A method for exploring the maximum detection distance under an underwater active light source illumination system

Abstract

The present invention provides a method for exploring the farthest detection distance under an underwater active light source lighting system, and belongs to the field of underwater optical imaging technology. By constructing an underwater optical system simulation model on a MATLAB platform, including a water medium photon transmission model, a lens model, a target model, and a detection plane model, it is innovatively proposed that under laboratory conditions, by fixing the input of three fixed parameters, namely, the water quality, the light source divergence angle, and the optical axis distance, and constantly adjusting a variable parameter, namely, the attenuation length AL of different multiples, the corresponding imaging simulation light spot image can be obtained, thereby evaluating the farthest detection distance of the human eye under active light source lighting, without the need to shoot the target object through a camera in the field. The method provided by the present invention improves the efficiency of detecting the farthest detection distance under an underwater active light source lighting system, and provides an intuitive, comprehensive, and economical and effective simulation model method for the research and application in the field of underwater optical imaging.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater optical imaging, and in particular relates to a method for exploring the farthest detection distance under an underwater active light source illumination system. Background Art

[0002] As a key branch of modern marine science research, underwater optical imaging technology and its related technical theories constitute the theoretical basis of the present invention. The underwater environment is different from the terrestrial environment. Due to the complexity of the water environment, artificial active light source illumination is often required to ensure the safety and effectiveness of underwater operations. For example, underwater search for shipwrecks and aircraft wreckage and inspection of underwater submarine pipelines, all require artificial active light source illumination. In addition, in actual scenarios, it is often necessary to obtain the farthest detection distance that the human eye can detect under artificial active light source illumination. And by studying the farthest detection distance of the human eye in the underwater environment, the characteristics of light propagation in water and the attenuation of light can be understood. This information is very important for the development of underwater imaging technology. However, in the prior art, most of the targets under illumination are photographed by cameras, and the farthest detection distance of the human eye is determined by adjusting the distance. There is no complete set of technical solutions that can detect the farthest detection distance of the human eye under underwater active light source illumination under laboratory conditions. Summary of the invention

[0003] In view of the above problems, the present invention simulates water quality, light source, and camera factors to obtain a method for obtaining the farthest detection distance under artificial light illumination conditions. The method can simulate the imaging contour of underwater targets under the conditions of water quality, light source divergence angle, and optical axis distance, and evaluate the imaging contour result map to obtain the farthest detection distance when imaging underwater targets under artificial light illumination at a certain angle.

[0004] The present invention proposes a method for exploring the maximum detection distance under an underwater active light source illumination system, comprising the following steps:

[0005] Step 1: Build an underwater optical imaging system simulation model based on the MATLAB platform, including a water medium photon transmission model, a lens model, a target model, and a detection plane model;

[0006] Step 2, setting imaging simulation parameters in the constructed simulation model, including water quality parameters, optical axis distance parameters, light source divergence angle parameters and attenuation length parameters, to perform imaging simulation; the optical axis distance is the distance between the simulated light source and the optical axis distance of the lens model, wherein the center of the simulated light source and the receiving plane of the lens model are on the same vertical plane; the light source divergence angle parameter is the degree of the set light source divergence angle; the attenuation length parameter is the attenuation length AL between the simulated light source or the lens model and the receiving surface of the target object model;

[0007] Step 3, only the attenuation length AL is changed, and different multiples of the attenuation length AL are received respectively. After receiving the photon energy, the target model transmits it in the direction of the lens model. The detection plane model behind the lens model receives the photon energy position information and performs visualization processing to obtain the imaging light spot images under different attenuation lengths;

[0008] Step 4, compare the received imaging light spot images under different attenuation lengths under three parameters of a fixed water quality, a fixed optical axis distance and a fixed light source divergence angle, evaluate the fuzziness of the light spot image, and obtain the attenuation length AL of the farthest detection distance.

[0009] Preferably, the water medium photon transmission model in step 1 includes constructing a simulated light source model and constructing a photon propagation process model under water;

[0010] Among them, constructing a simulated light source model is to construct a three-dimensional point light source; using a Cartesian coordinate system to establish coordinate axes, and using a Lambertian light source as a simulated light source to initialize the photon energy; among them, constructing a model of the propagation process of photons underwater is to use the Monte Carlo method to simulate the propagation process of photons underwater.

[0011] Preferably, the constructing of the three-dimensional point light source is specifically:

[0012] Set the Z axis as I 0 The angle between each photon and the Z axis is the zenith angle θ lightsource , and the angle between the projection in the XoY plane and the positive direction of the X axis is the azimuth angle φ lightsource , respectively, in the range of [0°, 90°] and [0°, 360°], with equal spacing, using a point light source with a small angle divergence, and setting the zenith angle θ lightsource The range is [0.1°, 20°]; perform cyclic stepping, zenith angle θ lightsource Each step angle is 0.0001°, and the azimuth angle φ lightsource The step angle is 0.5°;

[0013] Using Lambertian light source as the simulated light source, when initializing the photon energy, the energy in the normal direction is set to the initial value I 0 According to Lambert's law, the radiation intensity I in the direction of the cosine angle θ in the normal direction θ For I θ =I 0 × cosθ, therefore, I 0 The energy of the photon emitted in the direction is W 0 , the photon energy in other emission directions is W 0 ×cosθ.

[0014] Preferably, the Monte Carlo method is used to simulate the propagation process of photons underwater, specifically:

[0015] Determine the path length of the photon; the energy decay of light follows an exponential distribution: p(l) = e -l ,l≥0, where l is the optical depth and e is the natural base;

[0016] From the cumulative distribution function: Let P(l) = q, we can get l = -ln(1-q) = -lnq, 0≤q≤1;

[0017] By the following formula: The photon geometric path length s is calculated, where c is the attenuation coefficient;

[0018] The direction of photon movement is updated; the initial position coordinates of the photon in this photon event (x 0 ,y 0 ,z 0 ), initial direction cosines (μ x ,μ y ,μ z ), the length of the photon's path is s, then the position coordinates (x, y, z) of the photon after movement can be obtained:

[0019]

[0020] The polar angle θ and azimuth φ of this photon event are known, and the direction cosine (μ x ,μ y ,μ z ):

[0021]

[0022] Direction cosine (μ x ,μ y ,μ z ) coordinate transformation, we can get the direction information (μ) after the photon event ends. x ′,μ y ′,μ z ′):

[0023]

[0024] Among them, 0≤θ≤π; 0≤φ≤2π.

[0025] Preferably, the lens model is based on the spherical equation x 2 +y 2 +(zd) 2 =R 2Construct the upper and lower surfaces of the lens, where R is the radius of curvature of the lens and d is the coordinate of its spatial position; to determine whether the photon propagates through the lens, first calculate the photon position to determine whether the photon has passed through the upper surface of the lens. If the front and rear positions of the photon are on both sides of the plane, it proves that the photon has passed through the upper surface. The judgment process for the lower surface is the same as above. Calculate and record the intersection of the light path and the lens; after obtaining the intersection, calculate the normal vector at this intersection according to the equation expression of the lens surface; then calculate the light path after refraction according to Snell's refraction law, and calculate and record the information value of the photon falling on the receiving plane.

[0026] Preferably, the target object model simulates a H*W receiving plane as the target object, counts the number of photons hitting the receiving plane and energy information, and re-emits photons by forming a rectangular surface light source composed of multiple Lambertian point light sources.

[0027] Preferably, the receiving plane model is a rectangular target constructed using multiple Lambertian point light sources for imaging simulation, and the zenith angle θ of each point light source is object Range is The cycle step length is Scattering angle φ object scope The cycle step length is Δ φobjecy , the emitted rectangular model is h*w, and the interval between the face elements is Δ point .

[0028] Preferably, the water quality parameters include absorption coefficient a and scattering coefficient b; the attenuation length AL of the water body is:

[0029]

[0030] The detection distance is obtained based on different multiples of the attenuation length AL.

[0031] Compared with the prior art, the present invention proposes a method for exploring the maximum detection distance under an underwater active light source illumination system, and produces the following beneficial effects:

[0032] By constructing an underwater optical system simulation model on the MATLAB platform, it is innovatively proposed that under laboratory conditions, by fixing the three fixed parameters of input water quality, light source divergence angle and optical axis distance, and constantly adjusting a variable parameter, that is, different multiples of attenuation length AL, the corresponding imaging simulation light spot image can be obtained, thereby evaluating the farthest detection distance of the human eye under active light source illumination, without the need to actually shoot the target object through a camera. The method provided by the present invention improves the efficiency of detecting the farthest detection distance under the underwater active light source illumination system, and can obtain underwater optical imaging simulation images, providing an intuitive, comprehensive, and economical simulation model method for the research and application of underwater optical imaging. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 This is a flow chart of a method for exploring the farthest detection distance under the underwater active light source lighting system of the present invention.

[0034] Figure 2 It is a schematic diagram of a simulation model of the present invention.

[0035] Figure 3 Schematic diagram of the Lambertian light source of the present invention.

[0036] Figure 4 This is the Monte Carlo-based underwater photon propagation flow chart of the present invention.

[0037] Figure 5 This is a lens model diagram of the present invention.

[0038] Figure 6 This is a 3-fold attenuation imaging diagram of the port water area when the divergence angle is 1° and the optical axis distance is 0.5 meter in Example 1.

[0039] Figure 7 This is a 5-fold attenuation imaging diagram of the port water area when the divergence angle is 1° and the optical axis distance is 0.5 meters in Example 1.

[0040] Figure 8 This is a 7-fold attenuation imaging diagram of the port water area when the divergence angle is 1° and the optical axis distance is 0.5 meters in Example 1.

[0041] Fig. 9 This is an 8-fold attenuation imaging diagram of the port water area when the divergence angle is 1° and the optical axis distance is 0.5 meters in Example 1.

[0042] Fig.10 This is an imaging diagram of the 7 times attenuation length of the ocean water area when the divergence angle is 1° and the optical axis distance is 0.5 meter in Example 2.

[0043] Fig.11 This is an imaging diagram of 6 times the attenuation length of coastal waters when the divergence angle is 1° and the optical axis distance is 0.5 meter in Example 2.

[0044] Fig.12 This is an imaging diagram of 6 times the attenuation length in the port water area when the divergence angle is 1° and the optical axis distance is 1 meter in Example 2.

[0045] Fig.13 This is an imaging diagram of 6 times the attenuation length of ocean waters when the divergence angle is 1° and the optical axis distance is 1 meter in Example 2.

[0046] Fig.14 This is an imaging diagram of 5 times the attenuation length of coastal waters when the divergence angle is 1° and the optical axis distance is 1 meter in Example 2.

[0047] Fig.15This is an imaging diagram of the 7 times attenuation length in the port water area when the divergence angle is 3° and the optical axis distance is 0.5 meter in Example 3.

[0048] Fig.16 This is an imaging diagram of the 7 times attenuation length of the ocean water area when the divergence angle is 3° and the optical axis distance is 0.5 meter in Example 3.

[0049] Fig.17 This is an imaging diagram of 6 times the attenuation length of coastal waters when the divergence angle is 3° and the optical axis distance is 0.5 meter in Example 3. DETAILED DESCRIPTION

[0050] The invention will be further described below in conjunction with specific embodiments.

[0051] The present invention proposes a method for exploring the maximum detection distance under an underwater active light source illumination system. The method takes underwater photoelectric imaging technology as the theoretical basis, simulates the transmission process of underwater photons based on the Monte Carlo method, establishes an optical model of the lens, and conducts underwater imaging experiments. Finally, the imaging results of photons passing through the lens surface are observed to explore the maximum detection distance under fixed water quality conditions, optical axis distance and light source divergence angle. The overall process is as follows Figure 1 As shown in Figure 2, the structure of the constructed simulation model is as follows: Figure 2 shown.

[0052] Embodiment 1:

[0053] Step 1: Build an underwater optical imaging system simulation model based on the MATLAB platform, including a water medium photon transmission model, a lens model, a target model, and a detection plane model.

[0054] The specific simulation process is:

[0055] S1. Constructing a photon transmission model in water

[0056] S1.1. Constructing the light source model

[0057] S1.1.1 Constructing a 3D point light source model

[0058] Use the Cartesian coordinate system to establish the coordinate axis, with the Z axis as the I 0 The angle between each photon and the Z axis is the zenith angle θ lightsource , and the angle between the projection in the XoY plane and the positive direction of the X axis is the azimuth angle φ lightsource , respectively, in the range of [0°, 90°] and [0°, 360°], with equal spacing, using a point light source with a small angle divergence, and setting the zenith angle θ lightsource The range is [0.1°, 20°]. Cyclic stepping, zenith angle θ lightsource Each step angle is 0.0001°, and the azimuth angle φ lightsourceThe step angle is 0.5°. Set the inherent optical properties of the simulated water body, including the absorption coefficient a, scattering coefficient b, and attenuation coefficient c.

[0059] S1.1.2. Initialize the photon energy

[0060] The schematic diagram of the Lambert light source is attached. Figure 3 As shown. The energy in the normal direction sets the initial value I 0 According to the definition of Lambertian surface, the radiation intensity I in the direction of the cosine angle θ in the normal direction θ For I θ =I 0 × cosθ. Therefore, I 0 The energy of the photon emitted in the direction is W 0 , in this embodiment, it is set to 100, and the photon energy in other emission directions is W 0 ×cosθ.

[0061] S1.2. Constructing a model of the photon propagation process underwater

[0062] The Monte Carlo method is used to simulate the propagation process of photons underwater. The simulation flow chart is shown in the attached figure. Figure 4 As shown, specifically including:

[0063] S1.2.1. Determine the path length s of a photon

[0064] The energy attenuation of light follows an exponential distribution: p(l) = e -l ,l≥0, where l is the optical depth and e is the natural base.

[0065] From the cumulative distribution function: Let P(l)=q, then we can obtain l=-ln(1-q)=-ln q, 0≤q≤1.

[0066] By the following formula: The photon geometric path length s is calculated, where c is the attenuation coefficient.

[0067] S1.2.2. Update of photon motion direction

[0068] The initial position coordinates of the photon in this photon event (x 0 ,y 0 ,z 0 ), the initial direction cosines

[0069] (μ x ,μ y ,μ z ), the length of the photon's path is s, then the position coordinates of the photon after movement can be obtained

[0070]

[0071] The polar angle θ (0≤θ≤π) and azimuth angle φ (0≤φ≤2π) of this photon event are known, and the direction cosine (μ x ,μ y ,μ z ):

[0072]

[0073] Direction cosine (μ x ,μ y ,μ z ) coordinate transformation, we can get the direction information (μ) after the photon event ends. x ′,μ y ′,μ z ′):

[0074]

[0075] S2. Constructing lens model

[0076] Using the spherical equation x 2 +y 2 +(zd) 2 =R 2 The upper and lower surfaces of the lens are constructed, where R is the radius of curvature of the lens and d is the coordinate of its spatial position. The lens model constructed in the present invention is as shown in the attached figure. Figure 5 As shown, A is the target, B is the imaging surface, and L is a thin lens; in this embodiment, the thickness is 5mm, the aperture is 10mm, the upper surface is 1cm away from the lower surface, and the refractive index is 1.5168. To determine whether the photon propagates through the lens, first calculate the photon position to determine whether the photon has passed through the upper surface of the lens. If the front and rear positions of the photon are on both sides of the plane, it proves that the photon has passed through the upper surface. The determination process of the lower surface is the same as above. Calculate and record the intersection of the light path and the lens; after obtaining the intersection, calculate the normal vector at this intersection according to the equation of the lens surface; then according to Snell's refraction law: sinθ 1 n 1 = sinθ 2 n 2 , calculate the light path after refraction, and calculate and record the information value of the photon falling on the receiving plane. After the above steps, the lens model is built.

[0077] S3. Constructing the illuminated target model

[0078] A H*W receiving plane is simulated as the target object, where the units of H and W are cm. The number and energy information of photons hitting the receiving plane are counted, and a rectangular surface light source composed of multiple Lambertian point light sources re-emits photons.

[0079] This embodiment simulates a 10cm*10cm receiving plane as a target object, counts the number and energy information of photons hitting the receiving plane, and re-emits photons by forming a rectangular surface light source composed of multiple Lambertian point light sources.

[0080] S4. Constructing the detection plane model

[0081] Imaging simulation of a rectangular target constructed using multiple Lambertian point light sources, with the zenith angle θ of each point light source object Range is The cycle step length is Scattering angle φ object scope The cycle step length is The rectangular model of the emission is h*w (in cm), and the interval between the face elements is Δ point .

[0082] This embodiment uses a rectangular target constructed by multiple Lambertian point light sources for imaging simulation. The object distance is 1.5m, the zenith angle θ of each point light source ranges from [0.1°, 30°], the cycle step is 0.1°, the scattering angle φ ranges from [0.1°, 360°], the cycle step is 2°, the emitted rectangular model is 2cm*2cm, the interval between the facets is 5mm, and the number of emitted photons is 1,350,000.

[0083] Step 2: Set the imaging simulation parameters in the simulation model, including water quality, optical axis distance, light source divergence angle and attenuation length, and perform imaging simulation. The specific simulation process is as follows:

[0084] S1. Setting imaging simulation parameters

[0085] In this embodiment, the port waters are set with an absorption coefficient of a=0.374 and an attenuation coefficient of b=1.826, and a Lambertian point light source with a divergence angle of 1 degree is simulated to emit about 200 million photons. The horizontal distance between the point light source and the simulated lens is kept at 0.5 meters. The photons reach the receiving surface of the target object model after 3 attenuation lengths.

[0086] S2. Imaging Simulation

[0087] Only the attenuation length between the target and the lens is changed, and the imaging diagrams are drawn after 3 times, 5 times, 7 times, and 8 times the attenuation length, respectively, as shown in the attached figure. Figure 6 , attached Figure 7 , attached Figure 8 , attached Fig. 9 shown.

[0088] Step 3, compare the received imaging light spot diagrams under different attenuation lengths under fixed water quality, optical axis distance and light source divergence angle parameters to obtain the farthest detection distance. The specific process is as follows:

[0089] By comparing the imaging light spot diagrams after 3, 5, 7, and 8 times the attenuation length, it can be seen that with the increase of the attenuation length, the outline of the target becomes more and more blurred, until the target is no longer clearly visible at 8 times the attenuation length. Therefore, it can be considered that 7 times the attenuation length is the farthest distance that can be detected underwater.

[0090] Experiments have shown that under active light illumination, the maximum detection distance has little to do with the brightness of the active light source. Therefore, we simulate the three main parameters, namely water quality, light source divergence angle, and imaging contour result diagram under optical axis distance, and evaluate the imaging result contour diagram to obtain the maximum detection distance when the target object is imaged under artificial active light illumination at a certain angle.

[0091] Embodiment 2:

[0092] The difference between this embodiment and embodiment 1 is that the imaging simulation parameters are set differently.

[0093] Change the water quality parameters. Set the absorption coefficient to 0.426 and the scattering coefficient to 0.577 to simulate ocean waters; set the absorption coefficient to 0.18 and the scattering coefficient to 0.22 to simulate coastal waters. Set a Lambertian point light source with a divergence angle of 1 degree to emit approximately 200 million photons, and keep the point light source at a horizontal distance of 0.5 meters from the simulated lens. The photons pass through three attenuation lengths to reach the receiving surface of the target model. In the two simulated water conditions, the longest detection distance imaging diagram is obtained after 3, 5, 7, and 8 times the attenuation length. When the absorption coefficient is 0.426 and the scattering coefficient is 0.577, the imaging result of the target after 7 times the attenuation length is as follows Fig.10 As shown; when the absorption coefficient is 0.18 and the scattering coefficient is 0.22, the imaging result of the target after 6 times the attenuation length is as follows Fig.11 shown.

[0094] Embodiment 3:

[0095] The difference between this embodiment and embodiment 1 is that the imaging simulation parameters are set differently.

[0096] Change the optical axis distance. Set the absorption coefficient a=0.374 and the attenuation coefficient b=1.826 for port waters; the absorption coefficient is 0.426 and the scattering coefficient is 0.577 to simulate ocean waters; the absorption coefficient is 0.18 and the scattering coefficient is 0.22 to simulate coastal waters. Set a Lambertian point light source with a divergence angle of 1 degree to emit approximately 200 million photons, and keep the point light source and the simulated lens horizontally at a distance of 1 meter. The photons reach the receiving plane of the target after 3 attenuation lengths. In the three simulated water conditions, the longest detection distance imaging diagram is obtained after 3 times, 5 times, 7 times, and 8 times the attenuation length. When the absorption coefficient is 0.374 and the scattering coefficient is 1.826, the imaging result of the target after 6 times the attenuation length is as shown in the figure below. Fig.12 As shown; when the absorption coefficient is 0.426 and the scattering coefficient is 0.577, the imaging result of the target after 6 times the attenuation length is shown in the figure Fig.13 As shown; when the absorption coefficient is 0.18 and the scattering coefficient is 0.22, the imaging result of the target after 5 times the attenuation length is as follows Fig.14 shown.

[0097] Embodiment 4:

[0098] The difference between this embodiment and embodiment 1 is that the imaging simulation parameters are set differently.

[0099] Change the divergence angle of the light source. Set the absorption coefficient a=0.374 and the attenuation coefficient b=1.826 for port waters; the absorption coefficient is 0.426 and the scattering coefficient is 0.577 to simulate ocean waters; the absorption coefficient is 0.18 and the scattering coefficient is 0.22 to simulate coastal waters. Set the Lambertian point light source with a divergence angle of 3 degrees to emit approximately 200 million photons, and keep the horizontal distance between the point light source and the simulated lens at 0.5 meters. The photons pass through 3 attenuation lengths to reach the receiving plane of the target object. In the three simulated water conditions, the longest detection distance imaging diagram is obtained after 3 times, 5 times, 7 times, and 8 times the attenuation length. When the absorption coefficient is 0.374 and the scattering coefficient is 1.826, the imaging result of the target after 7 times the attenuation length is as follows Fig.15 As shown; when the absorption coefficient is 0.426 and the scattering coefficient is 0.577, the imaging result of the target after 7 times the attenuation length is as follows Fig.16 As shown; when the absorption coefficient is 0.18 and the scattering coefficient is 0.22, the imaging result of the target after 6 times the attenuation length is as follows Fig.17 shown.

[0100] Table 1 Maximum detection distance under different water qualities

[0101] Water Quality Light source divergence angle Optical wheelbase Maximum detection distance Port waters 1° 0.5m 7AL Ocean waters 1° 0.5m 7AL Coastal waters 1° 0.5m 6AL

[0102] It can be seen from Table 1 that when the light source divergence angle is 1° and the optical axis distance is 0.5 m, the maximum detection distance in port waters is 7AL, the maximum detection distance in ocean waters is 7AL, and the maximum detection distance in coastal waters is 6AL.

[0103] Table 2 Maximum detection distance under different optical axis distances

[0104] Water Quality Light source divergence angle Optical wheelbase Maximum detection distance Port waters 1° 1 meter 6AL Ocean waters 1° 1 meter 6AL Coastal waters 1° 1 meter 5AL

[0105] It can be seen from Table 2 that when the light source divergence angle is 1° and the optical axis distance is 1 meter, the maximum detection distance in port waters is 6AL, the maximum detection distance in ocean waters is 6AL, and the maximum detection distance in coastal waters is 5AL.

[0106] Table 3 Maximum detection distance under different light source divergence angles

[0107] Water Quality Light source divergence angle Optical wheelbase Maximum detection distance Port waters 3° 0.5m 7AL Ocean waters 3° 0.5m 7AL Coastal waters 3° 0.5m 6AL

[0108] It can be seen from Table 3 that when the light source divergence angle is 3° and the optical axis distance is 0.5 m, the maximum detection distance in port waters is 7AL, the maximum detection distance in ocean waters is 7AL, and the maximum detection distance in coastal waters is 6AL.

[0109] The above description is only the preferred embodiment of the present application and is not intended to limit the present application. For those skilled in the art, the present application may have various modifications and variations. Any modification, equivalent replacement, improvement, etc. made within the spirit and principle of the present application shall be included in the protection scope of the present application.

[0110] Although the above describes the specific implementation methods of the present invention, it is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art on the basis of the technical solution of the present invention without creative work are still within the scope of protection of the present invention.

Claims

1. A method for exploring the maximum detection distance under an underwater active light source illumination system, characterized in that: The following steps are involved: Step 1: Build an underwater optical imaging system simulation model based on the MATLAB platform, including a water medium photon transmission model, a lens model, a target model, and a detection plane model; Step 2, setting imaging simulation parameters in the constructed simulation model, including water quality parameters, optical axis distance parameters, light source divergence angle parameters and attenuation length parameters, to perform imaging simulation; the optical axis distance is the distance between the simulated light source and the optical axis distance of the lens model, wherein the center of the simulated light source and the receiving plane of the lens model are on the same vertical plane; the light source divergence angle parameter is the degree of the set light source divergence angle; the attenuation length parameter is the attenuation length between the simulated light source or the lens model and the receiving surface of the target model ; Step 3, change only the decay length , respectively, after different multiples of attenuation length After receiving the photon energy, the target model emits it in the direction of the lens model. The detection plane model behind the lens model receives the photon energy position information and performs visualization processing to obtain the imaging light spot images under different attenuation lengths. Step 4: Compare the received imaging light spot images at different attenuation lengths under three parameters: fixed water quality, fixed optical axis distance, and fixed light source divergence angle, evaluate the fuzziness of the light spot images, and obtain the attenuation length of the farthest detection distance. .

2. The method for exploring the maximum detection distance under an underwater active light source illumination system as claimed in claim 1, characterized in that: The water medium photon transmission model in step 1 includes constructing a simulated light source model and constructing a photon propagation process model under water; Among them, constructing a simulated light source model is to construct a three-dimensional point light source; using a Cartesian coordinate system to establish coordinate axes, and using a Lambertian light source as a simulated light source to initialize the photon energy; among them, constructing a model of the propagation process of photons underwater is to use the Monte Carlo method to simulate the propagation process of photons underwater.

3. The method for exploring the maximum detection distance under an underwater active light source illumination system as claimed in claim 2, characterized in that: The construction of the three-dimensional point light source is specifically as follows: The Z axis is The angle between each photon and the Z axis is the zenith angle ,and Projection in the plane and The angle between the positive axis and the azimuth , respectively and The range is divided into equal intervals, using a point light source with a small angle divergence angle, and setting the zenith angle Range is ; Perform circular stepping, zenith angle Each step angle is , azimuth The step angle is ; Using Lambertian light source as the simulated light source, when initializing the photon energy, the energy in the normal direction is set to the initial value , according to Lambert's law, the cosine of the angle in the normal direction Directional radiation intensity for Therefore, the regulation The energy of the photon emitted in the direction is , the photon energy in other emission directions is .

4. The method for exploring the maximum detection distance under an underwater active light source illumination system as claimed in claim 3, characterized in that: The Monte Carlo method is used to simulate the propagation process of photons underwater, specifically: Determine the path length of the photon; the energy decay of the light follows an exponential distribution: ,in is the optical depth, e is the natural base; From the cumulative distribution function: ; make , can be obtained ; By the following formula: , calculate the photon geometric path length s, where is the attenuation coefficient; The direction of photon movement is updated; the initial position coordinates of the photon in this photon event are known , the initial direction cosines , the length of the photon's path is s, then the position coordinates of the photon after movement can be obtained ； The polar angle of this photon event is known and azimuth , direction cosines : Direction cosine By transforming the coordinates, we can get the direction information after the photon event ends. : in, ; .

5. The method for exploring the maximum detection distance under an underwater active light source illumination system as claimed in claim 1, characterized in that: The lens model is based on the spherical equation Construct the upper and lower surfaces of the lens, where R is the radius of curvature of the lens, is the coordinate of its spatial position; to determine whether the photon propagates through the lens, first calculate the photon position to determine whether the photon has passed through the upper surface of the lens. If the front and rear positions of the photon are on both sides of the plane, it proves that the photon has passed through the upper surface. The determination process for the lower surface is the same as above. Calculate and record the intersection of the light path and the lens; After obtaining the intersection point, the normal vector at this intersection point is calculated according to the equation of the lens surface; then according to Snell's refraction law, the light path after refraction is calculated, and the information value of the recorded photon falling on the receiving plane is calculated.

6. The method for exploring the maximum detection distance under an underwater active light source illumination system as claimed in claim 1, characterized in that: The target model simulates a * The receiving plane is taken as the target object, the number and energy information of photons hitting the receiving plane are counted, and a rectangular surface light source composed of multiple Lambertian point light sources re-emits photons.

7. The method for exploring the maximum detection distance under an underwater active light source illumination system as claimed in claim 1, characterized in that: The receiving plane model is a rectangular target constructed by using multiple Lambertian point light sources for imaging simulation. The zenith angle of each point light source is Range is The cycle step length is , scattering angle scope , the cycle step length is , the emitted rectangular model is * , the interval between the face elements is .

8. The method for exploring the maximum detection distance under an underwater active light source illumination system as claimed in claim 1, characterized in that: The water quality parameters include the absorption coefficient a and scattering coefficient b ; The attenuation length of this water quality for: Detection distance according to different multiples of attenuation length Conclude.

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