CN111208522A - Shore-based high-frequency multi-beam image sonar system - Google Patents
Shore-based high-frequency multi-beam image sonar system Download PDFInfo
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- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/88—Sonar systems specially adapted for specific applications
- G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
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- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/88—Sonar systems specially adapted for specific applications
- G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
- G01S15/8906—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
- G01S15/8909—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using a static transducer configuration
- G01S15/8915—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using a static transducer configuration using a transducer array
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- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/88—Sonar systems specially adapted for specific applications
- G01S15/89—Sonar systems specially adapted for specific applications for mapping or imaging
- G01S15/8906—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques
- G01S15/8977—Short-range imaging systems; Acoustic microscope systems using pulse-echo techniques using special techniques for image reconstruction, e.g. FFT, geometrical transformations, spatial deconvolution, time deconvolution
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- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
- G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
- G01S7/52023—Details of receivers
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- G01S7/52026—Extracting wanted echo signals
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
- G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
- G01S7/52046—Techniques for image enhancement involving transmitter or receiver
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
- G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
- G01S7/52077—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging with means for elimination of unwanted signals, e.g. noise or interference
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- G—PHYSICS
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- G01S—RADIO DIRECTION-FINDING; RADIO NAVIGATION; DETERMINING DISTANCE OR VELOCITY BY USE OF RADIO WAVES; LOCATING OR PRESENCE-DETECTING BY USE OF THE REFLECTION OR RERADIATION OF RADIO WAVES; ANALOGOUS ARRANGEMENTS USING OTHER WAVES
- G01S7/00—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00
- G01S7/52—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00
- G01S7/52017—Details of systems according to groups G01S13/00, G01S15/00, G01S17/00 of systems according to group G01S15/00 particularly adapted to short-range imaging
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Abstract
The invention provides a shore-based high-frequency multi-beam image sonar system which comprises a display control unit, a transmitter, a transmitting array, a receiving array, a receiver and a signal processor, wherein the display control unit is used for displaying a plurality of images; the display control unit sends sonar working instructions and working parameter information; receiving data processed by the annunciator, displaying sonar images in real time, and receiving sonar sensor data at the same time; the transmitter signal source generates a plurality of paths of transmitting pulse signals according to the sonar working instruction, adjusts a plurality of paths of transmitting time delay according to the working parameter information, amplifies the power of the plurality of paths of transmitting signals and then sends the signals to the transmitting array; receiving an acoustic signal returned by a receiving target of the array, and sending the acoustic signal to a receiver; the receiver finishes the digital acquisition of the target return acoustic signal; the signal processor forms a plurality of receiving beams according to the digital acquisition signals, performs autocorrelation calculation on each beam by combining signals transmitted by a signal source of the transmitter after the spatial beams are formed, and transmits the calculated signals to the display control unit.
Description
Technical Field
The invention relates to the technical field of underwater imaging, in particular to a shore-based high-frequency multi-beam image sonar system.
Background
The high-resolution image sonar has more types and wide application range, and can be used for underwater environment monitoring, dam leakage detection, forward-looking obstacle avoidance during navigation, underwater anti-terrorism warning and the like. In the underwater short-range defense of the harbor, most of the fixed installations are early warning sonars which are responsible for early warning of threat targets at a longer distance; for the close-range target threat, particularly on the entrance and exit of the navigation channel, a means for manually and directly participating in the target discrimination is lacked, and the secondary confirmation and the fence type blockage of the navigation channel can be more effectively carried out on the threat target. Furthermore, defense at the port requires a combination of long range and short range defense, which requires that sonar imaging have high resolution at both long and short range. High-frequency image sonar is fixedly installed at an entrance and an exit of the airway to perform imaging processing on a target at a certain distance, so that partial image information of the target can be provided, the target identification degree is increased, and the overall performance of target detection and identification can be improved. Meanwhile, the multi-beam high-resolution image sonar has the characteristics of narrow beams, short pulses, high data refresh rate, clear and stable images and the like, has obvious performance advantages and has wider application prospect.
Patent document No. CN109959915A discloses a multi-beam sonar array, which includes an electronic cabin housing, a transducer array, a sonar housing, a sound-transparent cover, and an O-ring. The electronic cabin is used for placing electronic equipment and is hermetically connected with the sonar shell; the transducer is a piezoelectric ceramic acoustic unit integrating receiving and transmitting and is arranged on the sonar shell; the sonar shell is in a structural form that a cylindrical section shell and a hemispherical shell are combined, the cylindrical section shell is divided into a plurality of layers, each layer contains a plurality of elements, and small targets in 360 degrees in the horizontal direction and in a certain vertical included angle range are detected by scanning electronic beams on the horizontal plane. The high-resolution image sonar which takes the small target as the detection object can realize the detection of the small target within a range of 360 degrees in the horizontal direction and a certain vertical included angle. However, this solution only provides a hardware structure, and does not disclose the way of beam transmission and reception and how to process the received beam to obtain high resolution real-time imaging.
Disclosure of Invention
Aiming at the defects in the prior art, the invention aims to provide a shore-based high-frequency multi-beam image sonar system.
The shore-based high-frequency multi-beam image sonar system comprises a display and control unit, a transmitter, a transmitting array, a receiving array, a receiver and a signal processor, wherein the display and control unit is sequentially connected with the signal processor, the transmitter and the transmitting array;
the display control unit sends sonar working instructions and working parameter information; receiving data processed by the annunciator to display sonar images in real time, receiving data of a sonar sensor at the same time, and displaying sonar temperature and humidity information;
the transmitter signal source generates a plurality of paths of transmitting pulse signals according to the sonar working instruction, adjusts a plurality of paths of transmitting time delay according to the working parameter information, amplifies the power of the plurality of paths of transmitting signals and then sends the signals to the transmitting array;
the receiving array receives the acoustic signal returned by the target and sends the acoustic signal to the receiver;
the receiver receives and receives the acoustic signals transmitted by the array through the multi-channel receiving, amplifying and conditioning circuit and finishes the digital acquisition of the target return acoustic signals;
the signal processor performs autocorrelation calculation on each beam according to a plurality of receiving beams formed by the digital acquisition signals and signals transmitted by a signal source of the transmitter after the spatial beams are formed, and sends the calculated signals to the display control unit.
Preferably, the transmitting array comprises a plurality of transmitting elements and adopts a cylindrical array; the receiving array comprises a plurality of receiving elements and adopts a linear array.
Preferably, the pitch range of the transmitting beam of the transmitting array in the vertical direction reaches 20 degrees, and the pitch precision reaches 1.2 degrees;
the horizontal observation sector range of the receiving array is within 90 degrees, and the horizontal width of a receiving beam formed by the signal processor is not more than 0.3 degrees.
Preferably, the receiver adopts weighted beam forming when acquiring signals;
designing a beam former according to a plane wave model in a far field, calculating a time delay parameter, completing time delay compensation of each path of received signals, and adding and outputting the delayed multipath received signals;
and designing a beam former according to a spherical wave model in the near field, carrying out real-time segmented time delay compensation, selecting a distance central point of each segment as a focusing point to calculate a time delay parameter in each segment, completing the time delay compensation of each path of received signals, and adding and outputting the delayed multipath received signals.
Preferably, the observation angle range is divided into a plurality of sections in the near field according to the size of the actual target image and the observation angle range and the limitation of the storage capacity of the signal processor, so that the segmented beam forming is realized.
Preferably, the transmitter generates a plurality of paths of pulse signals with adjustable phases and adjustable waveforms, the adjustable phases are realized by adopting delay, a transmitting matrix array comprises N transmitting elements, the distance between the transmitting elements is d, the 1 st element is taken as a reference point, and the beam delay time tau of other transmitting elements is setiCalculated using the following formula:
τi＝(i-1)*d/c*sinθ,i＝1,2,3,…,N
where i denotes the ith emission element, τiRepresenting the beam delay time of the ith transmitting element, c representing the light speed, and theta representing the transmitting preset angle;
the digital delay implementation is divided into a coarse delay implementation part and a fine delay implementation part, and based on a waveform sampling clock, a coarse delay value is an integral multiple of sampling, and a fine delay value is a decimal multiple of sampling;
delay amount m of coarse delayiCalculated using the following formula:
mi＝INT(τi*fs),i＝1,2,3,…,N
where the INT () function represents the rounding down of a real number to the nearest integer, fsRepresenting a coarse delay waveform sampling clock frequency;
delay amount n of fine delayiCalculated using the following formula:
ni＝INT(fs1*mod(τi,fs)),i＝1,2,3,…,N
where mod () represents the remainder function, fs1Representing the fine delay waveform sampling clock frequency.
Preferably, the horizontal width L of the receiving matrix is calculated by using the following formula:
L＝kλ/b
where k denotes a line fixing coefficient, λ denotes a wavelength of the reception beam, and b denotes a horizontal width of the reception beam.
Preferably, the condition of the far field should satisfy that the distance from the receiving matrix is greater than L2/λ。
Preferably, the signal processor calculates the autocorrelation of the beam by using a FIR filter, and the FIR filter coefficients FIR (x) are calculated as follows:
fir(x)＝s*(T×Fs-x),x＝0,1,2,…,T×Fs
where s (t) denotes the transmit beam signal, s*(T) denotes the complex conjugate function of s (T), x denotes the number of sample points, T denotes the pulse width of the signal, FsRepresents the beam output frequency;
the reception beam matching output signal y (x) is calculated by the following formula:
wherein y (x) represents a receive beamforming output signal,
represents a complex multiplication; and obtaining and outputting an absolute value abs (Y (x)) by a modular approximation algorithm.
Preferably, the display control unit is used for displaying the target image in real time, processing each pixel point in the image based on a median filtering theory, and inhibiting nonlinear signal noise; and local amplification of the image is realized by adopting a nearest neighbor interpolation algorithm.
Compared with the prior art, the invention has the following beneficial effects:
1. the invention adopts multi-channel signal transmission and multi-channel signal reception, and can obtain high-precision target azimuth and distance resolution; through multi-channel focusing beam forming and beam autocorrelation processing, beam performance is remarkably improved, and imaging quality of the image sonar is improved.
2. The invention adopts different beam processing methods for the near field and the far field, and improves the image fineness of the near field and the far field.
3. The sonar image refreshing speed is high, the whole image is subjected to noise reduction processing, the image quality is excellent, and meanwhile, the sonar image refreshing method has a local image amplification function.
Drawings
Other features, objects and advantages of the invention will become more apparent upon reading of the detailed description of non-limiting embodiments with reference to the following drawings:
FIG. 1 is a block diagram of the components of the present invention.
Fig. 2 is a functional block diagram of a transmitter of the present invention.
FIG. 3 is a timing diagram of a received data acquisition signal according to the present invention.
Fig. 4 is a functional block diagram of the signal processor of the present invention.
Fig. 5 is a diagram illustrating taylor weighted beamforming according to the present invention.
FIG. 6 is a diagram illustrating a storage format of a beam forming compensation coefficient RAM according to the present invention.
Fig. 7 is a diagram of the actual imaging effect of observing the frogman under water according to the invention.
Fig. 8 is a diagram showing the actual imaging effect of the observation disk according to the present invention.
Detailed Description
The present invention will be described in detail with reference to specific examples. The following examples will assist those skilled in the art in further understanding the invention, but are not intended to limit the invention in any way. It should be noted that it would be obvious to those skilled in the art that various changes and modifications can be made without departing from the spirit of the invention. All falling within the scope of the present invention.
In the description of the present application, it is to be understood that the terms "upper", "lower", "front", "rear", "left", "right", "vertical", "horizontal", "top", "bottom", "inner", "outer", and the like indicate orientations or positional relationships based on those shown in the drawings, and are only for convenience in describing the present application and simplifying the description, but do not indicate or imply that the referred device or element must have a specific orientation, be constructed in a specific orientation, and be operated, and thus, should not be construed as limiting the present application.
The invention relates to a design and realization of a shore-based high-frequency multi-beam image sonar, which mainly comprises the following components: the display control unit sends sonar working instructions to each underwater unit module; the transmitter generates a transmitting signal according to the working instruction and transmits the transmitting signal through the 16-channel transmitting array; the receiving array receives the acoustic signal returned by the target, and receives, conditions, amplifies, filters and digitizes the acoustic signal through 338 paths; and the signal processing machine is used for forming 360 receiving beams according to the received digital signals, performing autocorrelation calculation on each beam after the space beams are formed, and transmitting the calculated signals to the display and control unit for sonar two-dimensional image display. The invention achieves the fine effect of the sonar image by realizing the weighted beam forming and the near-field real-time beam focusing, further improves the processing gain by the autocorrelation processing, and has good human-computer interface and local image amplification function for the sonar image display.
The shore-based high-frequency multi-beam image sonar system provided by the invention comprises a display and control unit, a transmitter, a transmitting array, a receiving array, a receiver and a signal processor, wherein the display and control unit is sequentially connected with the signal processor, the transmitter and the transmitting array; the display control unit sends sonar working instructions and working parameter information; receiving data processed by the annunciator to display sonar images in real time, receiving data of a sonar sensor at the same time, and displaying sonar temperature and humidity information; the transmitter signal source generates a plurality of paths of transmitting pulse signals according to the sonar working instruction, adjusts a plurality of paths of transmitting time delay according to the working parameter information, amplifies the power of the plurality of paths of transmitting signals and then sends the signals to the transmitting array; the receiving array receives the acoustic signal returned by the target and sends the acoustic signal to the receiver; the receiver receives and receives the acoustic signals transmitted by the array through the multi-channel receiving, amplifying and conditioning circuit and finishes the digital acquisition of the target return acoustic signals; the signal processor performs autocorrelation calculation on each beam according to a plurality of receiving beams formed by the digital acquisition signals and signals transmitted by a signal source of the transmitter after the spatial beams are formed, and sends the calculated signals to the display control unit.
The transmitting array comprises a plurality of transmitting elements and adopts a cylindrical array; the receiving array comprises a plurality of receiving elements and adopts a linear array. The pitching range of the transmitting beam of the transmitting array in the vertical direction reaches 20 degrees, and the pitching precision reaches 1.2 degrees; the horizontal observation sector range of the receiving array is within 90 degrees, and the horizontal width of a receiving beam formed by the signal processor is not more than 0.3 degrees.
The receiver adopts weighted beam forming when acquiring signals; designing a beam former according to a plane wave model in a far field, calculating a time delay parameter, completing time delay compensation of each path of received signals, and adding and outputting the delayed multipath received signals; and designing a beam former according to a spherical wave model in the near field, carrying out real-time segmented time delay compensation, selecting a distance central point of each segment as a focusing point to calculate a time delay parameter in each segment, completing the time delay compensation of each path of received signals, and adding and outputting the delayed multipath received signals. And dividing the observation angle range into a plurality of sections according to the size of the actual target image and the observation angle range in the near field by combining the limitation of the storage capacity of the signal processor, thereby realizing the segmented beam forming. Preferably, according to actual application requirements such as actual image target size and observation range, and in combination with the limitation of storage capacity of the signal processor, four segments can be divided within a large opening angle of 90 degrees to realize segmented beam forming, and ten segments can be divided within a small opening angle of 30 degrees to realize finer segmented beam forming.
The transmitter generates multiple paths of pulse signals with adjustable phase and adjustable waveform, the adjustable phase is realized by adopting delay, a transmitting matrix comprises N transmitting elements, and the transmitting elements are arranged among each otherWith the 1 st array element as a reference point, the beam delay time tau of other emission elementsiCalculated using the following formula:
τi＝(i-1)*d/c*sinθ,i＝1,2,3,…,N
where i denotes the ith emission element, τiRepresenting the beam delay time of the ith transmitting element, c representing the light speed, and theta representing the transmitting preset angle;
the digital delay implementation is divided into a coarse delay implementation part and a fine delay implementation part, and based on a waveform sampling clock, a coarse delay value is an integral multiple of sampling, and a fine delay value is a decimal multiple of sampling;
delay amount m of coarse delayiCalculated using the following formula:
mi＝INT(τi*fs),i＝1,2,3,…,N
where the INT () function represents the rounding down of a real number to the nearest integer, fsRepresenting a coarse delay waveform sampling clock frequency;
delay amount n of fine delayiCalculated using the following formula:
ni＝INT(fs1*mod(τi,fs)),i＝1,2,3,…,N
where mod () represents the remainder function, fs1Representing the fine delay waveform sampling clock frequency.
The horizontal width L of the receiving array is calculated by adopting the following formula:
L＝kλ/b
where k denotes a line fixing coefficient, λ denotes a wavelength of the reception beam, and b denotes a horizontal width of the reception beam.
The far field condition should satisfy that the distance from the receiving matrix is greater than L2/λ。
The signal processor adopts an FIR filter to carry out autocorrelation calculation on the wave beam, and the FIR filter coefficient FIR (x) is calculated by adopting the following method:
fir(x)＝s*(T×Fs-x),x＝0,1,2,…,T×Fs
where s (t) denotes the transmit beam signal, s*(T) denotes the complex conjugate function of s (T), x denotes the number of sample points, T denotes the pulse width of the signal, FsRepresents the beam output frequency; where t represents a variable, s in the FIR filter coefficients FIR (x)*T in (T) ═ T × Fs-x；
The reception beam matching output signal y (x) is calculated by the following formula:
wherein y (x) represents a receive beamforming output signal,
representing a complex multiplication (kronecker product); and obtaining and outputting an absolute value abs (Y (x)) by a modular approximation algorithm.
The display control unit is connected with a real-time display target image, processes each pixel point in the image based on a median filtering theory, and inhibits nonlinear signal noise; and local amplification of the image is realized by adopting a nearest neighbor interpolation algorithm.
The preferred embodiment:
the present example mainly includes: the system comprises a transmitter, a receiver, a signal processor, a display control unit (industrial control computer), a transmitting array and a receiving array. The display control unit sends information such as sonar working instructions and working parameters, receives data processed by sonar to display sonar images in real time, receives data of a sonar sensor at the same time, and displays information such as sonar temperature and humidity. The transmitter signal source generates a transmitting pulse signal according to a sonar working instruction, adjusts 16 paths of transmitting time delay according to transmitting pitch angle information, amplifies the power of the 16 paths of transmitting signals and then sends the signals to a transmitting array; the 338 channel receives the acoustic signal returned by the array receiving target, and sends the acoustic signal to the 338 channel receiving, amplifying and conditioning circuit, and completes digital acquisition; the digital acquisition signals form 360 receiving beams, after the space beams are formed, autocorrelation calculation is carried out on each beam, and the calculated signals are sent to the display and control unit for sonar image display. The image sonar function is shown in a block diagram in fig. 1.
The transmitter signal source receives the working parameters sent by the display control unit through the gigabit network port and generates 16 paths of pulse signals with adjustable phase and adjustable waveform. The phase of the signal source is adjustable by adopting delay. The distance d between 16 array elements (namely N is 16) of the transmitting array is 0.8 times of the wavelength, the No. 1 array element is taken as a reference point, and the wave beams of other array elements are delayed by tauiThe calculation formula is as follows:
τi＝(i-1)*d/c*sinθ,i＝1,2,3,…,N
where i denotes the ith emission element, τiRepresenting the beam delay time of the ith transmitting element, c representing the light speed, and theta representing the transmitting preset angle;
the digital delay implementation is divided into a coarse delay implementation and a fine delay implementation. Based on the waveform sampling clock, the coarse delay value is an integer multiple of the sampling, and the fine delay is a decimal multiple of the sampling.
Delay amount m of coarse delayiCalculated using the following formula:
mi＝INT(τi*fs),i＝1,2,3,…,N
where the INT () function represents the rounding down of a real number to the nearest integer, fsRepresenting a coarse delay waveform sampling clock frequency;
delay amount n of fine delayiCalculated using the following formula:
ni＝INT(fs1*mod(τi,fs)),i＝1,2,3,…,N
where mod () represents the remainder function, fs1Representing the fine delay waveform sampling clock frequency.
In this example, the signal center frequency f0Taking a sampling clock f of a coarse delay waveform at 400kHzsAt 5MHz, the delay amount of the coarse delay is:
mi＝INT(τi*fs),i＝1,2,3,…,N
the maximum deflection angle corresponds to about 42 retardation amounts.
For the implementation of fine delay, the sampling clock f is delayed finelys1Increasing to 125MHz, the amount of fine delay is:
ni＝INT(fs1*mod(τi,fs)),i＝1,2,3,…,N
the maximum delay amount is about 25.
The phase precision of the design is f0/fs1*360°＝1.15°。
The transmitter signal source adopts the FPGA to implement the above functions, and an implementation functional block diagram thereof is shown in fig. 2.
The transmitting array is uniformly arranged at intervals in a cylindrical array mode. According to the beam scanning angle of the array and the directivity requirement of the single array element, the effective height of the transmitting transducer array (transmitting array) is 48mm, the transmitting transducer array is divided into 16 layers in the vertical direction, and the layer spacing 48/16 is 3 mm.
The working frequency of the image sonar is 400kHz, the receiving array adopts a linear array form, the range of a horizontal observation sector is 90 degrees, the beam width is 0.3 degrees, and the horizontal width L of the receiving array is calculated by adopting the following formula:
L＝kλ/b
where k denotes a line fixing coefficient, λ denotes a wavelength of the reception beam, and b denotes a horizontal width of the reception beam.
In this embodiment, k is 50.6, and the horizontal scale of the planar receiving matrix is:
L＝50.6×λ÷0.3＝50.6×1500÷40000÷0.3＝0.6325m＝632.5mm
the receiving array is arranged according to the half-wavelength interval, and the required element number a:
a＝L÷(λ/2)＝338
the receiver amplifies, filters and collects 338 paths of analog signals output by the receiving array, and sends the collected data to the signal processor. The input stage of the receiver adopts a low-noise differential amplifier, and the minimum gain is 30dB so as to ensure the requirement of 0.5uV of input sensitivity. The second stage adopts a voltage control type TVG gain control circuit, the gain control range is-32 dB- +38dB (the maximum chip can achieve-40 dB- +40dB), and the first stage amplification is performed after the gain control circuit, so that the mutual influence caused by the direct connection of the gain control chip and the filter chip is eliminated, and a channel self-checking signal is introduced. The last stage is a post-amplifier and emitter follower to solve the input DC offset problem of AD. The important factor influencing the finding distance of the image sonar is the noise of a receiving conditioning channel, and in order to effectively inhibit the interference of the multi-channel receiving noise, the band-pass filtering of the receiver adopts an integrated ceramic filter, although the consistency of the phase and amplitude of each channel is poorer than that of a filter realized by an amplifier. But the ceramic filter has strong stop band inhibition capability, low noise and smaller volume.
The AD7690BRMZ chip from ADI company is selected for digital acquisition of the received signal. The chip is internally provided with a low-power-consumption high-speed 18-bit code-loss-free sampling ADC, an internal conversion clock and a universal serial interface, the kernel adopts a single power supply from 4.75V to 5.25V to supply power, and the highest throughput can reach 400 Ksps. The conversion process and data acquisition of the AD7690BRMZ are controlled by a CNV signal and an internal oscillator, the pressure difference of two differential input pins is sampled at the rising edge of the CNV, and the conversion result is output after the SCK is input. The signal acquisition unit uses 60-channel acquisition as a unit to carry out modular circuit board design, and 6 acquisition units are needed. 60 AD7690 chips utilize CNV conversion signals to realize synchronous acquisition of 60 paths of analog input signals, an AD7690 chip adopts a link mode, every 3 AD7690 chips are connected in series, and conversion results are all output by the last AD in series. Since the sampling rate is required to be 200K in this design, the period of the CNV is 5 us. The timing diagram of the acquisition signal is shown in fig. 3.
The signal processor adopts a high-speed FPGA to receive 338-path collected signals, forms 360 wave beams in a 90-degree observation range according to a 0.25-degree wave beam interval, and simultaneously combines, packs and stores wave beam forming data, parameter information, state information and the like. The signal processor carries out modular processing by a group of 60 signal acquisition channels, beam forming of 338-path acquisition signals is completed in parallel by 6 modules, each signal processing unit completes beam forming of 60 channels according to calculated parameters, and processed data are transmitted to the transmission processing unit through the optical fiber gigabit network port. A functional block diagram of a signal processor is shown in fig. 4.
In order to reduce the beam side lobe and improve the spatial resolution, the weighting coefficient of the beam forming array element can adopt Taylor weighting. Simulating by taking the direction of 0 degrees as the signal incidence direction, wherein the beam width of a-3 dB beam of the unweighted beam pattern is about 0.30, and the first side lobe is about-13.34 dB; the taylor weighted beam pattern-3 dB beam width is about 0.380 and the first side lobe is about-30.41 dB, the taylor weighted beam pattern being shown in figure 5.
In order to improve the fineness of the image, the signal processor designs a beam former according to a plane wave model in a far field, and carries out real-time segmented focusing compensation according to a spherical wave model in a near field. The size of the sonar receiving array is 633mm, and the far field condition of a sound field is more than or equal to
L2/λ＝0.6325×0.6325×400000/1500＝107m
The phase delay coefficient of the near field focusing can be calculated through the display control unit, forwarded to the signal processor through the optical fiber Ethernet and written into the storage RAM inside the FPGA so as to meet the requirement of dynamic focusing beam forming.
Dynamic focusing can only guarantee the beam performance near the distance point in a short time. When dynamic focusing is not used, considering BRAM resources of the FPGA, the distance is divided into four sections, the distances are respectively focused by R1, R2 and R3, and the phase delay coefficient of 4 multiplied by 60 multiplied by 360 multiplied by 2 multiplied by 16bit data quantity and the time delay coefficient of 4 multiplied by 60 multiplied by 360 multiplied by 6bit are shared. The storage space of a single RAM is 2048 multiplied by 16 bits, 2 18K BRAM resources are consumed, 60 real parts and 60 imaginary parts are shared, the time delay coefficient is 6 bits, 1 18K BRAM resource is consumed, and 300 18K BRAM resources are required. When a synchronous signal comes, the counter is cleared, the sampling points are counted, 4 groups of beam forming coefficients are output respectively, and the function of sectional focusing is realized.
Due to the limitation of storage resources, 4-segment segmented focusing is realized in the range of 90 degrees, and the precision is low. 10-segment segmented focusing can be realized in the range of 30 degrees. There are three options for the focus range: -45 °: -15 °, -15 °:15 °, 15 °: the memory format of the RAM is shown in fig. 6 at 45 °. In the focusing range-15 °: for example, the focusing coefficient is 1-9, the focusing distance R1-R9 ranges from-15 degrees to 15 degrees, and the number of coefficients in each group is 120. When a synchronous signal comes, clearing the counter, counting sampling points, and controlling a second group of read addresses according to the sampling points, wherein the first section is 0-119, the second section is 120-239, the third section is 240-359, the fourth section is 512-631 … …, and the ninth section is 1264-1383. The final beam is at-45 °: -15 ° and 15 °: far field coefficients were used over a 45 ° range, at-15 °: the 9-segment sectional focusing on the distance is realized within the range of 15 degrees.
To improve the image-forming distance, the signal processor performs autocorrelation processing on each beam after beam formation. The autocorrelation processing is realized in the FPGA by using an FIR filter, that is, the reference signal is set to an FIR filter coefficient, and the matching processing can be completed by convolution, where the FIR filter coefficient FIR (x) is shown as follows:
fir(x)＝s*(T×Fs-x),x＝0,1,2,…,T×Fs
where s (t) denotes a transmit beam signal obtained from quadrature demodulation of the transmit signal, s*(T) denotes the complex conjugate function of s (T), x denotes the number of sample points, T denotes the pulse width of the signal, FsRepresents the beam output frequency;
the total beam output has 338 complex time sequences with the sampling rate of 200kHz, and the autocorrelation processing is realized by convolution, that is, the received beam matching output signal y (x) is calculated by the following formula:
wherein y (x) represents a receive beamforming output signal,
representing a complex multiplication (kronecker product); and obtaining and outputting an absolute value abs (Y (x)) by a modular approximation algorithm. The signal incidence orientation estimate may be implemented by parabolic amplitude interpolation.
The signal processor packs and uploads signals processed by the processor to the display and control unit for real-time display through the gigabit network port controller developed based on the MAC core in the FPGA, and sensor data such as temperature, humidity and the like are uploaded together with the data.
The shore-based high-frequency multi-beam image sonar system completes experiments on round plates and frogmans on lakes, and the actual imaging effect is observed as shown in fig. 7 and 8.
The shore-based high-frequency multi-beam image sonar system has high processing speed and short transmission periodThe image refreshing speed can reach 10 frames per second, the image denoising processing based on bilateral filtering improves the image display quality, and meanwhile, the image denoising processing has an image local amplification function. In order to improve the image display quality, each pixel point in the image is processed based on a median filtering theory, and nonlinear signal noise is suppressed. The image display simultaneously adopts a nearest neighbor interpolation algorithm to realize the local amplification function of the image, namely, an interested area is selected, the pixel size of a source image A is expected to be u x v, the pixel size of a target image B after being amplified by R is expected to be g x h, wherein g is R x u, h is R v, and the final aim is to calculate g x h pixel values of the image B. Any point (x) of the image B can be obtained according to the proportional relation1，y1) The corresponding coordinates on the source image A should be (x)1*u/g，y1V/h), assuming that point P is (x) of the target image1，y1) The points correspond to the positions in the source image according to the proportion, and the value of the P point is a floating point number generally. The floating point number P is rounded, i.e. the pixel value of the P point directly takes the closest pixel value to this floating point number.
The foregoing description of specific embodiments of the present invention has been presented. It is to be understood that the present invention is not limited to the specific embodiments described above, and that various changes or modifications may be made by one skilled in the art within the scope of the appended claims without departing from the spirit of the invention. The embodiments and features of the embodiments of the present application may be combined with each other arbitrarily without conflict.
Claims (10)
1. A shore-based high-frequency multi-beam image sonar system is characterized by comprising a display and control unit, a transmitter, a transmitting array, a receiving array, a receiver and a signal processor, wherein the display and control unit is sequentially connected with the signal processor, the transmitter and the transmitting array;
the display control unit sends sonar working instructions and working parameter information; receiving data processed by the annunciator to display sonar images in real time, receiving data of a sonar sensor at the same time, and displaying sonar temperature and humidity information;
the transmitter signal source generates a plurality of paths of transmitting pulse signals according to the sonar working instruction, adjusts a plurality of paths of transmitting time delay according to the working parameter information, amplifies the power of the plurality of paths of transmitting signals and then sends the signals to the transmitting array;
the receiving array receives the acoustic signal returned by the target and sends the acoustic signal to the receiver;
the receiver receives and receives the acoustic signals transmitted by the array through the multi-channel receiving, amplifying and conditioning circuit and finishes the digital acquisition of the target return acoustic signals;
the signal processor performs autocorrelation calculation on each beam according to a plurality of receiving beams formed by the digital acquisition signals and signals transmitted by a signal source of the transmitter after the spatial beams are formed, and sends the calculated signals to the display control unit.
2. The shore-based high frequency multi-beam image sonar system of claim 1, wherein the transmit matrix comprises a plurality of transmit elements and is in the form of a cylindrical array; the receiving array comprises a plurality of receiving elements and adopts a linear array.
3. The bank-based high frequency multi-beam image sonar system of claim 1, wherein the transmit array transmit beams are pitched in the vertical direction to a range of 20 ° with a pitch accuracy of 1.2 °;
the horizontal observation sector range of the receiving array is within 90 degrees, and the horizontal width of a receiving beam formed by the signal processor is not more than 0.3 degrees.
4. The shore-based high frequency multibeam image sonar system of claim 1, wherein the receivers employ weighted beamforming when acquiring signals;
designing a beam former according to a plane wave model in a far field, calculating a time delay parameter, completing time delay compensation of each path of received signals, and adding and outputting the delayed multipath received signals;
and designing a beam former according to a spherical wave model in the near field, carrying out real-time segmented time delay compensation, selecting a distance central point of each segment as a focusing point to calculate a time delay parameter in each segment, completing the time delay compensation of each path of received signals, and adding and outputting the delayed multipath received signals.
5. The shore-based high frequency multi-beam image sonar system according to claim 4, wherein segmented beamforming is implemented by dividing an observation angle range into a plurality of segments in the near field according to an actual target image size, the observation angle range, and a limitation on a storage capacity of a signal processor.
6. The shore-based high frequency multi-beam image sonar system according to claim 1, wherein the transmitter generates multiple pulse signals with adjustable phase and adjustable waveform, the adjustable phase is realized by using delay, the transmission matrix comprises N transmission elements, the interval between the transmission elements is d, the 1 st element is used as a reference point, and the beam delay time τ of other transmission elements isiCalculated using the following formula:
τi＝(i-1)*d/c*sinθ,i＝1,2,3,…,N
where i denotes the ith emission element, τiRepresenting the beam delay time of the ith transmitting element, c representing the light speed, and theta representing the transmitting preset angle;
the digital delay implementation is divided into a coarse delay implementation part and a fine delay implementation part, and based on a waveform sampling clock, a coarse delay value is an integral multiple of sampling, and a fine delay value is a decimal multiple of sampling;
delay amount m of coarse delayiCalculated using the following formula:
mi＝INT(τi*fs),i＝1,2,3,…,N
where the INT () function represents the rounding down of a real number to the nearest integer, fsRepresenting a coarse delay waveform sampling clock frequency;
delay amount n of fine delayiCalculated using the following formula:
ni＝INT(fs1*mod(τi,fs)),i＝1,2,3,…,N
where mod () represents the remainder function, fs1Representing the fine delay waveform sampling clock frequency.
7. The shore-based high frequency multi-beam image sonar system of claim 1, wherein the horizontal width L of the receiving matrix is calculated using the formula:
L＝kλ/b
where k denotes a line fixing coefficient, λ denotes a wavelength of the reception beam, and b denotes a horizontal width of the reception beam.
8. The shore-based high frequency multi-beam image sonar system of claim 4, wherein the far field is conditioned to be a distance from the receiving matrix greater than L2/λ。
9. The shore-based high frequency multi-beam image sonar system of claim 1, wherein the signal processor uses FIR filters to perform autocorrelation calculations on the beams, and wherein the FIR filter coefficients FIR (x) are calculated as follows:
fir(x)＝s*(T×Fs-x),x＝0,1,2,…,T×Fs
where s (t) denotes the transmit beam signal, s*(T) denotes the complex conjugate function of s (T), x denotes the number of sample points, T denotes the pulse width of the signal, FsRepresents the beam output frequency;
the reception beam matching output signal y (x) is calculated by the following formula:
wherein y (x) represents a receive beamforming output signal,
represents a complex multiplication; and obtaining and outputting an absolute value abs (Y (x)) by a modular approximation algorithm.
10. The shore-based high-frequency multi-beam image sonar system according to claim 1, wherein the display and control unit is configured to display a target image in real time, process each pixel point in the image based on a median filtering theory, and suppress nonlinear signal noise; and local amplification of the image is realized by adopting a nearest neighbor interpolation algorithm.
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