A method for rapid detection of ship wake by airborne lidar and experimental device

Abstract

The application discloses a stern wake rapid detection method and experimental device of an airborne laser radar, and belongs to the technical field of laser radar ocean detection. The method comprises the following steps: collecting laser echo signals of a ship body and a sea-air interface stern wake and pre-processing; roughly classifying the sea-air interface stern wake according to different backscattering characteristics; designing a classification algorithm to exclude invalid signals to reduce the calculation amount; and acquiring polarization information of an effective area to extract ship body echo signals. The application can solve the interference of the stern wake signal during the marine detection of the airborne laser radar, and can quickly and effectively distinguish the ship body, and has strong practical significance and application prospect.

Description

Technical Field

[0001] This invention belongs to the field of lidar detection technology, specifically relating to a rapid detection method for ship wake currents using airborne lidar. Background Technology

[0002] Solid-state lidar in the 905nm band features high precision, high resolution, low cost, and strong anti-interference capabilities, enabling it to monitor and guide ships at sea. However, the presence of turbulence and bubble curtains behind the ship can affect the scattering and absorption of light signals, interfering with the discrimination of lidar echo signals. Research on the characteristics of turbulence signals based on back-propagation has significant strategic and practical value for real-time monitoring and precision guidance of maritime targets.

[0003] The wake generated by a moving ship mainly includes three types: 1. Surface waves generated by the hull—Kelvin wake; 2. Internal waves generated upon reaching the mezzosphere or thermocline; 3. Turbulent wake. There is extensive research on Kelvin wakes in China, which are commonly used for infrared detection and identification of ships. However, in actual detection, Kelvin wakes are severely interfered with by wind and wave fields, and the detection effect is limited by the observation angle. Detectors can only effectively detect them at near-vertical incident angles. Turbulent wakes, on the other hand, are clearly visible from all angles and are a major source of interference with the ship's echo signal.

[0004] Turbulence behind a ship manifests in many forms. Bubbles in turbulence are mainly generated by the interaction between the ship's hull, propeller, and seawater, including propeller cavitation, stern undulation, and splashing. Regarding theoretical research and modeling of turbulence and foam, GuDaiFang and Phillips studied the strong turbulent jet generated by a propeller in a light breeze, where the intensity and average velocity of its vortex structure are affected by ship type, speed, and path of motion. Sun Rongqing used the GRG approximation for non-spherical particles and studied the relationship between the backscattering effect caused by volume-surface scattering and the foam particles and foam layer thickness. Zhang Jiansheng et al. proposed a mathematical and physical model of the radius distribution of bubbles in a bubble curtain. Qi Xiao discussed the backscattering characteristics of foamy sea surfaces in the blue-green laser band. Many similar studies exist, but research on turbulent foam wakes largely remains at the level of simplified calculations under multiple constraints, which are not entirely applicable to the practical application scenarios of airborne lidar. Therefore, designing a rapid detection technology based on measured data is essential. Summary of the Invention

[0005] To address the classification problem of ship hull and wake echoes during sea surface detection using airborne lidar, this invention provides a rapid detection method and experimental apparatus for ship wakes using airborne lidar. This method is applicable to practical application scenarios of airborne lidar.

[0006] To achieve the above objectives, the present invention provides the following technical solution:

[0007] A method for rapid detection of ship wake using airborne lidar includes:

[0008] Step (1): Use a 905nm lidar to acquire the backscattered echo signal of the ship's wake at the sea-air interface, remove background noise, and calculate the normalized pulse peak value A and the average detection probability P. D Select the judgment thresholds A0 and P0 under the lowest false alarm rate and false alarm rate, and determine the effective area based on the area classification;

[0009] Step (2): Obtain the polarization information of the effective region, obtain the incident light parameter S and the outgoing light parameter S' based on the Stokes vector method, calculate the polarization degree P of the scattered light, derive the 4*4 Mueller matrix under the area array measurement, and calculate the medium depolarization degree D in this region.

[0010] Step (3): Keep other parameters unchanged, select the threshold D0 with the lowest false alarm rate and false alarm rate based on the solution bias D. When D>D0, the region is the ship hull signal.

[0011] Furthermore, the region classification is based on backscattering characteristics to classify the hull and the wake.

[0012] Furthermore, the specific regional classification includes: the hull and propeller as region A, propeller white waves as region B, high-speed white wave jets as region C, weak scattering turbulence below the threshold as region D, and the region covered by the foam layer as region E.

[0013] Furthermore, determining the effective region based on regional classification specifically includes:

[0014] Extract a set of data containing N waveforms from the backscattered echo signal. If the normalized average pulse peak value A is less than the threshold A0, the echo signal is determined to be from region D or a non-wake water body signal, i.e., an invalid region. Conversely, if the detection probability P D If the signal is greater than the threshold P0, the echo is determined to be a valid signal from region A, B, or E, and is considered a valid region; otherwise, it is considered a valid signal from region C or other invalid regions.

[0015] Furthermore, the depolarization degree D takes values ​​in the range of [1,4]. When D=1, the scattered light is completely depolarized, and when D=4, the scattered light has the same polarization state as the incident light.

[0016] Further, the system includes a 905nm pulsed lidar (1), a digital oscilloscope (2), a regulated power supply (3), a CCD camera (4), a water tank (5) containing pure seawater (9), a hull (6), a propeller (7), a light-absorbing black screen (8), pure seawater (9), a movable fixed bracket (10), and an optical platform (11). The hull (6) is placed in the water tank (5), and a propeller (7) is installed on it. The 905nm pulsed lidar (1) is fixed above the water tank (5) and connected to the digital oscilloscope (2) and the regulated power supply (3) to acquire the backscattered echo signal in the wake region. The CCD camera (4) is directly above the water tank (5) and is fixed on the optical platform (11) by the movable fixed bracket (10) to monitor whether the light spot is at the desired target point.

[0017] Compared with the prior art, the significant advantages of the present invention are as follows:

[0018] 1) This invention is a technology for rapidly distinguishing ship hulls by acquiring the backscattered signal and polarization information of the wake of an airborne lidar; 2) The complex distribution of the wake is classified according to its backscattering characteristics, and an algorithm is designed to eliminate interference and reduce invalid calculations; 3) Based on the above algorithm theory, the solution polarization degree of the regional surface is calculated, and the ship hull and wake signals can be quickly and effectively separated by setting a simple threshold; 4) This invention can be applied to the field of airborne lidar marine detection, and has considerable strategic significance and practical value for real-time monitoring and precision guidance of ship targets. Attached Figure Description

[0019] Figure 1 This invention provides an experimental device for laser radar wake detection.

[0020] Figure 2 This is a schematic diagram of the lidar structure used in an embodiment of the present invention;

[0021] Figure 3 This is a flowchart of the wake detection technology used in the embodiments of the present invention. Detailed Implementation

[0022] 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.

[0023] Combination Figure 3 A method for rapid detection of ship wake using airborne lidar, comprising:

[0024] Step (1): Use a 905nm lidar to acquire the backscattered echo signal of the ship's wake at the sea-air interface, remove background noise, and calculate the normalized pulse peak value A and the average detection probability P. D Based on parameters such as pulse width τ, the wake is classified into regions according to the backscattering characteristics. The judgment thresholds A0 and P0 with the lowest false alarm rate and missed alarm rate are selected to filter out the background water body and the weak scattering region of the wake, thereby reducing the acquisition of unnecessary polarization information and optimizing the algorithm speed.

[0025] Step (2): Obtain the polarization information of the effective region, obtain the incident light parameter S and the outgoing light parameter S' based on the Stokes vector method, calculate the polarization degree P of the scattered light, derive the 4*4 Mueller matrix under the area array measurement, and calculate the medium depolarization degree D in this region.

[0026] Step (3): Keep other parameters unchanged, select the threshold D0 with the lowest false alarm rate and false alarm rate based on the solution bias D. When D>D0, the region is the ship hull signal.

[0027] Step (1) includes:

[0028] Based on backscattering characteristics, the hull and stern flow are classified into the following regions: Hull and propeller A, propeller white wave B, high-speed white wave jet C, weak scattering turbulence D, region covered by foam layer E.

[0029] The energy of the wake behind the ship mainly decreases with increasing distance, accompanied by different optical characteristics and echo signal characteristics. The hull and propeller are in region A, the "white waves" at close range behind the ship are in region BC, the medium and long distances are mainly a complex combination of weak scattering regions CD, and the far distance region E is mainly a foam layer.

[0030] Based on the above classification method, an algorithm is designed to filter out invalid interference signals. A set of data containing N waveforms is extracted from the echo of a certain region. If the normalized average pulse peak value A is less than the set threshold A0, the echo signal is determined to be from region D or a non-wake water body signal; if it is greater than or equal to A0, the next step is performed. If the detection probability P... D If the signal exceeds the set threshold P0, the echo is determined to be a strong scattering effective signal from the hull or regions B and E; otherwise, it is a signal from region C or other invalid signals. In other words, the interference signal mainly originates from regions B and E of the strong scattering echo, so the polarization information of the scattered light from regions CD and other water bodies is ignored to save computing power.

[0031] Step (2) includes:

[0032] Based on the above filtering algorithm, the polarization information of the scattered light in the effective region (ABE region) is obtained. The Stokes vectors S and S' of the incident light and scattered light are obtained. There are four Stokes parameters in each group. The polarization degree P represents the proportion of the fully polarized light to the total light intensity. The Mueller matrix of the medium under the area array measurement is derived and the depolarization degree D (Dop) of the scattered light in this region is calculated to describe the depolarization capability of the medium in this region.

[0033] The value of D is in the range of [1,4]. When D=1, the scattered light is completely depolarized. When D=4, the polarization state of the scattered light is the same as that of the incident light. Therefore, the smaller D is, the more obvious the depolarization effect of the medium is. The threshold D0 is set under the condition of minimizing the false alarm rate and the missed alarm rate. When D>D0, the echo signal is judged to be the ship's signal.

[0034] Based on the depolarization effect caused by multiple scattering, linearly polarized light incident on regions B and E will be scattered multiple times in white waves and foam media and change its propagation direction, accompanied by a significant depolarization effect. However, single or few scatterings of ship echoes will not cause depolarization. This allows for accurate determination of whether it is a ship echo.

[0035] The salinity of the seawater is taken as the global average salinity value of 3.25%, and the temperature is 25℃. This invention adopts a sweep angle of near-vertical incident. The scattering characteristics of the sea surface are mainly affected by the large-scale roughness (θ<20°). The white wave phenomenon in the B region near the ship can be considered as the roughness of the sea surface being significantly changed when the ship passes by. The incident laser undergoes multiple scatterings in the high-roughness medium of the B region, colliding with different droplet particles and changing the propagation direction, causing a depolarization effect.

[0036] When the foam is sparse, the foam layer is considered as a discrete foam model of a standard sphere, taking into account the influence of the thickness of the outer foam film, including changes in the propagation direction, absorption and dispersion of the laser by the film, etc. In this case, the laser transmittance can be calculated according to the Lambbeer law, but the corresponding echo energy and detection probability are relatively small, which do not reach the detection threshold where both are effective. When the foam is dense, the echo energy is large and can be effectively detected. The foam layer is considered as a foam cloud structure of spherical foams that are stuck together. In this case, the propagation process of the laser in the foam should take into account the adhesion film and multiple scattering between foams.

[0037] In practical applications, the distribution of the wake current is complex and varies depending on the hull, propeller, seawater, and wind conditions. However, the methods described in this invention can be used to classify and distinguish the hull according to the above methods.

[0038] This technology can solve the interference of ship wake signals during airborne lidar maritime detection and quickly and effectively distinguish ship hulls, which has strong practical significance and application prospects.

[0039] A rapid wake detection and processing device for an airborne lidar includes: a memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the rapid wake detection method for the airborne lidar.

[0040] A computer storage medium storing an executable program, the executable program being executed by a processor to implement the steps of the airborne lidar rapid wake detection method.

[0041] Example 1

[0042] The present invention will be further described below with reference to the accompanying drawings and specific embodiments. The present invention includes, but is not limited to, the following embodiments.

[0043] An experimental device for acquiring backscattered echo signals in the wake region of a ship, such as... Figure 1 As shown, the system includes: a 905nm pulsed lidar (1), a high-speed digital oscilloscope (2), a regulated power supply (3), a CCD camera (4), a water tank (5), a hull (6), a propeller (7), a light-absorbing black screen (8), pure seawater (9), a movable fixed support (10), and an optical platform (11). The setup and data acquisition preprocessing are as follows:

[0044] Among them, the 905nm lidar (1) is as follows Figure 2 As shown, it includes a laser transmitter (I), a laser receiver (II), a fixed base (III), and an embedded signal processing module, which acquires the digital signal of the signal processing module as the sampling source of the high-speed digital oscilloscope (2).

[0045] The high-speed digital oscilloscope, regulated power supply, CCD camera, and propeller are powered by 220V AC power, while the regulated power supply (3) provides 12V DC power to the pulsed laser radar (1) to output 905nm pulsed laser.

[0046] The CCD camera is fixed to the top of the experimental setup with a movable bracket, and the other end is fixed to the optical platform to ensure its stability, thereby monitoring whether the light spot is at the ideal target point;

[0047] To ensure that the lidar acquires the coordinates (x, y, z) and (x', y', z') of the laser spot, it can obtain the stern echo signal with a fixed elevation angle β0 and a fixed detection distance L0. The formula is as follows:

[0048]

[0049]

[0050] Where z > z' is assumed, the ship's coordinates are set to point O on the coordinate axis, and the long side of the pool is made parallel to the edge of the optical platform table during measurement to determine the positive direction of the wake. At the same time, the lidar is fixed to be perpendicular to the edge of the optical platform table. Thus, y = y'. The above formula can cancel out the y and y' terms, simplifying the calculation.

[0051] Obtain the detection probability of lidar based on measured data, divide it into segments according to the distance sampling interval, and calculate the detection probability P within each distance segment. D :

[0052]

[0053] In the formula, N is the number of sampling points within the distance interval, and M is the number of discovery points within the interval;

[0054] Tap water and sea salt were added to a 100*50*30mm pool to prepare pure seawater with a salinity of 3.5%. At the same time, a light-absorbing black curtain was added to the bottom to prevent the reception of stray light from the bottom wall of the pool. Since pure seawater has a strong absorption of 905nm infrared laser, this ensures that only the signals of the ship's hull and wake are received from the water surface.

[0055] 2. The sampling method and classification criteria for ship wakes in this invention are as follows:

[0056] Using the hull and propeller as coordinate axis point O, and taking the wake jet direction as positive, an echo sampling point is taken every 5 cm. Based on the backscattering characteristics, the hull and wake are classified into the following regions: Hull and propeller A, Propeller splash B1, High-speed white wave jet B2, High-speed jet confluence point C1, Confluence turbulence C2, High-speed foam turbulence D1, Low-foam turbulence D2, Foam layer generation region E1, Slow-moving dense foam layer E2, Relatively static dense foam region E3. A more detailed division is required for laboratory-scale data collection, and the classification criteria are as follows:

[0057] (1) Using twin propellers as wave-making devices, due to limitations of experimental equipment and site, the energy of the wake flow mainly decreases with increasing distance, and the regional distribution is relatively obvious, mainly changing significantly with increasing distance.

[0058] The area near the stern of the ship is mainly a white wave region (0-15cm) generated by the interaction of the propeller with seawater and air. In region C, the floating wave peak is reached at 15cm-20cm and gradually weakens. Region B is mainly a white wave composed of water swirling with air and a large number of bubbles, which will cause multiple scattering of incident light, with a strong backscattering coefficient and depolarization effect, which is manifested in the waveform as a large peak pulse and echo power.

[0059] (2) The turbulent white wave phenomenon gradually weakens after the jet flow convergence point C2 (20cm), and the potential energy is converted into kinetic energy, leaving a section of sparse foam and weak white wave phenomenon of strong turbulent jet, mainly distributed in the D region (25-35cm); since water molecules are polarized molecules, they will have strong resonance in the infrared band, which will result in a strong absorption effect on the light in this band. It is difficult for lidar to receive the wake signal in this part of the seawater.

[0060] (3) Due to the high viscosity of seawater, the rising of underwater bubbles and the interaction between the jet and the surrounding water will gradually generate a foam layer at point E1, which will remain on the sea surface for a long time. The characteristics of the foam layer are: the greater the thickness of the foam coverage, the greater the surface roughness for laser reflection, the weaker the specular reflection, and the stronger the scattering.

[0061] 3. The classification algorithm designed based on the above classification criteria is as follows:

[0062] First, extract a set of data containing N waveforms from the echoes in this area. N is usually 100. Take at least 5 sets of continuous and stable valid echoes as a valid echo set. Extract the normalized pulse peak value and root mean square voltage value of this set, extract the average pulse width τ, and calculate the average detection probability of each set of data in this area. If there is no valid echo set, calculate the total average value of the echo data in this set.

[0063] If the normalized average pulse peak value A is less than the set threshold A0 and the detection probability P D If the pulse width is less than the set threshold P0, the echo signal is determined to be from region D or other non-wake signals. If the pulse width is greater than the threshold, the next step is performed. The pulse width is extracted and the standard deviation of the pulse width fluctuation is calculated. If the average pulse width is not within the set pulse width statistical interval [τ1,τ2] or the standard deviation of the pulse width fluctuation is greater than the threshold σ0, the echo signal is determined to be from region B or part of the high-coverage foam layer in region E. Region C is characterized by a lower detection probability and a gradually weakening pulse peak value.

[0064] Furthermore, the seawater outside the stern is unlikely to generate an effective echo for the 905nm lidar. However, interference from wind, waves, algae, and fish cannot be ruled out. The foam and whitecaps generated by wind and waves are relatively random in distribution and have a much lower density than the bubbles in the stern. The echoes generated by algae are significantly weaker than those from the hull and stern. Whitecaps caused by fish have a relatively fast dissipation rate. By comparing and analyzing A, τ, and P... D , σ0, U RMS Echo parameters can effectively distinguish wake, hull, and such interference echoes; if A, U RMS Very small but P D If A and U are at a relatively large value, the signal is determined to be algae near the water surface; if A and U are at a relatively large value, the signal is determined to be algae near the water surface. RMS It's very big, but P D If the value is relatively small, the echo signal is determined to be either a school of fish or interference from wind and waves.

[0065] 4. Based on the above classification results, this invention calculates the backscattered light polarization characteristics of the effective region:

[0066] This invention employs the Stokes vector method to mathematically describe polarization state information, using a set of four Stokes parameters for characterization:

[0067]

[0068] Where S0 represents the total power or intensity of the beam, usually normalized to 1, and the other three values ​​are normalized according to S0; S1 represents the difference between the intensity of horizontally polarized light and the intensity of vertically polarized light, S2 is the difference between the intensity of +45° polarized light and -45° polarized light, and S3 is the difference between the intensity of right-handed and left-handed polarized light. The proportion of fully polarized light to the total light intensity is called the degree of polarization.

[0069]

[0070] For fully polarized light, there is S0 2 =S1 2 +S2 2 +S3 2 ;

[0071] The Mueller matrix of this region is calculated to describe the optical transformation effect of the medium on the incident polarized light. The Mueller matrix of this region is derived using the Stokes parameters of the incident and outgoing light:

[0072] S′=MS, where

[0073] Where S and S' represent the Stokes matrices describing the incident and outgoing light, and M is a 4*4 Mueller matrix that describes the polarization state transformation of any incident polarized light by the medium.

[0074] The Muller matrix calculated here uses a planar array measurement method, and the measurement object is the backscattered light within the spot area of ​​this region. The solution bias (Dop) of the medium is defined as:

[0075]

[0076] The value of D ranges from [1,4]. When D=1, the scattered light is completely depolarized. When D=4, the scattered light has the same polarization state as the incident light. Therefore, the smaller D is, the more obvious the depolarization effect of the medium is. The threshold D0 is set to minimize the false alarm rate and the missed alarm rate. When D>D0, the echo signal is judged to be the ship's signal.

[0077] 5. The backscattering model for wake regions B and E is as follows:

[0078] The salinity of the seawater is taken as the global average salinity of 3.25%, and the temperature is 25℃. This invention uses a near-perpendicular incident sweep angle (θ<20°). The scattering characteristics of the sea surface are mainly affected by large-scale roughness. The white waves observed near the ship can be considered as a significant change in the roughness of the sea surface when the ship passes by. The variance and correlation length of the surface height undulation are much greater than the incident wavelength (905nm). According to the Kirchooff approximation of large-scale undulating surfaces, the surface field equation on the tangent plane of a random surface unit element is expressed as:

[0079]

[0080] The surface field of the tangent plane can be written as the sum of the Kirchhoff surface field and its complementary field, then the incident light Scattered light Kirchhoff field of tangent plane complementary fields The following relationships exist:

[0081]

[0082]

[0083]

[0084] Average scattering energy P qp With backscattering coefficient It can be calculated using the following formula:

[0085]

[0086]

[0087] Where E qp S E qp k E qp c The tangential surface field and the standard Kirchhoff surface field and complementary field of the medium surface are represented by the Stratton-Chu integral formula, and the average energy is represented by the sum of the Kirchhoff term, the cross term and the complementary term.

[0088] Region C has a large roughness but a small slope, so the multiple scattering term can be approximately ignored. The single scattering conforms to the standard Kirchhoff model mentioned above. Region B has a large slope and roughness, so multiple scattering needs to be calculated, along with the depolarization effect.

[0089] The scattering theory of layered media was used to calculate the long-distance turbulent foam layer behind the ship. The seawater thickness d2 was considered to be infinite, and the scattering model of the foam layer d1 adopted geometric optics theory. The single reflectivity R and transmissivity T of the laser in the foam were calculated using Fresnel formulas.

[0090]

[0091] Where I represents light intensity and E represents the electric vector. Since the vertical and horizontal components of the electric vectors of reflected and refracted light are different, they are respectively represented as:

[0092]

[0093]

[0094] The reflectivity R and refractive index T for the second and third times are derived by analogy according to Fresnel's formula. The value of the nth reflection is the cumulative product of the previous results. The number of reflections to be calculated is selected according to the actual requirements. The calculation of backscattered light is the superposition of light in the direction opposite to the incident angle. Therefore, the attenuation effect of foam on laser light must also be considered.

[0095] When the foam is sparse, the foam layer is considered as a discrete foam model with a standard sphere. The influence of the outer foam film thickness must also be taken into account, including changes in propagation direction, absorption of the laser by the film, and dispersion. In this case, the laser transmittance can be calculated using Beer-Lambert's law.

[0096] Γ=exp[-B(λ)CR]

[0097] Where C represents the concentration of discrete foam, R represents the thickness of discrete foam, and B(λ) is the foam mass extinction coefficient related to foam composition, bubble size, and incident light wavelength. The discrete foam concentration at point (x, y, z) in the foam layer can be obtained by performing a line integral along the laser path on the discrete foam concentration.

[0098]

[0099] When the foam is dense, the foam layer is considered as a foam cloud structure of spherical foams bonded together. In this case, the laser propagation process within the foam should consider the bonding film and multiple scattering between foams. This can be addressed using boundary conditions of the electromagnetic field and matrix analysis of multilayer thin films. The laser energy attenuation value D as it passes through m layers of bonded foam cloud is calculated. m for:

[0100]

[0101] Where t i Let τ be the Fresnel coefficient on the i-th layer of the membrane. m Let a be the transmittance of the m-layered bonded foam cloud. 11 The coefficients can be obtained through matrix analysis.

Claims

1. A method for rapid detection of ship wake using airborne lidar, characterized in that, include: Step 1: Use a 905nm lidar to acquire the backscattered echo signal of the ship's wake at the sea-air interface, remove background noise, and calculate the normalized pulse peak value A and the average detection probability P. D Select the judgment thresholds A0 and P0 under the lowest false alarm rate and false alarm rate, and determine the effective area based on the area classification; Step 2: Obtain the polarization information of the effective region. Based on the Stokes vector method, obtain the incident light parameter S and the outgoing light parameter S', calculate the polarization degree P of the scattered light, derive the 4*4 Mueller matrix under the area array measurement, and calculate the medium depolarization degree D in this region. Step 3: Keeping other parameters unchanged, select the threshold D0 with the lowest false alarm rate and false alarm rate based on the solution bias D. When D>D0, the region is the ship hull signal.

2. The method for rapid detection of ship wake by airborne lidar according to claim 1, characterized in that, The region classification is based on backscattering characteristics to categorize the hull and wake.

3. The method for rapid detection of ship wake by airborne lidar according to claim 2, characterized in that, The specific regional classification includes: the hull and propeller as region A, propeller white waves as region B, high-speed white wave jets as region C, weak scattering turbulence below the threshold as region D, and the region covered by the foam layer as region E.

4. The method for rapid detection of ship wake by airborne lidar according to claim 3, characterized in that, Determining valid regions based on regional classification specifically includes: Extract a set of data containing N waveforms from the backscattered echo signal. If the normalized average pulse peak value A is less than the threshold A0, the echo signal is determined to be from region D or a non-wake water body signal, i.e., an invalid region. Conversely, if the detection probability P D If the signal is greater than the threshold P0, the echo is determined to be a valid signal from region A, B, or E, and is considered a valid region; otherwise, it is considered a valid signal from region C or other invalid regions.

5. The method for rapid detection of ship wake by airborne lidar according to claim 1, characterized in that, The depolarization degree D ranges from [1, 4]. When D = 1, the scattered light is completely depolarized, and when D = 4, the scattered light has the same polarization state as the incident light.

6. An experimental apparatus for collecting data in the rapid wake detection method according to any one of claims 1-5, characterized in that, The system includes a 905nm pulsed lidar (1), a digital oscilloscope (2), a regulated power supply (3), a CCD camera (4), a water tank (5) containing pure seawater (9), a hull (6), a propeller (7), a light-absorbing black screen (8), pure seawater (9), a movable fixed bracket (10), and an optical platform (11). The hull (6) is placed in the water tank (5) and a propeller (7) is installed on it. The 905nm pulsed lidar (1) is fixed above the water tank (5) and connected to the digital oscilloscope (2) and the regulated power supply (3) to acquire the backscattered echo signal in the wake region. The CCD camera (4) is directly above the water tank (5) and is fixed on the optical platform (11) by the movable fixed bracket (10) to monitor whether the light spot is at the desired target point.

7. A rapid detection and processing device for ship wakes using airborne lidar, characterized in that, include: A memory, a processor, and a computer program stored in the memory, wherein the processor executes the computer program to implement the steps of the rapid wake detection method for an airborne lidar according to any one of claims 1-5.

8. A computer storage medium, characterized in that, The computer storage medium stores an executable program, which is executed by a processor to implement the steps of the rapid wake detection method of airborne lidar according to any one of claims 1-5.

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