CN113970746B - Continuous frequency conversion multi-beam sonar and frequency conversion method - Google Patents
Continuous frequency conversion multi-beam sonar and frequency conversion method Download PDFInfo
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- CN113970746B CN113970746B CN202111592851.6A CN202111592851A CN113970746B CN 113970746 B CN113970746 B CN 113970746B CN 202111592851 A CN202111592851 A CN 202111592851A CN 113970746 B CN113970746 B CN 113970746B
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01S15/00—Systems using the reflection or reradiation of acoustic waves, e.g. sonar systems
- G01S15/88—Sonar systems specially adapted for specific applications
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
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- G—PHYSICS
- G01—MEASURING; TESTING
- 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
- G01S7/52001—Auxiliary means for detecting or identifying sonar signals or the like, e.g. sonar jamming signals
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Abstract
The invention relates to the technical field of marine geological exploration, and provides a continuous frequency conversion multi-beam sonar and a frequency conversion method, wherein the sonar comprises an upper computer, an FPGA module, a transmitting array, a receiving array, an analog signal processing unit, an AD conversion module and a power supply module; the device also comprises an envelope extraction module used for extracting an envelope signal of the echo simulation signal; the envelope comparison module is used for outputting a feedback signal; the AD conversion module is also used for converting the envelope signal and the feedback signal into digital signals; the FPGA module is also used for adjusting the center frequency of the transmitted linear frequency modulation signal according to the envelope signal, the feedback signal and a preset envelope detection threshold value. The continuous frequency conversion multi-beam sonar provided by the invention can judge and adjust the condition of the submarine echo signals in the environment with varied seawater depths in real time without occupying too many computing resources of an FPGA module, ensures the real-time adaptation of the transmitted linear frequency modulation signals and submarine topography, and improves the detection precision.
Description
Technical Field
The invention relates to the technical field of marine geological exploration, in particular to a continuous frequency conversion multi-beam sonar and a frequency conversion method.
Background
Multi-beam sounding sonar is one of the important devices for current submarine topography surveying. With the continuous progress of modern scientific technology, shallow water multi-beam sounding sonar technology and equipment are continuously developed and perfected, and are widely applied to the fields of national defense and national economic construction, such as submarine pipeline detection, submarine cable laying, ocean engineering measurement, submarine resource surveying, submarine sediment detection, water safety sailing and the like. The signals used by the conventional multi-beam sonar signals are usually a combination signal of Linear Frequency Modulated (LFM) pulse signals and single Frequency Wave (CW) pulses. The linear frequency modulation multi-beam echo signal pulse compression method using the variable window function reduces the coherent loss of each beam, reduces the loss of signal to noise ratio, improves the distance resolution and improves the depth sounding quality of the submarine topography.
Chirp is a spread spectrum modulation technique that does not require a pseudo-random code sequence. Because the frequency bandwidth occupied by the chirp signal is much larger than the information bandwidth, a large system processing gain can be obtained. The linear frequency modulation technology is widely applied to radar and sonar technologies, for example, in a radar positioning technology, the linear frequency modulation technology can increase the radio frequency pulse width, improve the average transmitting power, increase the communication distance, simultaneously maintain enough signal spectrum width, and does not reduce the distance resolution of the radar.
The FPGA device belongs to a semi-custom circuit in an application-specific integrated circuit, is a programmable logic array, and can effectively solve the problem of less gate circuits of the original device. The basic structure of the FPGA comprises a programmable input/output unit, a configurable logic block, a digital clock management module, an embedded block RAM, wiring resources, an embedded special hard core, a bottom layer embedded functional unit and the like.
The existing multi-beam adopts a CW pulse signal with fixed frequency and an LFM pulse signal with fixed center frequency, so that the signal frequency can not be effectively selected according to the submarine topography, the multi-beam is inaccurate in measurement precision in the environment with variable topography, and the actual requirement can not be met.
Disclosure of Invention
The invention aims to overcome the defects in the prior art, and provides a continuous frequency conversion multi-beam sonar based on an FPGA and a method for continuously converting a linear frequency modulation signal emitted by the same, so that the multi-beam sonar can effectively measure submarine topography under the environment with variable seawater depth, and the measurement accuracy and the distance resolution of the multi-beam sonar are improved.
In order to achieve the above object, an aspect of the present application provides a continuous frequency conversion multi-beam sonar, including an upper computer, an FPGA module, a transmitting array, a receiving array, an analog signal processing unit, an AD conversion module and a power module, where the upper computer is installed with upper computer software for sending a control instruction to the FPGA module and receiving an echo digital signal that is subjected to beam forming and detection processing by the FPGA module; the FPGA module receives the control instruction, sets the center frequency of a linear frequency modulation signal, and controls the transmitting array to transmit the linear frequency modulation signal to the seabed; the receiving array receives the submarine echo signal and converts the submarine echo signal into an echo electric signal; the analog signal processing unit converts the echo electric signal into an echo analog signal which meets the input requirement of the AD conversion module; the AD conversion module converts the echo analog signal into an echo digital signal and sends the echo digital signal to the FPGA module, and the FPGA module performs beam forming and wave detection processing; the power supply module is used for supplying power to the continuous variable frequency multi-beam sonar; the continuous frequency conversion multi-beam sonar also comprises:
the envelope extraction module is used for extracting an envelope signal of the echo simulation signal;
the envelope comparison module outputs a feedback signal according to the envelope signal and preset upper limit voltage and lower limit voltage, wherein the upper limit voltage is greater than the lower limit voltage;
the AD conversion module is also used for converting the envelope signal and the feedback signal into digital signals and outputting the digital signals to the FPGA module;
the FPGA module is further used for adjusting the center frequency of the linear frequency modulation signal according to the envelope signal converted into the digital signal, the feedback signal and a preset envelope detection threshold value.
Further, the envelope comparison module outputs the feedback signal at a high level when the amplitude of the envelope signal is greater than the upper limit voltage or the amplitude of the envelope signal is less than the lower limit voltage; the feedback signal output is at a low level when the amplitude of the envelope signal is greater than the lower limit voltage and the amplitude of the envelope signal is less than the upper limit voltage.
Further, the upper limit voltage and the lower limit voltage are estimated and determined based on the transmitting sound source level of the transmitting array, the receiving performance of the receiving array, and the propagation characteristic and the reflection characteristic of the sound wave in the seawater.
Further, when the feedback signal is at a high level and the amplitude of the envelope signal is smaller than the envelope detection threshold, the FPGA module increases the center frequency of the chirp signal; reducing the center frequency of the chirp signal when the feedback signal is high and the amplitude of the envelope signal is greater than the envelope detection threshold; and when the feedback signal is at a low level, keeping the center frequency of the linear frequency modulation signal unchanged.
Preferably, the envelope detection threshold is determined based on a mean of the upper limit voltage and the lower limit voltage.
Preferably, the FPGA module further includes an abnormal signal detection sub-module, and determines whether the sea bottom echo signal is a false sea bottom echo signal according to the chirp signal and the envelope signal.
Further, the analog signal processing unit includes:
the pre-amplification module is used for pre-amplifying the echo electric signal;
the gain adjusting module is used for adjusting the gain of the pre-amplified echo electric signal;
the band-pass filter is used for carrying out band-pass filtering processing on the echo electric signal subjected to the gain processing;
and the voltage conversion and post-amplification module is used for carrying out voltage shifting and amplification on the echo electric signal subjected to filtering processing to generate an echo analog signal meeting the input requirement of the AD conversion module.
Another aspect of the present application provides a frequency conversion method for adjusting the center frequency of the chirp signal emitted by the above-mentioned continuous frequency conversion multibeam sonar, including the following steps:
the first step is as follows: setting the center frequency of a chirp signal and transmitting the chirp signal;
the second step is that: receiving a submarine echo signal and converting the submarine echo signal into an echo electric signal;
the third step: processing the echo electric signal to generate an echo analog signal which meets the input requirement of the AD conversion module;
the fourth step: extracting an envelope signal of the echo simulation signal;
the fifth step: generating a feedback signal according to the envelope signal and a preset upper limit voltage and a preset lower limit voltage, wherein the upper limit voltage is greater than the lower limit voltage;
and a sixth step: performing digital signal conversion on the envelope signal and the feedback signal;
the seventh step: and adjusting the center frequency of the linear frequency modulation signal according to the envelope signal converted into the digital signal, the feedback signal and a preset envelope detection threshold value.
Further, the outputting a feedback signal according to the envelope signal and preset upper and lower limit voltages includes:
when the amplitude of the envelope signal is greater than the upper limit voltage or the amplitude of the envelope signal is less than the lower limit voltage, the output feedback signal is at a high level;
the feedback signal output is at a low level when the amplitude of the envelope signal is greater than the lower limit voltage and the amplitude of the envelope signal is less than the upper limit voltage.
Further, the upper limit voltage and the lower limit voltage are estimated and determined based on the transmitting sound source level of the transmitting array, the receiving performance of the receiving array, and the propagation characteristic and the reflection characteristic of the sound wave in the seawater.
Further, the adjusting the center frequency of the chirp signal according to the envelope signal converted into a digital signal, the feedback signal, and a preset envelope detection threshold includes:
increasing the center frequency of the chirp signal when the feedback signal is high and the amplitude of the envelope signal is less than the envelope detection threshold;
reducing the center frequency of the chirp signal when the feedback signal is high and the amplitude of the envelope signal is greater than the envelope detection threshold;
and when the feedback signal is at a low level, keeping the center frequency of the linear frequency modulation signal unchanged.
Further, the envelope detection threshold is determined based on a mean of the upper limit voltage and the lower limit voltage.
Preferably, the frequency conversion method further includes an abnormal signal detection step of determining whether the sea bottom echo signal is a false sea bottom echo signal according to the chirp signal and the envelope signal.
Further, the processing the echo electric signal to generate an echo analog signal meeting the input requirement of the AD conversion module includes the following steps:
pre-amplifying the echo electric signal;
adjusting the gain of the pre-amplified echo electric signal;
performing band-pass filtering processing on the echo electric signal subjected to gain processing;
and carrying out voltage shifting and amplification on the echo electric signal subjected to filtering processing to generate an echo analog signal meeting the input requirement of the AD conversion module.
The continuous frequency conversion multi-beam sonar and the frequency conversion method provided by the embodiment of the application have the following beneficial effects:
(1) the envelope extraction module and the envelope comparison module are used for extracting envelope signals from the echo analog signals, high-level feedback signals are triggered when the amplitude of the envelope signals exceeds a preset range, the FPGA module is used for preferentially judging whether the envelope signals exceed the preset range according to the feedback signals, and then comparing the envelope signals with a preset threshold value when the envelope signals exceed the preset range so as to determine the direction of adjusting the center frequency of the linear frequency modulation signals.
(2) The abnormal signal judgment sub-module judges whether the echo signal is a false seabed echo signal or not based on the correlation between the envelope of the echo signal and the transmitted linear frequency modulation signal, so that false echo signals generated by fish and other underwater objects are eliminated in advance, wherein the envelope of the echo signal directly uses a result output by an analog circuit of the envelope extraction module in real time, and compared with the technical scheme of obtaining the echo envelope in an FPGA module through algorithm calculation in the prior art, the method can effectively save the calculation resources of the FPGA.
Drawings
Fig. 1 is a block diagram of a system composition of a continuous frequency conversion multi-beam sonar according to an embodiment of the present application;
fig. 2 is a schematic diagram of a signal transmission direction of a continuous frequency conversion multi-beam sonar according to an embodiment of the present application;
fig. 3 is an envelope signal extracted by the envelope extraction module according to an embodiment of the present application;
FIG. 4 is a circuit diagram of a window voltage comparator used by the envelope comparison module of an embodiment of the present application;
FIG. 5 is a graph showing the input-output voltage relationship of the window voltage comparator of FIG. 4;
fig. 6 is a flowchart of a frequency conversion method according to an embodiment of the present application;
fig. 7 is a specific flow of adjusting the center frequency of the chirp signal in fig. 6.
Detailed Description
Hereinafter, the present application will be further described based on preferred embodiments with reference to the accompanying drawings.
In addition, various components on the drawings are enlarged or reduced for convenience of understanding, but this is not intended to limit the scope of the present application.
Singular references also include plural references and vice versa.
In the description of the embodiments of the present application, it should be noted that if the terms "upper", "lower", "inner", "outer", etc. are used for indicating the orientation or positional relationship based on the orientation or positional relationship shown in the drawings or the orientation or positional relationship which is usually arranged when the products of the embodiments of the present application are used, the description is only for convenience and simplicity, but the indication or suggestion that the referred device or element must have a specific orientation, be constructed in a specific orientation and be operated, and thus, the application cannot be construed as being limited. Moreover, the terms first, second, etc. may be used in the description to distinguish between different elements, but these should not be limited by the order of manufacture or by importance to be understood as indicating or implying any particular importance, and their names may differ from their names in the detailed description of the application and the claims.
The terminology used in the description is for the purpose of describing the embodiments of the application and is not intended to be limiting of the application. It is also to be understood that, unless otherwise expressly stated or limited, the terms "disposed," "connected," and "connected" are intended to be open-ended, i.e., may be fixedly connected, detachably connected, or integrally connected; they may be mechanically coupled, directly coupled, indirectly coupled through intervening media, or may be interconnected between two elements. The specific meaning of the above terms in the present application will be specifically understood by those skilled in the art.
One aspect of the embodiment of the present application provides a continuous frequency conversion multi-beam sonar, as shown in fig. 1, including host computer, FPGA module, transmission array, receiving array, analog signal processing unit, AD conversion module and power module.
In some embodiments of the present application, the analog signal processing unit further comprises a pre-amplification module, a gain adjustment module, a band-pass filter, and a voltage conversion and post-amplification module.
Fig. 2 shows a schematic diagram of a continuous frequency conversion multi-beam sonar signal transmission direction provided by an embodiment of the present application.
Specifically, the host computer is installed host computer software, sends control command to the FPGA module, and control command includes: starting a transmitting array, transmitting a linear frequency modulation signal to the seabed by using the initial central frequency, setting the gain of a gain adjusting module, starting a receiving array to receive the seabed echo signal and the like;
after receiving a command of an upper computer, the FPGA module generates a linear frequency modulation signal according to an initial central frequency and outputs the linear frequency modulation signal to a transmitting array; the transmitting array is an array formed by transmitting transducers, the linear frequency modulation signals are converted into multi-beam acoustic signals with directivity under the control of the FPGA module and are transmitted to the seabed, the receiving array is used for receiving seabed echo signals, and the receiving array is an array formed by receiving transducers and is used for converting the seabed echo signals in the form of the received acoustic signals into echo electric signals;
the echo electric signal received by the receiving array is weak, so that the echo electric signal generally needs to be amplified, filtered, voltage-converted and the like through an analog signal processing unit, specifically, the echo electric signal is pre-amplified through a pre-amplification module, the gain of the pre-amplified echo electric signal is adjusted through a gain adjustment module, the echo electric signal subjected to gain processing is subjected to band-pass filtering processing through a band-pass filter, and the echo electric signal subjected to filtering processing is subjected to voltage shifting and amplification through a voltage conversion and post-amplification module to generate an echo analog signal meeting the input requirement of an AD conversion module;
the AD conversion module converts the echo analog signal into an echo digital signal and sends the echo digital signal to the FPGA module, the FPGA module carries out beam forming and wave detection processing, and the echo digital signal which is subjected to the beam forming and the wave detection processing is sent to an upper computer for further signal display, signal analysis and other operations;
the power module is used for supplying power to the parts.
The above components and their working principle are conventional technologies known to those skilled in the art, and further, in the continuous frequency conversion multi-beam sonar provided in the embodiment of the present application, the method further includes:
the envelope extraction module is used for extracting an envelope signal of the echo simulation signal; the envelope comparison module outputs a feedback signal according to an envelope signal and preset upper limit voltage and lower limit voltage, wherein the upper limit voltage is greater than the lower limit voltage; the AD conversion module is also used for converting the envelope signal and the feedback signal into digital signals and outputting the digital signals to the FPGA module; the FPGA module is further used for adjusting the center frequency of the linear frequency modulation signal according to the envelope signal, the feedback signal and a preset envelope detection threshold value.
Specifically, the echo analog signal generated by the voltage conversion and post-amplification module is output to an envelope extraction module, and an envelope line of the echo analog signal is extracted by the envelope extraction module to generate an envelope signal in the form of an analog signal; the technology for obtaining the envelope signal from the single-frequency or frequency-modulated signal is known to those skilled in the art, and those skilled in the art may adopt a specific analog circuit to extract the envelope signal according to actual needs. Fig. 3 shows an envelope signal (contour line pointed by arrow in fig. 3) extracted by the envelope extraction module based on the echo simulated signal in a specific embodiment.
The envelope extracting module extracts an envelope signal of the echo simulation signal and outputs the envelope signal to an envelope comparing module, the envelope comparing module outputs a comparison result of the amplitude of the envelope signal and preset upper limit voltage and lower limit voltage (wherein the upper limit voltage is greater than the lower limit voltage) as a feedback signal, when the amplitude of the envelope signal is greater than the upper limit voltage or the amplitude of the envelope signal is less than the lower limit voltage, the feedback signal is at a high level, and when the amplitude of the envelope signal is between the upper limit voltage and the lower limit voltage, the feedback signal is at a low level.
In some embodiments of the present application, the generating of the output signal with a high level or a low level according to whether the input signal falls into the preset voltage range may be implemented by a window voltage comparator, and fig. 4 shows a circuit diagram of the window voltage comparator used in a specific envelope comparison module, as shown in fig. 4, the window voltage comparator applies an upper limit voltage
And lower limit voltage
Wherein
Resistance of
、
And a voltage regulator tube
Constituting a clipping circuit. The window voltage comparator has two threshold voltages, and when the input voltage changes from large to small or from small to large, the output voltage changes twice. The window voltage comparator adopts two integrated operational amplifiers with different power supply modes, when the integrated operational amplifier is used as the window comparator, the integrated operational amplifier is in a nonlinear working mode, and the voltage of the output end is equal to the power supply voltage. When the input voltage is
When the temperature of the water is higher than the set temperature,
，
thus, a diode
The power-on state is carried out,
is turned off so that the output voltage of the circuit
(ii) a When the input voltage is
When the temperature of the water is higher than the set temperature,
，
thus, a diode
The power-on state is carried out,
is turned off so that the output voltage of the circuit
(ii) a When the input voltage is
When the temperature of the water is higher than the set temperature,
，
thus, a diode
And
are all turned off, so that the circuit outputs a voltage
. Fig. 5 shows the input-output voltage relationship of the window voltage comparator.
Further, the upper limit voltage and the lower limit voltage are calculated according to a sonar equation based on the transmitting sound source level of the transmitting array, the receiving performance of the receiving array and the propagation characteristic and the reflection characteristic of the sound wave in the seawater, a voltage window range formed by the upper limit voltage and the lower limit voltage represents a voltage amplitude range of the echo analog signal suitable for analysis processing, when the amplitude of the envelope of the echo analog signal is not within the range, the envelope comparison module outputs a high-level feedback signal, which indicates that the seabed depth or the reflection characteristic and the like are changed relative to a pre-estimated value, and at this time, the center frequency of the transmitted chirp signal needs to be adjusted to ensure that the echo analog signal reenters the voltage amplitude range suitable for analysis processing.
The envelope signal extracted by the envelope extraction module and the feedback signal output by the envelope comparison module are both in analog signal form, and after the envelope signal and the feedback signal are input to the AD conversion module and converted into digital signal form, the envelope signal and the feedback signal are further input to the FPGA module for subsequent processing.
After receiving the envelope signal and the feedback signal converted into the digital signal form, the FPGA module correspondingly adjusts the center frequency of the transmitted chirp signal based on the level high-low state of the feedback signal and the comparison result of the envelope signal and a preset envelope detection threshold, wherein the envelope detection threshold is determined based on the average value of the upper limit voltage and the lower limit voltage. Specifically, when the feedback signal is at a low level, the FPGA module keeps the center frequency of the transmitted chirp signal unchanged; when the feedback signal is at a high level and the amplitude of the envelope signal is smaller than the envelope detection threshold, the FPGA module increases the center frequency of the transmitted linear frequency modulation signal; when the feedback signal is high and the amplitude of the envelope signal is greater than the envelope detection threshold, the center frequency of the transmitted chirp signal is reduced.
The process of comparing and adjusting the center frequency by the FPGA module is a continuous process, namely, the FPGA module continuously receives the submarine echo signal along with the receiving array, and adjusts the center frequency of the transmitted linear frequency modulation signal in real time so that the echo analog signal is always in a voltage amplitude range suitable for analysis and processing, thereby ensuring the real-time adaptation of the transmitted linear frequency modulation signal and submarine topography and improving the detection precision.
In the embodiment, an envelope extracting module and an envelope comparing module are used for extracting an envelope signal from an echo analog signal, and a high-level feedback signal is triggered when the amplitude of the envelope signal exceeds a preset range, an FPGA module preferentially judges whether the envelope signal exceeds the preset range according to the feedback signal, when the envelope signal is within the preset range, the echo signal is in a more ideal signal analysis processing range, and at the moment, the FGPA module does not judge the amplitude of the echo signal any more, and the computing resource of the FGPA module is not consumed; only when the envelope of the echo signal exceeds the range, the direction of adjusting the center frequency of the linear frequency modulation signal is determined by comparing the envelope with a preset threshold value, and the condition of the submarine echo signal in a sea depth variable environment can be rapidly judged and correspondingly adjusted under the condition of not occupying excessive computing resources of an FPGA module, so that the real-time adaptation of the transmitted linear frequency modulation signal and the submarine topography is ensured, and the detection precision is improved.
Preferably, the FPGA module of the embodiment of the present application further includes an abnormal signal detection sub-module, which determines whether the bottom echo signal is a false bottom echo signal according to the transmitted chirp signal and the envelope signal.
Specifically, when the received seafloor echo signal contains a false seafloor echo signal reflected by a fish school or other objects, the envelope of the seafloor echo signal and the waveform characteristics of the transmitted chirp signal have a large difference, so that the correlation between the transmitted chirp signal and the envelope of the echo analog signal can be compared to detect an abnormal signal, and whether the seafloor echo signal is the false seafloor echo signal can be judged. The technology for calculating the correlation between the detection signal and the envelope signal is known to those skilled in the art, and in the embodiment of the application, the envelope of the echo signal directly uses the result output in real time by the analog circuit of the envelope extraction module, so that compared with the technical scheme in the prior art that the echo envelope is calculated and obtained by an algorithm in the FPGA module, the calculation resource of the FPGA can be effectively saved.
Another aspect of the embodiments of the present application provides a frequency conversion method, configured to adjust a center frequency of a chirp signal emitted by the above-mentioned continuous frequency conversion multi-beam sonar, where fig. 6 is a flowchart of the frequency conversion method, as shown in fig. 6, including the following steps:
the first step is as follows: setting the center frequency of a chirp signal and transmitting the chirp signal;
the second step is that: receiving a submarine echo signal and converting the submarine echo signal into an echo electric signal;
the third step: processing the echo electric signal to generate an echo analog signal which meets the input requirement of the AD conversion module;
the fourth step: extracting an envelope signal of the echo simulation signal;
the fifth step: generating a feedback signal according to the envelope signal and a preset upper limit voltage and a preset lower limit voltage, wherein the upper limit voltage is greater than the lower limit voltage;
and a sixth step: performing digital signal conversion on the envelope signal and the feedback signal;
the seventh step: and adjusting the center frequency of the linear frequency modulation signal according to the envelope signal converted into the digital signal, the feedback signal and a preset envelope detection threshold value.
Further, the outputting a feedback signal according to the envelope signal and preset upper and lower limit voltages includes:
when the amplitude of the envelope signal is greater than the upper limit voltage or the amplitude of the envelope signal is less than the lower limit voltage, the output feedback signal is at a high level; the feedback signal output is at a low level when the amplitude of the envelope signal is greater than the lower limit voltage and the amplitude of the envelope signal is less than the upper limit voltage.
The upper limit voltage and the lower limit voltage are estimated and determined based on the transmitting sound source level of the transmitting array, the receiving performance of the receiving array, and the propagation characteristic and the reflection characteristic of sound waves in seawater.
Further, the adjusting the center frequency of the chirp signal according to the envelope signal converted into a digital signal, the feedback signal, and a preset envelope detection threshold includes: increasing the center frequency of the chirp signal when the feedback signal is high and the amplitude of the envelope signal is less than the envelope detection threshold; reducing the center frequency of the chirp signal when the feedback signal is high and the amplitude of the envelope signal is greater than the envelope detection threshold; and when the feedback signal is at a low level, keeping the center frequency of the linear frequency modulation signal unchanged.
Fig. 7 shows a flowchart of a seventh step in some embodiments of the present application, and as shown in fig. 7, first, the FGPA module receives the envelope signal and the feedback signal in the form of the digital signal output by the AD conversion module; then judging whether the feedback signal is at a low level, if so, keeping the center frequency of the transmitted linear frequency modulation signal unchanged by the FPGA module; if the envelope signal is at a high level, the FPGA module further compares the envelope signal with a preset envelope detection threshold, if the envelope signal is smaller than the envelope detection threshold, the center frequency of the transmitted chirp signal is increased, and if the envelope signal is larger than the envelope detection threshold, the center frequency of the transmitted chirp signal is decreased.
Further, the envelope detection threshold is determined based on a mean of the upper limit voltage and the lower limit voltage.
Preferably, the frequency conversion method further includes an abnormal signal detection step of determining whether the sea bottom echo signal is a false sea bottom echo signal according to the chirp signal and the envelope signal.
Further, the processing the echo electric signal to generate an echo analog signal meeting the input requirement of the AD conversion module includes the following steps:
pre-amplifying the echo electric signal; adjusting the gain of the pre-amplified echo electric signal; performing band-pass filtering processing on the echo electric signal subjected to gain processing; and carrying out voltage shifting and amplification on the echo electric signal subjected to filtering processing to generate an echo analog signal meeting the input requirement of the AD conversion module.
While the present invention has been described in detail and with reference to specific embodiments thereof, it will be apparent to one skilled in the art that various changes and modifications can be made therein without departing from the spirit and scope thereof as defined in the appended claims.
Claims (14)
1. A continuous frequency conversion multi-beam sonar comprises an upper computer, an FPGA module, a transmitting array, a receiving array, an analog signal processing unit, an AD conversion module and a power supply module, wherein the upper computer is provided with upper computer software and is used for sending a control instruction to the FPGA module and receiving an echo digital signal which is subjected to beam forming and wave detection processing by the FPGA module; the FPGA module receives the control instruction, sets the center frequency of a linear frequency modulation signal, and controls the transmitting array to transmit the linear frequency modulation signal to the seabed; the receiving array receives the submarine echo signal and converts the submarine echo signal into an echo electric signal; the analog signal processing unit converts the echo electric signal into an echo analog signal which meets the input requirement of the AD conversion module; the AD conversion module converts the echo analog signal into an echo digital signal and sends the echo digital signal to the FPGA module, and the FPGA module performs beam forming and wave detection processing; the power supply module is used for supplying power to the continuous variable frequency multi-beam sonar; it is characterized by also comprising:
the envelope extraction module is used for extracting an envelope signal of the echo simulation signal;
the envelope comparison module outputs a feedback signal according to the envelope signal and preset upper limit voltage and lower limit voltage, wherein the upper limit voltage is greater than the lower limit voltage;
the AD conversion module is also used for converting the envelope signal and the feedback signal into digital signals and outputting the digital signals to the FPGA module;
the FPGA module is further used for adjusting the center frequency of the linear frequency modulation signal according to the envelope signal and the feedback signal which are converted into digital signals and a preset envelope detection threshold value.
2. The continuous frequency conversion multi-beam sonar according to claim 1, wherein:
the envelope comparison module outputs the feedback signal at a high level when the amplitude of the envelope signal is greater than the upper limit voltage or the amplitude of the envelope signal is less than the lower limit voltage; the feedback signal output is at a low level when the amplitude of the envelope signal is greater than the lower limit voltage and the amplitude of the envelope signal is less than the upper limit voltage.
3. A continuous frequency conversion multi-beam sonar according to claim 2, wherein:
the upper limit voltage and the lower limit voltage are estimated and determined based on the transmitting sound source level of the transmitting array, the receiving performance of the receiving array, and the propagation characteristic and the reflection characteristic of sound waves in seawater.
4. A continuous frequency conversion multi-beam sonar according to claim 2, wherein:
when the feedback signal is at a high level and the amplitude of the envelope signal is smaller than the envelope detection threshold, the FPGA module increases the center frequency of the linear frequency modulation signal; reducing the center frequency of the chirp signal when the feedback signal is high and the amplitude of the envelope signal is greater than the envelope detection threshold; and when the feedback signal is at a low level, keeping the center frequency of the linear frequency modulation signal unchanged.
5. The continuous frequency conversion multi-beam sonar according to claim 4, wherein:
the envelope detection threshold is determined based on a mean of the upper limit voltage and the lower limit voltage.
6. The continuous-conversion multi-beam sonar according to claim 1, wherein the FPGA module comprises:
and the abnormal signal detection submodule judges whether the submarine echo signal is a false submarine echo signal according to the linear frequency modulation signal and the envelope signal.
7. The continuous-conversion multi-beam sonar according to claim 1, wherein the analog signal processing unit includes:
the pre-amplification module is used for pre-amplifying the echo electric signal;
the gain adjusting module is used for adjusting the gain of the pre-amplified echo electric signal;
the band-pass filter is used for carrying out band-pass filtering processing on the echo electric signal subjected to the gain processing;
and the voltage conversion and post-amplification module is used for carrying out voltage shifting and amplification on the echo electric signal subjected to filtering processing to generate an echo analog signal meeting the input requirement of the AD conversion module.
8. A frequency conversion method for adjusting the center frequency of the chirp signal emitted by the continuous frequency conversion multi-beam sonar according to claim 1, comprising the steps of:
the first step is as follows: setting the center frequency of a chirp signal and transmitting the chirp signal;
the second step is that: receiving a submarine echo signal and converting the submarine echo signal into an echo electric signal;
the third step: processing the echo electric signal to generate an echo analog signal which meets the input requirement of the AD conversion module;
the fourth step: extracting an envelope signal of the echo simulation signal;
the fifth step: generating a feedback signal according to the envelope signal and a preset upper limit voltage and a preset lower limit voltage, wherein the upper limit voltage is greater than the lower limit voltage;
and a sixth step: performing digital signal conversion on the envelope signal and the feedback signal;
the seventh step: and adjusting the center frequency of the linear frequency modulation signal according to the envelope signal and the feedback signal which are converted into digital signals and a preset envelope detection threshold value.
9. The method of claim 8, wherein outputting the feedback signal according to the envelope signal and the preset upper limit voltage and lower limit voltage comprises:
when the amplitude of the envelope signal is greater than the upper limit voltage or the amplitude of the envelope signal is less than the lower limit voltage, the output feedback signal is at a high level;
the feedback signal output is at a low level when the amplitude of the envelope signal is greater than the lower limit voltage and the amplitude of the envelope signal is less than the upper limit voltage.
10. A method of frequency conversion as claimed in claim 9, characterized by:
the upper limit voltage and the lower limit voltage are estimated and determined based on the transmitting sound source level of the transmitting array, the receiving performance of the receiving array, and the propagation characteristic and the reflection characteristic of sound waves in seawater.
11. The method of claim 9, wherein the adjusting the center frequency of the chirp signal according to the envelope signal converted to a digital signal, the feedback signal, and a preset envelope detection threshold comprises:
increasing the center frequency of the chirp signal when the feedback signal is high and the amplitude of the envelope signal is less than the envelope detection threshold;
reducing the center frequency of the chirp signal when the feedback signal is high and the amplitude of the envelope signal is greater than the envelope detection threshold;
and when the feedback signal is at a low level, keeping the center frequency of the linear frequency modulation signal unchanged.
12. A method of frequency conversion as claimed in claim 11, characterized by:
the envelope detection threshold is determined based on a mean of the upper limit voltage and the lower limit voltage.
13. A method of frequency conversion as claimed in claim 8, characterized by:
the frequency conversion method also comprises an abnormal signal detection step, and whether the submarine echo signal is a false submarine echo signal is judged according to the linear frequency modulation signal and the envelope signal.
14. The frequency conversion method according to claim 9, wherein the processing the echo electric signal to generate an echo analog signal meeting the input requirement of the AD conversion module comprises the following steps:
pre-amplifying the echo electric signal;
adjusting the gain of the pre-amplified echo electric signal;
performing band-pass filtering processing on the echo electric signal subjected to gain processing;
and carrying out voltage shifting and amplification on the echo electric signal subjected to filtering processing to generate an echo analog signal meeting the input requirement of the AD conversion module.
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