Distributed three-dimensional imaging sonar system based on front-end gain correction

Abstract

The application belongs to the technical field of underwater acoustic signal processing, and provides a distributed three-dimensional imaging sonar system based on front-end gain correction, which comprises a sound source and a hydrophone array; a plurality of distributed processing units and gain conversion modules included therein, which are used for gain amplification and analog-to-digital conversion of original received signals of each channel and output as digital signals; a master control unit, which comprises a sound source control module, a synchronous module, a collection module and a gain correction module; the sound source control module controls the sound source to emit underwater acoustic signals in a detection mode or a correction mode; the synchronous module is used for controlling the synchronization of the distributed processing units; the collection module is used for collecting digital signals output by each channel; the gain correction module corrects the gain control parameters of each gain conversion module in the correction mode; and a data processing unit is used for determining the three-dimensional position and reflection characteristics of a detection target. The technical scheme of the application can realize the consistency of the gain amplitudes of different channels under the distributed collection architecture, and effectively improve the overall imaging quality and stability of the three-dimensional imaging sonar.

Description

Technical Field

[0001] This application belongs to the field of underwater acoustic signal processing technology, specifically, it provides a distributed three-dimensional imaging sonar system based on front-end gain correction. Background Technology

[0002] Three-dimensional imaging sonar systems have wide applications in underwater target detection, topographic mapping, and marine resource exploration. These systems typically contain a large number of transducer elements, receiving underwater reflected echo signals in parallel through hundreds or even thousands of channels. The signals are then processed to form a three-dimensional image. However, due to the limited I / O resources of a single acquisition board, it cannot meet the requirements of acquiring hundreds or thousands of acoustic data channels for real-time three-dimensional imaging. Furthermore, due to differences in the sensitivity of the transducer elements themselves, the discreteness of the parameters of the front-end analog amplifier circuit components, and the aging of components after long-term use, signals of the same intensity often exhibit amplitude inconsistencies when processed by different channels. This amplitude inconsistency directly affects the amplitude calibration accuracy of the echo signal, leading to target brightness distortion, increased noise, and even loss of detail in the three-dimensional imaging results.

[0003] Existing amplitude consistency correction methods mostly perform amplitude compensation in the digital domain after data acquisition. This correction method cannot avoid real-time amplitude distortion caused by differences in amplification of the front-end analog circuit, cannot guarantee the amplitude consistency of the signal in real time, and when the signal is saturated or clipped, the true amplitude cannot be recovered from the digital signal stored at the back end. Summary of the Invention

[0004] This application provides a distributed three-dimensional imaging sonar system based on front-end gain correction through embodiments. The system includes a sound source and a hydrophone array. The sound source is used to transmit underwater acoustic signals, and the hydrophone array is used to receive and output raw signals from multiple channels. It also includes:

[0005] Several distributed processing units, each of which includes several gain conversion modules. Each gain conversion module is used to receive the raw signals from several channels, amplify their gain, and perform analog-to-digital conversion before outputting a digital signal.

[0006] The main control unit includes a sound source control module, a synchronization module, an acquisition module, and a gain correction module. The sound source control module controls the sound source to emit detection signals and correction signals in detection mode and correction mode, respectively. The synchronization module controls each distributed processing unit to synchronously amplify the gain and perform analog-to-digital conversion on the raw signals of each channel. The acquisition module acquires and outputs the digital signals of each channel. The gain correction module corrects the gain control parameters of each gain conversion module based on the digital signals output by each gain conversion module in correction mode.

[0007] The data processing unit determines the three-dimensional position and reflection intensity characteristics of the target based on the digital signals of each channel output by each gain conversion module in the detection mode.

[0008] Preferably, in detection mode, the sound source periodically emits detection signals at a preset detection time interval; in correction mode, it emits a single correction signal, and the intensity of the correction signal is much smaller than the intensity of the detection signal.

[0009] Preferably, after each sound source emits a detection signal, the synchronization module synchronously triggers each gain conversion module to synchronously amplify the gain and perform analog-to-digital conversion on the echo signal of that detection signal; after each sound source emits a correction signal, the synchronization module synchronously triggers each gain conversion module to synchronously amplify the gain and perform analog-to-digital conversion on the direct wave signal of that correction signal.

[0010] Furthermore, after each sound source emits a correction signal, the gain correction module corrects the gain control parameters of each gain conversion module through the following steps:

[0011] A1, Obtain the digital signal sequence output by the reference gain conversion module. ,in, For sequence length, The result of gain amplification and analog-to-digital conversion of the direct wave signal of the corrected signal by the reference gain conversion module;

[0012] A2, select a gain conversion module and obtain its output digital signal sequence. ,in, This is the result of the gain conversion module performing gain amplification and analog-to-digital conversion on the direct wave signal of the corrected signal;

[0013] A3, the gain correction coefficient of the gain conversion module after this correction is determined based on the following formula. :

[0014] ,

[0015] in, This refers to the gain correction factor for the gain conversion module determined after this correction. This refers to the gain correction factor for the gain conversion module, as determined after the last revision. To obtain the root mean square operation, This is the position correction factor for the gain conversion module relative to the reference gain conversion module. , These are the preset lower and upper limits for the ratio jump;

[0016] A4, the gain control parameters of the gain conversion module after this correction are determined based on the following formula. :

[0017] ,

[0018] in, These are the basic gain control parameters for this correction module. , These are the lower and upper gain limits, respectively, in dB. The number of bits in the digital-to-analog conversion;

[0019] A5: Determine whether all gain conversion modules have been traversed. If the result is no, return to step A2. If the result is yes, end the correction.

[0020] Preferably, the gain conversion module includes: a variable gain amplifier, which amplifies the original signals received by each channel of the gain conversion module based on the gain control parameters corresponding to the gain conversion module; and an analog-to-digital converter, which converts the amplified signals into digital signals and outputs them to the acquisition module.

[0021] Preferably, for the reference gain conversion module, Given a digital signal sequence output from one of its several channels; for any gain conversion module, It is the sequence of digital signals output from one of its several channels.

[0022] Preferably, for the reference gain conversion module, during each correction process, data is read from different channels. For any gain conversion module, during each correction process, data is read from its different channels. .

[0023] Preferably, the main control unit controls the sound source to enter the correction mode and corrects the gain control parameters of each gain conversion module when any of the following conditions occur: the number of times the sound source emits detection signals reaches the preset detection limit; or, the digital signals of each channel acquired by the acquisition module are in an overexposed or underexposed state.

[0024] Preferably, the distributed three-dimensional imaging sonar system based on front-end gain correction further includes a display unit for displaying the digital signals of each channel output by the acquisition module in real time.

[0025] Preferably, the main control unit also manually corrects the gain control parameters of each gain conversion module in the detection mode based on the display results of the display unit.

[0026] The distributed 3D imaging sonar system based on front-end gain correction provided in the embodiments of this application adds a correction mode in addition to the normal detection mode used by conventional 3D imaging sonar. In the correction mode, the sound source emits a single correction signal. The gain correction module updates the gain control parameters of each gain conversion module based on the processing results of the direct wave of the correction signal by each gain conversion module. This realizes dynamic adjustment of gain at the front end of the signal processing flow, so as to eliminate the problem of inaccurate digital signals output by each channel at the back end due to device inconsistency, and effectively improve the uniformity and reliability of the imaging effect. Attached Figure Description

[0027] Figure 1 This is a schematic diagram of the architecture of a distributed three-dimensional imaging sonar system based on front-end correction according to an embodiment of this application;

[0028] Figure 2 This is a schematic diagram of the architecture of the gain conversion module provided according to an embodiment of this application;

[0029] Figure 3 This is a schematic diagram of eight channels of digital signals output by a gain conversion module in one embodiment;

[0030] Figure 4 This is a schematic diagram of the 8-channel digital signal output by another gain conversion module in one embodiment;

[0031] Figure 5 This is a flowchart illustrating the gain correction process performed by the gain correction module according to an embodiment of this application.

[0032] Figure 6 This is a schematic diagram of the eight-channel digital signal output after gain correction of a gain conversion module in one embodiment. Detailed Implementation

[0033] The present application will now be further described based on preferred embodiments and with reference to the accompanying drawings.

[0034] In the description of the embodiments of this application, it should be noted that the terms "upper," "lower," "inner," and "outer," etc., indicating orientation or positional relationships based on the orientation or positional relationships shown in the accompanying drawings, or the orientation or positional relationships commonly used when the product of this application is in use, are only for the convenience of describing this application and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation, and therefore should not be construed as a limitation on this application. Furthermore, in the description of this application, the terms "first," "second," etc., are used to distinguish different units, but these are not limited by the manufacturing order, nor should they be construed as indicating or implying relative importance. Their names may differ in the detailed description and claims of this application. In addition, for ease of understanding, various components in the drawings have been enlarged or reduced, but this is not intended to limit the scope of protection of this application.

[0035] The vocabulary used in this specification is for illustrative purposes and is not intended to limit the scope of this application. It should also be noted that, unless otherwise expressly specified and limited, the terms "set," "connected," and "linked" should be interpreted broadly. For example, they can refer to a fixed connection, a detachable connection, or an integral connection; they can refer to a mechanical connection, a direct connection, or an indirect connection via an intermediate medium; or they can refer to the internal communication between two components. Those skilled in the art will understand the specific meaning of these terms in this application.

[0036] Three-dimensional imaging sonar is a device that reconstructs the three-dimensional spatial information of underwater targets by collecting echoes of active signals. It has been widely used in marine exploration, underwater archaeology, marine engineering and other fields. Its basic working principle is to emit sound waves towards the underwater target through a sound source, and receive the echo signals from multiple channels (each channel represents a two-dimensional coordinate point) through a multi-array hydrophone. The echo signals are amplified, filtered and converted from analog to digital. By using the propagation time, intensity and other information of the signals from each channel, the depth and reflection characteristics of the underwater target can be obtained. By combining the two-dimensional coordinate information of the underwater target corresponding to each receiving channel, a three-dimensional point cloud model of the target can be established.

[0037] The 3D imaging accuracy (i.e., resolution) of a 3D imaging sonar is directly related to the number of output channels of the hydrophone array. To obtain high-resolution spatial information of the target, a large number of channels of underwater acoustic signal data are required. For example, when detecting underwater terrain, it is generally required that the number of channels acquired be no less than 512. Obviously, the I / O resources of a single signal acquisition and processing device (such as the ZYNQ7020 series core board) cannot meet the needs of synchronous data acquisition and processing under such multi-channel conditions.

[0038] Furthermore, during the processing of multi-channel signals, factors such as the sensitivity differences of the hydrophone array elements, the discreteness of the parameters of the front-end analog amplifier circuit devices, and the aging of devices after long-term use will all lead to inconsistencies in the output of different channels. That is, the original signal of the same intensity will be converted into digital signals of different amplitudes after being received and amplified by different channels. This amplitude inconsistency will directly affect the amplitude calibration accuracy of the echo signal, resulting in distortion of target brightness, increased noise, and even loss of detail in the 3D imaging results. Currently, common amplitude consistency correction methods focus on amplitude compensation of the back-end digital domain signal. That is, after completing the acquisition, amplification, and analog-to-digital conversion of multi-channel signals, the amplitude difference of the digital signal of each channel is calculated using RMS, peak value, or other statistical methods. A compensation coefficient is calculated based on the amplitude difference, and the digital signal of each channel is corrected accordingly.

[0039] Since this correction is performed after the analog signal at the front end is converted and stored as a digital signal, it not only fails to correct the real-time distortion caused by the amplitude difference of the front-end analog circuit in a timely manner, but also fails to accurately correct the amplitude inconsistency through the digital signal stored at the back end when the signal is saturated or clipped.

[0040] To address the aforementioned issues, this application provides a distributed three-dimensional imaging sonar system based on front-end gain correction. This three-dimensional imaging sonar system supports the synchronous acquisition, gain, and conversion of massive channels of underwater acoustic signals. Furthermore, it can advance the correction of amplitude inconsistencies among various channels to the gain amplification stage of the front-end analog signal, ensuring that the analog signals of each channel are free from the influence of equipment differences before analog-to-digital conversion.

[0041] Figure 1 The architecture of this distributed 3D imaging sonar system based on front-end gain correction is shown in some embodiments, such as Figure 1 As shown, it includes a sound source, a hydrophone array, several distributed processing units, a main control unit, and a data processing unit.

[0042] The sound source is used to emit underwater acoustic signals, the hydrophone array is used to receive and output raw signals from multiple channels, and each distributed processing unit includes several gain conversion modules. Each gain conversion module is used to receive raw signals from several channels, amplify their gain, and perform analog-to-digital conversion before outputting digital signals.

[0043] Figure 2 The architecture of a gain conversion module according to some specific embodiments is shown, with reference to Figure 2Each gain conversion module consists of a variable gain amplifier (VGA) and an analog-to-digital converter (ADC). Each VGA can receive raw signals from several channels and, based on its corresponding gain control parameters (which are obviously the gain control parameters of the gain conversion module containing the VGA), amplifies the raw signals received from each channel. The amplified signals are then input to the ADC, which converts them into digital signals for each corresponding channel, and outputs them to the acquisition module described later.

[0044] A variable gain amplifier (VGA) is an analog amplifier capable of dynamically adjusting its amplification factor, specifically designed for gain control of analog signals. Its gain amplitude can be adjusted via gain control parameters, typically digital signals (also known as control codes) of varying magnitudes. These parameters are converted from digital to analog signals by a digital-to-analog converter (DAC) chip located inside or outside the VGA, proportionally mapped to control voltages of different amplitudes, and input to the VGA's gain control pin. This allows for smooth and continuous variation of the analog signal gain within a specific range (e.g., -40dB to 40dB). In some preferred embodiments, VGAs with multi-channel signal processing capabilities can be directly selected, such as the Analog Devices ADL5385 and Maxim Integrated MAX3263x, which, when used individually, support gain amplification for up to 8 channels of analog signals. In another preferred embodiment, multiple chips can be connected in parallel, allowing each VGA to support gain amplification for 16, 32, or more channels of the original signal.

[0045] In some preferred embodiments, an analog-to-digital converter (ADC) matching the variable gain amplifier can be selected based on its specifications, such as the number of channels. For example, when each variable gain amplifier amplifies the raw data of 8 channels, an AD7608 ADC can be selected. This ADC can perform AD conversion of 8 channels of analog signals simultaneously, with an input voltage range of 0-3.3V and a 14-bit conversion bit depth (i.e., it can convert 0-3.3V analog signals into 16384 discrete quantization levels).

[0046] It should be known that, Figure 1 , Figure 2The embodiments shown are only intended to illustrate the number of distributed processing units, the number of gain conversion modules included in each distributed processing unit, and the number of channels that each gain conversion module can process, and are not intended to limit the technical solution of this application. Those skilled in the art can select an appropriate size hydrophone array to determine the number of channels based on the required accuracy of three-dimensional imaging of underwater targets such as seabed topography, and select equipment based on the number of channels and available hardware resources to construct a suitable number of distributed processing units. For example, in some optional embodiments, the hydrophone array collects and outputs 512 channels of raw signals. These 512 channels of raw signals are processed synchronously by four distributed processing units. Each distributed processing unit is equipped with four sets of variable gain amplifiers and matching analog-to-digital converters. Each set of variable gain amplifiers and analog-to-digital converters can perform gain and analog-to-digital conversion on 32 channels of raw signals. Through this configuration, 512 channels of digital signals can be output synchronously. Obviously, as the size of the hydrophone array increases, the number of distributed processing units can be increased accordingly, or the number of variable gain amplifiers and analog-to-digital converters contained in each distributed processing unit can be increased, or the number of channels that each variable gain amplifier and analog-to-digital converter can handle can be increased, thereby enabling the processing of more channel signals.

[0047] Back Figure 1 In the embodiments of this application, the main control unit includes a sound source control module, a synchronization module, an acquisition module, and a gain correction module. The sound source control module triggers the sound source to emit a detection signal in detection mode and a correction signal in correction mode by sending different sound source control signals (including parameters such as emission frequency, duration, and intensity) to the sound source. The synchronization module is used to control each distributed processing unit to synchronously perform gain amplification and analog-to-digital conversion on the original signals of each channel. The acquisition module is used to acquire and output the digital signals of each channel after gain amplification and conversion.

[0048] In the detection mode, the multi-channel digital signal is input to the data processing unit, which determines the three-dimensional position (including two horizontal coordinates and one depth coordinate) and reflection intensity characteristics of the target based on the propagation time and intensity of the digital signal from each channel. In the correction mode, the multi-channel digital signal is acquired by the acquisition module and then read by the gain correction module. The gain correction module corrects the gain control parameters of each gain conversion module based on the digital signal output by each gain conversion module in the correction mode.

[0049] The following detailed description of the workflow of each module in the detection mode and correction mode, in conjunction with the accompanying drawings and specific embodiments, is provided.

[0050] A. Detection Mode

[0051] The detection mode is the normal operating mode of the distributed three-dimensional imaging sonar provided in this application, which is to transmit detection signals through a sound source, receive echo signals from various locations of the underwater target by a hydrophone array, and output raw signals from multiple channels. Generally, the raw signals are analog electrical signals whose amplitude varies with time.

[0052] Specifically, in the detection mode, the sound source control module periodically sends a sound source control signal corresponding to the detection mode to the sound source at a preset detection time interval to trigger the sound source to emit a detection signal. In the embodiments of this application, the detection signal emitted by the sound source can be a broadband pulse signal or a single-frequency signal with a certain duration, etc. Each emission of a detection signal can be called a Ping. The detection time interval between two adjacent Pings should satisfy the requirement that the signal echo signal of the previous Ping received by each hydrophone array element is significantly separated from the direct wave signal of the next Ping.

[0053] Since the sound source needs to emit a high-intensity detection signal to increase the echo intensity in detection mode, the result of amplifying the direct wave of the detection signal often exceeds the bit limit of the analog-to-digital converter. Therefore, the main control unit can use the synchronization module to control the analog-to-digital converters (ADCs) of each gain conversion module in each distributed processing unit to perform synchronous analog-to-digital conversion only on the gain amplification result of the echo signal part.

[0054] For example, after the sound source control module triggers the sound source to emit a Ping detection signal, the main control unit starts timing and estimates the fastest echo arrival time based on the pre-detection information of the underwater target. , distance a certain time interval before The time is determined as the detection start time for receiving the detection signal echo. ,Right now At the start of the detection, the synchronization module sends a synchronization control signal through the I / O pins that are interconnected with each distributed processing unit. After each distributed control unit detects the rising edge of the synchronization control signal, it triggers the ADC in each gain conversion module to start working synchronously, thereby ensuring that each distributed processing unit can synchronously perform gain and analog-to-digital conversion on the echo components in the original signals of each channel, and avoids collecting the gain and analog-to-digital conversion results of the direct wave components.

[0055] The gain factor of the original signal in each channel of each gain conversion module is determined by the gain control parameters of the variable gain amplifier in that module. The operation of the gain conversion module has been explained in detail above and will not be repeated here. Since the amplitude of the echo signal decreases significantly after a certain period, the main control unit generally presets a certain duration... As a detection period, The process The moment as the end of the probe At this moment, the synchronization module also controls the ADCs in each gain conversion module to stop the analog-to-digital conversion of the Ping echo signal, thereby ending the gain and analog-to-digital conversion of the original signals of each channel by each distributed processing unit.

[0056] The acquisition module can employ multi-channel digital signal acquisition devices such as FPGA-based multi-channel data acquisition cards, which are capable of simultaneously acquiring 512 or more channels of digital signals at a preset sampling rate. In some optional embodiments, the acquisition module can continuously acquire multi-channel digital signals; in other optional embodiments, the acquisition module can also, under the control of the synchronization module, only acquire signals from a single channel. Time to Data is collected and stored continuously, and then processed in the next Ping. Data will be sent out in a unified manner before arrival.

[0057] The multi-channel digital signals acquired by the acquisition module can be transmitted to the processing unit via the high-speed PCIe communication bus. The processing unit extracts information such as the propagation time and intensity of the echo signals corresponding to each channel, and finally obtains the three-dimensional position and reflection intensity characteristics of each channel.

[0058] In some optional embodiments, the processing results of the data processing unit can be displayed in a visual manner. For example, the detection target can be displayed in the form of a three-dimensional point cloud, where the position of each point cloud point can characterize the depth information of the previous echo reflection position of the detection target, and the brightness of each point cloud point reflects the reflection intensity at that position. Alternatively, the point cloud can be further converted into a mesh model or a solid model through various point cloud-based surface reconstruction algorithms. Or, the reflection intensity at each position of the detection target can be displayed in the form of a two-dimensional heat map.

[0059] In some alternative embodiments, the processing results of the data processing unit can also be saved to storage devices such as hard disk drives (HDDs), solid-state drives (SSDs), network storage devices (NAS), and dedicated data storage arrays for subsequent offline analysis, data storage, and sharing.

[0060] B. Correction Mode

[0061] In the process of multi-channel echo signal gain and acquisition using the above distributed architecture, since the system contains multiple distributed processing units, and each distributed processing unit contains several independent gain conversion modules, the output results of each gain conversion module may produce inconsistent amplitudes. This amplitude difference will directly affect the overall consistency and accuracy of the acoustic imaging results.

[0062] The main causes of this problem include: differences in gain amplifier circuit parameters, differences in ADC chip performance, differences in PCB design and wiring, and environmental and time factors such as device aging. When there are amplitude inconsistencies between channels, the imaging results will be significantly affected. For example, the contrast between light and dark in the image may be unclear, or there may be excessive differences in light and dark, thereby weakening the quality and usability of 3D imaging.

[0063] It is worth noting that this type of amplitude inconsistency does not occur completely randomly in the output results of each Ping, but rather exhibits a certain degree of stability and repeatability on a per-gain conversion module basis. That is, once a difference occurs between the output result and the accurate value of the same gain conversion module, the relative difference relationship of the digital signals output by each channel remains basically unchanged in the subsequent acquisition process of each Ping.

[0064] Figure 3 This illustration shows, in one specific embodiment, a sequence of digital signals output from eight different channels of a gain conversion module in probe mode. Figure 4 The diagram shows the digital signal sequences output from eight different channels of another gain conversion module, where the x-axis represents the sampling point and the y-axis represents the amplitude of the digital signal after analog-to-digital conversion. (Comparison) Figure 3 and Figure 4 It can be seen that the digital signals output from multiple channels of the same gain conversion module often exhibit a consistent offset; furthermore, through Figure 4 It can also be seen that once the digital signal exceeds the upper limit of the analog-to-digital conversion, all the excess amplitude can only be displayed as the maximum value.

[0065] It is evident that if the amplitude consistency of multi-channel signals is corrected directly based on the digital signals output in the detection mode, it will not only fail to correct the real-time distortion caused by the amplitude difference of the front-end analog circuit in a timely manner, but may also cause the digital signal to be clipped due to the analog signal exceeding the maximum conversion voltage of the ADC, thus making it impossible to make accurate corrections based on the true amplitude difference. In addition, if the background noise signal without echo information is collected as the correction benchmark, a large amount of storage resources will be wasted, resulting in a decrease in the proportion of effective information.

[0066] Based on the causes and characteristics of the amplitude inconsistencies in the distributed three-dimensional imaging sonar system, the embodiments of this application add a correction mode in addition to the normal detection mode. The correction mode is used to correct the gain control parameters (i.e., the mathematical form of the gain control code, or the gain control voltage obtained after digital-to-analog conversion) of each gain conversion module, thereby realizing dynamic adjustment of gain at the front end to eliminate the amplitude differences of digital signals in each channel at the back end caused by device inconsistency, effectively improving the uniformity and reliability of the imaging effect.

[0067] Specifically, in correction mode, the main control unit sends a control signal corresponding to the correction mode to the sound source through the sound source control module, triggering the sound source to emit a single correction signal. It also triggers the gain conversion modules of each distributed processing unit through the synchronization unit, so that their analog-to-digital converters synchronously receive the result of the variable gain amplifier amplifying the direct wave of the correction signal and perform analog-to-digital conversion. The multi-channel digital signal corresponding to the direct wave is acquired by the acquisition module and then read by the gain correction module. The gain correction module corrects the gain control parameters of each gain conversion module according to the digital signals output by each gain conversion module in correction mode.

[0068] Preferably, the intensity of the correction signal emitted by the sound source (e.g., the sound pressure level of the signal peak) is much smaller than the intensity of the detection signal it emits (e.g., in some embodiments, the intensity of the correction signal is 60 dB less than the intensity of the detection signal, or even lower), to avoid the amplitude of the direct wave of the correction signal received by each hydrophone exceeding the upper limit of the conversion voltage of the analog-to-digital converter after amplification, thus being clipped.

[0069] After each sound source transmits a correction signal, the direct wave signal of that correction signal received by each channel is amplified and converted into a digital signal by the corresponding gain conversion module. This digital signal is then obtained by the gain correction module, which adjusts the gain control parameters of each gain conversion module. In some preferred embodiments, such as... Figure 5 As shown, the gain correction module performs corrections through the following steps:

[0070] Step A1: Obtain the digital signal sequence output by the reference gain conversion module. ,in, For sequence length, The result of gain amplification and analog-to-digital conversion of the direct wave signal of the corrected signal by the reference gain conversion module.

[0071] Specifically, the reference gain conversion module can be pre-selected from various gain conversion modules. For example, the first gain conversion module in the distributed processing unit numbered 1 can be selected and designated as the reference gain conversion module. The processing result of the direct wave signal of the corrected signal output from one of the channels of the reference gain conversion module can then be obtained. , The length can be determined based on the duration of the correction signal and the sampling frequency.

[0072] Step A2: Select a gain conversion module and obtain its output digital signal sequence. ,in, This is the result of the gain conversion module performing gain amplification and analog-to-digital conversion on the direct wave signal of the corrected signal.

[0073] Specifically, a process similar to step A1 can be performed on each gain conversion module other than the reference gain conversion module. That is, the processing result of the direct wave signal of the corrected signal output from one of the channels of each gain conversion module is read, thereby obtaining the digital signal sequence corresponding to each gain conversion module. .

[0074] Alternatively, the reference gain conversion module can also be considered as a gain conversion module and step A2 can be performed on it. Clearly, for the reference gain conversion module, its... and Maintain consistency.

[0075] Step A3: Determine the gain correction coefficient of the gain conversion module after this correction based on the following formula. :

[0076] (1),

[0077] in, This refers to the gain correction factor for the gain conversion module determined after this correction. This refers to the gain correction factor for the gain conversion module, as determined after the last revision. To obtain the root mean square operation, This is the position correction factor for the gain conversion module relative to the reference gain conversion module. , These are the preset lower and upper limits for the ratio jump.

[0078] Specifically, in equation (1), the sequence is first obtained. , root mean square , , , This represents the results of processing the same direct wave signal by one channel in the reference gain conversion module and another channel in the current gain conversion module. Furthermore, considering the difference in distance between the hydrophone elements corresponding to the two channels and the sound source, resulting in inherent differences in attenuation when the direct wave reaches the corresponding hydrophone elements, a position correction coefficient relative to the reference gain conversion module needs to be added to the ratio of the two values. , The value can be predetermined using a hydrophone attenuation model based on the distance from the sound source to the hydrophone. When the relative distances between each hydrophone element and the sound source are not significantly different, the value can also be directly determined. Set to 1.

[0079] Since the digital signal used for each correction is the result of gain adjustment using the gain control parameters after the previous correction, the gain correction coefficient of the gain conversion module determined after the previous correction should also be taken into account when redetermining the gain correction coefficient, thus obtaining equation (1). , , The product of the three, where if this is the first revision, then... The value is set to 1.

[0080] because , The processing results of the reference gain conversion module and a specific channel within that module are taken separately. If the selected channel has a fault, causing its processing result to be incorrect, determining the gain correction coefficient based on the incorrect result will inevitably lead to the gain conversion module of that channel being unable to output accurate processing results during subsequent detection processes. Therefore, it is necessary to set a lower limit for the ratio jump. and the upper limit of the ratio jump ,exist , If the ratio changes significantly, discard the current correction result and retain the result determined by the previous correction. This serves as the gain correction coefficient obtained in this correction.

[0081] Step A4: Determine the gain control parameters of the gain conversion module after this correction based on the following formula. :

[0082] (2),

[0083] in, These are the basic gain control parameters for this correction module. , These are the lower and upper gain limits, respectively, in dB. The number of bits for the digital-to-analog conversion.

[0084] For example, in some specific embodiments, each adjustable gain amplifier employs a 14-bit digital-to-analog converter chip to convert the received gain control code (ranging from 0 to 16383) into a control voltage of corresponding amplitude, used to adjust the gain of the original signal within the range of -40 dB to +40 dB. , and The values ​​were set to -40, 40, and 14 respectively. The intensity difference between the echo signal and the detection signal during the actual detection process can be pre-assessed and determined, and then combined with the determination in step A3. This allows us to obtain the gain control parameters of the gain conversion module in subsequent detection modes after this correction. Furthermore, due to the calculation obtained from equation (2) The value is usually a non-integer floating-point number. Therefore, a rounding operation can be performed on it, such as rounding to the nearest integer or rounding down, to ensure that the gain control code sent to the digital-to-analog converter chip of the adjustable gain amplifier is an integer value.

[0085] A5: Determine whether all gain conversion modules have been traversed. If the result is no, return to step A2. If the result is yes, end the correction.

[0086] Through the above steps, the gain control parameters of each gain conversion module can be corrected each time the correction mode is entered, based on the processing results of the direct wave of the correction signal by each gain conversion module. This ensures that the signal amplitude inconsistency caused by the differences in the front-end equipment can be effectively suppressed during subsequent detection, so that the digital signals of each channel at the back end can accurately reflect the true intensity differences of the echo signal.

[0087] Figure 6 The above steps demonstrate how to... Figure 4 The result shown is the gain correction result after the gain conversion module has been applied. Similarly, the horizontal axis of each channel represents the sampling point, and the vertical axis represents the amplitude of the digital signal. By comparison... Figure 4 , Figure 6 It can be seen that the method provided in this application can realize timely correction of the amplitude of analog signal from the signal processing front end, thereby effectively suppressing the problem of inaccurate digital signals in each channel of the back end caused by inconsistent performance of front-end devices.

[0088] Furthermore, if a specific channel's data is consistently selected as the reference for calculating the gain correction coefficient during each correction process, then when the ADC chip or other components involved in that channel malfunction, the gain control parameters determined by that channel will be abnormal. This will cause other normal channels in the gain conversion module to be incorrectly amplified. Therefore, in some preferred embodiments, for the reference gain conversion module, data is read from different channels during each correction process. For any gain conversion module, during each correction process, data is read from its different channels. .

[0089] For example, during the first correction, the reference gain conversion module and the 01 channel of each gain conversion module can be used. and During the second correction, data was read from channel 02 of each gain conversion module. and This process continues until all channels participate in the gain correction of their respective gain conversion modules, thus preventing any abnormal data from a single channel from having a lasting impact on the output of the entire gain conversion module.

[0090] Since the correction of the gain control parameters is performed during normal detection, and as mentioned above, the amplitude inconsistency caused by equipment issues is not random but exhibits a certain degree of persistence and consistency after it occurs, it is not necessary to frequently switch from detection mode to correction mode. Based on the above considerations, in some preferred embodiments, the main control unit controls the sound source to enter correction mode and corrects the gain control parameters of each gain conversion module when any of the following conditions occur:

[0091] a) The number of times the sound source emits detection signals reaches the preset detection limit.

[0092] Specifically, a fixed or variable upper limit for the number of detections can be set. For example, in some optional embodiments, the upper limit for the number of detections can be set to a fixed value, such as 1000. Then, the sound source switches to correction mode and emits a correction signal every 1000 Ping detection signals. In other optional embodiments, the upper limit for the number of detections can also be set to a variable value based on the lifespan and performance degradation characteristics of the components. Within a certain working time limit, the components are likely to be in a healthy working state. At this time, the upper limit for the number of detections can be set higher, such as 10000, to avoid frequent corrections affecting normal detection efficiency. When a certain working time limit is exceeded, the probability of component damage will increase significantly. At this time, the upper limit for the number of detections can be set lower, such as 500, so as to respond to gain anomalies in a timely manner and avoid serious degradation of the output digital signal quality.

[0093] b) The digital signals of each channel acquired by the acquisition module are either overexposed or underexposed.

[0094] refer to Figure 4 When the digital output of a certain channel reaches the upper limit of its analog-to-digital conversion, clipping or saturation will occur, indicating that the signal amplitude after gain of that channel has exceeded the upper limit of analog-to-digital conversion. In the imaged 3D point cloud model, the brightness of the corresponding point reaches the highest value. Conversely, if the gain of a certain channel is insufficient, the digital output can only take a value close to 0. In the imaged 3D point cloud model, the corresponding point is in a completely dark state. When only a few channels have this phenomenon, it may be because the intensity of the actual echo signal of the corresponding channel exceeds the current processing range of the 3D sonar system. However, when more than a certain proportion (such as 1 / 5 or 1 / 10) of the digital signals of each channel acquired by the acquisition module have clipping or take values ​​close to 0, there is a high probability that there is a problem with the improper setting of the gain control parameters. In the embodiments of this application, such a state in which more than a certain proportion of the digital signals of the channel output are clipped or take small values ​​is called overexposure state and underexposure state, respectively. Obviously, after the above phenomenon occurs, a correction mode should be entered to correct the gain control parameters of each gain conversion module.

[0095] In addition, in some preferred embodiments, the distributed three-dimensional imaging sonar system based on front-end gain correction also includes a display unit. The display unit can be any device or equipment known to those skilled in the art, such as a desktop or laptop monitor, or a device with a display screen, such as a tablet or mobile phone, for real-time display of the digital signals of each channel output by the acquisition module.

[0096] As mentioned earlier, the digital signals from each channel output by the acquisition module can be visualized using 3D point clouds or 2D heatmaps. By setting up a display unit, these visualization results can be displayed in real time. When the detected target (such as the 3D seabed) displayed by the display unit exhibits insufficient brightness or excessive brightness overall, it indicates that the basic gain control parameters set for all gain conversion modules are too small or too large. Therefore, in some preferred embodiments, the main control unit can also manually adjust the gain control parameters of each gain conversion module in detection mode based on the display results from the display unit. Obviously, the specific method for manually adjusting the gain control parameters of each gain conversion module in detection mode can be to adjust the basic gain control parameters of each correction module. This allows for an overall increase or decrease in gain.

[0097] The specific embodiments of this application have been described in detail above. For those skilled in the art, several improvements and modifications can be made to this application without departing from the principle of this application, and these improvements and modifications also fall within the protection scope of the claims of this application.

Claims

1. A distributed three-dimensional imaging sonar system based on front-end gain correction, comprising a sound source and a hydrophone array, the sound source is used to emit underwater acoustic signals, and the hydrophone array is used to receive and output original signals of multiple channels; characterized in that, Also comprising: a plurality of distributed processing units, each of which comprises a plurality of gain conversion modules, each of which is configured to receive original signals of a plurality of channels, amplify the original signals by gain, and output the amplified signals as digital signals after analog-to-digital conversion; a main control unit comprising a sound source control module, a synchronization module, an acquisition module, and a gain correction module, the sound source control module being configured to control the sound source to emit detection signals and correction signals in a detection mode and a correction mode, respectively, the synchronization module being configured to control the distributed processing units to synchronously amplify the original signals of the channels by gain and perform analog-to-digital conversion, the acquisition module being configured to acquire and output the digital signals of the channels, and the gain correction module being configured to correct gain control parameters of the gain conversion modules based on the digital signals output by the gain conversion modules in the correction mode; a data processing unit configured to determine a three-dimensional position and a reflection intensity feature of a detection target based on the digital signals of the channels output by the gain conversion modules in the detection mode; the sound source is configured to periodically emit detection signals at a preset detection time interval in the detection mode; the sound source is configured to emit a single correction signal in the correction mode, and the intensity of the correction signal is much smaller than that of the detection signal; the gain correction module is configured to correct the gain control parameters of the gain conversion modules by the following steps after the sound source emits the correction signal each time: A1, obtaining the digital signal sequence output by the reference gain conversion module wherein, is the sequence length, is the result of gain amplification and analog-to-digital conversion of the direct wave signal of the modified signal by the reference gain conversion module; A2, a gain conversion module is selected, and a sequence of digital signals output by the gain conversion module is obtained wherein, is a result of gain amplification and analog-digital conversion of the direct wave signal of the secondary correction signal by the gain conversion module A3, determines the gain correction coefficient of the gain conversion module after this correction based on the following formula : ， wherein, is the gain correction factor of the gain conversion module determined in the last correction, is the gain correction factor of the gain conversion module determined in the last correction, is a root mean square operation, is a position correction factor of the gain conversion module relative to a reference gain conversion module, , are a preset ratio jump lower limit and a ratio jump upper limit. A4, the gain control parameter of the gain conversion module is determined based on the following formula : ， wherein, is the base gain control parameter for the correction module, , are the lower and upper gain limits, respectively, in dB, is the number of bits for the digital-to-analog conversion; A5, determining whether all the gain conversion modules have been traversed, if the result of the determination is no, returning to step A2, and if the result of the determination is yes, ending the correction; For the reference gain conversion module, a sequence of digital signals output for one of the channels thereof; for any one gain conversion module, a sequence of digital signals output for one of the channels thereof; For the reference gain conversion module, in each correction process, different channels thereof are read respectively ; For any one gain conversion module, in each correction process, respectively from its different channels read .

2. The distributed three-dimensional imaging sonar system based on front-end gain correction according to claim 1, wherein the synchronization module is configured to synchronously trigger the gain conversion modules to synchronously amplify the echo signals of the detection signals by gain and perform analog-to-digital conversion after the sound source emits the detection signals each time; the synchronization module is configured to synchronously trigger the gain conversion modules to synchronously amplify the direct wave signals of the correction signals by gain and perform analog-to-digital conversion after the sound source emits the correction signals each time. 3.The front-end gain correction based distributed 3D imaging sonar system according to claim 1, characterized in that, the gain conversion module comprises: a variable gain amplifier configured to amplify the original signals received by the gain conversion module by gain based on the gain control parameters corresponding to the gain conversion module; an analog-to-digital converter configured to convert the amplified signals into digital signals and output the digital signals to the acquisition module.

4. The front-end gain correction based distributed three-dimensional imaging sonar system of claim 1, wherein, the main control unit is configured to control the sound source to enter the correction mode and correct the gain control parameters of the gain conversion modules when any of the following conditions occurs: the number of times the sound source emits the detection signals reaches a preset upper limit of the detection times; the digital signals of the channels acquired by the acquisition module are in an overexposed or overdark state.

5. The distributed three-dimensional imaging sonar system based on front-end gain correction according to claim 4, wherein further comprising a display unit configured to display the digital signals of the channels output by the acquisition module in real time.

6. The distributed three-dimensional imaging sonar system based on front-end gain correction according to claim 5, wherein The main control unit also manually corrects the gain control parameter of each gain conversion module in the detection mode based on the display result of the display unit.

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