JP2011058886A - Device for obtaining underwater video image and acquisition method - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a clear underwater acoustic image by reducing the volume of data of reception signals, enabling reduction of the scale of an electronic circuit and the size of a device, and suppressing noise and harmonic components. <P>SOLUTION: The device for obtaining an underwater video image includes an acoustic lens on a front face of a wave receiving unit, for steering a transmission beam of a sound wave emitted from a wave transmission unit 104 in a horizontal or perpendicular direction by changing the frequency of an electric signal to be input to the wave transmission unit 104, and for converging a reflected sound wave from a target. The wave receiving unit is configured by a plurality of wave receiving elements 105 divided in the direction perpendicular to the steering direction of the wave transmission unit 104, and includes: a plurality of active mixers 107 for down-converted received signals from the wave receiving elements to those of a predetermined frequency by multiplying two signals of each reflected signal (received signal) received from the target and a local oscillator signal of a frequency set in accordance with a transmission frequency; and a signal processing/control means 101 for generating an underwater video image from the received frequency-converted signals. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to an underwater image acquisition device and an acquisition method, and more particularly to an underwater image acquisition device and an acquisition method for generating an underwater image by transmitting / receiving ultrasonic waves of a wideband and frequency swept frequency such as a sonar and a fish finder About.

  Applying a frequency sweep method that enables steering of the ultrasonic wave transmission beam by changing the frequency of the electric signal input to the ultrasonic wave transmitter composed of electroacoustic transducers such as piezo elements. A technique of an underwater image acquisition device that processes and reflects a reflected sound wave is known and described in, for example, Patent Document 1 and the like. This underwater image acquisition device efficiently acquires underwater images by providing an acoustic lens for converging the reflected wave from the target on the front surface of a receiver composed of a piezo element or the like, similar to a transmitter. It is something that can be done.

Special table 2007-535195

  The underwater image acquisition device according to the prior art applies a frequency sweep method that enables steering of an ultrasonic transmission beam by changing the frequency of an electric signal input to the transmitter, and converges the reflected sound wave from the target. By providing an acoustic lens in front of the receiver, it is a device that can efficiently acquire acoustic images, but the amount of received signal data is large, and the scale of the electronic circuit required for signal processing and computation including data transmission However, there is a problem that it is difficult to reduce the size and weight of the apparatus.

  That is, since the frequency sweep method used in the prior art steers the transmission beam by frequency, the upper limit frequency is about 2 × fa and a bandwidth of fa to 2 × fa. For this reason, the transmitter, the receiver, and the receiving circuit are required to have a wide band characteristic so as to transmit and receive a signal of this use frequency bandwidth. However, the above-described prior art device effectively corrects the output level that varies depending on the frequency of the transmitter and receiver, and has no means to optimize the acoustic performance of the transmitter and receiver, and obtains noise and harmonic components. The sound image is displayed, and the sound image becomes unclear.

  The object of the present invention is to solve the above-mentioned problems of the prior art, reduce the amount of received signal data, reduce the size of the electronic circuit and downsize the device, and suppress noise and harmonic components. Another object of the present invention is to provide an underwater video acquisition device and an acquisition method capable of obtaining a clear acoustic image by optimizing transmission / reception acoustic performance.

  According to the present invention, the object is to steer a transmitted beam of sound waves emitted from the transmitter in a horizontal direction or a vertical direction by using a frequency sweep method that changes the frequency of an electric signal input to the transmitter. In the underwater image acquisition device having an acoustic lens for converging the reflected sound wave from the target on the front surface of the receiver, the receiver includes a plurality of receivers divided in a direction perpendicular to the steering direction of the transmitter. Each of the reflected signals (received signals) from the target, which is composed of wave elements and received by the plurality of wave receiving elements, and the local oscillator signal whose frequency is set in accordance with the transmission frequency are multiplied. By means of this, a plurality of active mixers that convert the received signal from each receiving element to a fixed frequency (down-converted) received signal and a fixed frequency It is accomplished by several transformed received signal and a signal processing / control unit for generating a water image.

  According to the present invention, the electronic circuit scale can be reduced and the apparatus can be reduced in size, and a clear acoustic image can be obtained.

It is a block diagram which shows the structure of the underwater image acquisition apparatus by one Embodiment of this invention. It is a figure explaining the principle of operation of a transmitter and a receiver to which a frequency sweep method is applied. It is a figure explaining the azimuth | direction of the transmission beam of the ultrasonic wave by a frequency sweep system. It is a figure explaining the example of the output level error for every frequency of a transmitter and a receiver.

  Hereinafter, embodiments of an underwater image acquisition apparatus and acquisition method according to the present invention will be described in detail with reference to the drawings.

  FIG. 1 is a block diagram showing the configuration of an underwater video acquisition apparatus according to an embodiment of the present invention, FIG. 2 is a diagram for explaining the operating principle of a transmitter and a receiver to which a frequency sweep method is applied, and FIG. 3 is a frequency sweep. FIG. 4 is a diagram for explaining an example of an output level error for each frequency of a transmitter and a receiver.

  Before describing the configuration of the underwater image acquisition apparatus according to the embodiment of the present invention shown in FIG. 1, first, the orientation of the ultrasonic transmission beam in the frequency sweep method will be described with reference to FIG.

  As shown in FIG. 3, the transmitter used in the embodiment of the present invention is configured by alternately inverting the polarities and arranging a plurality of electroacoustic transducers in the horizontal direction. This electroacoustic transducer is made of, for example, barium titanate. Although FIG. 3 shows that the electroacoustic transducer elements are arranged in two rows in the horizontal direction, it may be in one row.

  In the transmitter configured as described above, a transmission electric signal having a different frequency (transmission electric signal swept in frequency) is input to all of the plurality of electroacoustic transducers from the transmission circuit. The wave beam can be steered. In addition, since the frequency of the ultrasonic wave transmitted from the illustrated transmitter varies depending on the transmission direction, the reception side receives the reflected signal from the target with the acoustic lens and the receiver, and the received signal is converted to the FFT ( It can be separated into receiving directions only by fast Fourier transform.

  Note that, as already described, the frequency bandwidth of the ultrasonic signal used in the embodiment of the present invention is approximately 2 × fa when the lower limit frequency is fa. In principle, the upper limit frequency is about 2 × fa, and fa˜2 × fa. Bandwidth.

  Now, if the lower limit frequency in the use frequency range of the transmitter and receiver is 500 kHz, the upper limit frequency is 1 MHz. In this case, when the transmission circuit inputs a 1 MHz transmission electrical signal with the frequency f1 to the transmitter in accordance with control from the control unit for the transmitter, the ultrasonic transmission beam is indicated by an arrow (A) as shown in FIG. When a transmission electrical signal having a frequency f2 of 500 kHz is input to the transmitter, the ultrasonic transmission beam is transmitted in the direction of arrow (B).

  As can be seen from the above, when the transmission circuit that inputs the transmission electrical signal to the transmitter changes the frequency from frequency f1 to f2, and the transmission electrical signal is input to the transmitter, the transmitter follows the change in frequency. As schematically shown in FIG. 3, an ultrasonic beam is transmitted while steering a narrow fan-shaped beam in the horizontal direction from (A) to (B), and the beam is directed to the horizontal direction within a predetermined angular range. Will be irradiated. When a transmission electrical signal is input to the transmitter while changing the frequency from frequencies f1 to f2, the transmitter is deviated by an angle θ from the center of the element with respect to the horizontal direction as shown in FIG. A group of irradiation ranges is formed, but as is known in the prior art, either one can be disabled, and if a wider continuous irradiation range is desired, two sets of It is only necessary that the wave generators are shifted by a predetermined angle so that the irradiation ranges of the ultrasonic waves are continuous from the two sets of transmitters. In addition, in the above description, the horizontal narrow fan-shaped ultrasonic beam emitted by the transmitter according to the change in frequency irradiates a wide range in the vertical direction (direction perpendicular to the paper on which FIG. 3 is drawn). is doing. Thereby, an ultrasonic beam can be irradiated with respect to the predetermined range of the horizontal direction of the target which is going to acquire an underwater image, and a perpendicular direction.

  Then, the ultrasonic signal reflected and reflected from the target is received by an arrangement of a plurality of electroacoustic transducer elements in the same manner as the transmitter via an acoustic lens provided on the front surface of the receiver. Converged to a vessel. If the target is at the position of the arrow (A) shown in FIG. 3, an ultrasonic reflected wave having a frequency of 1 MHz arrives at the receiver, and if the target is at the position of the arrow (B), the frequency is 500 kHz. The reflected wave of the ultrasonic wave arrives at the receiver.

  The prior art described above has a receiving circuit configured to receive an electric signal (received signal) that has been subjected to acoustoelectric conversion by a receiver while maintaining a wide receiving frequency from 500 kHz to 1 MHz. It was necessary to carry out the treatment.

  In this case, in order to perform signal processing on the analog reception signal from each transducer (electroacoustic conversion element) constituting the receiver, the sampling frequency of the AD converter that converts the analog signal into a digital signal is In the example described, 2 MHz or more is required, and the amount of data of the converted digital signal is enormous, resulting in an increase in circuit scale. The data amount of the digital signal shown here is defined by a value obtained by multiplying the number of transducers of the receiver, the number of bits of the AD converter, and the sampling frequency.

  The wideband received signal, the high-speed sampling frequency, and the clock frequency are factors that generate noise and harmonic components in the receiving circuit. As a result, noise and harmonic components are superimposed on the obtained image. As a result, the acquired acoustic image was made ambiguous.

  Therefore, in the embodiment of the present invention, the reflected signal (received signal) from the target input from each of the plurality of transducers of the receiver to the receiving circuit and the frequency of the received signal, that is, the transmission frequency A signal obtained by frequency conversion (down-converting) to a certain fixed frequency is processed as a received signal by multiplying two signals of the local oscillator signal (LO signal) with the frequency set by an active mixer.

Here, the operation of the active mixer will be described as follows. That is,
Now, the received signal is a (t), the LO signal is b (t), the respective frequencies are f1, f2 (f1> f2), the amplitudes of the signals a (t), b (t) are A, B, and the frequency Is a single sine wave ω1 = 2πf1 and ω2 = 2πf2, the received signal a (t) and LO signal b (t) are
a (t) = Asin (ω1t) (1)
b (t) = Bsin (ω2t) (2)
Can be expressed as

And when these two signals are input to the active mixer and multiplied,
a (t) × b (t) = AB · sin (ω1t) · sin (ω2t)
= AB / 2 · [cos (ω1-ω2) t-cos (ω1 + ω2) t] (3)
It becomes.

  As can be seen from this equation (3), by multiplying the two signals a (t) and b (t) by an active mixer, the sum and difference of the signals a (t) and b (t) A frequency component is created.

  In the embodiment of the present invention, the signal on the difference side of the sum and difference frequency components obtained by multiplication by the active mixer is frequency-converted (down-converted) so as to have a certain frequency. For this reason, a local oscillator signal (LO signal) whose frequency is set so that the difference-side signal from the active mixer becomes a constant frequency according to the frequency of the received signal, that is, the transmission frequency is prepared.

  For example, when the transmission frequency, that is, the frequency of the received signal is 1 MHz, the frequency of the LO signal is set to 900 kHz. At this time, according to the equation (3), the frequency of the received signal having the frequency component of the difference after the active mixer processing is 100 kHz. When the transmission frequency, that is, the frequency of the reception signal is 500 kHz, the LO signal frequency is set to 400 kHz. At this time, according to the equation (3), the frequency of the received signal having the frequency component of the difference after the active mixer processing is 100 kHz. As can be seen from this, when the image is created by continuously changing the transmission frequency from 1 MHz to 500 kHz and steering the ultrasonic beam in the horizontal direction, the frequency of the LO signal is continuously changed from 900 kHz to 400 kHz. When this is changed, a signal having a frequency of 100 kHz that does not change in frequency can be obtained from the active mixer as a received signal having the frequency component of the difference regardless of the change in the transmission frequency.

  As described above, by performing frequency conversion (down-converting) on the received signal to a certain frequency, the sampling frequency of the AD converter required for each transducer of the receiver can be lowered. It becomes.

  Incidentally, in the case of the prior art, a sampling frequency of 2 MHz or more is required to convert a received signal having an upper limit frequency of 1 MHz into a digital signal by an AD converter, whereas in the embodiment of the present invention, As described above, the received signal having the upper limit frequency of 1 MHz is frequency-converted to 100 kHz by the active mixer, whereby the sampling frequency of the AD converter can be set to 200 kHz, and the signal processing including the receiving circuit and the calculation is performed. Can be reduced to about 1/10.

  Next, operations of a transmitter and a receiver to which a frequency sweep method is applied will be described with reference to FIG. 2 and a method for forming a two-dimensional still image from a received signal obtained by the receiver.

  2A shows the direction of the ultrasonic transmission beam in the frequency sweep method described with reference to FIG. 3 and the reflected wave of the transmission beam steered by the frequency sweep via the acoustic lens. FIG. 2B is a diagram for explaining a method of forming a two-dimensional still image.

  On the upper left side of FIG. 2 (a), the transmission beam (narrow beam) of the ultrasonic waves in the horizontal direction in the frequency sweep method at different frequencies is swept and steered to an operating sector range of 30 degrees as a whole. The state of irradiation is shown. A state in which reflected waves from these irradiation transmission beams (narrow beams) are input to the receiver via the acoustic lens is shown on the upper right side of FIG. Here, as the wave receiver, one formed by a wave receiver array (element array) that matches the convergence characteristics of the acoustic lens is prepared. In this case, there is no channel division of the receiver, and a received signal having a frequency from a sound wave arrival direction determined by the frequency is input to the receiver and detected.

  Further, the lower left side of FIG. 2A shows a state in which each of the transmission beams (narrow beams) at different frequencies of the ultrasonic waves in the horizontal direction irradiates the beams in the vertical direction. As already described with reference to FIG. 3, the above-mentioned narrow beam irradiates a wide range with respect to the vertical direction (in the example shown in FIG. 2A, the operating sector range is 30 degrees). A state in which a reflected wave from such an irradiation transmission beam is input to the receiver via the acoustic lens is shown on the lower right side of FIG. Here, as the wave receiver, one formed by a wave receiver array (element array) combined with convergence characteristics by an acoustic lens is prepared. In this case, the receiver is a channel-divided one. In the example shown in FIG. 2A, it is assumed that 64 divisions, that is, the receiver is configured by a receiver array of 64 receiving elements. Then, since the sound ray is converged depending on the sound wave arrival direction by the acoustic lens depending on the sound wave arrival direction, by detecting the signal from each receiving element of the 64 divided channels, the reflected super The arrival direction of the sound wave signal can be calculated.

  As described in FIG. 2A, when the fan-shaped ultrasonic beam from the transmitter shown in FIG. 3 is radiated toward the target object, the combined wavefront of the sound waves radiated from each element of the transmitter is It is formed in a direction determined by the frequency. For this reason, the entire operating sector can be irradiated by steering the beam by sweeping the frequency. The reflected wave from the object surface that has been irradiated with ultrasonic waves is formed as an acoustic image by the acoustic lens and the receiver.

  The receiver receives the reflected wave as shown in FIG. 2A. Next, referring to FIG. 2B, a method of forming a two-dimensional still image from the received signal of the receiver. explain.

  As shown in FIG. 2B, the receiver is divided into 64 pieces in the vertical direction and is constituted by a plurality of receiving elements. When frequency analysis is performed on each of the ch outputs from the receiving elements, the receiving element corresponds to the frequency component. Thus, a reception signal of the reflected wave from each position in the horizontal direction of the object is obtained. Also, since the vertical position corresponds to the position of each divided receiving element, it can be obtained as a received signal of a reflected wave from each position in the vertical direction of the object corresponding to each receiving element. become.

  On the left side of FIG. 2 (b), each receiving element of the reflected wave when the H-shaped target is irradiated with ultrasonic waves as described above is steered by frequency sweep, and the reflected wave in the horizontal direction is displayed. Further, on the right side of FIG. 2B, the reception level of the reception signal corresponding to the sweep frequency (horizontal position) at each receiving element is shown. In the embodiment of the present invention, an image of a target can be acquired by synthesizing and processing all such received signals for each channel.

  By the way, when the underwater image acquisition device is configured by applying the frequency sweep method as in the embodiment of the present invention, the output level for each frequency is required in a transmitter and a receiver that require a wide use frequency bandwidth. An error occurs. The level error generated for each frequency is one of the factors that generate an unclear acoustic image.

  As a method of suppressing the error, a method of changing the resonance frequency of the transmitter / receiver using an electric matching circuit, a method of weighting the amplitude level of the transmission signal for each transmission frequency, or a digital signal For example, there is a method of performing level correction for each received signal for each frequency. However, each of the above-described methods can suppress errors, but cannot improve the S / N ratio, so that the sensitivity is lowered, noise is generated outside the operating frequency range, and the circuit scale is increased. Also have.

  Therefore, in the embodiment of the present invention, by adjusting the conversion gain (LO signal amplitude level) of the active mixer for each transmission / reception frequency, different output levels are corrected for each frequency of the transmitter and receiver. It is said. The active mixer is assumed to be configured using active elements such as transistors and FETs.

  Next, in the embodiment of the present invention, a method for suppressing the output level error of the transmitter and receiver generated for each frequency swept will be described.

  As shown in FIG. 4 for explaining an example of an output level error for each frequency of the transmitter and receiver, for example, the maximum output level when the transmitter and receiver are at a transmission frequency of 600 kHz, and the minimum at 800 kHz. Suppose that the output level is characteristic. When an ultrasonic transmission beam is transmitted from a transmitter having such characteristics, the reflected signal (received signal) from the target that is input from the receiver to the receiving circuit is assumed to be the frequency of the receiver. If there is no level error for each, it can be easily understood that the signal has the maximum signal level at 600 kHz and the minimum signal level at 800 kHz.

  Therefore, in the embodiment of the present invention, the value of the amplitude level B of the LO signal shown in the equation (3) described above is transmitted and received so that different output levels can be corrected for each frequency of the transmitter and receiver. It is supposed to be adjusted according to the frequency. As a result, the frequency characteristic of the processed received signal is flattened by multiplying the reflected signal (received signal) from the target and the LO signal whose amplitude level is set for each transmission / reception frequency by an active mixer. And a clear acoustic image can be obtained.

  In the above description, the embodiment of the present invention performs frequency conversion to a certain frequency by an active mixer and corrects different output levels for each frequency of the transmitter and receiver. Explained. However, as shown in Equation (3), after the active mixer processing, not only the difference frequency component but also the sum frequency component is generated.

  Since only the difference frequency component is required in the embodiment of the present invention, an active pass filter that passes only the difference frequency component composed of an operational amplifier, a capacitor, and a resistor is provided on the output side of the active mixer, Unnecessary signal, noise and harmonic components are removed. The attenuation of the received signal due to the distance reached by the ultrasonic wave is corrected by a variable gain amplifier whose amplification factor can be set by a control signal.

  Next, the configuration of the underwater image acquisition apparatus according to the embodiment of the present invention configured based on the consideration described above will be described with reference to FIG.

  The underwater image acquisition device according to the embodiment of the present invention is generated by a signal processing / control unit 101 that generates a transmission signal and sets a frequency and an amplitude level of a local oscillator signal (LO signal), and the signal processing / control unit 101. A transmission circuit 102 that amplifies the transmitted signal to a predetermined magnitude, an amplifier 103 that amplifies the power of the signal from the transmission circuit 102, and a transmitter 104 that converts the signal from the amplifier 103 into an ultrasonic wave and radiates it into water. And a plurality of wave receiving elements 105 (64 in the case of the example described with reference to FIG. 2) that constitutes a wave receiver that receives the reflected wave of the ultrasonic wave radiated from the wave transmitter 104 together with an acoustic lens (not shown), Each receiving element receives ultrasonic signals from 64 different vertical directions), and is connected to each of the plurality of receiving elements 105, and receives an electrical reception signal from each receiving element 105. A plurality of first-stage amplifiers 106 that are widened, and a plurality of active mixers 107 that are composed of operational amplifiers, capacitors, and resistors that receive the output signals and local oscillator signals (LO signals) from the respective first-stage amplifiers 106 and perform frequency conversion. , A plurality of band-pass type active filters (BPFs) 108 for passing an output signal of a predetermined frequency down-converted from the output of each active mixer 107, and signals from the respective BPFs 108 are received as ultrasonic signals. In order to compensate for the attenuation due to the propagation distance due to the irradiation and reflection of the light, a plurality of variable gain amplifiers 109 that variably amplify the signal from each BPF 108, and the analog signal from each variable gain amplifier 109 A plurality of AD converters 110 that convert digital signals, and a plurality of AD converters 110 A data multiplexing unit 111 that multiplexes digital signals, a digital electrical signal from the data multiplexing unit 111 is converted into an optical signal, and is transmitted to the signal processing / control unit 101 via a signal cable using an optical fiber. An EO converter 112 that converts an optical signal from the control unit 101 into a digital electric signal, and a frequency and amplitude level are set according to an instruction from the signal processing / control unit 101 to generate a local oscillator signal (LO signal). And a control signal generation unit 114 that generates a control signal for controlling the amplification degree of the variable gain amplifier 109 in accordance with an instruction from the signal processing / control unit 101.

  As described above, the signal processing / control unit 101 generates a transmission signal, sets the frequency and amplitude level of the local oscillator signal (LO signal), and sets the amplification factor of the variable gain amplifier 109. The transmission signal is amplified by the transmission circuit 102, amplified by the amplifier 103, and then supplied to the transmitter 104 via the signal cable and subjected to electroacoustic conversion. It is sent out as a sound wave. A setting signal for setting the frequency and amplitude level of the local oscillator signal (LO signal) is input to the local oscillator 113, and the amplitude for compensating the frequency characteristics of the transmitter and the receiver described in FIG. An LO signal having a level and a frequency for converting the frequency of the transmission signal being frequency swept into a predetermined frequency is generated. An instruction signal for setting the amplification factor of the variable gain amplifier 109 is input to the control signal generation unit 114, and causes the control signal generation unit 114 to generate a control signal for setting the amplification factor of the variable gain amplifier 109.

  In addition, an electrical signal (received signal) that has been subjected to acoustoelectric conversion by each of the plurality of receiving elements 105 that constitutes the receiver is a first-stage amplifier 106, a local oscillator 113, an active mixer 107, a BPF filter 108, and a variable gain amplifier. 109, received by a receiving circuit including an AD converter 110, passed through a data multiplexing unit 111 and an EO converter 112, and then passed to a signal processing / control unit via a signal cable to be subjected to OE conversion, arithmetic processing, etc. And displayed on the display device.

  Since the embodiment of the present invention adopts a frequency sweep method, the frequency of the ultrasonic wave transmitted in the horizontal direction (the vertical direction is changed when the direction of the transmitter is changed to the vertical direction) is swept differently. By performing frequency analysis (FFT) on the electrical signal received by one of the receiving elements 105, as described in the upper part of FIG. 2A and FIG. Is obtained.

  That is, the ultrasonic wave reflected by the target is converged on each wave receiving element 105 of the wave receiver via the acoustic lens. If the target is at the position of the transmission frequency f1, the reflected wave at the frequency f1 arrives at the receiver when the target is at the position of the transmission frequency fn. As a result of electrical conversion, an image for one channel in the horizontal direction is obtained.

  On the other hand, the reflected wave from the vertical direction is focused by the acoustic lens on the plurality of wave receiving elements 105 constituting the wave receiver, and the convergence position differs depending on the vertical direction. Accordingly, an image obtained by dividing the vertical direction from each wave receiving element 105 by arranging the wave receiver in the vertical direction for each convergence position is shown in the lower part of FIG. 2A and FIG. 2B. Can be obtained as described.

  As described above, according to the embodiment of the present invention, a two-dimensional acoustic image can be acquired from the image for one channel in the horizontal direction described above and the image obtained by dividing the vertical direction.

  According to the embodiments of the present invention described so far, the frequency sweep method that enables steering of the transmitted beam by changing the frequency of the electric signal input to the transmitter is applied, and the reflected sound wave from the target is applied. An acoustic lens that converges the signal is provided on the front of the receiver, and two signals of a reflected signal (received signal) from the target and a local oscillator signal (LO signal) set in frequency according to the transmission frequency are output by an active mixer. By multiplying, the received signal can be reduced in frequency by down-converting the received signal to a certain frequency. According to the embodiment of the present invention, this makes it possible to reduce the electronic circuit scale and data amount in the underwater video acquisition device, downsize the device, suppress noise and harmonic components, and transmit and receive waves. A clear acoustic image can be obtained by optimizing the acoustic performance.

  Further, according to the embodiment of the present invention described above, AD conversion necessary for each transducer (wave receiving element) of the receiver is performed by performing frequency conversion (down converting) on the received signal. The sampling frequency of the device can be lowered, the amount of data of the digitally converted received signal can be reduced, and the circuit scale required for signal processing and calculation including data transmission can be reduced.

  Further, according to the above-described embodiment of the present invention, the conversion gain (LO signal amplitude level) of the active mixer is adjusted for each transmission / reception frequency, so that the frequency varies depending on the frequency of the transmitter and the receiver. It is possible to correct the output level, flatten the characteristics within the operating frequency range, improve the SN ratio, and to clarify the acquired acoustic image.

  Furthermore, according to the above-described embodiment of the present invention, the variable gain amplifier that can set the amplification factor by the control signal for the received signal corrected for frequency conversion and for each frequency is changed by the distance reached by the ultrasonic wave. By performing attenuation correction and having a BPF, only the received signal frequency-converted to a certain frequency is passed, unnecessary signals, noise and harmonic components are removed, and the scale of the electronic circuit is minimized. The size of the sound image can be clarified.

DESCRIPTION OF SYMBOLS 101 Signal processing / control part 102 Transmitting circuit 103 Amplifier 104 Transmitter 105 Receiving element 106 First stage amplifier 107 Active mixer 108 Band pass type active filter (BPF)
109 Variable Gain Amplifier 110 AD Converter 111 Data Multiplexing Unit 112 EO Converter 113 Local Oscillator 114 Control Signal Generation Unit

Claims (4)

Using a frequency sweep method that changes the frequency of the electrical signal input to the transmitter, the transmitted wave of the sound wave emitted from the transmitter is steered horizontally or vertically to converge the reflected sound wave from the target. In the underwater image acquisition device equipped with an acoustic lens on the front of the receiver,
The wave receiver is composed of a plurality of wave receiving elements divided in a direction perpendicular to the steering direction of the wave transmitter,
Each receiving element is obtained by multiplying each of the reflected signals (received signals) from the target received by the plurality of receiving elements and a local oscillator signal whose frequency is set in accordance with the transmission frequency. A plurality of active mixers that convert the received signal from the frequency into a certain frequency (down-converted) as a received signal, and signal processing / control means for generating an underwater video from the frequency-converted received signal An underwater image acquisition device comprising:   The signal processing / control means adjusts the amplitude level of the local oscillator signal for each transmission / reception frequency in order to correct a different output level for each frequency of the transmitter and receiver. The underwater image acquisition apparatus according to claim 1, wherein the conversion gain is controlled.   Each of the plurality of active mixers is connected with a BPF and a variable gain amplifier in the subsequent stage, and the BPF passes only the received signal frequency-converted to a certain frequency, and the variable mixer 2. The gain amplifier according to claim 1, wherein the gain amplifier is for compensating a level of a reception signal attenuated by a propagation distance due to irradiation and reflection of ultrasonic waves under the control of the signal processing / control means. 2. The underwater image acquisition device according to 2. Using a frequency sweep method that changes the frequency of the electrical signal input to the transmitter, the transmitted wave of the sound wave emitted from the transmitter is steered horizontally or vertically to converge the reflected sound wave from the target. In the underwater image acquisition method with an acoustic lens on the front of the receiver,
The wave receiver is composed of a plurality of wave receiving elements divided in a direction perpendicular to the steering direction of the wave transmitter,
By multiplying each of the reflected signals (received signals) from the target received by the plurality of receiving elements and the local oscillator signal set in frequency according to the transmission frequency by an active mixer An underwater image acquisition method comprising: converting a received signal from each receiving element to a certain frequency and obtaining an underwater image from the received signal frequency-converted to a certain frequency.