A Monte Carlo-based method for evaluating the limiting resolution distance of underwater luminous objects

Abstract

The present invention provides an evaluation method for the limiting resolution distance of an underwater luminous body based on Monte Carlo, and belongs to the field of underwater optical imaging technology. The photons emitted by the luminous body model are simulated for transmission, and the initial energy, random step size, direction after collision and residual energy after collision of the photons are determined by the Monte Carlo method to simulate the process of photon propagation in water, and a lens model is constructed, and the photons passing through the lens model are traced by light, and a receiving plane is constructed to obtain an imaging simulation image, and the limiting resolution distance of the underwater luminous body is studied by changing the parameter setting and observing the imaging result image after the photons pass through the lens. The experimental difficulty of the limiting resolution distance of the underwater luminous body is greatly simplified, and the problems of the long distance between different water bodies and different attenuation lengths in the actual physical space and the difficulty of experimental operation are solved, thereby saving the experimental cost.

Description

Technical Field

[0001] The invention belongs to the technical field of underwater optical imaging, and in particular relates to an evaluation method for the limiting resolution distance of an underwater luminous body based on Monte Carlo. Background Art

[0002] Direct resolution of underwater luminous bodies has many application scenarios, such as the resolution of underwater vehicles for landmarks and the recovery of underwater light-emitting devices. However, photons are more likely to be scattered or refracted in water, which poses a great challenge to the imaging and detection capabilities of underwater luminous bodies. At this time, it is necessary to introduce the concept of limiting resolution distance to measure the impact of different factors on the imaging and detection capabilities of luminous bodies. The limiting resolution distance refers to the distance at which the light source can still be resolved under certain conditions. For underwater luminous bodies, their limiting resolution distance is affected by factors such as the underwater environment, the structure and performance of the luminous body. Therefore, by studying the limiting resolution distance of underwater luminous bodies, we can gain a deeper understanding of the optical properties of the underwater environment.

[0003] At present, most methods for determining the limit resolution distance of underwater luminous bodies use visual measurement, which involves placing the luminous body in water and then photographing it at different distances with a camera to record the limit resolution distance. However, this method is too demanding on the experimental environment and cannot study the impact of different factors on the limit resolution distance of the luminous body. Summary of the invention

[0004] In view of the above problems, the present invention simulates the process of photon transmission and imaging underwater based on the Monte Carlo simulation method, and can analyze the limiting resolution distance of the light source under different water bodies and different light sources.

[0005] The present invention proposes a Monte Carlo-based method for evaluating the limiting resolution distance of underwater luminous bodies, comprising the following steps:

[0006] Step 1, constructing an underwater optical imaging system simulation model based on the MATLAB platform, including a light source model, a lens model, and a receiving plane model;

[0007] Step 2, under specific water quality parameters and a certain initial attenuation length parameter, based on the Monte Carlo method, simulate the transmission of photons emitted by the luminous body model, and trace the photons that finally pass through the lens model, count the number of photons, energy, and coordinate information received by the receiving plane model after the lens model, and perform visualization processing to obtain the imaging light spot image under the initial attenuation length parameter; the attenuation length parameter is the attenuation length between the luminous body model and the lens model position distance. ;

[0008] Step 3, change only the decay length , i.e. the distance between the lens model and the illuminant model, repeat the process of step 2 to obtain the imaging light spot images under different attenuation lengths respectively;

[0009] Step 4: For the imaging light spot images under different attenuation lengths, the fuzziness of the light spot images is evaluated to obtain the attenuation length of the farthest detection distance of the luminous body under specific water quality parameters. .

[0010] Preferably, the construction of the luminous body model is specifically as follows:

[0011] The luminous body light source selects the Lambert point light source model and adopts the Cartesian coordinate system, that is, the three-dimensional plane rectangular coordinate system; the initial position of the light source is set, and the light source position is used as the coordinate origin. The initial position of the photon is related to the shape and division of the luminous body model; the square light source with a certain area is divided into grids, and the points on the grid are the initial positions of the photons. ; The initial direction of the photon is related to the scattering angle With azimuth In order to ensure uniform distribution of photons during emission, the azimuth angle is divided equally from 0° to 360°, and the scattering angle is divided equally from 0° to 90°, and the following formula is used:

[0012]

[0013] The initial direction vector of the photon can be calculated .

[0014] Preferably, the lens model is constructed as follows:

[0015] Use several sub-surface elements to simulate the surface of the lens, set the parameters of the lens, and use the spherical equation Construct the upper and lower surfaces of the lens, where is the radius of curvature of the upper and lower surfaces of the lens, The spatial position of the lens in the coordinate system; set the position coordinates of the lens .

[0016] Preferably, the construction of the receiving plane model is specifically as follows:

[0017] Imaging simulation of a rectangular target constructed using multiple Lambertian point light sources. The scattering 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 facets is .

[0018] Preferably, the specific process of step 3 includes:

[0019] S1, simulate the transmission of photons emitted by the luminous body model, and use the Monte Carlo method to determine the initial energy, random step size, direction after collision and residual energy after collision of the photons to simulate the process of photon propagation in water;

[0020] S2, tracing the light rays of the photons passing through the lens model; including tracing the light rays of the incident light and calculating the direction vector of the refracted light rays according to the Neher refraction law;

[0021] S3, count the number of photons, energy, and coordinate information received by the plane model after the lens model is received, and perform visualization processing based on the absorption coefficient of the water body. , scattering coefficient and attenuation coefficient , calculate the attenuation length of the current water body , where the attenuation length is the attenuation coefficient The reciprocal of; obtaining the imaging simulation result under the initial attenuation length parameter, wherein the attenuation length parameter is the distance from the light source model to the lens model.

[0022] Preferably, the specific process of S1 is:

[0023] S11, determination of the initial energy of photons: according to the initial scattering angle The initial energy of the light source is adjusted. Lambert's theorem is defined as follows: the radiation intensity in a certain direction varies with the cosine of the angle between that direction and the surface normal, ,in, To be in the direction of the normal The initial energy of the photon of angle is is the initial energy of the photon in the normal direction;

[0024] S12, determination of random step length of photons: The absorption scattering probability at Satisfy the formula:

[0025]

[0026] exist The probability of being absorbed and scattered within the range is expressed as:

[0027]

[0028] The probability of photons scattering with water medium in other ranges is expressed as:

[0029]

[0030] Since the probability of a photon interacting with a certain point is random, let the random value , so there is a formula

[0031] , , ,

[0032] From this we can get the random step length formula:

[0033]

[0034] in is the natural base, is an arbitrary constant;

[0035] S13, Determination of the direction of photons after collision: When photons scatter from particles in water, they will have a new direction of travel, which can be determined by the scattering angle With azimuth Calculated, therefore, to refer to the direction of the scattered photon; among them, about Symmetrical and in Evenly distributed inside, for The random number between can be obtained:

[0036]

[0037] Using asymmetric factors To calculate the scattering angle ; This parameter is used to describe whether the probability of forward scattering or backward scattering is greater when photons are scattered; the value of this parameter is , the closer it is to 1, the greater the probability of forward scattering, and the smaller the angle of deviation from the propagation direction; the closer it is to -1, the greater the probability of backward scattering; after introducing this parameter, the new scattering angle of the photon It can be determined by the following formula:

[0038]

[0039] The new scattering angle of the photon is obtained from the above formula With azimuth After that, the new direction vector of the photon can be calculated;

[0040] S14, Determination of the residual energy after a photon collision: The photon retains the initial energy when it is emitted. , in order to simulate the energy attenuation of photons when they are scattered, the albedo is used To express the ratio of energy decay each time decay occurs; where, is the absorption coefficient, is the scattering coefficient, , is the underwater attenuation coefficient;

[0041]

[0042] Photon Experience After the second scattering, its energy is updated as:

[0043]

[0044] in, For the The energy of the photon after the second scattering.

[0045] Preferably, the specific process of S2 is:

[0046] Ray tracing of incident light: Surface fitting is performed on discrete points near the intersection of the incident light and the lens surface, and the intersection of the light path and the lens surface is calculated; the position information of the known photons and direction vector , then the straight line equation of the photon transmission path is expressed as:

[0047]

[0048] ; Compare it with the equation of the sphere where the upper and lower surfaces of the lens are located Joint, among which is the radius of curvature of the upper and lower surfaces of the lens, For the spatial position of the lens in the coordinate system, solve the coordinates of the intersection of the photon transmission path and the lens surface ;

[0049] According to the intersection coordinates The normal direction vector of the lens surface at the intersection is determined by the lens surface coordinates of the two points near this point. ;

[0050] Calculate the direction vector of the refracted light according to Neher's law of refraction:

[0051] The incident direction vector of the photon and the lens surface normal vector The geometric relationship:

[0052]

[0053] in ， , find the incident angle of the photon :

[0054]

[0055] Assume the normal vector of the photon incident surface is , then according to the photon incident direction vector , the normal direction vector of the lens surface and the incident surface normal vector The geometric relationship between the three:

[0056]

[0057] From this we can solve:

[0058]

[0059] Its specific expression is:

[0060]

[0061] Assume that the refraction angle of the photon refracted by the lens is , the refraction direction vector is ; When light passes through a The refractive index of the medium is When transmitting in a medium, according to Snell's law of refraction:

[0062]

[0063] In the formula is the incident angle, is the refraction angle, the refraction angle can be obtained:

[0064]

[0065] The refraction direction vector, the incident surface normal vector, and the lens surface normal vector The geometric relationship between the three:

[0066] ， ，

[0067] From this we can solve:

[0068] .

[0069] Preferably, the step 3 changes the attenuation length Specifically:

[0070] Change the position coordinates of the lens , so that its relative light source position coordinates Observation distance Equal to the attenuation length The different multiples of the lens are used, and the photon information received by the resolution plane after the lens is counted respectively to obtain the simulation results of underwater imaging of the target light source, where:

[0071] .

[0072] Compared with the prior art, the present invention proposes a Monte Carlo-based evaluation method for the limit resolution distance of underwater luminous bodies, and produces the following beneficial effects:

[0073] Compared with the existing methods, the present invention proposes a new method for exploring the limiting resolution distance of underwater luminous bodies. The transmission of photons emitted by the luminous body model is simulated, and the Monte Carlo method is used to determine the initial energy, random step size, direction after collision and residual energy after collision of the photons to simulate the process of photon propagation in water. A lens model is constructed, and ray tracing is performed on the photons passing through the lens model. A receiving plane is constructed to obtain an imaging simulation image. The limiting resolution distance of underwater luminous bodies is studied by changing the parameter settings and observing the imaging result image after the photons pass through the lens.

[0074] The experimental results show that the Monte Carlo method can be used to explore the limit resolution distance of underwater luminous bodies. The simulated underwater environment and the state of the luminous body can be changed accordingly through the set parameters. The limitations of the existing methods on the experimental environment have been broken through. In addition, by controlling the distance from the lens to the target object, that is, the attenuation length, the process of the luminous body from clear to blurred and then difficult to distinguish can be obtained from the simulated imaging images obtained at different distances, so that the change of the luminous body can be clearly obtained to obtain the accurate limit resolution distance.

[0075] The method of the present invention greatly simplifies the experimental difficulty of the limit resolution distance of underwater luminous bodies, solves the problems of different water bodies and different attenuation lengths being far apart in actual physical space and difficult experimental operations, and saves experimental costs. BRIEF DESCRIPTION OF THE DRAWINGS

[0076] Figure 1 It is a schematic diagram of the simulation model of the present invention.

[0077] Figure 2 Under the water quality conditions of Example 1 with an absorption coefficient of 0.114 and a scattering coefficient of 0.037, a small scattering angle and a high-intensity light source, the attenuation length is 5 The simulated imaging diagram obtained under the condition of .

[0078] Figure 3Under the water quality conditions of Example 1 with an absorption coefficient of 0.114 and a scattering coefficient of 0.037, a small scattering angle and a high-intensity light source, the attenuation length is 6 The simulated imaging diagram obtained under the condition of .

[0079] Figure 4 Under the water quality conditions of Example 1 with an absorption coefficient of 0.114 and a scattering coefficient of 0.037, a small scattering angle and a high-intensity light source, the attenuation length is 7 The simulated imaging diagram obtained under the condition of .

[0080] Figure 5 Under the water quality conditions of Example 1 with an absorption coefficient of 0.114 and a scattering coefficient of 0.037, a small scattering angle and a high-intensity light source, the attenuation length is 8 The simulated imaging diagram obtained under the condition of .

[0081] Figure 6 The clean seawater simulated by the water quality conditions of the absorption coefficient of 0.114 and the scattering coefficient of 0.037 in Example 2, with a small scattering angle and a high-intensity light source, has an attenuation length of 6 The simulated imaging diagram obtained under the condition of .

[0082] Figure 7 The water quality conditions in Example 2 are 0.179 for the absorption coefficient and 0.219 for the scattering coefficient, and the attenuation length is 6 The simulated imaging diagram obtained under the condition of .

[0083] Figure 8 The absorption coefficient of Example 2 is 0.366, the scattering coefficient is 1.824, and the attenuation length is 6 under the conditions of small scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0084] Fig. 9 The clean seawater simulated by the water quality conditions of Example 2 with an absorption coefficient of 0.114 and a scattering coefficient of 0.037, a small scattering angle, and a high-intensity light source, has an attenuation length of 7 The simulated imaging diagram obtained under the condition of .

[0085] Fig.10 The water quality conditions in Example 2 are 0.179 for the absorption coefficient and 0.219 for the scattering coefficient, and the attenuation length is 7 The simulated imaging diagram obtained under the condition of .

[0086] Fig.11The absorption coefficient of Example 2 is 0.366, the scattering coefficient is 1.824, and the attenuation length is 7 under the small scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0087] Fig.12 The clean seawater simulated by the water quality conditions of Example 2 with an absorption coefficient of 0.114 and a scattering coefficient of 0.037, a small scattering angle, and a high-intensity light source, has an attenuation length of 8 The simulated imaging diagram obtained under the condition of .

[0088] Fig.13 The water quality conditions in Example 2 are 0.179 for the absorption coefficient and 0.219 for the scattering coefficient, and the attenuation length is 8 under the conditions of small scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0089] Fig.14 The absorption coefficient of Example 2 is 0.366, the scattering coefficient is 1.824, and the attenuation length is 8 under the conditions of small scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0090] Fig.15 The water quality conditions in Example 3 are as follows: the absorption coefficient is 0.179, the scattering coefficient is 0.219, the attenuation length is 5 under the small scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0091] Fig.16 The water quality conditions in Example 3 are as follows: the absorption coefficient is 0.179, the scattering coefficient is 0.219, the attenuation length is 6 under the small scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0092] Fig.17 The water quality conditions in Example 3 are as follows: the absorption coefficient is 0.179, the scattering coefficient is 0.219, the attenuation length is 7 under the small scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0093] Fig.18 The water quality conditions in Example 3 are that the absorption coefficient is 0.179 and the scattering coefficient is 0.219, the attenuation length is 5 under the large scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0094] Fig.19The water quality conditions in Example 3 are that the absorption coefficient is 0.179 and the scattering coefficient is 0.219, the attenuation length is 6 under the large scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0095] Fig. 20 The water quality conditions in Example 3 are that the absorption coefficient is 0.179 and the scattering coefficient is 0.219, the attenuation length is 7 under the large scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0096] Fig.21 The water quality conditions in Example 4 are as follows: the absorption coefficient is 0.179, the scattering coefficient is 0.219, the attenuation length is 5 under the small scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0097] Fig. 22 The water quality conditions in Example 4 are that the absorption coefficient is 0.179 and the scattering coefficient is 0.219, the attenuation length is 6 under the small scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0098] Fig.23 The water quality conditions in Example 4 are as follows: the absorption coefficient is 0.179, the scattering coefficient is 0.219, the attenuation length is 7 under the small scattering angle and high intensity light source. The simulated imaging diagram obtained under the condition of .

[0099] Fig.24 The water quality conditions in Example 4 are that the absorption coefficient is 0.179 and the scattering coefficient is 0.219, the attenuation length is 5 under the small scattering angle and low intensity light source. The simulated imaging diagram obtained under the condition of .

[0100] Fig.25 The water quality conditions in Example 4 are that the absorption coefficient is 0.179 and the scattering coefficient is 0.219, the attenuation length is 6 under the small scattering angle and low intensity light source. The simulated imaging diagram obtained under the condition of .

[0101] Fig.26 The water quality conditions in Example 4 are that the absorption coefficient is 0.179 and the scattering coefficient is 0.219, the attenuation length is 7 under the small scattering angle and low intensity light source. The simulated imaging diagram obtained under the condition of . DETAILED DESCRIPTION

[0102] The present invention proposes a Monte Carlo-based evaluation method for the limiting resolution distance of underwater luminous bodies. The Monte Carlo method is used to randomly generate the random motion process of photons, so as to simulate the scene of scattering or refraction of photons during underwater transmission, and then generate a water model in which the photons move. At the same time, a self-luminous body model is constructed, and the photons in the self-luminous body model are introduced into the water model constructed by the Monte Carlo method, so as to complete the simulation imaging of the self-luminous body in water. For the construction of a complete model, the key parameters are modified to study the influence of changes in water factors and light source factors on the limiting resolution distance. The schematic diagram is shown in FIG. Figure 1 shown.

[0103] The invention will be further described below in conjunction with specific embodiments.

[0104] Embodiment 1:

[0105] Step 1: Build an underwater optical imaging system simulation model based on the MATLAB platform, including a light source model, a lens model, and a receiving plane model.

[0106] Construction of the luminous body model: The luminous body light source selects the Lambertian point light source model, that is, the three-dimensional plane rectangular coordinate system. Set the inherent optical properties of the water body, including the absorption coefficient a and the scattering coefficient c. Set the light source position coordinates. Let the light source position be the origin of the coordinates, and the initial position of the photon is related to the shape and division of the light source model. Divide the square light source with a certain area into grids, and the points on the grid are the initial positions of the photons. The initial direction of the photon is related to the scattering angle With azimuth In order to ensure uniform distribution of photons during emission, it is necessary to divide the azimuth angle into equal parts from 0° to 360° and the scattering angle into equal parts from 0° to 90°. The initial direction vector of the photon can be calculated according to the following formula: :

[0107]

[0108] Set the scattering angle of the light source scope , scattering angle Cycle step angle . With azimuth scope , azimuth Cycle step angle .

[0109] In this embodiment, the parameters are set as follows: a 2cm*2cm light source is used, and the light is divided into 0.1cm steps, so 1600 photons can be obtained. ) coordinates are taken from (-0.02, -0.02) every 0.001 until (0.02, 0.02), which is the initial coordinate of the photon. According to the set three-dimensional rectangular coordinate system, the azimuth of each photon can be calculated , according to the formula, we can get the direction vector of the photon ( , , ). Initial light intensity Set to 100, the scattering angle Limited to 0^°-40^°, the cyclic step angles of the scattering angle and azimuth angle are , asymmetric factor Set to 0.924.

[0110] Lens model establishment: Use a large number of sub-surface micro-elements to simulate the surface of the lens. Set the parameters of the lens and use the spherical equation Construct the upper and lower surfaces of the lens, where is the radius of curvature of the upper and lower surfaces of the lens, The spatial position of the lens in the coordinate system. Set the position coordinates of the lens .

[0111] Construction of the receiving plane: The receiving plane model is a rectangular target constructed using multiple Lambertian point light sources for imaging simulation. The scattering 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 facets is .

[0112] Step 2, under specific water quality parameters and a certain initial attenuation length parameter, based on the Monte Carlo method, simulate the transmission of photons emitted by the luminous body model, and trace the photons that finally pass through the lens model, count the number of photons, energy, and coordinate information received by the receiving plane model after the lens model, and perform visualization processing to obtain the imaging light spot image under the initial attenuation length parameter; the attenuation length parameter is the attenuation length between the luminous body model and the lens model position distance. , specifically including:

[0113] S1, simulate the transmission of photons emitted by the luminous body model, use the Monte Carlo method to determine the initial energy of the photons, random step size, direction after collision and residual energy after collision to simulate the process of photon propagation in water, including:

[0114] S1.1, Determination of the initial energy of photons: According to the initial scattering angle The initial energy of the light source is adjusted. The definition of a Lambertian surface is: the radiation intensity in a certain direction varies with the cosine of the angle between that direction and the surface normal, ,in, To be in the direction of the normal The initial energy of the photon of angle is is the initial energy of the photon in the normal direction.

[0115] S1.2, Determination of the random step length of photons: The absorption scattering probability at Satisfy the formula:

[0116]

[0117] exist The probability of being absorbed and scattered within the range is expressed as:

[0118]

[0119] The probability of photons scattering with water medium in other ranges is expressed as:

[0120]

[0121] Since the probability of a photon interacting with a certain point is random, let the random value , so there is a formula

[0122] , , ,

[0123] From this we can get the random step length formula:

[0124]

[0125] in is the natural base, is an arbitrary constant;

[0126] S1.3 Determination of the direction of photons after collision: When photons scatter from particles in water, they will have a new direction of travel, which can be determined by the scattering angle With azimuth Calculated, therefore, to refer to the direction of the scattered photon; among them, about Symmetrical and in Evenly distributed inside, for The random number between can be obtained:

[0127]

[0128] Using asymmetric factors To calculate the scattering angle ; This parameter is used to describe whether the probability of forward scattering or backward scattering is greater when photons are scattered; the value of this parameter is , the closer it is to 1, the greater the probability of forward scattering, and the smaller the angle of deviation from the propagation direction; the closer it is to -1, the greater the probability of backward scattering; after introducing this parameter, the new scattering angle of the photon It can be determined by the following formula:

[0129]

[0130] The new scattering angle of the photon is obtained from the above formula With azimuth After that, you can combine the above formula:

[0131]

[0132] Calculate the new direction vector of the photon;

[0133] S1.4, Determination of the residual energy after a photon collision: The photon retains the initial energy when it is emitted. , in order to simulate the energy attenuation of photons when they are scattered, the albedo is used To express the ratio of energy decay each time decay occurs; where, is the absorption coefficient, is the scattering coefficient, , is the underwater attenuation coefficient;

[0134]

[0135] Photon Experience After the second scattering, its energy is updated as:

[0136]

[0137] in, For the The energy of the photon after the second scattering.

[0138] S2, tracing the photons passing through the lens model, including:

[0139] Ray tracing of incident light: Surface fitting is performed on discrete points near the intersection of the incident light and the lens surface, and the intersection of the light path and the lens surface is calculated; the position information of the known photons and direction vector , then the straight line equation of the photon transmission path is expressed as:

[0140]

[0141] ; Compare it with the equation of the sphere where the upper and lower surfaces of the lens are located Joint, among which is the radius of curvature of the upper and lower surfaces of the lens, For the spatial position of the lens in the coordinate system, solve the coordinates of the intersection of the photon transmission path and the lens surface ;

[0142] According to the intersection coordinates The normal direction vector of the lens surface at the intersection is determined by the lens surface coordinates of the two points near this point. ;

[0143] Calculate the direction vector of the refracted light according to Neher's law of refraction:

[0144] The incident direction vector of the photon and the lens surface normal vector The geometric relationship:

[0145]

[0146] in ， , find the incident angle of the photon :

[0147]

[0148] Assume the normal vector of the photon incident surface is , then according to the photon incident direction vector , the normal direction vector of the lens surface and the incident surface normal vector The geometric relationship between the three:

[0149]

[0150] From this we can solve:

[0151]

[0152] Its specific expression is:

[0153]

[0154] Assume that the refraction angle of the photon refracted by the lens is , the refraction direction vector is ; When light passes through a The refractive index of the medium is When transmitting in a medium, according to Snell's law of refraction:

[0155]

[0156] In the formula is the incident angle, is the refraction angle, the refraction angle can be obtained:

[0157]

[0158] The refraction direction vector, the incident surface normal vector, and the lens surface normal vector The geometric relationship between the three:

[0159] ， ，

[0160] From this we can solve:

[0161]

[0162] S3, count the number of photons, energy, and coordinate information received by the plane model after the lens model is received, and perform visualization processing based on the absorption coefficient of the water body. , scattering coefficient and attenuation coefficient , calculate the attenuation length of the current water body The imaging simulation result under the initial attenuation length parameter is obtained; the attenuation length parameter is the distance from the illuminant model to the lens model.

[0163] In this embodiment, the lens parameters are set as follows: the radius of the lens surface is 0.01m, and the lens thickness is 0.01m.

[0164] Step 3: Count the number, energy, and coordinate information of photons received by the resolution plane behind the lens, perform visualization processing, and obtain the simulation results of underwater imaging of the target light source.

[0165] In this embodiment, the position of the lens is 5 The imaging simulation results are shown in Figure 2 As shown: the target has a clear outline; the lens is located 6 The imaging simulation results are shown in Figure 3 As shown, the target has a clear outline; the lens is located 7 The imaging simulation results are shown in Figure 4 As shown, the target object is blurred; the lens is located 8 The imaging simulation results are as follows: Figure 5 As shown, the outline of the target is difficult to distinguish.

[0166] Step 4: Analyze the imaging simulation results and evaluate the limiting resolution distance under different simulation conditions.

[0167] In this embodiment, based on the above evaluation of underwater imaging simulation results at different observation distances with different attenuation lengths, it can be concluded that the limit resolution distance under water conditions with an absorption coefficient of 0.114 and a scattering coefficient of 0.037 is 7 .

[0168] Embodiment 2:

[0169] The difference between this embodiment and embodiment 1 is that the model parameter settings are different.

[0170] The inherent optical properties of the water body are set, including the absorption coefficient a and the scattering coefficient c. In this embodiment, the absorption coefficient is set to 0.114 and the scattering coefficient is set to 0.037 to simulate clean seawater; the absorption coefficient is set to 0.179 and the scattering coefficient is set to 0.219 to simulate seawater along the harbor; the absorption coefficient is set to 0.366 and the scattering coefficient is set to 1.824 to simulate harbor water; the position of the lens under the three water quality conditions is 6 away from the target , the obtained imaging simulation results are as follows Figure 6 , 7, 8, the target has a clear outline; the lens is located 7 The obtained imaging simulation results are as follows Fig. 9 , 10, 11, the target object outline is blurred; the position of the lens is 8 The obtained imaging simulation results are as follows Fig.12 , 13, 14, the target outline is difficult to distinguish. Finally, based on the above evaluation of underwater imaging simulation results at different observation distances with different attenuation lengths, it can be concluded that the limit resolution distance under different absorption and attenuation water conditions is 7 ,From the perspective of water bodies, the imaging performance in different water bodies at the same attenuation length is similar, and the limit resolution distance is about 7 attenuation lengths. Since the more turbid the water, the shorter the actual distance corresponding to one attenuation length, the shorter the actual distance that can be resolved.

[0171] Embodiment 3:

[0172] The difference between this embodiment and embodiment 1 is that the model parameter settings are different.

[0173] Set the inherent optical properties of water, including absorption coefficient , scattering coefficient , attenuation coefficient In this embodiment, the absorption coefficient of the water body is 0.179, the scattering coefficient is 0.219, and the scattering angle of the light source is set to a small scattering angle (the scattering angle is less than ), the position of the lens is 5 , 6 ,7 When , the obtained imaging simulation results are as follows Fig.15 , 16, and 17, the outline of the target gradually changes from clear to blurred until it is difficult to distinguish. The scattering angle of the light source is set to a large scattering angle (the scattering angle is greater than 40°), and the position of the lens is 5 , 6 ,7 When , the obtained imaging simulation results are as follows Fig.18 , 19, 20, the outline of the target gradually changes from clear to blurred until it is difficult to distinguish. It can be found that at the same attenuation length, the imaging effect of the small-angle light source is slightly better than that of the large-angle light source. Compared with the large-angle light source, the energy of the small-angle light source is more concentrated, so more photons will enter the lens and hit the receiving plane. However, the limit resolution distance under different scattering angle conditions is still 7 .

[0174] Embodiment 4:

[0175] The difference between this embodiment and embodiment 1 is that the model parameter settings are different.

[0176] The inherent optical properties of the water body are set, including the absorption coefficient a and the scattering coefficient c. In this embodiment, the absorption coefficient of the water body is 0.179, the scattering coefficient is 0.219, the light source is set to a high-intensity light source, and the position of the lens is 5 , 6 ,7 When , the obtained imaging simulation results are as follows Fig.21 , 22, 23, the outline of the target gradually changes from clear to blurred until it is difficult to distinguish. The light source is set to a low-intensity light source, and the position of the lens is 5 , 6 ,7 When , the obtained imaging simulation results are as follows Fig.24 , 25, 26, the outline of the target object gradually changes from clear to blurred until it is difficult to distinguish. It can be seen that there is not much difference between the two in the recognition of the target object, and the performance becomes very poor at 7 attenuation lengths. However, the imaging brightness of the high-intensity light source is greater than that of the low-intensity light source. Therefore, if we only consider whether the light source can be observed, the high-intensity light source has a better performance. However, the content of the present invention is the limit resolution distance of the light source. If we consider it from the perspective of the resolution distance, the intensity of the light source will not have a great impact on it.

[0177] 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.

[0178] 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 Monte Carlo-based method for evaluating the limiting resolution distance of underwater luminous objects, characterized in that: The following steps are involved: Step 1, constructing an underwater optical imaging system simulation model based on the MATLAB platform, including a light source model, a lens model, and a receiving plane model; Step 2, under specific water quality parameters and a certain initial attenuation length parameter, based on the Monte Carlo method, simulate the transmission of photons emitted by the luminous body model, and perform ray tracing on the photons that finally pass through the lens model, count the number, energy, and coordinate information of photons received by the receiving plane model after the lens model, perform visualization processing, and obtain an imaging light spot image under the initial attenuation length parameter; the attenuation length parameter is the attenuation length between the luminous body model and the lens model position; Step 3, only changing the attenuation length, that is, the distance between the lens model and the illuminant model, repeating the process of step 2, and obtaining imaging light spot images under different attenuation lengths respectively; Step 4, for the imaging light spot images under different attenuation lengths, the fuzziness of the light spot images is evaluated to obtain the attenuation length of the farthest detection distance of the light source under specific water quality parameters.

2. The method for evaluating the limiting resolution distance of underwater luminous bodies based on Monte Carlo as claimed in claim 1, characterized in that: The construction of the luminous body model is specifically as follows: The luminous body light source selects the Lambert point light source model and adopts the Cartesian coordinate system, that is, the three-dimensional plane rectangular coordinate system; the initial position of the light source is set, and the light source position is used as the coordinate origin. The initial position of the photon is related to the shape and division of the luminous body model; the square light source with a certain area is divided into grids, and the points on the grid are the initial positions of the photons. ; The initial direction of the photon is related to the scattering angle With azimuth In order to ensure uniform distribution of photons during emission, the azimuth angle is divided equally from 0° to 360°, and the scattering angle is divided equally from 0° to 90°, and the following formula is used: The initial direction vector of the photon can be calculated .

3. The Monte Carlo-based evaluation method for the limiting resolution distance of underwater luminous bodies as claimed in claim 1, characterized in that: The construction of the lens model is specifically as follows: Use several sub-surface elements to simulate the surface of the lens, set the parameters of the lens, and use the spherical equation Construct the upper and lower surfaces of the lens, where is the radius of curvature of the upper and lower surfaces of the lens, The spatial position of the lens in the coordinate system; set the position coordinates of the lens .

4. The Monte Carlo-based evaluation method for the limiting resolution distance of underwater luminous bodies as claimed in claim 1, characterized in that: The construction of the receiving plane model is specifically as follows: Imaging simulation of a rectangular target constructed using multiple Lambertian point light sources. The scattering 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 facets is .

5. The Monte Carlo-based evaluation method for the limiting resolution distance of underwater luminous bodies as claimed in claim 1, characterized in that: The specific process of step 3 includes: S1, simulate the transmission of photons emitted by the luminous body model, and use the Monte Carlo method to determine the initial energy, random step size, direction after collision and residual energy after collision of the photons to simulate the process of photon propagation in water; S2, tracing the light rays of the photons passing through the lens model; including tracing the light rays of the incident light and calculating the direction vector of the refracted light rays according to the Neher refraction law; S3, count the number of photons, energy, and coordinate information received by the plane model after the lens model is received, and perform visualization processing based on the absorption coefficient of the water body. , scattering coefficient and attenuation coefficient , calculate the attenuation length of the current water body , where the attenuation length is the attenuation coefficient The reciprocal of; obtaining the imaging simulation result under the initial attenuation length parameter, wherein the attenuation length parameter is the distance from the light source model to the lens model.

6. The Monte Carlo-based method for evaluating the limiting resolution distance of underwater luminous bodies as claimed in claim 5, characterized in that: The specific process of S1 is as follows: S11, determination of the initial energy of photons: according to the initial scattering angle The initial energy of the light source is adjusted. Lambert's theorem is defined as follows: the radiation intensity in a certain direction varies with the cosine of the angle between that direction and the surface normal, ,in, To be in the direction of the normal The initial energy of the photon of angle is is the initial energy of the photon in the normal direction; S12, determination of random step length of photons: The absorption scattering probability at Satisfy the formula: exist The probability of being absorbed and scattered within the range is expressed as: The probability of photons scattering with water medium in other ranges is expressed as: Since the probability of a photon interacting with a certain point is random, let the random value , so there is a formula ， ， ， From this we can get the random step length formula: in is the natural base, is an arbitrary constant; S13, Determination of the direction of photons after collision: When photons scatter from particles in water, they will have a new direction of travel, which can be determined by the scattering angle With azimuth Calculated, therefore, to refer to the direction of the photon after scattering; among them, about Symmetrical and in Evenly distributed inside, for The random number between can be obtained: Using asymmetric factors To calculate the scattering angle ; This parameter is used to describe whether the probability of forward scattering or backward scattering is greater when photons are scattered; the value of this parameter is , the closer it is to 1, the greater the probability of forward scattering, and the smaller the angle of deviation from the propagation direction; the closer it is to -1, the greater the probability of backward scattering; after introducing this parameter, the new scattering angle of the photon It can be determined by the following formula: The new scattering angle of the photon is obtained from the above formula With azimuth After that, the new direction vector of the photon can be calculated; S14, Determination of the residual energy after a photon collision: The photon retains the initial energy when it is emitted. , in order to simulate the energy attenuation of photons when they are scattered, the albedo is used To express the ratio of energy decay each time decay occurs; where, is the absorption coefficient, is the scattering coefficient, , is the underwater attenuation coefficient; Photon Experience After the second scattering, its energy is updated as: in, For the The energy of the photon after the second scattering.

7. The Monte Carlo-based evaluation method for the limiting resolution distance of underwater luminous bodies as claimed in claim 5, characterized in that: The specific process of S2 is: Ray tracing of incident light: Surface fitting is performed on discrete points near the intersection of the incident light and the lens surface, and the intersection of the light path and the lens surface is calculated; the position information of the known photons and direction vector , then the straight line equation of the photon transmission path is expressed as: ; Compare it with the equation of the sphere where the upper and lower surfaces of the lens are located Joint, among which is the radius of curvature of the upper and lower surfaces of the lens, For the spatial position of the lens in the coordinate system, solve the coordinates of the intersection of the photon transmission path and the lens surface ; According to the intersection coordinates The normal direction vector of the lens surface at the intersection is determined by the lens surface coordinates of the two points near this point. ; Calculate the direction vector of the refracted light according to Neher's law of refraction: The incident direction vector of the photon and the lens surface normal vector The geometric relationship: in ， , find the incident angle of the photon : Assume the normal vector of the photon incident surface is , then according to the photon incident direction vector , the normal direction vector of the lens surface and the incident surface normal vector The geometric relationship between the three: From this we can solve: Its specific expression is: Assume that the refraction angle of the photon refracted by the lens is , the refraction direction vector is ; When light passes through a The refractive index of the medium is When transmitting in a medium, according to Snell's law of refraction: In the formula is the incident angle, is the refraction angle, the refraction angle can be obtained: The refraction direction vector, the incident surface normal vector, and the lens surface normal vector The geometric relationship between the three: ， ， From this we can solve: 。 8. The Monte Carlo-based evaluation method for the limiting resolution distance of underwater luminous bodies as claimed in claim 1, characterized in that: Step 3 changes the decay length Specifically: Change the position coordinates of the lens , so that its relative light source position coordinates Observation distance Equal to the attenuation length The different multiples of the lens are used, and the photon information received by the resolution plane after the lens is counted respectively to obtain the simulation results of underwater imaging of the target light source, where: 。

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