Self-adaptive underwater vehicle suitable for estuary high-salinity and high-turbidity environment and detection method

Abstract

The invention relates to the technical field of underwater vehicle detection, and discloses a self-adaptive underwater vehicle suitable for an estuary high-salinity and high-turbidity environment and a detection method, and the vehicle integrates an environment perception module, a density inversion module, an acoustic configuration module, a buoyancy control module, a silent observation module and the like. By fusing the temperature-salinity-depth and acoustic backscattering data, the additional density caused by the suspended sediment is inverted, and a total environment density parameter is constructed; according to the parameter, a variable buoyancy system is driven by feedforward control logic to adjust the drainage volume, and buoyancy fluctuation caused by density abrupt change is counteracted in advance. The system dynamically switches the acoustic detection frequency according to the local turbidity and corrects the time-varying gain curve; cutting off propelling power in a neutral hovering state to enter a silent drifting mode, and executing sediment flux observation without mechanical disturbance. According to the invention, the problems of buoyancy adjustment lag, acoustic signal attenuation and propulsion disturbance in the complex water body of the estuary are effectively solved, and the dynamic stability and the observation data quality are remarkably improved.

Description

TECHNICAL FIELD

[0001] The present application relates to the technical field of underwater vehicle detection, in particular to a self-adaptive underwater vehicle suitable for estuary high-salt and high-turbidity environment and a detection method. BACKGROUND

[0002] The estuary region is the intersection of rivers and oceans, with strong physical, chemical and geological coupling characteristics. There are significant salt-freshwater mixing processes and high-intensity sediment transport phenomena in the water body, forming special dynamic structures such as saltwater wedge and maximum turbidity zone. Using autonomous underwater vehicles to conduct fine observation in this area can obtain high spatiotemporal resolution of water stratification structure and material transport flux data, which is of great significance to understanding the dynamic process of estuary and the mechanism of sediment transport.

[0003] The existing underwater vehicles usually carry standard payloads such as temperature-salinity-depth instruments and acoustic Doppler current profilers when performing such observation tasks. The conventional operation mode is to use the conductivity, temperature and pressure data collected by the temperature-salinity-depth instrument to calculate the fluid density based on the international seawater equation, and then control the buoyancy adjustment system or vertical thruster to maintain the navigation depth. At the same time, the acoustic detection equipment usually presets fixed working frequency and gain parameters, and measures the water flow rate and suspended matter during navigation. The data collection of each sensor is usually only based on time stamp for simple linear alignment.

[0004] However, the traditional density calculation method of the existing self-adaptive underwater vehicle only considers the contribution of dissolved salt, ignoring the additional density introduced by high-concentration suspended sediment, resulting in physical deviation in buoyancy trim calculation. The underwater vehicle is prone to vertical instability when crossing the density current or the interface of the floating mud layer. The fixed parameters of the acoustic equipment cannot take into account the spatial non-uniformity of the estuary turbidity. In the high-turbidity core area, the signal is often lost due to excessive attenuation of the sound wave, and the fixed gain compensation cannot offset the strong absorption effect of suspended particles. In addition, the continuous active propulsion of the underwater vehicle will generate mechanical turbulence and shear force, which will destroy the structure of the fragile sediment floc and the in-situ flow field, resulting in distorted flux observation data. Therefore, the present application provides a self-adaptive underwater vehicle suitable for estuary high-salt and high-turbidity environment and a detection method to solve the problems existing in the prior art. SUMMARY

[0005] In view of the deficiencies of the prior art, the present application provides a self-adaptive underwater vehicle suitable for estuary high-salt and high-turbidity environment and a detection method, which solves the problem that the existing underwater vehicle is prone to buoyancy adjustment lag, acoustic detection signal severe attenuation and mechanical disturbance of suspended sediment laminar flow structure due to the sharp change of density gradient in the estuary high-salinity and high-turbidity complex water environment.

[0006] To achieve the above object, the present application is implemented by the following technical solutions: The present application provides a self-adaptive underwater vehicle suitable for estuary high-salt and high-turbidity environment, comprising an environment perception module, a density inversion module, an acoustic configuration module, a buoyancy control module, a silent observation module and a navigation monitoring module interacting with a central control unit through a data bus; The environment perception module is used for collecting and outputting multi-dimensional environment reference data aligned in space-time; The density inversion module is used for superimposing the additional density component of suspended sediments inverted from acoustic backscattering intensity on the basis fluid density to generate a total environment density parameter representing the real buoyancy characteristics of the current water layer; The acoustic configuration module is used for establishing a turbidity-acoustic parameter linkage mechanism, and dynamically adjusting the transmission frequency and gain curve slope of the acoustic device according to the local turbidity and the inverted additional density component of suspended sediments; The buoyancy control module is used for feeding forward calculating the target displacement volume according to the total environment density parameter and driving the variable buoyancy system to act to offset the buoyancy fluctuation by using the Archimedes principle; The silent observation module is used for generating a propeller shutdown instruction and triggering a silent flux observation mode after determining the neutral hovering state of the vertical propeller power being zero and the depth being stable; The navigation monitoring module is used for monitoring the trajectory during the silent drift, and forcibly taking over the propeller control when the safety boundary is touched.

[0007] Preferably, the environment perception module comprises a temperature-salinity-depth detection unit installed at the bow of the vehicle, an optical turbidity detection unit installed on the surface of the vehicle, and an acoustic detection unit installed at the abdomen of the vehicle; The environment perception module is provided with a space-time alignment mechanism based on hardware triggering, which sends a synchronous trigger pulse through the central control unit and establishes a space compensation buffer based on the navigation speed; The space compensation buffer is used for reading the real-time navigation speed, calculating the time difference of water quality points flowing from the bow to the abdomen, applying time delay compensation to the data collected by the temperature-salinity-depth detection unit, and aligning the profile data collected by the acoustic detection unit at the same time on the spatial element.

[0008] Preferably, the density inversion module comprises a basis fluid density calculation unit, a suspended sediment concentration inversion unit and a total density synthesis unit; The basis fluid density calculation unit is used for converting the conductivity into practical salinity according to the practical salinity scale, combining the on-site temperature and hydrostatic pressure, and calculating the pure liquid phase density without suspended particles as the basis fluid density through the international seawater state equation; The suspended sediment concentration inversion unit is configured to use the volume backscattering strength to invert the suspended sediment mass concentration of each depth measuring point according to a pre-stored acoustic inversion model, and correct the near-field inversion result using the local turbidity value, wherein the acoustic inversion model describes a logarithmic linear relationship between the volume backscattering strength and the suspended sediment mass concentration. The total density synthesis unit is configured to calculate an additional density component caused by the suspended sediment mass according to a mixture density principle, and add the additional density component to the base fluid density to obtain a total environmental density parameter, wherein the additional density component is determined by a ratio relationship of the suspended sediment mass concentration, the base fluid density and the average physical density of the suspended sediment particles.

[0009] Preferably, the acoustic configuration module comprises a turbidity threshold discrimination unit, a frequency switching control unit and a time-varying gain dynamic correction unit. The turbidity threshold discrimination unit is configured to use a Schmitt trigger logic with hysteresis to compare the local turbidity value with a pre-set low turbidity switching threshold and a high turbidity switching threshold to determine whether the current water area is a clear water area or a high turbidity area. The frequency switching control unit is configured to drive the acoustic detection device to work in a high-frequency high-resolution mode when the current water area is determined to be a clear water area, and to switch the acoustic detection device to a low-frequency strong penetration mode and increase the emission source level voltage when the current water area is determined to be a high turbidity area. The time-varying gain dynamic correction unit is configured to calculate a total sound absorption coefficient according to the current working frequency and the inverted suspended sediment concentration, wherein the total sound absorption coefficient includes a pure seawater sound absorption coefficient and an additional sound attenuation coefficient caused by the suspended sediment.

[0010] Preferably, the buoyancy control module comprises a drive controller and a variable buoyancy system adopting a closed hydraulic oil discharge structure, wherein the variable buoyancy system comprises a rigid oil storage tank, a bidirectional hydraulic pump set and an external elastic oil bag. The drive controller is provided with a volume trim algorithm unit, wherein the volume trim algorithm unit adopts a feedforward control strategy based on the density parameter, calculates a target displacement volume required to maintain neutral buoyancy according to a ratio of the total mass of the vehicle to the total environmental density parameter, and calculates a difference between the target displacement volume and the current actual displacement volume to generate a volume adjustment amount. When the volume adjustment amount indicates that the displacement volume needs to be increased, the bidirectional hydraulic pump set is driven to inject oil into the external elastic oil bag; when it indicates that the displacement volume needs to be reduced, the bidirectional hydraulic pump set is driven to pump oil from the external elastic oil bag, and physical trimming is completed before the vehicle contacts the density jump layer interface.

[0011] Preferably, the silent observation module comprises a neutral balance state discrimination unit and a silent control sequence execution unit. The neutral balance state judging unit is configured to adopt a multi-parameter joint convergence criterion to integrate the normalized power of the vertical propeller in a sliding observation time window, and set a neutral hovering state flag when the integral value is lower than a preset zero noise threshold and the depth variation rate in the same period converges to zero. The silence control sequence executing unit is configured to forcibly cut off the power supply circuit of the horizontal propeller and the vertical propeller to eliminate mechanical turbulence and electromagnetic noise, and control the acoustic detection device to open the pulse coherent processing function to observe the flocculation and sedimentation process of the suspended sediment by using the stream drift characteristics of the vehicle, in response to the neutral hovering state flag.

[0012] Preferably, the navigation monitoring module comprises a drift trajectory calculating unit and a safety boundary judging unit. The drift trajectory calculating unit is configured to calculate and output the geographic coordinates and the height above the bottom of the vehicle by using the accelerometer and gyroscope data of the inertial navigation assembly for pure inertial integration calculation and introducing the bottom speed data of the Doppler speedometer as a measurement update value during the shutdown of the propulsion system. The safety boundary judging unit is configured to calculate the comprehensive safety margin of the current position of the vehicle and the preset geographic fence boundary and the lower threshold of the safety height by using an electronic fence algorithm based on the Euclidean distance. When the comprehensive safety margin is not positive, the emergency takeover control unit is triggered to perform the operation of terminating the silence observation, restarting the propeller and leaving the dangerous area.

[0013] The second aspect of the present application provides a self-adaptive underwater vehicle detection method suitable for estuary high-salt and high-turbidity environments, comprising the following steps: S1, collecting the conductivity, temperature, pressure, local turbidity and acoustic volume backscatter intensity data synchronously during the navigation process, and performing time delay compensation on the data of different position sensors based on the navigation speed; S2, calculating the total environmental density containing the contribution of suspended sediment based on the collected data, and judging whether to switch the acoustic detection frequency and correct the gain parameter according to the local turbidity; S3, calculating the target displacement volume by using the Archimedes principle under the feedforward control logic according to the total environmental density parameter, and driving the variable buoyancy system to adjust the actual displacement volume of the vehicle to offset the sudden change of the buoyancy when entering different density water layers; S4, monitoring the vertical motion state of the vehicle in real time, and determining that the neutral hovering state is entered when it is confirmed that the vertical propeller is unloaded and the depth is maintained constant; S5, closing all propellers, and obtaining undisturbed suspended sediment flux data in the stream drift state by using the acoustic detection device until the silence mode is exited and the propeller is restarted after reaching the safety boundary.

[0014] Preferably, step S2 further includes: The basic fluid density of the pure liquid phase is calculated using temperature, salinity, and depth data. At the same time, the mass concentration of suspended sediments is inverted based on the acoustic volume backscattering intensity, and the additional density component caused by the mass concentration of suspended sediments is calculated. Finally, the basic fluid density and the additional density component are superimposed to generate the total environmental density. The local turbidity is compared with the preset high and low turbidity thresholds. When the local turbidity exceeds the high threshold, the acoustic transducer is controlled to reduce the frequency to the low frequency transmission band and increase the source voltage. At the same time, the additional acoustic attenuation coefficient is calculated using the inverted suspended sediment mass concentration, and the slope of the time-varying gain curve at the receiver is increased in real time.

[0015] Preferably, step S3 further includes: calculating the difference between the theoretical drainage volume required to maintain a neutral hovering state and the actual drainage volume of the current variable buoyancy system, and generating a volume adjustment amount in the corresponding direction based on the positive or negative polarity of the drainage volume difference to drive the variable buoyancy system to perform oil injection or oil extraction operations.

[0016] This invention provides an adaptive underwater vehicle and detection method suitable for high-salinity and high-turbidity environments in estuaries. It offers the following advantages: 1. This invention constructs a total environmental density calculation model that includes the additional density component of suspended sediments by integrating temperature, salinity, and depth data with acoustic backscattering intensity data. Based on this model, a feedforward buoyancy-driven control is implemented, thereby overcoming the physical bias of traditional methods that rely solely on temperature and salinity parameters to calculate density in high-sediment-content water bodies. This allows the vehicle to pre-balance its drainage volume in advance based on actual fluid density changes when crossing strong density transition interfaces such as estuarine brine wedges or high-concentration floating mud layers. This effectively suppresses vertical oscillations caused by sudden changes in net buoyancy and improves the dynamic stability and energy efficiency of the vehicle in complex heterogeneous fluid environments.

[0017] 2. This invention establishes an adaptive configuration mechanism for acoustic parameters based on optical turbidity and suspended sediment concentration, solving the technical challenge of adapting a single fixed-frequency acoustic device to the spatially non-uniform distribution of turbidity in estuaries. The system can dynamically switch acoustic detection frequencies according to the real-time monitored water turbidity state and specifically correct the linear slope term of the receiver's time-varying gain curve using inverted sediment concentration. In low-turbidity waters, high frequencies are used to acquire fine structures, while in high-turbidity waters, low-frequency strong sound sources and high-gain compensation ensure penetration depth, thereby guaranteeing the integrity and effectiveness of detection data even in extreme acoustic attenuation environments such as the core area of ​​the maximum turbidity zone.

[0018] 3. This invention designs a silent flux observation strategy based on neutral hovering state determination, realizing a seamless switch from active-powered navigation to Lagrange drift mode. By forcibly cutting off the power supply circuit of the propulsion system after confirming buoyancy balance, the high-frequency electromagnetic noise of the motor coil and the disturbance of the propeller mechanical turbulence on the in-situ laminar structure of the water body are eliminated. Combined with the pulse coherence measurement mode of the acoustic equipment, the vehicle can accurately capture the flocculation and sedimentation flux of fine suspended particles and the microscale turbulent pulsation characteristics in a state of almost no relative motion with the water mass, and obtain high-fidelity physical process data that are difficult to detect under the traditional underway observation mode. Attached Figure Description

[0019] Figure 1 This is a system architecture diagram of the present invention; Figure 2 This is a flowchart of the method steps of the present invention. Detailed Implementation

[0020] The technical solutions in the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present invention, and not all embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those skilled in the art without creative effort are within the scope of protection of the present invention.

[0021] See attached document Figure 1 , Figure 1 This is a schematic diagram of an adaptive underwater vehicle architecture according to an embodiment of the present invention. The present invention provides an adaptive underwater vehicle suitable for high-salinity and high-turbidity environments in estuaries. Built on an underwater vehicle platform, it can dynamically adjust the vehicle's physical properties and detection parameters based on real-time monitored hydrological and acoustic parameters. The vehicle includes an environmental perception module, a density inversion module, an acoustic configuration module, a buoyancy control module, a silent observation module, and a navigation and monitoring module. Each module interacts with and transmits commands to the central control unit via a data bus.

[0022] The environmental perception module is used to acquire raw observation data reflecting the current physical characteristics of the water body. The environmental perception module includes a temperature, salinity and depth gauge installed at the bow of the vehicle, an optical turbidimeter installed on the surface of the vehicle, and an acoustic Doppler current profiler or side-scan sonar installed on the belly of the vehicle. All sensors achieve data time alignment through a unified clock synchronization protocol.

[0023] The density inversion module is used to calculate the total environmental density of the water body. This module receives conductivity, temperature, pressure, and acoustic volumetric backscattering intensity data collected by the environmental sensing module. The module not only calculates the basic fluid density using the seawater equation of state, but also inverts the suspended sediment concentration based on the acoustic backscattering intensity, and calculates the additional density component caused by the suspended sediment. Finally, the basic fluid density and the additional density component are superimposed to generate the total environmental density parameter.

[0024] The acoustic configuration module is used to control the working mode of the acoustic detection equipment. Based on the local turbidity value fed back by the optical turbidimeter and the suspended sediment concentration obtained by inversion, the acoustic configuration module adjusts the transmission frequency of the acoustic transducer, the source intensity, and the slope of the time-varying gain curve of the receiver in real time, so as to ensure that the acoustic equipment adopts a high-frequency high-resolution mode in low-turbidity waters and a low-frequency strong-penetration mode in high-turbidity waters.

[0025] The buoyancy control module is used to maintain the dynamic balance of the vehicle. The buoyancy control module is connected to the vehicle's variable buoyancy system, which includes a fuel tank, a two-way pump and a corresponding valve assembly. Based on the total environmental density parameters output by the density inversion module, the buoyancy control module uses Archimedes' principle to calculate the target displacement volume required to maintain neutral buoyancy and generates volume adjustment commands to drive the variable buoyancy system to compensate for buoyancy fluctuations caused by changes in water density.

[0026] The silent observation module is used to perform detection tasks without mechanical disturbance. This silent observation module monitors the output power of the vertical thruster and the rate of change of the depth sensor to determine whether the vehicle is in a neutral hovering state. When the vehicle is determined to have reached neutral equilibrium, the silent observation module generates a thruster shutdown command and triggers the acoustic detection equipment to enter a high-frequency sampling mode, utilizing the vehicle's drift characteristics to conduct flux observation in a laminar flow environment.

[0027] The navigation monitoring module is used to ensure the safety of the vehicle's operation. The navigation monitoring module uses inertial navigation components and Doppler velocimeters to calculate the vehicle's geographical location and altitude above the ground. During silent flux observation, the navigation monitoring module continuously monitors the drift trajectory. Once it detects that the position exceeds the preset geofence or the altitude above the ground is below the safety threshold, it generates an interrupt command and takes over the control of the thrusters.

[0028] See attached document Figure 2 , Figure 2 This is a schematic flowchart of a method according to an embodiment of the present invention. The present invention provides an adaptive underwater vehicle detection method suitable for high-salinity and high-turbidity environments in estuaries, comprising the following steps: S1 synchronously collects environmental reference data such as conductivity, temperature, pressure, local turbidity, and acoustic volume backscattering intensity during navigation; S2, calculates the total environmental density including the contribution of suspended sediments based on the collected data, and determines whether to switch the acoustic detection frequency and correct the gain parameters based on the local turbidity; S3 calculates the target drainage volume under the feedforward control logic based on the total environmental density change rate, and drives the variable buoyancy system to adjust the actual drainage volume of the vehicle to offset the sudden change in buoyancy when entering water layers of different densities. S4: Real-time monitoring of the vehicle's vertical motion status. When it is confirmed that the vertical thruster is unloaded and the depth remains constant, it is determined to enter the neutral hovering state. S5, shut down all thrusters, use acoustic devices to acquire undisturbed suspended sediment flux data in a drifting state until a safe boundary is reached, then exit the silent mode and restart the thrusters.

[0029] See attached document Figure 1 The environmental perception module includes a temperature, salinity, and depth detection unit, an optical turbidity detection unit, and an acoustic detection unit. Each unit is connected to the central control unit inside the aircraft via a pressure-resistant watertight cable.

[0030] The CTD (Conductivity, Temperature, Depth) detection unit specifically employs a high-response frequency CTD sensor assembly. This CTD sensor assembly is rigidly fixed to the bow tip or nose cone of the underwater vehicle. Choosing the bow as the mounting point ensures that the sensor probe contacts the water body before the vehicle body, thereby avoiding the boundary layer effect generated by the vehicle's hull and the disturbance of the water temperature and conductivity fields by the propeller wake. This ensures that the collected physical quantities reflect the true state of the original flow field. The CTD detection unit is configured to output real-time data on the conductivity, temperature, and hydrostatic pressure of the current water body at a sampling rate of not less than 4Hz. For the specific circuit implementation and calibration process of the CTD sensor, those skilled in the art can refer to the national standards or industry specifications commonly used in marine instruments; these are well-known technologies in the field and will not be elaborated upon here.

[0031] The optical turbidity detection unit employs an infrared scattering optical turbidity meter. This sensor is embedded within the side or dorsal fairing of the aircraft, with its optical window flush with the aircraft skin to reduce fluid resistance. The optical turbidity meter emits a near-infrared beam and receives the intensity of scattered light from suspended particles in the water, outputting a localized turbidity value characterizing the degree of turbidity in the microenvironment surrounding the aircraft. This local turbidity value is not directly involved in the full-profile density calculation in subsequent processing. Instead, it serves as a gating trigger signal to determine whether the region is within the core area of ​​the "maximum turbidity zone" and is used to correct the near-field boundary conditions in the acoustic inversion algorithm.

[0032] The acoustic detection unit employs an acoustic Doppler current profiler or side-scan sonar array with dual-frequency or broadband operation capabilities, mounted on a flat area of ​​the vehicle's belly, with the transducer array facing vertically downwards. Unlike conventional configurations that only output velocity data, the acoustic detection unit in this embodiment is configured in "echo intensity recording mode," meaning it can output the raw echo intensity values ​​at each measuring point (Bin) along the sound beam direction. The acoustic detection unit integrates a signal preprocessing circuit to convert the received transducer voltage signal into volumetric backscatter intensity. The conversion process is based on corrections to the sonar equations to eliminate the effects of spherical diffusion loss and water absorption loss on the echo energy.

[0033] Volume backscattering intensity The calculation model is shown below: ; In the formula, These are calibration constants based on the hardware characteristics of the sonar system; This is the measured echo intensity count value; This serves as the baseline value for system background noise. The slant distance between the measuring point and the transducer; This is the absorption coefficient of sound waves in water, which is related to the current water temperature, salinity, and emission frequency. The transmit pulse width; This is the equivalent beamwidth of the transducer.

[0034] The above formula clarifies the conversion logic from the original electrical signal to the physical scattering intensity, providing a basis for subsequent applications. Inverting suspended sediment concentration provides standardized input variables.

[0035] To address the spatiotemporal mismatch caused by the dispersed installation locations and asynchronous sampling frequencies of sensors, the environmental perception module established a hardware-triggered spatiotemporal alignment mechanism. The central control unit incorporates a high-precision timing module, which sends synchronization trigger pulses to the temperature, salinity, and depth (CTD) detection unit, optical turbidity detection unit, and acoustic detection unit via physical level signals. Considering the longitudinal physical distance (e.g., 1.5 meters) between the CTD sensor located at the bow and the acoustic equipment at the belly, the control unit establishes a spatial compensation buffer based on the navigation speed. The system reads the real-time speed, calculates the time difference between water particles flowing from the bow to the belly, delays the CTD-acquired temperature and salinity data by the corresponding number of milliseconds, and then matches it with the profile data collected by the acoustic detection unit at the same time. This ensures that the salinity data and acoustic scattering data used in density inversion calculations originate from the same water body micro-element, eliminating spatial sampling errors during dynamic navigation. All multi-source data, after timestamp alignment and spatial compensation, are aggregated via RS-422 or Ethernet bus to the heterogeneous data fusion and density inversion module for further processing.

[0036] The density inversion module runs in the embedded processor of the central control unit. It is used to solve the physical deviation problem of calculating fluid density by relying solely on temperature and salinity parameters in the high turbidity environment of the estuary. By establishing a mapping relationship between acoustic scattering intensity and suspended sediment concentration, it solves the total environmental density, which includes the dual contributions of dissolved salts and suspended particulate matter.

[0037] The density inversion module includes a basic fluid density calculation unit, a suspended sediment concentration inversion unit, and a total density synthesis unit.

[0038] The basic fluid density calculation unit is configured to receive conductivity, temperature, and pressure data transmitted from the environmental sensing module. Based on the 1978 Practical Salinity Standard (PSS78), this unit converts conductivity into practical salinity, calls the international seawater state equation algorithm library, and, upon inputting practical salinity, on-site temperature, and hydrostatic pressure, calculates the density of the pure liquid phase without suspended particulate matter, i.e., the basic fluid density. The calculation process considers the nonlinear variation of the tangent modulus with pressure to ensure calculation accuracy at different depths. For the specific polynomial expansion form of the seawater equation of state, those skilled in the art can refer to the UNESCO Handbook of Commonly Used Oceanographic Algorithms, which is a publicly known technique.

[0039] The suspended sediment concentration inversion unit is configured to receive the volumetric backscatter intensity output by the acoustic detection unit. Profile data. Due to the significant vertical stratification of suspended sediment concentration in the estuary area, this suspended sediment concentration inversion unit performs inversion calculations for each depth measurement point in the acoustic profile. The suspended sediment concentration inversion unit stores an acoustic inversion model calibrated for specific estuarine sediment characteristics. This acoustic inversion model describes the logarithmic linear relationship between volume backscattering intensity and suspended sediment mass concentration.

[0040] The formula for inverting the suspended sediment mass concentration is as follows: ; In the formula, For depth The mass concentration of suspended sediment at the location; For depth Volume backscattering intensity at that location; is the acoustic backscattering target intensity coefficient. Wherein, It is not a fixed constant, but a comprehensive parameter related to the average grain size, shape factor, and acoustic frequency of the sediment particles. In this embodiment, The sediment concentration was obtained through on-site sampling and calibration, i.e., water samples were collected before the operation to determine the actual sediment content, combined with simultaneous measurements. The values ​​were determined by least squares fitting. Furthermore, when the local turbidity values ​​measured by the optical turbidimeter are valid, the suspended sediment concentration inversion unit uses optical turbidity data to weight and correct the near-field acoustic inversion results, thereby improving the inversion confidence at close range.

[0041] The total density synthesis unit is used to construct a model of the contribution of each fluid component to the overall density. In the high turbidity zone of the estuary, although suspended particulate matter is suspended in the water, it displaces an equal volume of water and introduces additional mass, thus changing the equivalent fluid density in Archimedes' law of buoyancy. Based on the principle of mixture density, this total density synthesis unit calculates the additional density component caused by suspended sediment. .

[0042] The calculation logic for the additional density component and the total environmental density is as follows: ; ; In the formula, This refers to the additional density increment caused by suspended sediments; The base fluid density is obtained from the aforementioned calculations; is the average physical density of suspended sediment particles, for typical estuarine silicate silt; This represents the final output total environmental density.

[0043] The additional density component depends not only on the sediment content but also on the ratio of the base fluid density to the particle physical density. When the suspended sediment concentration is extremely high (e.g., greater than 10 kg / m³), the additional density component is affected. 3 (floating mud layer) This will generate a density increment that directly corrects density deviations calculated solely based on the CTD. The total density synthesis unit will be refreshed at a frequency of at least 1 Hz. The data is processed and the parameter is output to the buoyancy control module in real time as the sole physical reference for calculating the target drainage volume, thereby ensuring that the buoyancy balance calculation of the vehicle can truly reflect the mechanical properties of the surrounding fluid when it passes through the saltwater wedge or high-concentration turbidity zone.

[0044] The acoustic configuration module addresses the detection blind zone or insufficient resolution issues that arise when using a single fixed-frequency acoustic device in estuarine environments with highly uneven turbidity distribution. This module achieves dynamic optimization of the detection frequency and gain by establishing a linkage mechanism between optical turbidity and acoustic parameters.

[0045] The acoustic configuration module logically includes a turbidity threshold discrimination unit, a frequency switching control unit, and a time-varying gain dynamic correction unit.

[0046] The turbidity threshold discrimination unit is used to receive the local turbidity value output by the optical turbidity detection unit. The turbidity threshold discrimination unit has two preset key threshold parameters in its internal register: a low turbidity switching threshold. High turbidity switching threshold To avoid frequent switching of acoustic equipment operating modes due to numerical fluctuations when the vehicle is navigating in the critical turbidity region, this unit uses Schmitt triggering logic with hysteresis characteristics for state determination. When the local turbidity value is consistently below the low turbidity switching threshold, the current water area is determined to be a "clear water area"; when the local turbidity value is consistently above the high turbidity switching threshold, the current water area is determined to be a "high turbidity area" or "maximum turbidity zone".

[0047] The frequency switching control unit is connected to the signal generator and power amplifier circuit of the acoustic detection unit. Based on the status flag bit output by the turbidity threshold discrimination unit, the frequency switching control unit sends frequency switching commands and source-level adjustment commands to the acoustic transducer.

[0048] In the "clear water zone" state, the frequency switching control unit generates high-frequency mode commands to drive the acoustic transducer to operate in the high-frequency range (e.g., 600kHz to 1200kHz). At this time, the transmitter stage maintains a standard power consumption level and utilizes the propagation characteristics of short-wavelength sound waves in a low-scattering environment to acquire fine water flow field structure or riverbed micro-topography data with centimeter-level vertical resolution.

[0049] In the "high turbidity zone" state, the frequency switching control unit generates a low-frequency mode command, driving the acoustic transducer to switch to the low-frequency band (e.g., the range of 75kHz to 300kHz). Since the wavelength of low-frequency sound waves is much larger than the characteristic particle size of suspended sediment, its Rayleigh scattering effect is significantly reduced, thereby decreasing the attenuation of sound waves in the turbid medium. The frequency switching control unit sends a high-power command to the power amplifier circuit, increasing the transmission voltage amplitude so that the transmitter stage of the acoustic detection equipment reaches the maximum value allowed by the hardware. This maximizes the acoustic energy injection, ensuring that sound waves can penetrate the high-concentration suspended sediment layer and obtain effective seabed reflection echoes, preventing bottom locking loss.

[0050] The time-varying gain dynamic correction unit is used to address the problem that fixed gain curves cannot adapt to drastically changing sediment attenuation. Traditional time-varying gain only compensates for spherical diffusion loss and pure water absorption loss. However, in high-turbidity environments, the viscous absorption and scattering attenuation of suspended particles become the dominant factors. This time-varying gain dynamic correction unit receives the suspended sediment concentration calculated by the density inversion module and the current operating frequency. Calculate the total sound absorption coefficient.

[0051] The calculation logic for the time-varying gain control curve is as follows: ; ; In the formula, For the corresponding detection distance The receiver gain compensation value at the location; This is the spherical diffusion loss term; The sound absorption coefficient of pure seawater; The additional sound attenuation coefficient caused by suspended sediments; Indicates the concentration of suspended sediments; The attenuation constant is related to the physical properties of the sediment; It is the frequency dependence index, and its value is usually between 0.5 and 1; This is the system's fixed gain constant.

[0052] When the aircraft enters an area with high sediment content As the numerical value increases, the time-varying gain dynamic correction unit automatically increases the slope of the TVG curve with increasing distance, applying a greater amplification factor to the deep echo signal to offset the additional energy loss caused by suspended sediment, thereby maintaining the grayscale uniformity of the echo image and preventing deep data from being masked by noise due to excessively low signal-to-noise ratio. This feedforward gain adjustment based on a physical model, unlike traditional automatic gain control based on echo intensity, can actively compensate before the signal is completely attenuated.

[0053] The buoyancy control module is used to actively adjust the displacement volume of the aircraft based on the total environmental density parameter calculated in real time, so as to counteract the sudden change in net buoyancy caused by the heterogeneous fluid interface.

[0054] The buoyancy control module includes a variable buoyancy system and its drive controller. The variable buoyancy system employs a closed-loop hydraulic oil discharge structure, comprising a rigid oil tank located inside the pressure hull of the vessel, a bidirectional hydraulic pump assembly, a solenoid valve assembly, and an elastic, corrosion-resistant oil bladder located outside the pressure hull. The external elastic oil bladder is connected to the internal hydraulic circuit via a through-hull pipe. The bidirectional hydraulic pump assembly is configured to bidirectionally transport hydraulic oil between the rigid oil tank and the elastic oil bladder under the command of the drive controller. When hydraulic oil is injected into the external elastic oil bladder, the bladder expands, increasing the total displacement volume of the vessel; conversely, when hydraulic oil is withdrawn from the internal rigid oil tank, the bladder contracts, decreasing the total displacement volume of the vessel. To achieve accurate measurement of volume changes, a high-precision flow meter is connected in series in the hydraulic circuit, or a level sensor (or a linear Hall displacement sensor if a piston-type VBS is used) is installed inside the rigid oil tank to provide real-time feedback on the actual displacement volume of the system. The selection of the hydraulic pump and the design of the sealing pipeline can be based on general deep-sea engineering standards for those skilled in the art, and will not be elaborated further here.

[0055] The drive controller internally operates a volume balancing algorithm unit based on Archimedes' principle. This volume balancing algorithm unit adopts a feedforward control strategy based on density parameters and receives the total environmental density output by the heterogeneous data fusion and density inversion module. The total environmental density already includes the increase in physical density caused by changes in salinity and suspended sediment concentration.

[0056] The volume balancing algorithm unit calculates the target displacement volume required for the vehicle to maintain a neutral buoyancy state (i.e., equilibrium between gravity and buoyancy) in the current density field. The calculation logic is as follows: ; ; In the formula, The target drainage volume required to maintain neutral equilibrium; This is the total mass of the aircraft in the air, which can be a fixed constant or a variable preset according to the load conditions. The total environmental density is input in real time; Based on the fluid density; Represents gravitational acceleration; Add density to suspended sediment; This refers to the current actual drainage volume fed back by the sensor. The volume adjustment amount generated by the control command.

[0057] The drive controller adjusts the volume based on the calculated amount. Generate pump control commands.

[0058] when When this occurs, it indicates a decrease in water density (e.g., from a high-salinity, high-sand bottom layer to a low-salinity surface layer), and the vehicle faces the risk of sinking due to negative buoyancy. The controller then drives the hydraulic pump to rotate forward, injecting a volume of [unspecified substance] into the external oil bladder. The hydraulic oil is used to increase the drainage volume to compensate for buoyancy loss.

[0059] when When this occurs, it indicates that the current water density has increased (e.g., entering the highest turbidity zone with high sediment content), and the vehicle faces the risk of rising due to positive buoyancy. The controller then drives the hydraulic pump to reverse, extracting a volume of oil from the external oil sump. The hydraulic oil reduces the drainage volume to suppress the tendency to float.

[0060] The control process responds instantly before or during the contact of the density gradient layer, using density inversion data to predict buoyancy changes in advance and complete mechanical trimming. This ensures that the vehicle can minimize vertical attitude disturbances when traversing the estuarine saltwater wedge structure with a sharp density gradient, thereby significantly reducing the intervention frequency and power consumption of the vertical thrusters and creating a stable dynamic basis for subsequent entry into silent observation mode.

[0061] The silent observation module addresses the technical challenge of traditional underwater vehicles (UVs) disrupting the in-situ laminar flow structure and morphology of suspended sediment flocculation due to mechanical turbulence and shear forces generated by their propulsion systems during precise suspended sediment observation. It establishes an interlocking mechanism between dynamic state monitoring and propulsion system control, enabling switching between active navigation mode and passive Lagrange drift mode.

[0062] The silent observation module is equipped with a neutral equilibrium state discrimination unit, which reads the output power command value (or duty cycle signal) of the vertical thruster and the high-frequency pressure data of the depth sensor in real time. During the feedforward trim operation of the buoyancy control module, the load change trend of the vertical thruster is continuously calculated. When the displacement volume adjusted by the variable buoyancy system gradually approaches the theoretical value required for the current water density, the vertical thrust required to maintain a constant depth will show a monotonically decreasing trend.

[0063] The neutral equilibrium state discrimination unit uses a multi-parameter joint convergence criterion to confirm whether the vehicle has reached ideal hydrostatic equilibrium. This criterion requires that both the thruster unloading condition and the depth stability condition be met simultaneously to eliminate misjudgments caused by external force interference (such as instantaneous water flow impact).

[0064] The logic for determining a neutral hovering state is as follows: ; In the formula, This is the neutral hovering state flag; 1 indicates that the vehicle has entered a balanced state. The length of the sliding time window; The current moment; For integration variables; This represents the instantaneous normalized power output value of the vertical thruster; This is the power zero-point noise threshold; The rate of change of depth; This is the depth drift tolerance threshold.

[0065] Only when the vertical thruster remains stationary or in a state of extremely low power consumption within a preset time window, and the vehicle's depth does not drift significantly, does the system determine that buoyancy trim is complete and the vehicle is hovering at the target layer entirely on static buoyancy.

[0066] Once the status flag is set Once set, the silent observation module immediately triggers the silent control sequence, which sends a hardware-level shutdown command to the underlying driver to forcibly cut off the power supply circuits of the horizontal and vertical thrusters. This is done to eliminate the high-frequency electromagnetic noise of the motor coils and the wake disturbances generated by the micro-rotation of the propellers, ensuring that the water flow field around the vehicle returns to its natural state.

[0067] The silent observation module sends a mode switching command to the acoustic detection unit, switching it from the conventional navigation velocity measurement mode to the "flux observation mode". In this mode, the acoustic Doppler current profiler adjusts the pulse repetition frequency to the maximum bandwidth allowable value and enables the pulse coherence processing function. The vehicle is in a passive drifting state in the water, and its trajectory is completely determined by the advection of the surrounding water mass. Since there is almost no relative motion between the vehicle and the water, the acoustic sensor can capture minute turbulent pulsation characteristics and the vertical settling flux of suspended sediments. This avoids the phenomenon of Doppler noise masking subtle physical processes caused by excessive speed in conventional navigation observation. This observation method enables the system to record the flocculation, sedimentation and resuspension processes of fine particles in the maximum turbidity zone of the estuary.

[0068] The navigation monitoring module is used to continuously calculate the vehicle's trajectory while the propulsion system is shut down, and to forcibly take over control when environmental or position parameters reach safety limits.

[0069] The navigation and safety monitoring module includes a drift trajectory calculation unit, a safety boundary determination unit, and an emergency takeover control unit.

[0070] The drift trajectory calculation unit is physically connected to the fiber optic inertial navigation system and the Doppler velocimeter. In silent observation mode, although the thrusters have stopped working, the vehicle undergoes Lagrange motion with the water mass. The drift trajectory calculation unit uses data from the high-frequency accelerometer and gyroscope of the inertial navigation system, combined with the initial latitude and longitude coordinates calibrated before entering the water, to perform pure inertial integration calculations.

[0071] When the acoustic environment permits, the drift trajectory estimation unit incorporates Doppler velocity data from the bottom velocity sensor as the measurement update value for the Kalman filter to suppress drift errors accumulated by inertial components over time, and outputs the vehicle's current geographic coordinates (longitude) at a frequency of not less than 10Hz. ,latitude and height from the bottom .

[0072] The safety boundary determination unit stores preset task planning geofence data and physical safety thresholds. This unit is configured to calculate the relative position of the vehicle's current location to the safety boundary in real time. Considering the complex flow field in the estuary area, simple time control cannot prevent the vehicle from drifting to busy waterways or shallow grounding areas. Therefore, this safety boundary determination unit adopts an electronic fence algorithm based on Euclidean distance.

[0073] The safety boundary determination logic is calculated based on the following safety margin formula: ; In the formula, for The overall safety margin at any given time; To define the permissible radius of a pre-set circular electronic fence; , The projected coordinates of the spacecraft at the current moment in the local northeast-north sky coordinate system with the launch point as the origin; , The coordinates of the center of the electronic fence; The real-time height above the bottom measured by an altimeter or DVL; The lower limit threshold for the safe height to prevent bottoming out.

[0074] Only when the vehicle is inside the electronic fence and its altitude above the bottom is higher than the safety lower limit, is the overall safety margin considered. Only then is it considered positive. Once... This indicates that the vehicle has either drifted out of the designated operating area or has experienced an abnormal depth drop due to the density current generated by the high concentration of sediment at the bottom of the estuary. In this case, the silent observation mission must be terminated immediately.

[0075] The emergency takeover control unit is connected to the interrupt request terminal of the central control unit. When it receives a non-positive safety margin alarm signal output by the safety boundary discrimination unit, the emergency takeover control unit has the highest priority control authority and performs the following timing actions: sending a stop acquisition command to the acoustic detection equipment and forcing it into a low-power standby state to protect the acoustic transducer from power surges during restart; releasing the power supply lockout of the thruster controller and sending a maximum lift command to the vertical thruster to quickly escape the danger depth; sending a course correction command to the horizontal thruster to drive the vehicle to navigate against the current or tangentially to return to the safe area. For the specific algorithm implementation of the inertial navigation component and the parameter tuning of the Kalman filter, those skilled in the art can refer to conventional technical manuals in the field of underwater integrated navigation, which will not be elaborated here.

[0076] See attached document Figure 2 The present invention provides an adaptive underwater vehicle detection method suitable for high-salinity and high-turbidity environments in estuaries, which specifically coordinates the various hardware modules to execute the following steps through a central control unit: In step S1, spatiotemporal synchronous acquisition of multidimensional environmental data is performed. After entering the water, the underwater vehicle activates the environmental perception module. The CTD (Conductivity, Temperature, Depth) meter outputs real-time data on the conductivity, temperature, and pressure of the water body at a preset frequency, while the optical turbidimeter simultaneously outputs local turbidity data. Simultaneously, the acoustic detection unit acquires flow velocity profiles and acoustic volumetric backscattering intensity data in navigation mode. To eliminate spatiotemporal mismatch caused by differences in sensor spatial layout, the control unit reads the vehicle's current ground speed, calculates the transit time of water particles from the bow CTD meter to the ventral acoustic detection unit, and applies millisecond-level time delay compensation to the CTD data accordingly. The time-aligned multidimensional data is encapsulated into an environmental state vector at the same moment and transmitted to the data processing bus.

[0077] In step S2, density decoupling and acoustic parameter configuration based on heterogeneous data fusion are performed. This step includes two parallel processing branches. In the density calculation branch, the system calls the international seawater equation of state algorithm library to calculate the basic fluid density using temperature, salinity, and depth data. Simultaneously, the system extracts acoustic volume backscattering intensity data and, combined with a preset estuarine sediment acoustic attenuation model, inverts the suspended sediment mass concentration. The system further calculates the additional density component caused by the suspended sediment mass and superimposes it with the basic fluid density to generate the total environmental density parameter characterizing the true buoyancy characteristics of the current water layer. In the acoustic configuration branch, the system compares the collected local turbidity value with a preset hysteresis threshold. When the local turbidity exceeds the high threshold, the system immediately generates a mode switching command, driving the acoustic transducer to reduce the transmission frequency to the low-frequency penetration band and increase the transmitter source voltage; simultaneously, the slope of the time-varying gain curve at the receiver is corrected in real time using the inverted suspended sediment concentration to compensate for the nonlinear attenuation of acoustic energy caused by high concentrations of suspended particles.

[0078] In step S3, density-feedforward-based dynamic pre-balancing is performed. The buoyancy control module reads the total environmental density parameter output in step S2, combines it with the vehicle's own mass data, and uses Archimedes' principle to calculate in real time the theoretical displacement volume required to maintain neutral hovering. The system calculates the difference between the theoretical displacement volume and the actual displacement volume of the current variable buoyancy system, generating a volume adjustment command. This command directly drives the bidirectional hydraulic pump to change the volume of the external oil bladder by suction or discharge of oil before the vehicle crosses a brine wedge interface or silt layer with a significant density gradient. This process is feedforward control and does not rely on error feedback from the depth sensor, thus eliminating the net buoyancy difference in advance when density abrupt changes occur and preventing the vehicle from experiencing large vertical oscillations.

[0079] In step S4, a neutral hovering state determination is performed. During buoyancy pre-trimming, the system continuously monitors the power output of the vertical thrusters and the rate of change of the depth sensor. When the volume adjustment of the variable buoyancy system causes the vehicle's own weight and environmental buoyancy to tend to balance, the load on the vertical thrusters used to maintain a constant depth will gradually decrease. The system integrates the normalized power of the vertical thrusters within a sliding observation time window. When the integral value is lower than a preset zero-point noise threshold, and the rate of change of depth converges to zero during the same period, the system determines that the vehicle has fully established hydrostatic equilibrium and sets the neutral hovering state flag.

[0080] In step S5, Lagrange silent flux observation and safe recovery are performed. In response to the neutral hovering state flag being set, the system cuts off the power supply circuits to the horizontal and vertical thrusters, eliminating mechanical vibration and electromagnetic noise, allowing the vehicle to enter a drift state. The acoustic detection equipment switches to high-frequency pulse coherence mode to perform high-resolution flux observation of the surrounding water, recording the flocculation, sedimentation, and resuspension processes of suspended sediments. During drift observation, the navigation monitoring module continuously calculates the vehicle's position using inertial navigation data. Once the vehicle's position is detected to exceed the preset geofence boundary, or its height above the bottom is below the safety threshold, the system immediately interrupts the silent mode, reconnects the thruster power, and performs a course adjustment or emergency surfacing maneuver until it leaves the danger zone or terminates the current detection mission.

[0081] Although embodiments of the invention have been shown and described, it will be understood by those skilled in the art that various changes, modifications, substitutions and alterations can be made to these embodiments without departing from the principles and spirit of the invention, the scope of which is defined by the appended claims and their equivalents.

Claims

1. An adaptive underwater vehicle suitable for high-salinity and high-turbidity environments in estuaries, characterized in that, It includes an environmental perception module, a density inversion module, an acoustic configuration module, a buoyancy control module, a silent observation module, and a navigation monitoring module that interact with the central control unit via a data bus; The environmental perception module is used to collect and output spatiotemporally aligned multidimensional environmental reference data; The density inversion module is used to generate a total environmental density parameter representing the true buoyancy characteristics of the current water layer by superimposing the additional density component of suspended sediments inverted by the acoustic backscattering intensity on the basic fluid density. The acoustic configuration module is used to establish a linkage mechanism between turbidity and acoustic parameters, and dynamically adjust the emission frequency and gain curve slope of the acoustic device based on the local turbidity and the inverted additional density component of suspended sediments. The buoyancy control module is used to calculate the target drainage volume based on the total environmental density parameter using Archimedes' principle and drive the variable buoyancy system to counteract buoyancy fluctuations. The silent observation module is used to generate a thruster shutdown command and trigger the silent flux observation mode after determining that the vertical thruster power is zero and the depth is stable in a neutral hovering state. The navigation monitoring module is used to monitor the trajectory during silent drift and forcibly take over propulsion control when a safe boundary is reached.

2. The adaptive underwater vehicle suitable for high-salinity and high-turbidity environments in estuaries according to claim 1, characterized in that, The environmental perception module includes a temperature, salinity, and depth detection unit installed at the bow of the vehicle, an optical turbidity detection unit installed on the surface of the vehicle, and an acoustic detection unit installed on the belly of the vehicle. The environmental perception module is equipped with a hardware-triggered spatiotemporal alignment mechanism. The spatiotemporal alignment mechanism sends a synchronization trigger pulse through the central control unit and establishes a spatial compensation buffer based on the navigation speed. The spatial compensation buffer is used to read real-time speed, calculate the time difference of water particles flowing from the bow to the belly, apply time delay compensation to the data collected by the temperature, salinity and depth detection unit, and align the profile data collected at the same time as the acoustic detection unit on the spatial micro-element.

3. The adaptive underwater vehicle suitable for high-salinity and high-turbidity environments in estuaries according to claim 1, characterized in that, The density inversion module includes a basic fluid density calculation unit, a suspended sediment concentration inversion unit, and a total density synthesis unit; The basic fluid density calculation unit is used to convert conductivity into practical salinity based on the practical salinity scale, and calculate the density of the pure liquid phase without suspended particulate matter as the basic fluid density by combining the on-site temperature and fluid static pressure through the international seawater state equation. The suspended sediment concentration inversion unit is used to invert the suspended sediment mass concentration at each depth measuring point based on a pre-stored acoustic inversion model and using the volume backscattering intensity. The acoustic inversion model describes the logarithmic linear relationship between the volume backscattering intensity and the suspended sediment mass concentration, and uses local turbidity values ​​to correct the near-field inversion results. The total density synthesis unit is used to calculate the additional density component caused by the mass of suspended sediments based on the principle of mixture density, and to add the additional density component to the base fluid density to obtain the total environmental density parameter. The additional density component is determined by the ratio of the mass concentration of suspended sediment, the base fluid density and the average physical density of suspended sediment particles.

4. The adaptive underwater vehicle suitable for high-salinity and high-turbidity environments in estuaries according to claim 1, characterized in that, The acoustic configuration module includes a turbidity threshold discrimination unit, a frequency switching control unit, and a time-varying gain dynamic correction unit. The turbidity threshold discrimination unit is used to compare the local turbidity value with the preset low turbidity switching threshold and high turbidity switching threshold using Schmitt triggering logic with hysteresis characteristics, so as to determine whether the current water area is a clear water area or a high turbidity area. The frequency switching control unit is used to drive the acoustic detection device to work in high-frequency, high-resolution mode when the area is determined to be clear water; and to drive the acoustic detection device to switch to low-frequency, strong-penetration mode and increase the voltage of the emission source stage when the area is determined to be turbid water. The time-varying gain dynamic correction unit is used to calculate the total acoustic absorption coefficient based on the current operating frequency and the inverted suspended sediment concentration. The total acoustic absorption coefficient includes the pure seawater acoustic absorption coefficient and the additional acoustic attenuation coefficient caused by suspended sediment.

5. An adaptive underwater vehicle suitable for high-salinity and high-turbidity environments in estuaries according to claim 1, characterized in that, The buoyancy control module includes a drive controller and a variable buoyancy system with a closed hydraulic oil discharge structure. The variable buoyancy system includes a rigid oil tank, a bidirectional hydraulic pump group, and an external elastic oil bladder. The drive controller is equipped with a volume balancing algorithm unit. The volume balancing algorithm unit adopts a feedforward control strategy based on density parameters. According to the ratio of the total mass of the aircraft to the total environmental density parameter, it calculates the target displacement volume required to maintain neutral buoyancy, and calculates the difference between the target displacement volume and the current actual displacement volume to generate a volume adjustment amount. When the volume adjustment indicates that the drainage volume needs to be increased, the bidirectional hydraulic pump group is driven to inject oil into the external elastic oil bladder; when the indication is that the drainage volume needs to be reduced, the bidirectional hydraulic pump group is driven to extract oil from the external elastic oil bladder, and physical balancing is completed before the vehicle contacts the density gradient interface.

6. An adaptive underwater vehicle suitable for high-salinity and high-turbidity environments in estuaries according to claim 1, characterized in that, The silent observation module includes a neutral equilibrium state discrimination unit and a silent control sequence execution unit; The neutral equilibrium state discrimination unit is used to integrate the normalized power of the vertical thruster within a sliding observation time window using a multi-parameter joint convergence criterion. When the integral value is lower than the preset zero-point noise threshold and the depth change rate within the same period converges to zero, the neutral hovering state flag is set. The silent control sequence execution unit is used to respond to the neutral hovering state flag, forcibly cut off the power supply circuit of the horizontal thruster and the vertical thruster to eliminate mechanical turbulence and electromagnetic noise, and at the same time control the acoustic detection equipment to start the pulse coherence processing function to observe the flocculation and sedimentation process of suspended sediments by utilizing the characteristics of the vehicle drifting with the current.

7. An adaptive underwater vehicle suitable for high-salinity and high-turbidity environments in estuaries according to claim 1, characterized in that, The navigation monitoring module includes a drift trajectory calculation unit and a safety boundary discrimination unit; The drift trajectory calculation unit is used to perform pure inertial integration calculation using accelerometer and gyroscope data from the inertial navigation component during the propulsion system shutdown, and to introduce bottom velocity data from the Doppler velocimeter as measurement update value, and output the geographic coordinates and altitude above the bottom of the vehicle. The safety boundary discrimination unit is used to calculate the comprehensive safety margin between the current position of the aircraft and the preset geographic fence boundary and the lower limit threshold of the safe height using an electronic fence algorithm based on Euclidean distance. When the overall safety margin is not positive, the emergency takeover control unit is triggered to terminate silent observation, restart the thrusters, and leave the danger zone.

8. An adaptive underwater vehicle detection method suitable for high-salinity and high-turbidity environments in estuaries, applied to the adaptive underwater vehicle suitable for high-salinity and high-turbidity environments in estuaries as described in any one of claims 1-7, characterized in that, Includes the following steps: S1 synchronously collects data on conductivity, temperature, pressure, local turbidity, and acoustic volume backscattering intensity during navigation, and compensates for time delays in the data from sensors at different positions based on the speed. S2, calculates the total environmental density including the contribution of suspended sediments based on the collected data, and determines whether to switch the acoustic detection frequency and correct the gain parameters based on the local turbidity; S3, based on the total environmental density parameter, calculate the target displacement volume using Archimedes' principle under feedforward control logic, and drive the variable buoyancy system to adjust the actual displacement volume of the vehicle to offset the sudden change in buoyancy when entering water layers of different densities. S4: Real-time monitoring of the vehicle's vertical motion status. When it is confirmed that the vertical thruster is unloaded and the depth remains constant, it is determined to enter the neutral hovering state. S5, shut down all thrusters, use acoustic detection equipment to acquire undisturbed suspended sediment flux data in a drifting state until a safe boundary is reached, then exit the silent mode and restart the thrusters.

9. The adaptive underwater vehicle detection method for high-salinity and high-turbidity environments in estuaries according to claim 8, characterized in that, Step S2 further includes: The basic fluid density of the pure liquid phase is calculated using temperature, salinity, and depth data. At the same time, the mass concentration of suspended sediments is inverted based on the acoustic volume backscattering intensity, and the additional density component caused by the mass concentration of suspended sediments is calculated. Finally, the basic fluid density and the additional density component are superimposed to generate the total environmental density. The local turbidity is compared with the preset high and low turbidity thresholds. When the local turbidity exceeds the high threshold, the acoustic transducer is controlled to reduce the frequency to the low frequency transmission band and increase the source voltage. At the same time, the additional acoustic attenuation coefficient is calculated using the inverted suspended sediment mass concentration, and the slope of the time-varying gain curve at the receiver is increased in real time.

10. The adaptive underwater vehicle detection method for high-salinity and high-turbidity environments in estuaries according to claim 8, characterized in that, Step S3 further includes: calculating the difference between the theoretical drainage volume required to maintain a neutral hovering state and the actual drainage volume of the current variable buoyancy system, and generating a corresponding volume adjustment amount based on the positive or negative polarity of the drainage volume difference to drive the variable buoyancy system to perform oil injection or oil extraction operations.

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