Dual-transducer underwater surveying and mapping sonar device and method thereof

Abstract

The invention relates to the technical field of underwater surveying and mapping, in particular to a dual-transducer underwater surveying and mapping sonar device and a method thereof.The device comprises a Z shaft capable of horizontally rotating and an X shaft capable of vertically swinging, and two transducers are installed at the two ends of the X shaft at an included angle of 90 degrees; the method comprises the following steps: controlling a Z axis to rotate and position step by step, and controlling an X axis to drive two transducers to perform swing scanning at each Z-axis angle; acquiring sonar echo data and correcting a scanning track in combination with the attitude information; determining a main transducer and an auxiliary transducer through frequency analysis, and constructing a compensation angle control sequence; spatial position correction and redundant structure correction are carried out on data acquired by the dual transducers, and a continuous and complete underwater three-dimensional surveying and mapping result is generated; the surveying and mapping precision and the structural stability can be improved in a disturbance environment.

Description

Technical Field

[0001] The present invention relates to the technical field of underwater surveying and mapping, and in particular to a dual-transducer underwater surveying and mapping sonar device and a method thereof. Background Art

[0002] In underwater mapping technology, sonar equipment is widely used to obtain information such as underwater terrain, structure outlines, and the spatial position of targets. Traditional systems often use a single transducer combined with a rotating mechanism for scanning. Although this can achieve sonar imaging within a certain range, in actual applications, especially in the presence of water disturbances, posture changes, or structural obstructions, problems such as scanning blind spots, discontinuous structural reconstruction, or data overlap errors are prone to occur, limiting the accuracy and efficiency of mapping. To address the above issues, this application designs a dual-transducer underwater mapping sonar device and method. Summary of the Invention

[0003] The technical problem to be solved by the present invention is to address the shortcomings of the existing technology and provide a dual-transducer underwater mapping sonar device and method thereof. The device includes a horizontally rotatable Z-axis and a vertically swingable X-axis, with two transducers mounted at 90° angles at both ends of the X-axis. The method includes: controlling the Z-axis to rotate and position in steps, controlling the X-axis to drive the two transducers to perform swing scanning at each Z-axis positioning angle; collecting sonar echo data and correcting the scanning trajectory in combination with attitude information; determining the primary and secondary transducers through frequency analysis and constructing a compensation angle control sequence; performing spatial position correction and redundant structure correction on the dual-transducer collected data to generate continuous and complete underwater three-dimensional mapping results. The present invention can improve mapping accuracy and structural stability in disturbed environments.

[0004] To achieve the above object, the present invention provides the following technical solutions:

[0005] A dual-transducer underwater mapping method is used for a dual-transducer underwater mapping sonar device, wherein the sonar device has a first transducer and a second transducer mounted at right angles on a vertical rotation mechanism, the vertical rotation mechanism including a horizontally rotatable Z-axis and a vertically swingable X-axis. The underwater mapping method comprises:

[0006] Controlling the Z-axis to rotate and position horizontally according to a preset step angle;

[0007] At each Z-axis positioning angle, controlling the X-axis to drive the first transducer and the second transducer to perform vertical scanning within a preset swing angle range to collect sonar echo data;

[0008] The sonar echo data is spatially corrected according to the rotational position information of the Z and X axes to generate the corresponding underwater three-dimensional mapping results.

[0009] Controlling the X-axis to drive the first transducer and the second transducer to perform vertical scanning within a preset swing angle range includes:

[0010] Synchronously collecting real-time attitude information during the scanning process, wherein the real-time attitude information includes pitch angle, roll angle and yaw angle;

[0011] The preset swing angle range is corrected according to the real-time posture information.

[0012] Correcting the preset swing angle range according to the real-time posture information includes:

[0013] Performing Fourier transform on the real-time attitude information to analyze the dominant frequency and amplitude of attitude disturbance;

[0014] constructing a resonance compensation angle control sequence with the same frequency or opposite frequency as the attitude disturbance according to the dominant frequency and amplitude, wherein the resonance compensation angle control sequence is a swing angle correction sequence that continuously changes with the scanning time;

[0015] During the X-axis driving of the first transducer or the second transducer for swing scanning, the resonance compensation angle control sequence is superimposed and executed.

[0016] Constructing a resonance compensation angle control sequence with the same frequency or opposite frequency as the attitude disturbance according to the dominant frequency and amplitude, including:

[0017] respectively extracting the dominant frequencies and amplitudes corresponding to the first transducer and the second transducer during the X-axis swing scanning process;

[0018] Performing local point cloud construction and grid reconstruction on the sonar echo data collected by the first transducer and the second transducer during their scanning cycles to form a corresponding local spatial structure surface;

[0019] In the local spatial structure plane, each grid unit is assigned the dominant frequency and dominant amplitude value of its source beam segment to construct a frequency-amplitude embedded grid;

[0020] Calculating the stability of the frequency amplitude distribution and the coherence of the structural surface morphology of the frequency amplitude embedded grid;

[0021] Determine the main transducer and the auxiliary transducer according to the frequency distribution stability and the structural surface morphology coherence, and construct a resonance compensation angle control sequence with the same frequency or anti-frequency as the attitude disturbance according to the scanning trajectory of the main transducer;

[0022] The resonance compensation angle control sequence is applied to the swing control of the auxiliary transducer during the next Z-axis rotation positioning.

[0023] Constructing a resonance compensation angle control sequence with the same frequency or anti-frequency as the attitude disturbance according to the dominant frequency and amplitude, further comprising:

[0024] Before the secondary transducer executes the resonance compensation angle control sequence, predicting the offset amplitude and coverage gap interval of the actual swing trajectory caused by the resonance compensation angle control sequence relative to the preset swing angle range;

[0025] The scanning angle amplitude of the main transducer is adjusted according to the offset amplitude and the coverage loss interval.

[0026] The spatial position correction of the sonar echo data according to the rotational position information of the Z axis and the X axis includes:

[0027] The first transducer and the second transducer are fixed on the device at a 90° angle to establish a spatial directional projection relationship between the scanning beams;

[0028] Constructing local spatial point clouds for the sonar echo data acquired by the first transducer and the second transducer at the same Z-axis positioning angle, and extracting boundary areas and geometric structure intersection areas;

[0029] Based on the spatial direction projection relationship, a directional conflict analysis is performed on the boundary area and the geometric structure intersection area to obtain redundant reconstruction segments;

[0030] performing a structure correction process on the redundant reconstruction segments to generate single structure information;

[0031] The single structure information and the local space point cloud are fused to generate corresponding underwater three-dimensional mapping results.

[0032] performing a structure correction process on the redundant reconstruction segment, comprising:

[0033] Constructing boundary structure surfaces respectively formed by the first transducer and the second transducer in the redundant reconstruction segment, and extracting edge lines thereof in space;

[0034] Compare the spatial orientation differences and geometric offset relationships of the two edge lines in the redundant reconstruction segments;

[0035] Fitting an intermediate geometric surface based on the spatial trend difference and the offset relationship as a structural reference surface of the redundant reconstruction segment;

[0036] Remapping operations are performed on the boundary structure surfaces to the structure reference surfaces respectively to obtain single structure information after spatial reconstruction.

[0037] A dual-transducer underwater mapping sonar device, comprising:

[0038] A vertical rotation mechanism comprising a Z-axis that can rotate horizontally and an X-axis that can swing vertically relative to the Z-axis, wherein the Z-axis and the X-axis are connected to form a two-dimensional rotation structure;

[0039] The first transducer and the second transducer are respectively installed on both sides of the X-axis at right angles and swing vertically together with the X-axis. The Z-axis drives the X-axis to rotate in steps around the vertical direction.

[0040] a control module, configured to control the Z-axis to rotate and position horizontally according to a preset step angle, and control the X-axis to drive the first transducer and the second transducer to scan within a preset swing angle range;

[0041] The data acquisition and processing module is used to collect sonar echo data of the first transducer and the second transducer in various rotational postures, and to perform spatial position correction on the sonar echo data based on the rotational position information of the Z axis and the X axis to generate corresponding underwater three-dimensional mapping results.

[0042] The control module is used to synchronously collect real-time posture information when the first transducer and the second transducer perform vertical swing scanning, and dynamically correct the swing angle range of the X-axis based on the real-time posture information.

[0043] The data acquisition and processing module is used for:

[0044] Analyzing boundary structure deviations of data collected by the first transducer and the second transducer at the same Z-axis positioning angle in a spatially overlapping region;

[0045] An intermediate fitting surface is generated based on the boundary structure deviation, and data from two transducers are mapped to the intermediate fitting surface to perform structure consistency correction.

[0046] Compared with the prior art, the present invention has the following beneficial effects:

[0047] This invention utilizes a dual-transducer structure arranged at a 90° angle, combining a horizontally rotatable Z-axis with a vertically oscillating X-axis to achieve complementary coverage in the vertical scanning direction, effectively improving the spatial integrity of underwater scanning. By collecting attitude information in real time and constructing a resonant compensation angle control sequence based on the dominant frequency and amplitude, the scanning trajectory can be dynamically corrected, enhancing disturbance resistance. BRIEF DESCRIPTION OF THE DRAWINGS

[0048] Other features, objects and advantages of the present invention will become more apparent upon reading the detailed description of non-limiting embodiments made with reference to the following drawings:

[0049] Figure 1 This is a schematic diagram of an exemplary application scenario of an embodiment of the present invention;

[0050] Figure 2 A schematic flow chart of a dual-transducer underwater mapping method according to an embodiment of the present invention;

[0051] Figure 3 This is a schematic diagram of the dual transducer arrangement principle of an embodiment of the present invention;

[0052] Figure 4 Schematic diagram of the dual-transducer rotation principle according to an embodiment of the present invention. DETAILED DESCRIPTION

[0053] The technical solutions in the embodiments of the present invention will be clearly and completely described below in conjunction with the drawings in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, rather than all the embodiments.

[0054] References to "embodiments" herein mean that a particular feature, structure, or characteristic described in connection with the embodiments may be included in at least one embodiment of the present application. The appearance of this phrase in various places in the specification does not necessarily refer to the same embodiment, nor does it refer to independent or alternative embodiments that are mutually exclusive of other embodiments. It will be understood, both explicitly and implicitly, by those skilled in the art that the embodiments described herein may be combined with other embodiments.

[0055] The embodiments of the present application provide a dual-transducer underwater mapping sonar device and method, which can achieve high-resolution, high-coverage underwater three-dimensional mapping in a dynamic environment. Specifically, the device improves the scanning coverage angle and the spatial consistency of the mapping data without increasing the complexity of the structure by orthogonally installing two transducers on a vertical rotation mechanism, combining a dual-axis collaborative control mechanism with an echo data fusion processing method.

[0056] See also Figure 1 , which is a schematic diagram of an exemplary application scenario provided in an embodiment of the present application.

[0057] like Figure 1 As shown, the dual-transducer underwater mapping sonar device is used for underwater mapping, wherein:

[0058] The dual-transducer underwater mapping sonar system includes a vertical rotation mechanism connecting a horizontally rotatable Z-axis and a vertically oscillating X-axis. The first and second transducers are mounted at either end of the X-axis, forming a 90° angle between them, covering the underwater detection area in different directions.

[0059] During operation, the Z-axis drives the entire X-axis to rotate in steps within the horizontal plane, while the X-axis drives the two transducers to oscillate back and forth around its axis, achieving scanning within a three-dimensional angle range. Because the two transducers are fixedly mounted and oriented at right angles to each other, complementary detection of the vertical scanning area can be achieved without changing the structural complexity, improving the integrity of spatial perception coverage.

[0060] Figure 1 The background of the underwater environment is shown in a streamlined manner, reflecting that the device is working in the water. The first and second transducers are set at both ends of the X-axis and move around the vertical rotation mechanism to implement three-dimensional sonar mapping tasks. Figure 1 The direction of the arrow indicates the direction of rotation.

[0061] Next, a dual-transducer underwater mapping method provided in an embodiment of the present application is introduced with reference to the accompanying drawings.

[0062] See also Figure 2 , this figure is a flow chart of a dual-transducer underwater mapping method provided in an embodiment of the present application. Figure 2 The method shown can be applied to a dual-transducer underwater mapping sonar device. Figure 2 The method shown includes the following steps S1-S3, and the specific steps are as follows:

[0063] S1: Control the Z axis to rotate horizontally according to a preset step angle;

[0064] In this embodiment, the Z-axis drives the rotating mechanism equipped with the X-axis for step-by-step angular positioning. The step angle can be set based on the mapping resolution and target area coverage requirements, for example, to 10°, 20°, or other equally spaced angles. By gradually rotating and positioning the Z-axis, the entire device can achieve full 360° coverage in the horizontal direction or prepare for equidistant scanning of a set area. This ensures that the transducer can perform precise directional sampling at each horizontal angle, providing a stable scanning reference for subsequent stereo reconstruction.

[0065] S2: At each Z-axis positioning angle, controlling the X-axis to drive the first transducer and the second transducer to perform vertical scanning within a preset swing angle range to collect sonar echo data;

[0066] In this embodiment, after each Z-axis positioning is completed, the X-axis drives the first and second transducers to oscillate back and forth around their centers within a preset angular range. The two transducers are arranged at a 90° angle, resulting in orthogonal scanning beam coverage directions. This allows for complementary coverage of a wider vertical cross-sectional area within a single oscillation cycle. This improves vertical mapping coverage efficiency per unit Z-axis angle and enables simultaneous acquisition of structural information at different angles, helping to reduce blind spots and enhance the integrity of the mapped structure.

[0067] S3: Perform spatial position correction on the sonar echo data based on the rotational position information of the Z axis and the X axis to generate the corresponding underwater 3D mapping results;

[0068] In this embodiment, spatial position correction is performed on the collected sonar echo data based on the real-time position information of each transducer on the Z and X axes. Specifically, the projection parameters of the scanning direction in three-dimensional space are constructed based on the transducer installation angle relationship. Boundary analysis and spatial conflict identification are then performed on the local point clouds collected by the two transducers. For redundant structural fragments in the intersection area, intermediate geometric surface fitting and mapping reconstruction are performed to generate a unified structural representation. This approach effectively resolves structural inconsistencies caused by transducer orientation differences and overlapping coverage, improving the boundary continuity and structural consistency of the 3D model.

[0069] Taking the dual transducer arrangement as an example, please refer to Figure 3 and Figure 4 To understand, Figure 3 This is a schematic diagram of the dual transducer arrangement principle provided in the embodiment of the present application. Figure 4 Schematic diagram of the dual-transducer rotation principle provided by an embodiment of the present invention.

[0070] Figure 3 A dual-transducer structural arrangement on the X-axis is shown, wherein the two transducers are symmetrically installed at both ends of the X-axis at an angle of 90°.

[0071] Figure 4 The following diagram shows the principle of rotational motion of the dual-transducer arrangement during underwater operation, including:

[0072] Step-by-step horizontal rotation of the Z axis: to achieve coverage in different directions;

[0073] The reciprocating vertical swing of the X-axis drives the two transducers to scan up and down;

[0074] An X-axis scan is performed at each Z-axis angle, forming a spatial scanning coverage of sectors, rings and solid angles.

[0075] Although single-transducer rotating scanning structures or multi-transducer collaborative sonar systems already exist in the prior art, they still face significant application limitations in complex underwater environments. In particular, in the presence of water flow disturbances, platform attitude changes, equipment shaking, etc., existing structures are prone to scanning trajectory deviation, data overlap confusion, or inaccurate spatial positioning. Taking the traditional single-transducer solution as an example, when the transducer performs omnidirectional mapping through a rotating mechanism, if there is a disturbance, the actual swing angle of the transducer beam will deviate from the preset trajectory, resulting in distortion of the projection of the sonar data in three-dimensional space. In this case, even if the amount of collected data is sufficient, it is difficult to form a continuous and real spatial structure, especially in large-scale terrain modeling, structural analysis, or space docking tasks, which will greatly reduce the practicality and accuracy of the system.

[0076] The dual-transducer orthogonal arrangement structure adopted in this embodiment effectively avoids the above-mentioned problems. The two transducers are installed at both ends of the same vertical swing axis at an angle of 90°, covering the vertical space orthogonally to each other. On the one hand, this structure avoids the formation of scanning blind spots, so that the angle area that may be missed by one transducer can be supplemented by the other transducer; on the other hand, in the disturbance scenario, the two sets of data have different characteristics of disturbed offset due to the difference in beam direction. This embodiment compares, fuses and dynamically adjusts the local structures collected by the two transducers, and can perform error equalization processing based on the complementarity of the main and auxiliary transducers. This geometric structure compensation mechanism is relatively rare in the prior art. It is an innovative design that achieves resistance to disturbance errors through the structural layout itself.

[0077] Furthermore, this embodiment uses frequency analysis and Fourier modeling to extract the dominant frequency and amplitude trends of the disturbance. By combining the directional differences of the dual transducers, when the scanning range of one transducer deviates due to a disturbance, structural compensation is performed using data collected by the other transducer with greater directional stability. This data is then used to generate a resonant compensation angle control sequence for angle correction in the next scan. This eliminates the need for a simple redundant configuration of the dual transducers, and instead allows them to participate in surveying and mapping decision-making as a collaborative structure with complementary and adaptive capabilities.

[0078] The specific steps of S2 are as follows:

[0079] S2.1: synchronously collecting real-time attitude information during the scanning process, wherein the real-time attitude information includes pitch angle, roll angle, and yaw angle;

[0080] Specifically, in order to ensure that the transducer can continuously maintain the spatial accuracy of its beam pointing during the swing scanning process in a dynamic underwater environment, it is necessary to obtain the spatial attitude information of the equipment platform in real time during the scanning synchronization phase. Due to unpredictable factors such as disturbances, water flow impact or slight offset of the equipment body in the underwater operating environment, the transducer will produce attitude deviations in pitch, roll and yaw angles relative to the reference reference (such as the equipment installation direction or the world coordinate system), which directly affects the projection accuracy of the sonar data collected in the spatial coordinate system. Therefore, in order to avoid geometric distortion or splicing misalignment in the data space mapping, the current attitude angle information must be synchronously recorded in each swing scanning action to support the subsequent dynamic angle correction and echo space correction process.

[0081] In this embodiment, the real-time attitude information is acquired via an inertial measurement unit (IMU) integrated into the transducer carrier body. This IMU, comprised of a gyroscope and an accelerometer, uses a six-axis sensor fusion algorithm to output spatial attitude data in three dimensions: pitch, roll, and yaw. A synchronized clock mechanism is established between the IMU and the X-axis drive control module to ensure that the attitude recording process is initiated before each swing scan begins and that the attitude trajectory information for the corresponding scan segment is stored after the scan is complete. This creates a one-to-one correspondence between the "transducer beam trajectory and attitude change curve," establishing a complete time-space mapping chain for subsequent dynamic compensation processing.

[0082] Furthermore, the attitude information not only includes the angle value at a discrete moment but also records the angular velocity trend over the continuous sampling time. This allows for determining whether the current attitude change is subject to periodic disturbances, transient offsets, or structural oscillations. This feature provides fundamental support for subsequent Fourier analysis and dominant frequency extraction, helping to identify the functional relationship between the disturbance source and the scanning deviation, and thereby establish an active compensation control mechanism. The timestamps of attitude information acquisition are synchronously aligned with the sonar sampling, serving as precise reference variables in the projection solution during the subsequent data fusion process.

[0083] S2.2: Modifying the preset swing angle range according to the real-time posture information;

[0084] Specifically, the theoretical swing angle range of the transducer when performing X-axis swing is set by the control instruction and is used to scan a fixed sector area. However, in actual operation, due to the pitch offset or dynamic change of the equipment's attitude, the actual path of the transducer's beam in space will deviate from the ideal sector trajectory. If this deviation is not dynamically corrected, the scanning result will be inconsistent with the expected area, which will manifest as errors in the projection position of the echo data, sparse overlap of the point cloud, and missing scans of local areas. Therefore, before the transducer performs the swing action, it is necessary to make advance corrections to its theoretical swing angle range based on the attitude change trend collected in the previous period, so as to guide the beam to perform actual swing scanning along an angle trajectory that is closer to the target space.

[0085] In this embodiment, after receiving attitude information, the control module first performs a fast Fourier transform (FFT) on its time series to extract the main disturbance frequency components and corresponding amplitude characteristics within the current time period. It then constructs a dominant disturbance model based on the spectral distribution. This model reflects the current platform's disturbance trends in pitch and roll and can be used to predict the direction and amplitude of beam offsets that may occur during the next round of scanning. Based on the extracted dominant disturbance frequency and angular influence range, a continuously changing resonant compensation angle control sequence is then generated. This control sequence is dynamically superimposed on the original control signal during the next round of X-axis swing, forming a "corrected swing angle trajectory." In other words, the transducer does not swing up and down along a preset fixed angle. Instead, a disturbance cancellation term is introduced into the control drive to make the actual swing path more consistent with theoretical expectations, thereby offsetting the structural offset caused by environmental disturbances.

[0086] Furthermore, to ensure controllable correction effects, the compensation amplitude and waveform morphology in the control sequence are evaluated and fed back by the data quality analysis module of the main transducer. If the attitude disturbance is severe, the control trajectory of the secondary transducer can be corrected to a greater extent. When the main transducer scan is stable and the disturbance is minimal, the compensation range can be reduced accordingly to avoid introducing additional interference. This strategy enables a dynamic control strategy based on real-time attitude perception, disturbance trend judgment, and transducer state differences. This improves data consistency and structural continuity while ensuring spatial coverage, forming a structural perception-attitude synchronization-angle adaptive scanning mechanism with strong practical feasibility and engineering application value.

[0087] The specific steps of S2.2 are as follows:

[0088] S2.2.1: Performing Fourier transform on the real-time attitude information to analyze the dominant frequency and amplitude of attitude disturbance;

[0089] Specifically, since the underwater platform is affected by environmental factors such as water flow pulsation, mechanical rebound, and wave disturbances during operation, the equipment will produce continuous dynamic offsets in the pitch, roll, and yaw directions. Although these disturbances may not cause drastic offsets immediately, they will accumulate periodically, affecting the correspondence between the actual beam path of the transducer and the theoretical angle. Traditional attitude correction methods are mostly based on static corrections based on the instantaneous angle value of the current frame, which makes it difficult to capture the frequency structure of periodic disturbances, resulting in the compensation behavior being lagging and localized, making it difficult to effectively predict future attitude trends. Therefore, this embodiment introduces Fourier transform analysis with the aim of extracting the frequency domain structure from the attitude angle sequence in the time domain, identifying the dominant disturbance frequency and periodic response amplitude, and thus providing a quantitative basis for the subsequent establishment of a dynamic resonance compensation model.

[0090] In this embodiment, a fast Fourier transform is performed on the attitude angle sequence collected by the transducer mounting platform in the period before scanning, its spectral energy distribution is calculated, and the frequency energy peak point in the spectrum is searched as the dominant disturbance frequency. Combined with the energy amplitude corresponding to the frequency, the amplitude estimate of the disturbance effect in the angle domain is further determined. This analysis process not only extracts the main frequency and secondary frequency of the disturbance behavior, but also quantifies the degree of its periodic influence. The Fourier analysis process is regularly updated in a sliding window manner to ensure that the dominant frequency always reflects the current disturbance state, with real-time and dynamic response capabilities.

[0091] To suppress the high-frequency interference introduced by sensor noise, the Fourier transform process uses windowing preprocessing. The window function can be a Hamming window or a Blackman window. This improves the clarity of the spectral boundary response and avoids false frequency peaks caused by short-term disturbances. In addition, by selecting the third- to fifth-order main frequency components for synthetic modeling, the model's ability to characterize complex disturbance structures is enhanced, providing multi-dimensional support for building more stable control curves.

[0092] S2.2.2: Construct a resonance compensation angle control sequence based on the dominant frequency and amplitude, which is co-frequency or anti-frequency with the attitude disturbance, wherein the resonance compensation angle control sequence is a swing angle correction sequence that continuously changes with the scanning time;

[0093] Specifically, after obtaining the dominant frequency and periodic amplitude of the attitude disturbance, it cannot be directly used for transducer control compensation, because the influence of the disturbance has time lag and structural nonlinearity, and an adaptive control sequence must be constructed in combination with the actual dynamic response law of the platform. In order to convert the frequency response into a control signal that can be used for angle correction, this embodiment designs a resonant compensation control method that is co-frequency or anti-frequency with the dominant disturbance frequency. This method generates a time-continuously changing angle correction trajectory, so that the actual swing path of the transducer is offset in real time during the entire scanning process to offset the attitude deviation caused by external disturbances.

[0094] In this embodiment, based on the dominant frequency and disturbance amplitude obtained in stage S2.2.1, the control module generates a continuous compensation angle control sequence that is consistent (in phase) or opposite (anti-phase) to the main frequency. This control sequence has a time step frequency consistent with the scanning step length, and constructs a modulation model using a cosine waveform. Its phase, period, and start delay are adjustable to align it with the actual swing time axis of the transducer. Depending on the directionality of the disturbance effect, if the disturbance manifests as a periodic shift that deviates from the center angle, a same-frequency and same-phase control strategy can be used; if the disturbance manifests as a symmetrical bending deviation or a structural swing, a same-frequency and anti-phase strategy can be used to achieve a control effect in which peaks and troughs cancel each other out.

[0095] S2.2.3: During the X-axis driving of the first transducer or the second transducer for swing scanning, superimpose the resonance compensation angle control sequence;

[0096] Specifically, the constructed resonant compensation angle control sequence is not executed separately as an independent drive signal, but is synchronously superimposed with the basic swing control instruction of the X-axis to form a dynamically corrected angle trajectory, which is used to actually drive the swing action of the first transducer or the second transducer. This angle correction action does not change the total scanning range of the transducer. It only applies a disturbance compensation amount to each instantaneous angle value during the swing process, thereby forming a disturbance cancellation curve that is substantially different from the original trajectory. The compensation behavior achieves angle path correction with minimal instruction changes, while maintaining the original system structure and scanning rhythm unchanged, facilitating control integration and platform adaptation.

[0097] In this embodiment, the X-axis drive motor is driven by a servo control unit, whose input angle signal source is a weighted combination of the original preset swing angle trajectory and the resonance compensation control sequence. Within each tiny time step, the system calculates the current target angle in real time based on the set angle output frequency (e.g., 20Hz to 100Hz) and transmits this value to the servo controller for precise positioning control. During the swing scanning process, the transducer's actual trajectory will exhibit slight deviations compared to its uncompensated state. However, these deviations are offset by external disturbances through the principle of interference cancellation. Ultimately, the transducer beam's pointing path in space more closely matches the theoretical scanning sector, effectively eliminating trajectory drift caused by disturbances.

[0098] The specific steps of S2.2.2 are as follows:

[0099] S2.2.2.1: Extract the dominant frequencies and amplitudes of the first transducer and the second transducer during the X-axis swing scanning process respectively;

[0100] Specifically, in order to achieve effective division of the primary and secondary transducers and construct differentiated resonance compensation strategies, it is necessary to understand the actual responses of the two transducers to posture disturbances during the scanning process. Due to the fixed 90° angle between the transducers, their beam propagation paths in space are different, and the perceived disturbance effects will have different spatial projections. Even on the same platform, their posture disturbances may appear different. To this end, the dominant disturbance frequencies and amplitude characteristics of the two transducers during the actual scanning process should be extracted separately, providing a basis for subsequent personalized modeling and structural judgment.

[0101] In this embodiment, independent frequency-domain analysis paths are used to perform fast Fourier transforms on the angle control records and attitude sensor output information of the first and second transducers during their respective scanning cycles, obtaining their respective dominant frequency peaks and amplitude characteristics. The frequency and amplitude extraction process is performed based on the attitude change time series. The extracted results are aligned with the time axis of the sonar scanning trajectory to establish a one-to-one data mapping between the transducer beam and the disturbance response. This method can reveal the disturbance stability of different transducers under the current environmental disturbance, laying a parameter foundation for subsequent structural stability judgment of the primary and secondary transducers.

[0102] Furthermore, in order to avoid spectral offset caused by short-term high-frequency noise or underwater transient waves, a three-window resampling verification mechanism is used to perform time period stability verification on the main components of the spectrum of each transducer, and only the disturbance components with interference persistence exceeding three consecutive scanning cycles are retained to ensure that the extraction results have engineering stability and can support the adaptive update of the dynamic control system.

[0103] S2.2.2.2: Perform local point cloud construction and mesh reconstruction on the sonar echo data collected by the first transducer and the second transducer during their scanning cycles to form a corresponding local spatial structure surface;

[0104] Specifically, to achieve geometric structural reference during the primary and secondary transducer determination process, the raw sonar data collected by the transducers must be restored to a recognizable spatial structural surface representation. Sonar scan results are essentially sequences of range echoes, which must undergo coordinate transformation, spatial interpolation, and point cloud splicing to form a point cloud morphology suitable for structural analysis in three-dimensional space. To this end, this step reconstructs the scanning echoes obtained by the transducer within a single oscillation cycle to construct a local spatial point cloud, and further performs triangulated mesh reconstruction to form a local structural surface with a topological structure.

[0105] In this embodiment, the collected sonar data is first converted into a scan sector point set in a polar coordinate system based on the X-axis swing angle and the Z-axis positioning angle. This is then mapped to a Cartesian coordinate system using a conversion function to form a discrete point cloud. This point cloud is then meshed using a normal-guided triangulation method to generate a local mesh structure with spatial topology. This structured surface serves as the geometric carrier for subsequent frequency embedding and coherence analysis. Each transducer generates a local structured surface for its own scanning trajectory, preserving its geometric statistical characteristics, such as point cloud density distribution and patch normal trends, to support subsequent structural comparison.

[0106] Furthermore, in order to improve the accuracy of edge areas, an adaptive patch expansion mechanism is used in the grid reconstruction process to perform weighted fitting on the slope change curvature of the scanning sector boundary, so that the boundary area can still maintain spatial coherence in the presence of interference data, laying a structural foundation for subsequent directional analysis and overlap judgment.

[0107] S2.2.2.3: In the local spatial structure plane, assign to each grid cell the dominant frequency and dominant amplitude value of the beam segment from which it originates, and construct a frequency-amplitude embedded grid;

[0108] Specifically, after obtaining the local structural surface, in order to parametrically incorporate the effects of disturbances into the structural analysis process, it is necessary to associate frequency characteristics with spatial structural data, thereby constructing a joint frequency-amplitude model of the structure that incorporates information about the disturbances originating from the beam. Traditional mesh data only reflects geometric form and cannot capture the extent to which the transducer was affected by disturbances during the acquisition process. Therefore, this step embeds frequency and amplitude information as additional attributes into the mesh cells, forming a frequency-amplitude embedded mesh.

[0109] In this embodiment, each structural surface grid cell locates and traces back its source transducer and scanning time interval based on the beam number of its formation point in the scanning sequence, and then extracts the dominant disturbance frequency and amplitude analyzed for that section of the scanning path, and embeds this pair of parameters as the disturbance metadata of the grid cell. In this way, a visual frequency and amplitude distribution layer is formed on the entire structural surface, revealing the degree and pattern of disturbance experienced by each area during the structural scanning process. This joint embedded structure will provide a key reference dimension for subsequent stability analysis and selection of primary and secondary transducers.

[0110] S2.2.2.4: Calculate the stability of the frequency distribution and the coherence of the structural surface morphology of the frequency embedded grid;

[0111] Specifically, to quantitatively assess the reliability of the two transducer structural surfaces, it is necessary to separately calculate the stability of their frequency-amplitude perturbation responses and the geometric coherence of the mesh structure, thereby constructing a set of composite structure-frequency evaluation metrics. Frequency-amplitude distribution stability characterizes the consistency of perturbations during transducer sampling, specifically whether the fluctuations are severe and random. Structural surface coherence, on the other hand, assesses whether the point cloud mesh contains folds, disconnected boundaries, or sudden slope changes.

[0112] In this embodiment, frequency stability is calculated by analyzing the frequency gradient, standard deviation, and fluctuation trend within the grid area to construct a frequency consistency scoring model. Structural surface coherence is evaluated by building a morphological consistency matrix based on indicators such as the normal vector variation trend, boundary closure, and internal angle continuity between grid segments. A comprehensive structural quality evaluation result for each transducer in the current cycle is obtained through the combined calculation of these two factors.

[0113] S2.2.2.5: Determine the main transducer and auxiliary transducer based on the stability of the frequency distribution and the coherence of the structural surface morphology, and construct a resonance compensation angle control sequence with the same frequency or anti-frequency as the attitude disturbance based on the scanning trajectory of the main transducer;

[0114] Specifically, because two transducers may exhibit different stability and data quality due to different directionality when scanning the same area, it is necessary to divide them into primary and secondary roles based on the aforementioned evaluation results to make the reference source for compensation control more reliable. The primary transducer is used to provide structural standards, while the secondary transducer performs directional compensation. Under the premise of a fixed transducer structure and synchronized scanning angles, this division allows for larger angle corrections to be performed on the secondary transducer, while the primary transducer serves as a stable reference to maintain the original scanning trajectory, thereby achieving asymmetric optimization in the control strategy.

[0115] In this embodiment, the control module compares the scores of the two transducers' frequency-amplitude embedded grids, preferentially selecting the one with the higher score as the primary transducer. Based on its scanning trajectory and attitude response, it constructs a resonant compensation angle control sequence. This sequence can be combined with the aforementioned dominant frequency modeling method to further enhance the compensation sequence's adaptability in spatial directions, achieving a higher-quality disturbance mitigation mechanism.

[0116] S2.2.2.6: Apply the resonance compensation angle control sequence to the swing control of the secondary transducer during the next Z-axis rotation positioning;

[0117] The specific steps for S3 are as follows:

[0118] S3.1: Using a structural mounting method in which the first transducer and the second transducer are fixed at a 90° angle on the device, a spatial directional projection relationship between the scanning beams is established;

[0119] Specifically, the structural design in which two transducers are installed at a 90° angle is one of the key innovations of this embodiment. Traditional multi-transducer solutions generally adopt the same direction or parallel arrangement, which easily causes strong overlap of beam directions and poor complementarity of spatial regions, resulting in occlusion blind spots or structural overlap in complex scenarios. In this structure, the first transducer and the second transducer are installed in opposite directions through the X-axis, and their respective main axes intersect in the vertical plane to form an orthogonal structure, ensuring that at the same Z-axis positioning angle, the two transducers can complementarily scan the same measurement area from two directions, providing a dual-perspective data source. In order to achieve subsequent spatial point cloud alignment and conflict area identification, it is necessary to establish a directional geometric model of the transducer beam in space, that is, a projection relationship.

[0120] In this embodiment, based on known structural parameters of the device, such as the relative transducer arrangement angle, installation position, and swing angle limit range, the spatial scanning cone axis direction and angular range of the two transducers in a given Z-axis posture are calculated to form a theoretical beam intersection spatial model. This model defines the location of intersection between the two beams in three-dimensional space, the angular overlap region, and its extended boundary, which is used for subsequent positioning and identification of redundant scanning data. The directional projection relationship model uses the transducer center position as the origin and the angle between the swing axis and the Z-axis as the projection variable to construct the propagation cone orientation representation in a three-dimensional Cartesian coordinate system.

[0121] S3.2: Constructing local spatial point clouds for the sonar echo data acquired by the first transducer and the second transducer at the same Z-axis positioning angle, and extracting boundary areas and geometric structure intersection areas;

[0122] Specifically, because the two transducers scan in different spatial directions at the same Z-axis positioning angle, the data they collect has different spatial perspectives. However, some areas are repeatedly scanned within the intersection of the two transducer beams. These areas are defined as geometric structure intersections. To accurately identify these areas and prepare for subsequent redundancy removal and reconstruction, the data from the two transducers must be converted into spatial point clouds and the intersection boundary areas extracted.

[0123] In this embodiment, the raw echo data of the first and second transducers are timestamped and converted into local point cloud sets. The point clouds are transformed using the transducer spatial coordinate system and projection model, projecting them into a unified world coordinate system. After the point cloud is generated, the edge regions of the point cloud are identified based on a boundary density analysis algorithm, i.e., the regions with prominent gradient changes at the boundaries of each point cloud. The intersection segments are determined by comparing the degree of overlap and the normal angle of the two transducer edge regions in three-dimensional space. These intersection segments are key areas for subsequent spatial conflict judgment and structural fusion.

[0124] S3.3: Based on the spatial directional projection relationship, perform directional conflict analysis on the boundary area and the geometric structure intersection area to obtain redundant reconstructed segments;

[0125] Specifically, while the point cloud data from the two transducers in the intersection area are complementary, if they are directly merged without prior identification, redundancy, reconstruction errors, and even structural collapse can easily occur. Especially in the presence of disturbances in the underwater environment and inconsistent scanning directions, the boundary structures constructed by the two transducers may exhibit inconsistent spatial orientations or relative offsets in the intersection section, leading to error accumulation. Therefore, it is necessary to perform directional conflict analysis on the point cloud boundaries in the intersection area to identify areas of data that produce geometric contradictions or duplicate definitions in the spatial structure and treat them separately as redundant fragments.

[0126] In this embodiment, a conflict identification algorithm based on the spatial projection direction angle is employed. The angle difference between the boundary normal vectors of the two transducers' corresponding point clouds and the spatial distance error are calculated. Regions exceeding a preset tolerance (e.g., a 10° angle or a 0.3m distance) are marked as directional conflict segments. Subsequently, the data density variation and boundary coherence within the region are further determined to determine whether they constitute redundant reconstruction segments. All conflicting regions are marked and stored in a "redundant point set" data pool for subsequent processing by the structure reconstruction module. This operation essentially separates the error segments caused by the inconsistency between the two directional structures from the main structure, a key step in ensuring the geometric consistency of the surveying and mapping model.

[0127] S3.4: performing structure correction processing on the redundant reconstruction segments to generate single structure information;

[0128] Specifically, redundant reconstructed segments are essentially structural ghosting caused by the difference between the two viewpoints. Directly removing or simply merging them will lead to problems such as missing boundaries and structural fractures. To maximize data utilization and maintain structural stability, redundant segments need to be geometrically corrected and remapped into a unified structural representation. This involves constructing an "intermediate structural surface" for fusion.

[0129] In this embodiment, boundary surfaces are constructed from the redundant segments of the first and second transducers, their spatial edge lines are extracted, and an intermediate geometric surface is fitted within the conflicting interval as a reference surface for structural merging. The point cloud data on the two structural surfaces is then reprojected onto this intermediate surface, eliminating the spatial differences caused by the angle. The positions are then adjusted based on the principle of nearest normal mapping to achieve spatial uniformity in the projected data. The structurally corrected point cloud is marked as a fused patch, replacing the original bidirectional conflicting segment and reintegrated into the structural synthesis process.

[0130] S3.5: Fusing the single structure information with the local spatial point cloud to generate a corresponding underwater three-dimensional mapping result;

[0131] Specifically, after structural correction is completed and unified meshes are generated, they must be merged with the original local point cloud data within the non-intersecting areas to form a complete spatial structure representation. The fusion process requires addressing the splicing of structural interfaces, the selection priority of overlapping point cloud areas, and the calibration consistency of global coordinates to ensure that the final constructed 3D model has spatial continuity, geometric consistency, and structural visibility.

[0132] In this embodiment, the structurally corrected fused patch and the local point cloud data of each transducer's non-intersecting area are stitched together in a unified coordinate system. A patch priority strategy is adopted to prioritize the primary transducer boundary data and use the secondary transducer data to complete the structural voids. A spatially weighted averaging mechanism is incorporated into the point cloud fusion process to smooth out differences in transition point density and eliminate structural gaps. The fused model is verified for curvature consistency and topological closure to confirm the overall structural integrity. The final output is a standard-format 3D mapping model file for subsequent analysis or visualization platforms.

[0133] The specific steps of S3.4 are as follows:

[0134] S3.4.1: Construct boundary structure surfaces formed by the first transducer and the second transducer in the redundant reconstruction segment, and extract their edge lines in space;

[0135] S3.4.2: Compare the spatial orientation differences and geometric offset relationships of the two edge lines in the redundant reconstructed segments;

[0136] S3.4.3: Fit an intermediate geometric surface based on the spatial orientation difference and the offset relationship as a structural reference surface for the redundant reconstruction segment;

[0137] S3.4.4: Perform remapping operations on the boundary structure surfaces to the structure reference surfaces respectively to obtain single structure information after spatial reconstruction.

[0138] A dual-transducer underwater mapping sonar device, comprising:

[0139] A vertical rotation mechanism comprising a Z-axis that can rotate horizontally and an X-axis that can swing vertically relative to the Z-axis, wherein the Z-axis and the X-axis are connected to form a two-dimensional rotation structure;

[0140] The first transducer and the second transducer are respectively installed on both sides of the X-axis at right angles and swing vertically together with the X-axis. The Z-axis drives the X-axis to rotate in steps around the vertical direction.

[0141] a control module, configured to control the Z-axis to rotate and position horizontally according to a preset step angle, and control the X-axis to drive the first transducer and the second transducer to scan within a preset swing angle range;

[0142] The data acquisition and processing module is used to collect sonar echo data of the first transducer and the second transducer in various rotational postures, and to perform spatial position correction on the sonar echo data based on the rotational position information of the Z axis and the X axis to generate corresponding underwater three-dimensional mapping results.

[0143] The control module is further configured to synchronously collect real-time posture information when the first transducer and the second transducer perform vertical swing scanning, and dynamically correct the swing angle range of the X-axis based on the real-time posture information.

[0144] The data acquisition and processing module is further used to:

[0145] Analyzing boundary structure deviations of data collected by the first transducer and the second transducer at the same Z-axis positioning angle in a spatially overlapping region;

[0146] An intermediate fitting surface is generated based on the boundary structure deviation, and data from two transducers are mapped to the intermediate fitting surface to perform structure consistency correction.

[0147] Although the embodiments of the present invention have been shown and described above, it will be understood that the above embodiments are illustrative and are not to be construed as limitations on the present invention. A person skilled in the art may change, modify, replace and modify the above embodiments within the scope of the present invention.

Claims

1. A dual-transducer underwater mapping method for a dual-transducer underwater mapping sonar device, wherein the sonar device has a first transducer and a second transducer mounted at right angles on a vertical rotation mechanism, the vertical rotation mechanism including a horizontally rotatable Z-axis and a vertically swingable X-axis, characterized in that: The underwater surveying and mapping method comprises: Controlling the Z-axis to rotate and position horizontally according to a preset step angle; At each Z-axis positioning angle, controlling the X-axis to drive the first transducer and the second transducer to perform vertical scanning within a preset swing angle range to collect sonar echo data; The sonar echo data is spatially corrected according to the rotational position information of the Z and X axes to generate the corresponding underwater three-dimensional mapping results.

2. A dual-transducer underwater surveying and mapping method according to claim 1, characterized in that: Controlling the X-axis to drive the first transducer and the second transducer to perform vertical scanning within a preset swing angle range includes: Synchronously collecting real-time attitude information during the scanning process, wherein the real-time attitude information includes pitch angle, roll angle and yaw angle; The preset swing angle range is corrected according to the real-time posture information.

3. A dual-transducer underwater surveying and mapping method according to claim 2, characterized in that: Correcting the preset swing angle range according to the real-time posture information includes: Performing Fourier transform on the real-time attitude information to analyze the dominant frequency and amplitude of attitude disturbance; constructing a resonance compensation angle control sequence with the same frequency or opposite frequency as the attitude disturbance according to the dominant frequency and amplitude, wherein the resonance compensation angle control sequence is a swing angle correction sequence that continuously changes with the scanning time; During the X-axis driving of the first transducer or the second transducer for swing scanning, the resonance compensation angle control sequence is superimposed and executed.

4. A dual-transducer underwater surveying and mapping method according to claim 3, characterized in that: Constructing a resonance compensation angle control sequence with the same frequency or opposite frequency as the attitude disturbance according to the dominant frequency and amplitude, including: respectively extracting the dominant frequencies and amplitudes corresponding to the first transducer and the second transducer during the X-axis swing scanning process; Performing local point cloud construction and grid reconstruction on the sonar echo data collected by the first transducer and the second transducer during their scanning cycles to form a corresponding local spatial structure surface; In the local spatial structure plane, each grid unit is assigned the dominant frequency and dominant amplitude value of its source beam segment to construct a frequency-amplitude embedded grid; Calculating the stability of the frequency amplitude distribution and the coherence of the structural surface morphology of the frequency amplitude embedded grid; Determine the main transducer and the auxiliary transducer according to the frequency distribution stability and the structural surface morphology coherence, and construct a resonance compensation angle control sequence with the same frequency or anti-frequency as the attitude disturbance according to the scanning trajectory of the main transducer; The resonance compensation angle control sequence is applied to the swing control of the auxiliary transducer during the next Z-axis rotation positioning.

5. A dual-transducer underwater surveying and mapping method according to claim 4, characterized in that: Constructing a resonance compensation angle control sequence with the same frequency or anti-frequency as the attitude disturbance according to the dominant frequency and amplitude, further comprising: Before the secondary transducer executes the resonance compensation angle control sequence, predicting the offset amplitude and coverage gap interval of the actual swing trajectory caused by the resonance compensation angle control sequence relative to the preset swing angle range; The scanning angle amplitude of the main transducer is adjusted according to the offset amplitude and the coverage loss interval.

6. A dual-transducer underwater surveying and mapping method according to claim 1, characterized in that: The spatial position correction of the sonar echo data according to the rotational position information of the Z axis and the X axis includes: The first transducer and the second transducer are fixed on the device at a 90° angle to establish a spatial directional projection relationship between the scanning beams; Constructing local spatial point clouds for the sonar echo data acquired by the first transducer and the second transducer at the same Z-axis positioning angle, and extracting boundary areas and geometric structure intersection areas; Based on the spatial direction projection relationship, a directional conflict analysis is performed on the boundary area and the geometric structure intersection area to obtain redundant reconstruction segments; performing a structure correction process on the redundant reconstruction segments to generate single structure information; The single structure information and the local space point cloud are fused to generate corresponding underwater three-dimensional mapping results.

7. A dual-transducer underwater surveying and mapping method according to claim 6, characterized in that: performing a structure correction process on the redundant reconstruction segment, comprising: Constructing boundary structure surfaces respectively formed by the first transducer and the second transducer in the redundant reconstruction segment, and extracting edge lines thereof in space; Compare the spatial orientation differences and geometric offset relationships of the two edge lines in the redundant reconstruction segments; Fitting an intermediate geometric surface based on the spatial trend difference and the offset relationship as a structural reference surface of the redundant reconstruction segment; Remapping operations are performed on the boundary structure surfaces to the structure reference surfaces respectively to obtain single structure information after spatial reconstruction.

8. A dual-transducer underwater mapping sonar device, used to implement a dual-transducer underwater mapping method according to any one of claims 1 to 7, characterized in that: The sonar device comprises: A vertical rotation mechanism comprising a Z-axis that can rotate horizontally and an X-axis that can swing vertically relative to the Z-axis, wherein the Z-axis and the X-axis are connected to form a two-dimensional rotation structure; The first transducer and the second transducer are respectively installed on both sides of the X-axis at right angles and swing vertically together with the X-axis. The Z-axis drives the X-axis to rotate in steps around the vertical direction. a control module, configured to control the Z-axis to rotate and position horizontally according to a preset step angle, and control the X-axis to drive the first transducer and the second transducer to scan within a preset swing angle range; The data acquisition and processing module is used to collect sonar echo data of the first transducer and the second transducer in various rotational postures, and to perform spatial position correction on the sonar echo data based on the rotational position information of the Z axis and the X axis to generate corresponding underwater three-dimensional mapping results.

9. The dual-transducer underwater mapping sonar device according to claim 8, characterized in that: The control module is used to synchronously collect real-time posture information when the first transducer and the second transducer perform vertical swing scanning, and dynamically correct the swing angle range of the X-axis based on the real-time posture information.

10. The dual-transducer underwater mapping sonar device according to claim 8, characterized in that: The data acquisition and processing module is used for: Analyzing boundary structure deviations of data collected by the first transducer and the second transducer at the same Z-axis positioning angle in a spatially overlapping region; An intermediate fitting surface is generated based on the boundary structure deviation, and data from two transducers are mapped to the intermediate fitting surface to perform structure consistency correction.

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