A laser illumination velocimetry method and system for deep-sea hydrothermal vents based on natural tracing.

Abstract

This invention discloses a laser illumination velocimetry method and system for deep-sea hydrothermal vents based on natural tracers, belonging to the field of deep-sea hydrothermal vent detection and fluid velocity measurement technology. The invention employs a green-band sheet laser perpendicular to the hydrothermal fluid principal axis to form an optical slice, exciting natural mineral particles, bubbles, and refractive index gradients as tracer signals. A high-speed deep-sea camera at a preset angle acquires time-series images, which are then preprocessed with high-pressure window correction, spatiotemporal joint filtering, and adaptive contrast enhancement. Based on the assumption of constant brightness, the optical flow equation is solved to obtain the velocity vector field. The perturbation flow and background noise are separated through intrinsic orthogonal decomposition, and the result is converted into a three-dimensional physical velocity through physical calibration and output as a cloud map. This invention eliminates the need for artificial tracer particles, enabling visualization and high-precision measurement of the flow field at low-velocity, low-contrast overflow-type hydrothermal vents, and is suitable for extreme deep-sea environments.

Description

Technical Field

[0001] This invention relates to the field of deep-sea hydrothermal vent detection and fluid velocity measurement technology, and in particular to a laser illumination velocity measurement method and system for deep-sea hydrothermal vents based on natural tracers. Background Technology

[0002] Deep-sea hydrothermal vents are key sites for seafloor tectonic activity and the exchange of matter and energy. Diffuse-flow vents are characterized by low-velocity, large-scale, diffuse seepage. The fluid has no concentrated outlet, the flow velocity is typically below 0.1 m / s, the contrast with the background seawater is extremely low, the boundaries are blurred, and the flow exhibits unstructured characteristics. Under conventional lighting conditions, diffuse-flow vents are almost invisible, making the observation of their velocity field a long-standing technical challenge in international deep-sea exploration.

[0003] Existing overflow-type hydrothermal flow velocity measurement technologies have significant drawbacks: 1) Invasive measurement equipment interferes with the natural flow field, resulting in large measurement errors and difficulty in reflecting the true flow state; 2) DFV (diffuse flow velocity) measurement relies on background refractive index distortion, which has stringent requirements for environmental and equipment accuracy, limiting its applicability; 3) Acoustic Doppler current profilers (ADCPs) have insufficient spatial resolution and cannot acquire fine flow field structures at the millimeter to decimeter level; 4) Traditional PIV / PTV (permeable flow velocity profiler) requires manual seeding of tracer particles, which cannot be engineered for use in deep-sea, high-temperature, acidic, and low-shear environments; 5) Conventional imaging and algorithms cannot cope with multiple noise interferences such as low contrast, weak tracer, strong scattering, and pressure window deformation, resulting in low signal-to-noise ratio and poor robustness.

[0004] In summary, existing technologies cannot achieve in-situ, non-invasive, visualized, and high-precision velocity field measurement of overflow hydrothermal vents, making it difficult to meet the scientific needs of hydrothermal dynamics, mass flux assessment, and ecological environment research. Summary of the Invention

[0005] To overcome the shortcomings of the prior art, the purpose of this invention is to provide a laser illumination velocimetry method and system for deep-sea hydrothermal vents based on natural tracing.

[0006] To achieve the above objectives, the technical solution adopted by the present invention is as follows:

[0007] This invention provides a laser illumination velocimetry method for deep-sea hydrothermal vents based on natural tracing, comprising:

[0008] S1: Employ a green-band sheet laser to emit a fan-shaped laser beam, adjust the laser attitude so that the laser plane is perpendicular to the main axis of the overflow hydrothermal vent and passes through the target flow field region, thereby exciting natural tracer signals. The natural tracer signals include scattered light from hydrothermal vents carrying mineral particles, bubble reflection, and schlieren signals formed by the refractive index gradient between the hydrothermal vent and the surrounding seawater.

[0009] S2: A deep-sea high-speed camera at a preset angle to the laser plane continuously acquires no less than two frames of time-series images, and a pre-calibration compensation algorithm is used to correct the non-uniform deformation of the pressure-resistant optical window and the imaging shift caused by the high pressure in the deep sea.

[0010] S3: Spatiotemporal joint filtering is performed on the acquired image sequence to remove multiplicative noise introduced by water turbidity and photon scattering, and adaptive histogram equalization is used to enhance the contrast between weak tracer particles and schlieren signals.

[0011] S4: Based on the assumption of constant brightness, optical flow constraint equations are established and solved iteratively using dense optical flow or sparse optical flow algorithms to obtain pixel-level instantaneous flow velocity vector fields. Local smoothing constraints are introduced to suppress non-fluid motion noise.

[0012] S5: By using intrinsic orthogonal decomposition or spatiotemporal frequency filtering algorithm, the velocity vector field is decomposed into the main component of hydrothermal driven disturbance flow and the residual components of background ocean current and equipment micro-vibration, and the purified hydrothermal velocity vector field is output.

[0013] S6: Based on a fixed-size scale reference within the field of view, establish the mapping relationship between pixel coordinates and physical space, convert pixel-level flow velocity into three-dimensional physical flow velocity in m / s, and generate a flow velocity field distribution cloud map.

[0014] Furthermore, in S2, the angle between the camera and the laser plane is set to 90°.

[0015] Furthermore, the basic optical flow equation in S4 is: Where (u, v) is the instantaneous velocity vector of the pixel to be determined, (I x , I y Let I be the spatial gradient of the image in the x and y directions. t This represents the time gradient.

[0016] Furthermore, S4 employs either the Farneback dense optical flow algorithm or the Lucas-Kanade sparse optical flow algorithm.

[0017] Furthermore, the physical velocity in S6 includes horizontal components, vertical components, and resultant velocity, and the output results include standard physical units and direction angles.

[0018] This invention also provides a laser illumination velocimetry system for deep-sea hydrothermal vents based on natural tracing, comprising:

[0019] Sheet laser illumination module: Used to emit a fan-shaped laser beam using a green band sheet laser, adjust the laser attitude so that the laser plane is perpendicular to the main axis of the overflow hydrothermal vent and passes through the target flow field area, and excite natural tracer signals, including scattered light from hydrothermal vents carrying mineral particles, bubble reflection, and schlieren signals formed by the refractive index gradient between the hydrothermal vent and the surrounding seawater.

[0020] Deep-sea high-speed camera module: Used to continuously acquire no less than two frames of time-series images using a deep-sea high-speed camera at a preset angle to the laser plane, and correct the non-uniform deformation of the pressure-resistant optical window and imaging shift caused by the high pressure in the deep sea through a pre-calibration compensation algorithm;

[0021] Image preprocessing module: used to perform spatiotemporal joint filtering on the acquired image sequence to remove multiplicative noise introduced by water turbidity and photon scattering, and to use adaptive histogram equalization to enhance the contrast between weak tracer particles and schlieren signals.

[0022] Optical flow velocity calculation module: It is used to establish optical flow constraint equations based on the assumption of constant brightness, and solve them iteratively using dense optical flow or sparse optical flow algorithms to obtain pixel-level instantaneous flow velocity vector field, and introduce local smoothing constraints to suppress non-fluid motion noise;

[0023] Flow field purification and separation module: It is used to decompose the flow velocity vector field into the main component of hydrothermal driven disturbance flow and the background ocean current and equipment micro-vibration residual components through intrinsic orthogonal decomposition or spatiotemporal frequency filtering algorithm, and output the purified hydrothermal flow velocity vector field;

[0024] Physical calibration and cloud map output module: It is used to establish the mapping relationship between pixel coordinates and physical space based on a scale reference object with a fixed size in the field of view, convert pixel-level flow velocity into three-dimensional physical flow velocity in m / s, and generate a flow velocity field distribution cloud map.

[0025] Compared with the prior art, the technical solution disclosed in this invention has the following beneficial effects:

[0026] Based on S1 sheet laser vertical illumination and natural tracer signal excitation, it eliminates the need for manual particle delivery, enabling non-invasive, in-situ, and visual measurement in extreme deep-sea environments, thus overcoming the fatal flaw of traditional PIVs that cannot deliver particles.

[0027] Based on the S2 high-pressure window deformation pre-calibration correction, the imaging distortion and offset caused by deep-sea hydrostatic pressure are eliminated, the geometric fidelity of the image is improved, and the accuracy of flow velocity calculation is significantly improved.

[0028] Based on S3 spatiotemporal joint filtering and adaptive contrast enhancement, it effectively suppresses water scattering, background stray light and random noise, significantly improves the signal-to-noise ratio of weak tracer signals, and ensures that low-speed flow can be measured.

[0029] Based on the S4 optical flow method and local smoothing constraints, it is highly adaptable to the low-speed, weak texture, irregular and large deformation flow characteristics of overflow nozzles, and the measurement accuracy and robustness are significantly better than the traditional cross-correlation PIV.

[0030] Based on the S5 intrinsic orthogonal decomposition flow field separation, interferences such as background ocean currents, equipment vibration, and platform drift are effectively eliminated, and a pure hydrothermal disturbance velocity field is output, which greatly improves the measurement reliability.

[0031] Based on S6 pixel-physical space calibration, it directly outputs three-dimensional flow velocity field and cloud map with physical units. The data can be directly used for hydrothermal flux calculation and scientific analysis, and has strong engineering applicability. Attached Figure Description

[0032] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the embodiments will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0033] Figure 1 This is a schematic diagram of the process for a laser illumination velocimetry method for deep-sea hydrothermal vents based on natural tracers, provided in an embodiment of the present invention. Detailed Implementation

[0034] The technical solutions of 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.

[0035] To make the above-mentioned objects, features and advantages of the present invention more apparent and understandable, the present invention will be further described in detail below with reference to the accompanying drawings and specific embodiments.

[0036] This invention provides a laser illumination velocimetry method and system for deep-sea hydrothermal vents based on natural tracers, which integrates accurate characterization of circulation, multi-physics field coupling calculation, load balancing distribution and coordinated heat dissipation.

[0037] like Figure 1 As shown, this embodiment of the invention provides a laser illumination velocimetry method for deep-sea hydrothermal vents based on natural tracing, comprising:

[0038] S1: Employ a green-band sheet laser to emit a fan-shaped laser beam, adjust the laser attitude so that the laser plane is perpendicular to the main axis of the overflow hydrothermal vent and passes through the target flow field region, thereby exciting natural tracer signals. The natural tracer signals include scattered light from hydrothermal vents carrying mineral particles, bubble reflection, and schlieren signals formed by the refractive index gradient between the hydrothermal vent and the surrounding seawater.

[0039] That is, a green band (532nm) fan-shaped laser beam is emitted using a sheet laser, and the spatial orientation of the fan-shaped laser beam is adjusted so that it is perpendicular to the main fluid axis of the overflow hydrothermal vent, passes through the target fluid area, and excites the naturally existing tracer signals in the area; the natural tracer signals include: scattered light from mineral particles carried by the hydrothermal vent, bubbles, and optical "scintillation" schlieren formed by the refractive index gradient between the hydrothermal vent and seawater.

[0040] Specifically, a 532nm green band sheet laser is positioned above the hydrothermal overflow area. The pitch and azimuth of the fan-shaped laser beam are adjusted via an attitude control mechanism to ensure the laser slice plane is perpendicular to the main hydrothermal fluid outflow axis, guaranteeing the laser plane completely penetrates the target flow field. The laser forms a thin optical slice underwater, directly exciting natural tracer signals within the flow field: including scattered light from mineral particles carried by the hydrothermal fluid, backscattered light from bubbles, and refractive index gradient schlieren signals formed by the density difference between the hydrothermal fluid and cold seawater. This transforms the previously invisible overflow fluid into a clearly imaged observation target.

[0041] S2: A deep-sea high-speed camera at a preset angle to the laser plane continuously acquires no less than two frames of time-series images, and a pre-calibration compensation algorithm is used to correct the non-uniform deformation of the pressure-resistant optical window and the imaging shift caused by the high pressure in the deep sea.

[0042] In S2, the angle between the camera and the laser plane is set to 90°.

[0043] That is, a deep-sea high-speed camera with a preset angle (preferably 90°) to the laser plane is used to continuously acquire N frames (N≥2) of high-resolution image sequence containing the natural tracer signal; at the same time, the non-uniform deformation of the camera's pressure-resistant optical window caused by the deep-sea high pressure is corrected by a pre-calibration compensation algorithm.

[0044] Specifically, a deep-sea high-definition high-speed camera is positioned at a 90° angle to the laser plane during observation, and the camera is equipped with a pressure-resistant optical window. Window deformation calibration is performed in advance at the maximum operating water depth, and a distortion correction model is established. During measurement, N≥2 frames of time-series images are continuously acquired, and a pre-calibrated compensation algorithm is invoked in real time to correct radial distortion, edge shift, and non-uniform blur caused by high pressure frame-by-frame, ensuring that the geometric accuracy of the images meets the requirements for flow velocity calculation.

[0045] S3: Spatiotemporal joint filtering is performed on the acquired image sequence to remove multiplicative noise introduced by water turbidity and photon scattering, and adaptive histogram equalization is used to enhance the contrast between weak tracer particles and schlieren signals.

[0046] That is, perform the following sub-steps on the acquired raw image sequence:

[0047] Noise reduction: Spatiotemporal joint filtering is used to remove multiplicative noise introduced by deep-sea turbidity and photon scattering;

[0048] Contrast Enhancement: Adaptive histogram equalization is performed to enhance the signal-to-noise ratio of weak tracer particles by taking advantage of the low attenuation characteristics of blue-green laser wavelengths (450nm-532nm) in seawater.

[0049] Specifically, the corrected image undergoes two-stage preprocessing: First, a spatiotemporal joint filtering algorithm is used to jointly denoise multiple adjacent frames, suppressing multiplicative noise and random noise caused by deep-sea turbidity, water scattering, and photon noise; then, adaptive histogram equalization is performed on the filtered image to locally enhance the contrast for weak tracer particles and schlieren signals, while avoiding excessive background magnification, so that the separation degree between the tracer signal and the background meets the input requirements for optical flow calculation.

[0050] S4: Based on the assumption of constant brightness, optical flow constraint equations are established and solved iteratively using dense or sparse optical flow algorithms to obtain pixel-level instantaneous flow velocity vector fields. Local smoothing constraints are introduced to suppress non-fluid motion noise. The basic optical flow equations in S4 are: Where (u, v) is the instantaneous velocity vector of the pixel to be determined, (I x , I y ) represents the spatial gradient of the image in the x and y directions, I t For the time gradient, S4 employs either the Farneback dense optical flow algorithm or the Lucas-Kanade sparse optical flow algorithm.

[0051] That is, based on the assumption of constant brightness, the basic optical flow equation is solved on the preprocessed adjacent frame images to obtain the instantaneous vector field of fluid motion; the basic optical flow equation is: Where (u, v) is the instantaneous velocity vector of the pixel to be determined, (I x , I y Let I be the spatial gradient of the image in the x and y directions. t The time gradient is used; dense optical flow algorithms (such as Farneback algorithm) or sparse optical flow algorithms (such as Lucas-Kanade algorithm) are used for iterative solution, and local smoothing constraints are introduced to suppress noise from non-fluid motion.

[0052] Specifically, the fundamental constraint equations for optical flow are established based on the assumption of constant brightness: The Farneback dense optical flow algorithm is used to iteratively solve adjacent frames of the preprocessed image to obtain the instantaneous velocity vector field (u,v) at the pixel level for the entire image. Local smoothing constraints are added during the solution process to filter isolated anomalous vectors and non-fluid motion noise, ensuring that the velocity field is continuous, smooth, and physically reliable.

[0053] S5: By using intrinsic orthogonal decomposition or spatiotemporal frequency filtering algorithm, the velocity vector field is decomposed into the main component of hydrothermal driven disturbance flow and the residual components of background ocean current and equipment micro-vibration, and the purified hydrothermal velocity vector field is output.

[0054] That is, based on the instantaneous vector field obtained in S4, a separation algorithm based on eigenorthogonal decomposition or spatiotemporal frequency filtering is applied to decompose the vector field into:

[0055] Principal component: Corresponding to the "turbulent flow" characteristics (target signal) driven by the heat exchange of the hydrothermal fluid itself;

[0056] Residual components: correspond to environmental noise such as background ocean currents and camera micro-vibrations;

[0057] It also outputs the purified hydrothermal vent velocity vector field.

[0058] Specifically, the instantaneous velocity field is decomposed spatiotemporally using intrinsic orthogonal decomposition (POD) or spatiotemporal frequency filtering algorithms: the vector field is decomposed into principal components and residual components. The principal components correspond to the perturbation flow fields (target signals) driven by hydrothermal buoyancy and diffusion; the residual components correspond to interference signals such as background ocean currents, camera micro-vibrations, and platform drift. After removing the residual components, the output is a purified velocity vector field that retains only the motion of the hydrothermal fluid itself.

[0059] S6: Based on a fixed-size scale reference within the field of view, a mapping relationship between pixel coordinates and physical space is established, converting pixel-level flow velocity into 3D physical flow velocity in m / s and generating a flow velocity field distribution cloud map. The physical flow velocity in S6 includes horizontal components, vertical components, and resultant velocity, and the output results include standard physical units and orientation angles.

[0060] That is, by using a reference object that acts as a scale in the image taken near the nozzle, a spatial mapping relationship between the image size and the actual physical size is established; the pixel domain velocity (u, v) obtained in step 5 is converted into the velocity value in the actual three-dimensional physical space (unit: m / s), and a velocity field distribution cloud map is generated.

[0061] Specifically, a scale reference object with known physical dimensions is introduced within the camera's field of view to establish a mapping relationship and scale conversion coefficient between image pixel coordinates and actual physical space coordinates. The purified pixel velocity (u,v) is mapped to the actual physical velocity (unit: m / s) according to the conversion coefficient. The horizontal velocity, vertical velocity, and resultant velocity are calculated, and velocity field vector cloud map, moiré map, or contour map containing amplitude and direction are generated. The output can be directly used for hydrothermal dynamics analysis and flux assessment.

[0062] This invention also provides a laser illumination velocimetry system for deep-sea hydrothermal vents based on natural tracing, comprising:

[0063] Sheet laser illumination module: Used to emit a fan-shaped laser beam using a green band sheet laser, adjust the laser attitude so that the laser plane is perpendicular to the main axis of the overflow hydrothermal vent and passes through the target flow field area, and excite natural tracer signals, including scattered light from hydrothermal vents carrying mineral particles, bubble reflection, and schlieren signals formed by the refractive index gradient between the hydrothermal vent and the surrounding seawater.

[0064] Deep-sea high-speed camera module: Used to continuously acquire no less than two frames of time-series images using a deep-sea high-speed camera at a preset angle to the laser plane, and correct the non-uniform deformation of the pressure-resistant optical window and imaging shift caused by the high pressure in the deep sea through a pre-calibration compensation algorithm;

[0065] Image preprocessing module: used to perform spatiotemporal joint filtering on the acquired image sequence to remove multiplicative noise introduced by water turbidity and photon scattering, and to use adaptive histogram equalization to enhance the contrast between weak tracer particles and schlieren signals.

[0066] Optical flow velocity calculation module: It is used to establish optical flow constraint equations based on the assumption of constant brightness, and solve them iteratively using dense optical flow or sparse optical flow algorithms to obtain pixel-level instantaneous flow velocity vector field, and introduce local smoothing constraints to suppress non-fluid motion noise;

[0067] Flow field purification and separation module: It is used to decompose the flow velocity vector field into the main component of hydrothermal driven disturbance flow and the background ocean current and equipment micro-vibration residual components through intrinsic orthogonal decomposition or spatiotemporal frequency filtering algorithm, and output the purified hydrothermal flow velocity vector field;

[0068] Physical calibration and cloud map output module: It is used to establish the mapping relationship between pixel coordinates and physical space based on a scale reference object with a fixed size in the field of view, convert pixel-level flow velocity into three-dimensional physical flow velocity in m / s, and generate a flow velocity field distribution cloud map.

[0069] This invention, through a laser illumination-based technical design, addresses many shortcomings of existing deep-sea overflow hydrothermal vent velocity measurement technologies, achieving several significant technical effects. All core effects are based on laser illumination, with some effects achieved in conjunction with related supporting technologies. Detailed explanations of the specific technical effects, advantages over existing technologies, and corresponding technological sources are as follows:

[0070] The primary technical effect of this invention is the first-ever "visualization" of overflow-type vents, completely solving the core problem of existing technologies' inability to clearly observe overflow fluid. In existing technologies, the fluid contrast of overflow-type hydrothermal vents is extremely low, making them almost invisible under ordinary light, thus hindering subsequent velocity measurements. This invention, through active laser illumination technology, transforms the previously invisible overflow fluid into a clearly observable state for the first time, laying the foundation for velocity field measurement. The core technology behind this effect stems from the laser illumination design in step 1. Specifically, blue-green lasers (wavelength 450nm–532nm) are selected, utilizing their low attenuation in seawater. Combined with the scattering effect of the laser on natural mineral particles in the target area and the schlieren effect generated by the fluid's refractive index gradient under laser irradiation, three natural tracer signals are excited, thereby achieving visualized observation of the overflow fluid and overcoming the limitation of existing technologies being "unobservable."

[0071] Secondly, the embodiments of this invention achieve the technical effect of completing velocity measurement without the need for manual seeding of tracer particles, significantly improving its engineering applicability in extreme deep-sea environments. Traditional particle image velocimetry (PIV) technology relies on the manual seeding of high-concentration, high-contrast tracer particles to achieve flow velocity measurement. However, in the extreme environments of the deep sea at depths of thousands of meters and in high-temperature, acidic conditions, manual seeding of tracer particles is impossible, severely limiting the practical application of the technology. In contrast, this invention eliminates the need for human intervention, directly utilizing laser illumination to excite naturally occurring mineral particles and bubbles within the target area as tracer signals. This transforms the traditional "manual seeding" mode into a "natural excitation" mode, completely solving the problem of tracer particle deployment in deep-sea environments. The core technology for this effect still originates from the laser illumination design in step 1. Through the scattering and excitation effect of laser on natural particles, the originally dispersed and weak natural particles become identifiable tracer signals, meeting the velocity measurement requirements without the need for additional artificial tracers.

[0072] Furthermore, the embodiments of this invention can effectively adapt to the low-velocity, low-contrast, and unstructured flow characteristics of overflow-type hydrothermal vents, solving the problem of poor adaptability of traditional technologies. Traditional cross-correlation PIV technology has stringent requirements for the measurement scenario, requiring the fluid to have high contrast and regular motion patterns. However, the fluid velocity of overflow-type hydrothermal vents is low, the contrast is extremely low, and the flow state is irregular, resulting in a high failure rate and unreliable results for traditional technologies in this scenario. In contrast, this invention significantly improves the contrast between the fluid and the background through laser illumination, creating favorable input conditions for subsequent velocity calculations. Combined with the advantages of optical flow, it achieves accurate measurement of unstructured flows. The technical source of this effect is the synergistic effect of laser illumination in step 1 and optical flow in step 4. Laser illumination is the core foundation, responsible for solving the key problem of "insufficient contrast," while optical flow adapts to the calculation requirements of low-contrast and unstructured flows. The combination of the two achieves accurate adaptation to overflow-type vent flows, and neither can be dispensed with.

[0073] Furthermore, the embodiments of this invention possess excellent adaptability to the deep-sea environment, enabling them to cope with the complex optical transmission environment of the deep sea. Deep-sea water significantly attenuates light, and ordinary light has weak penetration, making long-distance, clear observation impossible. However, this invention, in step 1, is specifically designed for the deep-sea optical transmission window, selecting blue-green lasers (wavelength 450nm–532nm). These wavelengths have the lowest attenuation coefficient in seawater and strong penetration, enabling effective illumination of the target area in the deep-sea environment. This ensures clear acquisition of the tracer signal, providing reliable assurance for subsequent measurement steps. The core technology behind this effect lies in the targeted selection of the laser wavelength in step 1, demonstrating the adaptability of laser illumination to the deep-sea environment.

[0074] Summary of Effects: The core technological breakthrough of this invention lies in the design and application of the laser illumination system. This system fundamentally solves the core problem of "unobstructed visibility" of overflow hydrothermal vents, providing a fundamental guarantee for the entire velocity field measurement process. Optical flow method, as an adaptive algorithm, is selected based on the visualization and contrast enhancement achieved by laser illumination. The synergistic effect of the two enables high-precision velocity field measurement. The core logic is: without laser illumination, the overflow fluid is invisible, the tracer signal cannot be excited, and the optical flow method cannot be implemented; with laser illumination as a foundation, even if various calculation schemes (such as different optical flow algorithms and different anti-interference methods) are replaced, effective velocity measurement can still be achieved. Therefore, laser illumination is the fundamental source of all the core technological effects of this invention.

[0075] In short, the technical solution includes the sequential execution of optical slicing construction, image acquisition, image preprocessing, optical flow calculation, and physical conversion steps. In the optical slicing construction step, a sheet laser is used to excite naturally occurring tracer signals such as mineral particles, bubbles, and refractive index gradients within the target area. This step is based on optical and fluid physics principles and has clear physical meaning. In the image acquisition step, a deep-sea camera continuously acquires a time-series image sequence containing the aforementioned natural tracer signals, and corresponding hardware control and imaging parameter settings are completed. In the image preprocessing step, adaptive contrast enhancement and boundary mask extraction operations are performed on the acquired images. This processing is designed for the specific physical image characteristics of deep-sea hydrothermal fluids and is not simply a mathematical operation. In the optical flow calculation step, the basic optical flow equation is solved based on the assumption of constant brightness and applied to a sequence of real physical fluid images, ultimately outputting a velocity vector field with clear physical meaning; therefore, it is not a pure algorithm without physical meaning. In the physical conversion step, the pixel-level flow velocity of the image is mapped to a fluid velocity with actual physical units, in m / s, giving the calculation results quantifiable physical meaning.

[0076] Furthermore, there are multiple alternative implementation schemes for each functional module of this invention. All alternative schemes retain the core concept of this invention, which is based on laser illumination, and differ only in the specific implementation method of each module. A summary is as follows:

[0077] The laser illumination module can employ several alternative solutions: replacing the sheet laser with a line-scanning laser paired with a galvanometer allows for dynamic adjustment of the illumination area thickness to adapt to different nozzle shapes; replacing the single-wavelength blue-green laser (450–532nm) with a dual-wavelength or multi-wavelength laser can excite different types of natural tracer signals to improve tracer density; replacing the continuous-wave laser with a pulsed laser and combining it with time-gated imaging can suppress backscattered light and improve the imaging signal-to-noise ratio in deep-sea turbidity environments; replacing unidirectional laser illumination with a dual-cross laser surface can acquire flow field depth direction information and support three-dimensional velocity field reconstruction; replacing the sheet laser with laser speckle illumination is suitable for extreme cases where natural tracer particles are extremely scarce, and flow velocity can be calculated through speckle cross-correlation; replacing the blue-green laser with an ultraviolet laser (approximately 355nm) is suitable for nozzles rich in specific fluorescent substances, resulting in lower background noise in the fluorescence signal.

[0078] Alternatives to the image acquisition module include: replacing a single camera with a dual-camera stereo vision system, which can acquire the complete three-dimensional velocity vector of the flow field, rather than just two-dimensional planar components; replacing a conventional high-speed camera with an event camera, which has a small data volume and a time resolution down to the microsecond level, making it suitable for capturing the subtle movements of low-speed fluids; replacing single-exposure imaging with double-exposure or multi-exposure frame overlay, which can record particle motion trajectories in a single frame image, suitable for long-term integration measurements at extremely low flow rates; and replacing the fixed-angle camera mounting with a variable-angle mounting mechanism, which can dynamically adjust the angle between the laser plane and the camera optical axis within the range of 45°-135° to adapt to different nozzle shapes and measurement accuracy requirements.

[0079] The image preprocessing module can adopt the following alternatives: replacing spatiotemporal joint filtering with guided filtering or nonlocal mean filtering can better preserve the fluid edge structure while denoising; replacing adaptive histogram equalization with contrast-limited adaptive histogram equalization (CLAHE) or Rayleigh distribution normalization can avoid over-enhancing background noise and is suitable for scenarios with extremely uneven particle distribution; or the above preprocessing methods can be replaced with deep learning-based image enhancement networks, which are suitable for scenarios with sufficient training data and end-to-end enhancement requirements.

[0080] Alternatives to flow velocity calculation algorithms include: replacing optical flow with cross-correlation particle image velocimetry (PIV) after laser illumination significantly enhances contrast, suitable for scenarios with high tracer particle density and relatively regular motion; replacing optical flow with particle tracking velocimetry (PTV), suitable for sparse tracer particle scenarios, capable of tracking the trajectory of individual particles; replacing traditional optical flow with deep learning optical flow networks, capable of handling large displacement and deformation flows with faster computation speed (GPU acceleration required); replacing optical flow based on the assumption of constant brightness with joint estimation of optical flow and occlusion based on deep learning, suitable for scenarios with significant occlusion in the fluid; and replacing two-dimensional optical flow with three-dimensional optical flow, combined with a dual-camera stereo vision system, to output a complete three-dimensional flow velocity field.

[0081] Alternatives to the physical calibration and cloud map output module include: replacing the reference scale method with laser triangulation calibration, which eliminates the need to place a scale within the field of view and is suitable for deep-sea environments where reference objects cannot be placed; or replacing the reference scale method with dual-laser parallel line calibration, which can acquire depth information in real time and improve the accuracy of three-dimensional flow velocity conversion.

[0082] Alternative deployment options for the system include: replacing the fixed deep-sea lander with a remotely operated vehicle (ROV) that can flexibly adjust the measurement position and is suitable for multi-nozzle traversal measurement; and replacing the ROV with an autonomous underwater vehicle (AUV) that is suitable for large-scale hydrothermal vent surveys without the need for real-time control from a mother ship.

[0083] The basic principles of the present invention have been described above with reference to specific embodiments. However, it should be noted that the advantages, benefits, and effects mentioned in the present invention are merely examples and not limitations, and should not be considered as essential features of each embodiment of the present invention. Furthermore, the specific details disclosed above are for illustrative and facilitative purposes only, and are not limitations. These details do not limit the present invention to the necessity of employing the aforementioned specific details.

[0084] The block diagrams of devices, apparatuses, devices, and systems involved in this invention are merely illustrative examples and are not intended to require or imply that they must be connected, arranged, or configured in the manner shown in the block diagrams. As those skilled in the art will recognize, these devices, apparatuses, devices, and systems can be connected, arranged, and configured in any manner. Words such as “comprising,” “including,” “having,” etc., are open-ended terms meaning “including but not limited to,” and are used interchangeably with them. The terms “or” and “and” as used herein refer to the terms “and / or,” and are used interchangeably with them unless the context clearly indicates otherwise. The term “such as” as used herein refers to the phrase “such as but not limited to,” and is used interchangeably with it.

[0085] It should also be noted that in the apparatus, device, and method of the present invention, the components or steps can be disassembled and / or recombined. These disassemblies and / or recombinations should be considered as equivalent solutions of the present invention.

[0086] The above description of the disclosed aspects is provided to enable any person skilled in the art to make or use the invention. Various modifications to these aspects will be readily apparent to those skilled in the art, and the general principles defined herein can be applied to other aspects without departing from the scope of the invention. Therefore, the invention is not intended to be limited to the aspects shown herein, but rather to be carried out within the widest scope consistent with the principles and novel features disclosed herein.

[0087] It should be understood that the qualifying terms "first", "second", "third", "fourth", "fifth" and "sixth" used in the description of the embodiments of the present invention are only used to more clearly illustrate the technical solutions and are not intended to limit the scope of protection of the present invention.

[0088] The above description has been given for purposes of illustration and description. Furthermore, this description is not intended to limit the embodiments of the invention to the forms disclosed herein. Although numerous exemplary aspects and embodiments have been discussed above, those skilled in the art will recognize certain variations, modifications, alterations, additions, and sub-combinations therein.

Claims

1. A laser illumination velocimetry method for deep-sea hydrothermal vents based on natural tracing, characterized in that, include: S1: Employ a green-band sheet laser to emit a fan-shaped laser beam, adjust the laser attitude so that the laser plane is perpendicular to the main axis of the overflow hydrothermal vent and passes through the target flow field region, thereby exciting natural tracer signals. The natural tracer signals include scattered light from hydrothermal vents carrying mineral particles, bubble reflection, and schlieren signals formed by the refractive index gradient between the hydrothermal vent and the surrounding seawater. S2: A deep-sea high-speed camera at a preset angle to the laser plane continuously acquires no less than two frames of time-series images, and a pre-calibration compensation algorithm is used to correct the non-uniform deformation of the pressure-resistant optical window and the imaging shift caused by the high pressure in the deep sea. S3: Spatiotemporal joint filtering is performed on the acquired image sequence to remove multiplicative noise introduced by water turbidity and photon scattering, and adaptive histogram equalization is used to enhance the contrast between weak tracer particles and schlieren signals. S4: Based on the assumption of constant brightness, optical flow constraint equations are established and solved iteratively using dense optical flow or sparse optical flow algorithms to obtain pixel-level instantaneous flow velocity vector fields. Local smoothing constraints are introduced to suppress non-fluid motion noise. S5: By using intrinsic orthogonal decomposition or spatiotemporal frequency filtering algorithm, the velocity vector field is decomposed into the main component of hydrothermal driven disturbance flow and the residual components of background ocean current and equipment micro-vibration, and the purified hydrothermal velocity vector field is output. S6: Based on a fixed-size scale reference within the field of view, establish the mapping relationship between pixel coordinates and physical space, convert pixel-level flow velocity into three-dimensional physical flow velocity in m / s, and generate a flow velocity field distribution cloud map.

2. The method according to claim 1, characterized in that, In S2, the angle between the camera and the laser plane is set to 90°.

3. The method according to claim 1, characterized in that, The basic optical flow equation in S4 is: ,in, (u, v) Let be the instantaneous flow velocity vector of the pixel to be determined. (I x , I y ) The spatial gradient of the image in the x and y directions. I t This represents the time gradient.

4. The method according to claim 1, characterized in that, S4 employs either the Farneback dense optical flow algorithm or the Lucas-Kanade sparse optical flow algorithm.

5. The method according to claim 1, characterized in that, In S6, the physical velocity includes horizontal components, vertical components, and resultant velocity, and the output results include standard physical units and direction angles.

6. A laser illumination velocimetry system for deep-sea hydrothermal vents based on natural tracing, characterized in that, include: Sheet laser illumination module: Used to emit a fan-shaped laser beam using a green band sheet laser, adjust the laser attitude so that the laser plane is perpendicular to the main axis of the overflow hydrothermal vent and passes through the target flow field area, and excite natural tracer signals, including scattered light from hydrothermal vents carrying mineral particles, bubble reflection, and schlieren signals formed by the refractive index gradient between the hydrothermal vent and the surrounding seawater. Deep-sea high-speed camera module: Used to continuously acquire no less than two frames of time-series images using a deep-sea high-speed camera at a preset angle to the laser plane, and correct the non-uniform deformation of the pressure-resistant optical window and imaging shift caused by the high pressure in the deep sea through a pre-calibration compensation algorithm; Image preprocessing module: used to perform spatiotemporal joint filtering on the acquired image sequence to remove multiplicative noise introduced by water turbidity and photon scattering, and to use adaptive histogram equalization to enhance the contrast between weak tracer particles and schlieren signals. Optical flow velocity calculation module: It is used to establish optical flow constraint equations based on the assumption of constant brightness, and solve them iteratively using dense optical flow or sparse optical flow algorithms to obtain pixel-level instantaneous flow velocity vector field, and introduce local smoothing constraints to suppress non-fluid motion noise; Flow field purification and separation module: It is used to decompose the flow velocity vector field into the main component of hydrothermal driven disturbance flow and the background ocean current and equipment micro-vibration residual components through intrinsic orthogonal decomposition or spatiotemporal frequency filtering algorithm, and output the purified hydrothermal flow velocity vector field; Physical calibration and cloud map output module: It is used to establish the mapping relationship between pixel coordinates and physical space based on a scale reference object with a fixed size in the field of view, convert pixel-level flow velocity into three-dimensional physical flow velocity in m / s, and generate a flow velocity field distribution cloud map.

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