corresponding to the video signal output from the receiver 50 on the display screen. The operation / display device 60 includes various input keys and the like, and is configured to be able to input various settings and various parameters necessary for transmission / reception of ultrasonic waves and video display. Depending on the setting of the receiver 50, a constant of an adaptive beam forming method to be described later may be input from the operation / display device 60.

  The receiver 50 includes an amplifier 51, an A / D converter 52, a detector 53, and a signal processing unit 54.

The amplifier 51 amplifies each electrical signal of the _K ultrasonic transducers 41 _{1 to} 41 _K shown in FIG. 8 and outputs K received signals. The A / D converter 52 converts the reception signal output from the amplifier 51 into a complex digital signal, and outputs it to the signal processing unit 54 as complex reception data. The detector 53 detects the digital signal output from the A / D converter 52 using a method such as IQ detection. The signal processing unit 54 processes the complex reception data output from the detector 53 to generate a video signal. The signal processing unit 54 performs processing for estimating the arrival direction of the incoming wave received by the receiving transducer 40 in the arrival direction estimation device 70 during signal processing such as generation of a video signal. An underwater cross-sectional image or the like can be formed using the estimation result of the arrival direction.

(2) Configuration of Arrival Direction Estimation Device Arrival direction estimation device 70 includes R calculation unit 71, spatial average processing unit 72, attenuation matrix addition unit 73, Capon method output calculation unit 74, arrival direction and intensity calculation unit. 75. The arrival direction estimation device 70 is composed of devices such as a CPU, FPGA, and memory (not shown). For example, the CPU reads out the program from the memory and executes it, thereby configuring the functions of the R calculator 71, the spatial average processor 72, the attenuation matrix adder 73, the Capon method output calculator 74, and the arrival direction and intensity calculator 75. be able to.

Before describing these configurations, the relationship between the reception data to be estimated by the arrival direction estimation device 70 and the reception transducer 40 will be described with reference to FIG. FIG. 8 is a conceptual diagram for explaining an adaptive array that forms a received beam. As shown in FIG. 8, the receiving transducer 40 is composed of, for example, K ultrasonic transducers 41 _{1 to} 41 _K arranged in a straight line, and the arrangement positions of the ultrasonic transducers 41 _{1 to} 41 _K are as follows. The distance from the reference point P is d ₁ to d _K. The interval between the adjacent transducers of the ultrasonic transducers 41 _{1 to} 41 _K is, for example, a half wavelength at the ultrasonic carrier frequency. FIG. 8 shows a state in which the desired wave is incident on the ultrasonic transducers 41 _{1 to} 41 _K at an angle θ.

The complex received signals of the ultrasonic transducers 41 _{1 to} 41 _K at time t can be collectively expressed as an input vector X (t), and X (t) = [x ₁ (t), x ₂ (t),. x _K (t)] ^T. Here, T represents transposition.

The R calculator 71 calculates a correlation matrix R (t) at time t from the input vector X (t). The correlation matrix R (t) is given by the following equation (1).
R (t) = E [X (t) X ^H (t)] (1)

  Here, E [•] represents an operation for obtaining an expected value (ensemble average), and H represents a complex conjugate transpose. The ensemble average is substituted by the time average. That is, when obtaining the correlation matrix R (t) at time t, input vectors at sampling times before and after that are also used. In the case of uniform time averaging:

  The time average of the correlation matrix R (t) is not uniform, and may be a time average with an appropriate weight. In addition, time averaging may not be performed. In the following description, the time average of the correlation matrix R (t) is not performed. Also, only the correlation matrix at a specific time is considered, and the correlation matrix and the input vector argument t are omitted.

The spatial average processing unit 72 calculates the spatial average correlation matrix R _av by performing spatial average of the correlation matrix R using the subarray. FIG. 8 shows an example in which N sub-arrays Sub _{1 to} Sub _n are taken out while shifting consecutive K ultrasonic transducers one by one.

The input vector Xn of the nth subarray is given by equation (2).
_Xn = [ _xn , _{xn + 1} ,... _{Xn + K-1} ] ^T (n = 1, 2,... N) (2)

Therefore, the partial correlation matrix R _n of the n-th sub-array is given by equation (3).
R _n = E [X _n X ^H _n ] (n = 1, 2,... N) (3)

Assuming that weighting for each partial correlation matrix R _n is w _n (n = 1, 2,... N), the average (spatial average) of the N partial correlation matrices gives the spatial average correlation matrix R _{av of} equation (4). It is done. An example of a weight is w _n = 1 / N, which is called a uniform spatial average. In order to perform such processing in the spatial average processing unit 72, the R calculation unit 71 calculates the partial correlation matrix R _n and outputs the calculated partial correlation matrix R _n to the spatial average processing unit 72. Is done.

The attenuation matrix adding unit 73 generates a diagonal matrix determined according to the constant s determined by the sensitivity of the receiving transducer 40 and the propagation distance r of the desired wave, and adds the generated diagonal matrix to the spatial average correlation matrix R _av . The constant s determined by the sensitivity of the receiving transducer 40 can be determined based on an actual measurement result using the receiving transducer 40, for example, a value at which the SN ratio is the best when the constant s is changed in actual measurement. Is selected. The propagation distance r is determined from the time from when the ultrasonic wave is transmitted from the receiving transducer 40 until the reflected wave is received by the receiving transducer 40. This attenuation matrix D is given by the following equation (5) using the unit matrix I when the attenuation of the incoming wave is proportional to the square of the propagation distance r, for example. Therefore, the output R _DL of the attenuation matrix adding unit 73 is given by the equation (6).
D = (s / r ² ) × I (5)
R _DL = R _av + δI (where δ = s / r ² ) (6)

The Capon method output calculation unit 74 calculates the output P (θ) of the Capon method using the correlation matrix R _DL that is the output of the attenuation matrix addition unit 73 instead of the correlation matrix R used in the conventional Capon method. . The angle spectrum P (θ) that is the output of the Capon method is given by the equation (7) using the steering vector a (θ).

  The steering vector a (θ) is determined by the shape of the array. When the element array is a linear array and the position is represented by d1 to dK when viewed from the reference point P as shown in FIG. 8, the steering vector a (θ) is given by the following equation. In the following equation, λ represents the wavelength of a carrier wave (ultrasound), and j represents an imaginary unit.

  From the angle spectrum of the Capon method expressed by the equation (7), the arrival direction and intensity calculation unit 75 detects the arrival direction from the position of the peak (maximum value) when the angle θ is changed, and depends on the height of the peak. The power of the incoming wave (intensity of the incoming wave) is detected.

(3) Arrival Direction Estimation Procedure A procedure for estimating the arrival direction in the arrival direction estimation device 70 described above will be described with reference to the flowchart of FIG. First, a transmission beam is transmitted from the transmission transducer 30 toward the seabed. Then, the reflected wave reflected on the seabed is received by the receiving transducer 40. At this time, the received beam is scanned in a range of a predetermined angle, for example, in the range of −60 degrees to 60 degrees with 0 degrees in the vertical direction, and the power is detected in the direction of arrival of the desired wave.

  FIG. 10 conceptually shows a situation where the ship 100 detects the seabed 101 using the transmitting transducer 30 and the receiving transducer 40. A position equidistant from the transmitting transducer 30 and the receiving transducer 40 spreads in a fan shape as shown by a broken line in FIG. Therefore, in order to detect the sea floor spreading laterally from the vertically lower side of the ship 100, the reception beam is scanned every predetermined time. For example, the direction of the desired wave of the received beam (the steering vector θ) is changed from −60 degrees to 60 degrees every time a predetermined time elapses, and the range from −60 degrees to 60 degrees is scanned. For this purpose, the process of performing adaptive beamforming is performed after the received data is temporarily stored in the signal processing unit 54. At this time, the reflected waves U1, U2, and U3 in FIG. 10 are different in waveform and have low correlation with each other because their transmitted directions are different if the reflected distances are assumed to be equal. That is, the waveforms of incoming waves received simultaneously by the receiving transducer 40 are different from each other. As a result, the reflected waves U1, U2, and U3 can be clearly distinguished and processed in adaptive beamforming.

For example, an input vector is generated every time a predetermined time elapses immediately after the ultrasonic wave is transmitted from the receiving transducer 40 (at time t = 0). For example, the input vector X at time t = ΔT is X (t ₁ ). Further, input vectors X (t ₂ ), X (t ₃ )... X (t _n ) are generated every time a predetermined time has elapsed from time t = γ. The input vector X (t) given from the receiving transducer 40 to the arrival direction estimating device 70 via the amplifier 51, the A / D converter 52 and the detector 53 is input into the input vectors X (t ₁ ) and X (t ₂ ). ..., X (t _n ) (step S1). For example, if the predetermined time is ΔT, the propagation distance r of the incoming wave of the input vector X (t _n ) is given by r = ΔT × n × v using the sound velocity v in the sea.

For each of these input vectors X (t), the R calculator 71 calculates a partial correlation matrix R _n (step S2). Then, using the partial correlation matrix R _n , the spatial average processing unit 72 performs spatial average processing to calculate the spatial average correlation matrix R _av (step S3).

Next, the attenuation matrix adding unit 73 calculates an attenuation matrix D from the ultrasonic wave propagation distance r. The constant s is a numerical value that can be determined in advance if the underwater detection device 10 is determined. For example, the value of each element of the attenuation matrix D (t ₁ ) of the input vector X (t ₁ ) is different from the value of each element of the attenuation matrix D (t ₃₀ ) of the input vector X (t ₃₀ ). The value of each element of the attenuation matrix D (t ₁ ) is larger than the value of each element of the attenuation matrix D (t ₃₀ ). The attenuation matrix adder 73 adds the attenuation matrix D to the spatial average correlation matrix R _av and outputs a correlation matrix R _DL every predetermined time (step S4).

Next, the Capon method output calculation unit 74 calculates an output P (θ), that is, an angle spectrum, based on the inverse matrix of the correlation matrix R _DL (step S5). At this time, as the steering vector a (θ) in the equation (7), the steering vector a (−60 °), a (−59 °),... With respect to each input vector X, for example, the input vector X (t _n ). a (0 °), ..., a (59 °), a (60 °) are used.

  In the arrival direction and intensity calculation section 75, the direction of arrival is estimated from the position of the peak (maximum value) by changing θ of the output P (θ) (step S6). Further, the arrival direction and intensity calculation unit 75 estimates the signal level (intensity) of the arrival wave from the maximum value (step S7).

Each input vector X (t ₁ ), X (t ₂ ),... X (t _n ) is scanned as described above, and an image is formed from the obtained angular spectrum (step S8). When the angle spectrum is calculated for one time (distance), it becomes grayscale data for one line of the image (the value of P (θ) corresponds to the color). If all of the angle spectrum P (θ) up to the target distance is acquired, a two-dimensional gray image with an angle-distance can be formed. An image to be displayed on the operation / display device 60 can be obtained by converting the angle-distance two-dimensional grayscale image data into a horizontal distance-vertical distance two-dimensional image. Therefore, image formation (step S8) can be performed without estimating the arrival direction (step S6) and the signal level of the incoming wave (step S7), and steps S6, S7 and step S8 are processed in parallel. can do.

<Features>
(1)
In FIG. 2 of the above embodiment, the three ultrasonic transducers 31 _{1 to} 31 ₃ (transmitting elements) have been described. For example, at least two ultrasonic vibrations of the transmitting transducer 30A (transmitting element array) are used. If the children 31 ₁ and 31 ₂ are provided, an effect of weakening the correlation can be obtained.

For example, the ultrasonic transducer 31 ₁ (first transmission element) and the ultrasonic transducer 31 ₂ (second transmission element) are arranged with a half wavelength λ / 2 of the carrier frequency. As shown in FIG. 2, to the ultrasonic transducer 31 _pulse wave transmitting from (first transmission device) P1 (first pulse wave), ultrasonic transducer ₃₁₂ (the second transmission The pulse wave P2 (second pulse wave) is delayed from the element and transmitted. Thus, a transmission signal is output from the transmitter 20 (see FIG. 1) to the transmission transducer 30A so that the pulse wave P2 is transmitted following the pulse wave P1.

  For example, when the reflected waves U1 and U3 (combined reflected waves) in FIG. 10 composed of the reflected waves of the pulse wave P1 and the pulse wave P2 transmitted in this way are reflected in different directions at the same distance, Since the phases of P1 and pulse wave P2 are different, the waveforms of reflected waves U1 and U3 are different as described with reference to FIG. 3, and the correlation between them is reduced.

  The arrival direction estimation device 70 of the receiver 50 applies the Capon method (adaptive beamforming method) to the reflected waves U1 and U3 having a reduced correlation in this way to calculate the output P (θ) of the Capon method (related to the incoming wave). Calculation).

For example, FIG. 11 shows the detection result Ma by the multi-beam method when the eight ultrasonic transducers shown in FIG. 4B are used, the calculation result Ca1 by the Capon method when the correlation is high, and the present embodiment. It is a graph which shows an example of the calculation result Ca2 by the underwater detection apparatus 10 by a form. If high correlation with sends the same pulse wave from the ultrasonic transducer 31 _{1-31 8} transmitting transducer 30C at the same time, the simulation results in the case of receiving by the receiving transducer 40 that is not sub-array of. Similarly, the detection result by the underwater detection device 10 uses the transmitting transducer 30C including _eight ultrasonic transducers 31 _{1 to} 318 and the receiving transducer 40 including _eight ultrasonic transducers 41 _{1 to} 418. This is a simulation result when three subarrays are used for both transmission and reception. In this underwater detection device 10, it can be seen that side lobes can be reduced compared to the multi-beam method, and the output is improved compared to the Capon method when the correlation is high.

As described above, since the ultrasonic transducer 31 ₁ and the ultrasonic transducer 31 ₂ are spaced apart from each other, the distance from the ultrasonic transducer 31 ₁ to the reflector and the distance from the ultrasonic transducer 31 ₂ are reduced. Changes depending on the direction, the waveform of the combined reflected wave changes variously depending on the direction when the combined reflected waves U1 and U3 return to the transmitting transducer 30C. This also is increasing the number of ultrasonic transducers are the same, for example the ultrasonic vibrator 31 ₃ are the same be added. To achieve the effect of the present invention, the above-mentioned ultrasonic vibrator 31 ₁ and satisfies ultrasonic transducers, such as ultrasound transducer 31 ₂ may be contained in at least two transmitting transducer 30 .

(2)
The transmitter 20 of the above embodiment includes a transmitting transducer 30A (transmitting element array) so that a combined pulse wave including a pulse wave P1 (first pulse wave) and a pulse wave P2 (second pulse wave) becomes a fan beam. Output transmission signal. For example, if a beam with high beam directivity such as a pencil beam is used as the transmission beam, there will be a region where reflected waves are not generated. It is advantageous to use a fan beam that generates a reflected wave.

(3)
Figure 4 as described with reference to the transmission signal transmitted from the transmitter 20, transmitting transducer 30B, 30C is subarrays Sua ₁ ~Sua _h, operates in units of Sua ₁₁ ~Sua _13. For example, it compares the subarray Sua ₂ configured by the ultrasonic oscillator 31 _1, 31 _2, 31 ₃ subarrays Sua ₁ which is composed of the ultrasonic transducer 31 _2, 31 _3, 31 _4. The subarray Sua ₁ (first transmission subarray) includes ultrasonic transducers 31 ₁ and 31 ₃ (first transmission element and third transmission element), and the subarray Sua ₂ (second transmission subarray) includes ultrasonic vibrations. It can be considered that the children 31 ₂ and 31 ₄ (second transmission element and fourth transmission element) are included. In this way, the acoustic center of the sub-array Sua _{11 and} the acoustic center of the sub-array Sua ₁₂ are arranged with a half wavelength λ / 2 of the carrier frequency.

For this reason, the two subarrays Sua ₁₁ and Sua ₁₂ can be handled in the same manner as one ultrasonic transducer disposed at the respective acoustic centers. As a result, the transmitting transducer 30B is an ultrasonic transducer 31 _{1-31 3} second subarray pulse wave transmitting following the first sub-array pulse wave transmitting from the ultrasonic transducer 31 _{2-31 4} Can be transmitted.

  For example, the reflected waves U1 and U3 (combined reflected waves) shown in FIG. 10 composed of the reflected waves of the first subarray pulse wave and the second subarray pulse wave transmitted in this way are reflected in different directions at the same distance. Since the acoustic centers are arranged apart from each other, the phases of the first subarray pulse wave and the second subarray pulse wave are slightly different and the waveforms of the reflected waves U1 and U3 are different from each other. Decreases.

  The transmission sub-array is not limited to the first transmission sub-array and the second transmission sub-array described above, and three transmission centers are separated from each other like the transmission transducers 30B and 30C described in the above embodiment. A transmission transducer (transmission element array) may be configured by the above transmission subarray. That is, another transmission subarray such as a third transmission subarray can be added to the transmission element array.

(4)
The transmitter of the above embodiment 20, subarray Sua ₁ ~Sua _h and subarray Sua ₁₁ composite pulse wave of the pulse wave ～Sua ₁₃ to transmit fan beams become as transmitting transducer 30B, 30C (the transmitter array) The transmission signal is output to. When the synthesized pulse wave is a fan beam, it is advantageous when a wide range of detection is performed, such as when searching for seabed topography.

(5)
In the above embodiment, as shown in Table 1, for example, the ultrasonic transducers 31 _{1 to} 31 ₄ (first transmission elements) constituting the subarrays Sua ₁₁ and Sua ₁₂ (first transmission subarray and second transmission subarray). The case where weighting of the second transmission element, the third transmission element, and the fourth transmission element) is performed is described. By performing such weighting, the transmission beam pattern of the pulse wave (the first subarray pulse wave and the second subarray pulse wave) transmitted from the subarrays Sua ₁₁ and Sua ₁₂ is, for example, as shown in FIG. It can be set appropriately according to the detection target. As a result, detection performance can be improved, such as suppression of virtual images.

(6)
In the above embodiment, as shown in Table 2, the transmitter 20 includes ultrasonic transducers 31 _{1 to} 31 ₄ (first transmitting element, second transmitting element, third transmitting element, and fourth transmitting element). By changing the respective weights, the amplitude characteristics are the same as the forward pulse wave of the subarray Sua ₁₁ (first subarray pulse wave) and the forward pulse wave of the subarray Sua ₁₂ (second subarray pulse wave), and the phase characteristic The sub-array Sua ₁₁ reverse-direction pulse wave (third sub-array pulse wave) and the sub-array Sua ₁₂ reverse-direction pulse wave (fourth sub-array pulse wave) are transmitted to the transmitting transducer 30C.

  As described above, the third subarray pulse wave and the fourth subarray pulse wave can be added to the first subarray pulse wave and the second subarray pulse wave, and the types of subarray pulse waves can be increased. The correlation can be further suppressed by forming the synthesized pulse wave with the sub-array pulse wave.

(7)
In the above-described embodiment, for example, the ultrasonic transducer 31 ₁ (first transmission element) and the ultrasonic transducer 31 ₂ (second transmission element) are arranged apart from each other by a half wavelength λ / 2 of the carrier frequency. ing. As shown in FIG. 2, to the ultrasonic transducer 31 _pulse wave transmitting from (first transmission device) P1 (first pulse wave), ultrasonic transducer ₃₁₂ (the second transmission The pulse wave P2 (second pulse wave) is delayed from the element and transmitted. At this time, the frequency and the pulse length of the pulse wave P1 and the pulse wave P2 are configured to be the same. With this configuration, the transmitter 20 can easily apply the same transmission signal to the ultrasonic transducer 31 ₁ (first transmission element) and the ultrasonic transducer 31 ₂ (second transmission element) with a delay. The detection device 10 can be realized with a simple configuration. Thereby, the configuration of the detection device 10 is simplified, and the detection device 10 can be provided at low cost.

(8)
The direction-of-arrival estimation apparatus 70 according to the above embodiment includes a receiving transducer 40 (receiving element array) including ultrasonic transducers 41 _{1 to} 41 _K (a plurality of receiving elements) as N subarrays Sub _{1 to} Sub _n (a plurality of receiving elements). And sub-arrays Sub _{1 to} Sub _n are used to perform spatial averaging.

The effect of suppressing the correlation by the spatial average is the first pulse wave transmitted from the at least two ultrasonic transducers 31 ₁ and 31 ₂ (first transmitting element and second transmitting element) described in (1) above. In addition, the correlation can be further suppressed in combination with the effect of suppressing the correlation by using the combined pulse wave of the second pulse wave.

<Modification>
(1)
In the above embodiment, the underwater detection device using ultrasonic waves in the sea has been described. However, the detection device using the vibration of the medium is not limited to the underwater detection device as in the above embodiment. For example, the present invention can be applied to the case of using vibration (transverse wave) that travels in the ground like an earthquake wave. The medium for transmitting vibrations may be other than water, such as metal and human tissue.

(2)
In the above embodiment, the Capon method has been described as an example of the adaptive beamforming method. However, the adaptive beamforming method to which the present invention can be applied is not limited to the Capon method, and the arrival directions such as the linear prediction method and the MUSIC method. It can also be applied to other adaptive beamforming methods for estimating

(3)
In the above embodiment, an ultrasonic linear array arranged in a straight line is used. However, three or more ultrasonic transducers 31 (transmitting element array) and three or more ultrasonic transducers 41 (receiving element array) are used. The arrangement is not limited to a straight line, and may be arranged in another shape such as a planar shape. Further, the interval between the three or more ultrasonic transducers 31 and 41 is not limited to an equal interval, and the interval is not limited to a half of the wavelength. The present invention can also be applied to a structure in which the vibrators 31 and 41 are arranged.

(4)
In the above embodiment, the case where the attenuation matrix adding unit 73 generates a diagonal matrix and adds the diagonal matrix to the spatial average correlation matrix R _av in the arrival direction estimation device has been described. However, the attenuation matrix adding unit 73 can be omitted.

(5)
In the above embodiment, the case where the synthesized pulse wave to be transmitted is changed stepwise for each azimuth has been described. However, as shown in FIG. 12, the waves are transmitted from the ultrasonic transducers 31 _{1 to} 31 _3. It is also possible to apply AM modulation to the pulse waves P11, P12, and P13 to change the synthesized pulse wave steplessly according to each direction. For example, one gradually reduce the amplitude of the end portion of the ultrasonic transducer 31 _first pulse wave P11, the ultrasonic vibrator 31 ₁ of the ultrasonic transducer 31 from where the amplitude starts to decrease pulse wave P11 ₂ Alternatively, the amplitude of the pulse wave P12 can be gradually increased.

(6)
In the above-described embodiment, the case where the transmission transducer 30 and the reception transducer 40 are used has been described. However, as shown in FIG. You may use both. In this case, the transducer 30A is not only a transmitting element array but also a receiving element array.

(7)
In the above embodiment, the function blocks of the transmission signal generator 21 of the transmitter 20 and the arrival direction estimation device 70 of the receiver 50 can execute the above-described processing procedure stored in a storage device (ROM, RAM, hard disk, etc.). In the above description, the program data is realized by being interpreted and executed by the CPU. This program data may be introduced into the storage device via a recording medium, or may be directly executed from the recording medium. The recording medium refers to a semiconductor memory such as a ROM, a RAM, or a flash memory, a magnetic disk memory such as a flexible disk or a hard disk, an optical disk memory such as a CD-ROM, DVD, or BD, and a memory card. The recording medium is a concept including a communication medium such as a telephone line or a conveyance path.

  In addition, all or some of the functional blocks constituting the transmission signal generation unit 21 and the arrival direction estimation device 70 of the above embodiment are typically integrated circuits such as LSIs (depending on the degree of integration, ICs, system LSIs, It is realized as a super LSI or an ultra LSI). These may be individually made into one chip, or may be made into one chip so as to include a part or all of them. Further, the method of circuit integration is not limited to LSI's, and implementation using dedicated circuitry or general purpose processors is also possible. Further, an FPGA (Field Programmable Gate Array) that can be programmed after manufacturing the LSI or a reconfigurable processor that can reconfigure the connection and setting of circuit cells inside the LSI may be used.

DESCRIPTION OF SYMBOLS 10 Underwater detection apparatus 20 Transmission apparatus 30,30A, 30B, 30C Transmission transducer 40 Reception transducer 50 Receiver 60 Operation / display apparatus 70 Arrival direction estimation apparatus

Claims (13)

An acoustic center of a first transmission subarray including a first transmission element , a second transmission element , a third transmission element, and a fourth transmission element that are spaced apart from each other, the first transmission subarray including the first transmission element and the third transmission element And a transmission element array in which the acoustic centers of the second transmission subarray including the second transmission element and the fourth transmission element are spaced apart from each other ;
The third pulse wave transmitting from the first pulse wave and the third transmission element is transmitting from said first transmission element, a second pulse wave, and the second being transmit from the second transmission element A second subarray pulse wave transmitted from the second transmission subarray following the first subarray pulse wave transmitted from the first transmission subarray by delaying the fourth pulse wave transmitted from the four transmission elements; A transmitter for outputting a transmission signal to the transmission element array so that
A receiving element array including a plurality of receiving elements arranged so as to receive a first subarray reflected wave generated by the first subarray pulse wave and a second subarray reflected wave generated by the second subarray pulse wave ;
An adaptive beam forming method is applied to a synthesized echo signal obtained from a synthesized reflected wave including the first sub-array reflected wave and the second sub-array reflected wave successively received by the receiving element array, and an operation relating to an incoming wave is performed. A receiver having a direction of arrival estimation device to perform ,
The transmitter outputs a transmission signal to the transmission element array so that the first transmission element, the second transmission element, the third transmission element, and the fourth transmission element are weighted, and outputs the transmission signal to the first subarray. The pulse wave and the second sub-array pulse wave are transmitted to the transmitting element array, and the first sub-array pulse wave and the second sub-array are changed by changing respective weights for the first to fourth transmitting elements. a pulse wave and the third sub-array pulse wave, and the fourth sub-array pulse wave phase characteristic amplitude characteristics identical differ by orientation Ru is transmitting to the transmitter array, the detection system. The transmitter transmits the first pulse wave and the second pulse wave having different phase characteristics depending on directions to the transmitting element array.
The detection device according to claim 1. The phase characteristic of the first pulse wave is different from the phase characteristic of the second pulse wave.
The detection device according to claim 2. The transmitter outputs a transmission signal to the transmission element array so that a combined pulse wave including the first pulse wave and the second pulse wave becomes a fan beam.
The detection device according to any one of claims 1 to 3. The transmitter transmits the first sub-array pulse wave and the second sub-array pulse wave having different phase characteristics depending on directions to the transmitting element array.
The detection device according to any one of claims 1 to 4 . The phase characteristic of the first subarray pulse wave is different from the phase characteristic of the second subarray pulse wave.
The detection device according to claim 5 . The transmitter outputs a transmission signal to the transmission element array so that a synthesized pulse wave including the first subarray pulse wave and the second subarray pulse wave becomes a fan beam;
The detection device according to any one of claims 1 to 6 . The transmitter transmits a transmission signal to the transmission element array so that the first pulse wave transmitted from the first transmission element and the second pulse wave transmitted from the second transmission element have the same frequency. Output,
The detection device according to any one of claims 1 to 7 . The transmitter transmits a transmission signal to the transmission element array so that a pulse length of the first pulse wave transmitted from the first transmission element is equal to a pulse length of the second pulse wave transmitted from the second transmission element. Output,
The detection device according to any one of claims 1 to 8 . The arrival direction estimation device divides a reception element array including a plurality of reception elements into a plurality of reception subarrays, and performs a spatial average using the plurality of reception subarrays.
The detection device according to any one of claims 1 to 9 . Each of the first transmitting element, the second transmitting element, and the plurality of receiving elements is an ultrasonic transducer,
The direction-of-arrival estimation device performs an operation on an incoming wave that propagates in water by applying an adaptive beamforming method.
The detection device according to any one of claims 1 to 10 . An acoustic center of a first transmission subarray including a first transmission element, a second transmission element, a third transmission element, and a fourth transmission element that are spaced apart from each other, the first transmission subarray including the first transmission element and the third transmission element And a first subarray pulse wave from the first transmission subarray in the transmission element array in which the acoustic centers of the second transmission subarray including the second transmission element and the fourth transmission element are spaced apart from each other with a pulse wave transmitting step in which the second sub-array pulse wave delayed with respect to the first sub-array pulse wave from the second transmission sub-array is transmitting subsequent to the first sub-array pulse wave,
A reflected wave receiving step of receiving a first subarray reflected wave generated by the first subarray pulse wave and a second subarray reflected wave generated by the second subarray pulse wave by a receiving element array comprising a plurality of receiving elements;
An adaptive beam forming method is applied to a synthesized echo signal obtained from a synthesized reflected wave including the first sub-array reflected wave and the second sub- array reflected wave successively received by the receiving element array, and an operation relating to an incoming wave is performed. A direction of arrival estimation step to perform , and
In the pulse wave transmission step, a transmission signal is output to the transmission element array so that the first transmission element, the second transmission element, the third transmission element, and the fourth transmission element are weighted. The first sub-array pulse wave and the second sub-array pulse wave are transmitted to the transmitting element array, and the first sub-array pulse wave and the fourth transmitting element are changed by changing respective weights. A detection method of transmitting a third sub-array pulse wave and a fourth sub-array pulse wave having the same amplitude characteristic as the second sub-array pulse wave and having different phase characteristics depending on directions to the transmitting element array. An acoustic center of a first transmission subarray including a first transmission element, a second transmission element, a third transmission element, and a fourth transmission element that are spaced apart from each other, the first transmission subarray including the first transmission element and the third transmission element And a first subarray pulse wave from the first transmission subarray in the transmission element array in which the acoustic centers of the second transmission subarray including the second transmission element and the fourth transmission element are spaced apart from each other with a pulse wave transmitting function to transmit subsequently a second sub-array pulse wave delayed with respect to the first sub-array pulse wave from the second transmission sub-array to said first sub-array pulse wave,
Echo signal reception for receiving a composite echo signal corresponding to a first subarray reflected wave generated by the first subarray pulse wave and a second subarray reflected wave generated by the second subarray pulse wave from a receiving element array including a plurality of receiving elements. Function and
An adaptive beam forming method is applied to a synthesized echo signal obtained from a synthesized reflected wave including the first sub-array reflected wave and the second sub- array reflected wave successively received by the receiving element array, and an operation relating to an incoming wave is performed. to realize the DOA estimation function for the computer,
In the pulse wave transmission function, a transmission signal is output to the transmission element array so that the first transmission element, the second transmission element, the third transmission element, and the fourth transmission element are weighted. The first sub-array pulse wave and the second sub-array pulse wave are transmitted to the transmitting element array, and the first sub-array pulse wave and the fourth transmitting element are changed by changing respective weights. because of sniffer to transmit the third sub-array pulse wave, and the fourth sub-array pulse wave same a phase characteristic second subarray pulse wave amplitude characteristics differ depending orientation to the transmitter array.

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