A downlink light field based cross-medium uplink imaging simulation method

Abstract

The application discloses a cross-medium uplink imaging simulation method based on a downlink light field, relates to the field of electric digital data processing, and comprises the following steps: based on a bidirectional reflectance distribution theory, an analysis model of laser reflection characteristics of an underwater target is established; based on an imaging simulation angle of the cross-medium, an imaging model of underwater forward scattering is established; through solving the geometric relation between the offset of a pixel point and a surface gradient, local geometric deformation is simulated and imaged; laser radar scanning imaging is simulated, and a cross-medium imaging simulation result is obtained; an ideal Lambert bidirectional reflectance distribution function is used to generate a target uplink light field, a point spread function model is used to solve target multiple scattering degradation imaging under the condition of a calm sea surface, and through constructing a nonlinear mapping of a wave surface gradient field and a light field phase offset, full-element dynamic simulation from laser emission, medium transmission to target imaging is completed.

Description

Technical Field

[0001] This invention relates to the field of electronic digital data processing, and in particular to a cross-medium uplink imaging simulation method based on downlink optical field. Background Technology

[0002] Laser cross-medium transmission technology has important application value in fields such as ocean exploration and underwater target identification. In existing technologies, the construction of laser cross-medium transmission models basically follows the simplification of the wave field at the air-sea interface into a statistical model, a single scattering model of the seawater channel, and a single link model.

[0003] First, in the actual marine environment, the dynamic changes in the wave field can cause non-uniform drift of the refraction path, and statistical models cannot accurately characterize this local refraction effect, thus causing the simulation results to deviate from the real scene.

[0004] Secondly, current models describe the scattering process of seawater channels based on the single scattering assumption of the HG scattering phase function. In turbid water, forward scattering dominates the light transmission process, and the light spot exhibits asymmetric diffusion characteristics. The HG phase function cannot fully analyze this complex scattering mechanism, especially the cumulative effect of multiple scattering on imaging resolution, resulting in insufficient simulation accuracy of the model in turbid water environments.

[0005] Finally, existing research focuses on local transmission modeling of a single uplink or downlink link and emphasizes the statistical characteristics analysis of photons. This point-domain communication modeling method is difficult to systematically reflect the global evolution characteristics of the continuous light field, especially the dynamic process of imaging degradation mechanism.

[0006] Therefore, a cross-medium uplink imaging simulation method based on downlink optical field is provided to solve the above problems. Summary of the Invention

[0007] The purpose of this invention is to provide a cross-medium uplink imaging simulation method based on downlink optical field, which can effectively realize the process simulation of cross-medium imaging under multiple parameters such as different detection depths, sea state levels, and water characteristics, and provide a priori theoretical tool for cross-medium underwater target imaging in complex marine exploration environments.

[0008] To achieve the above objectives, this invention provides a cross-medium uplink imaging simulation method based on downlink optical field, comprising the following steps:

[0009] S1: Based on the bidirectional reflection distribution theory, an analytical model for the laser reflection characteristics of underwater targets is established;

[0010] S2: Based on the imaging simulation angle across the medium, establish an underwater forward scattering imaging model;

[0011] S3: Simulate and image local geometric deformation by solving the geometric relationship between pixel offset and surface gradient;

[0012] S4: Simulate lidar scanning imaging to obtain cross-medium imaging simulation results.

[0013] Preferably, step S1 specifically includes the following steps:

[0014] S11: Combining the optical properties of microsurfaces with radiative transfer theory, through the bidirectional reflection distribution function Construct a Lambertian model and a two-way reflection distribution function. Specifically set as follows:

[0015] ;

[0016] in, L r This represents the reflected radiance of light radiation. Indicates incident irradiance, Indicates the angle of incidence at the zenith. Indicates the incident azimuth angle. Indicates the reflected zenith angle. Indicates the azimuth angle of the reflection;

[0017] S12: Perform pixel normalization mapping on the given image grayscale values ​​of the underwater target to obtain the surface reflectance of the underwater target. ;

[0018] S13: Treating the underwater target as an ideal Lambertian surface, construct the initial upward optical field of the laser reflection characteristics of the underwater target based on the Lambertian model, and the isotropic uniform reflection optical field of any incident direction. Specifically set as follows:

[0019] ;

[0020] in, This represents an isotropic, uniformly reflected light field with arbitrary incident directions. This represents the downlink optical field across the medium.

[0021] Preferably, in step S11, when the ideal Lambertian surface satisfies the ideal diffuse reflection condition, the bidirectional reflection distribution function of the ideal Lambertian surface is specifically set as follows:

[0022] ;

[0023] in, This represents the simplified constant value of the bidirectional reflection distribution function when an ideal Lambertian surface satisfies the ideal diffuse reflection condition. This represents the diffuse reflectance of the surface of an underwater target.

[0024] Preferably, in step S13, an initial upward optical field for the laser reflection characteristics of the underwater target is constructed. The initial upward optical field is an isotropic uniform reflection optical field with arbitrary incident direction. When the incident direction is perpendicular, the upward optical field with perpendicular incident direction is specifically set as follows:

[0025] .

[0026] Preferably, step S2 specifically includes the following steps:

[0027] S21: The response of laser imaging transmission in seawater is represented by the point spread function, which further represents the scattering broadening effect in the spatial domain. Specifically set as follows:

[0028] ;

[0029] in, This represents the response light field of laser imaging transmission in seawater, i.e., target imaging on a calm water surface. Represents the point spread function;

[0030] S22: Based on the Fourier transform principle, the time-domain convolution is transformed into a product relationship in the frequency domain. Specifically, it is expressed as follows:

[0031] ;

[0032] Among them, F -1 This represents the inverse Fourier transform process;

[0033] S23: Introduce the modulation transfer function MTF to obtain the intermediate optical field formed by seawater absorption and seawater scattering.

[0034] Preferably, step S3 specifically includes the following steps:

[0035] S31: When the sea is calm, the incident light... Refracted light rays and any fixed point on the sea surface P normal vector N The plane formed is perpendicular to Pixels on a plane with an upward light field I The local geometric relations in the quiescent state are specifically set as follows:

[0036] ;

[0037] in, Indicates the incident ray The geometric projection point of the virtual extension line on the receiving surface. R This indicates the spatial intersection point of the actual refracted light ray and the receiving surface under calm conditions.D Represents the normal vector in a calm state N orthogonal projection reference point, Indicates the angle of incidence. t Indicates the angle of refraction. express I ’ R The direction vector;

[0038] S32: Let Combining the law of refraction and the small-angle first-order approximation, the local geometric relationships in the calm state are simplified. The simplified local geometric relationships in the calm state are specifically set as follows:

[0039] ;

[0040] in, This represents the refractive index parameter in air. This represents the refractive index parameter in water;

[0041] S33: Pixels in the upward light field when the sea surface is fluctuating. I The local geometric relationships under wave conditions are specifically set as follows:

[0042] ;

[0043] ;

[0044] ;

[0045] in, The spatial intersection point of the actual refracted ray and the receiving surface under wave-like conditions. F Represents the normal vector under wave state N orthogonal projection reference point, Indicates the angle between the horizontal plane and the wavering sea surface. Indicates the incident ray The horizontal direction vector, N 0 represents the normal vector N The intersection of the extended line and the receiving plane, Normal vector N and z The included angle of the axis;

[0046] S34: Combining the law of refraction and the first-order approximation of small angles, the local geometric relationships in the wave state are simplified. The specific local geometric relationships in the calm state of the wave are set as follows:

[0047] ;

[0048] S35: Obtain the surface gradient at a small angle. Normal vector N and incident light exist z Direction vector of the axis Z Relationship;

[0049] S36: Obtain the mapping relationship between the offset of the pixel and the surface gradient;

[0050] S37: Introducing discrete resolution into pixel mapping relationships Introducing discrete resolution l The pixel offset is specifically set as follows:

[0051] ;

[0052] in, h eq Indicates the equivalent disturbance height ;

[0053] S38: For receiving surface pixels Corresponding underwater target original pixel Perform the mapping, and set the mapping result as follows:

[0054] .

[0055] Preferably, step S35 specifically includes the following steps:

[0056] Step 1: Calculate any fixed point P gradient arbitrarily fixed point P gradient Specifically set as follows:

[0057] ;

[0058] in, The mathematical representation of gradient data computation. Represents the Laplace operator;

[0059] Step 2: Using the gradient formula, obtain the approximate surface gradient at small angles. Normal vector N and incident light exist z Direction vector of the axis Z The relationship between small-angle surface gradient Normal vector N and incident light exist z Direction vector of the axis Z The relationship is specifically set as follows:

[0060] .

[0061] Preferably, step S36 specifically includes the following steps:

[0062] Step 1: Incident light Normal vector N and horizontal direction vector The relationship is specifically set as follows:

[0063] ;

[0064] Step 2: Adjust the incident light... Normal vector N and horizontal direction vector n The relationship is derived, and the specific derivation result is set as follows:

[0065] ;

[0066] Step 3: Simplify the derivation result for the first time using a small-angle first-order approximation. The specific settings for the first simplification are as follows:

[0067] ;

[0068] ;

[0069] ;

[0070] ;

[0071] ;

[0072] Step 4: Combining The derivation result is simplified a second time, and the specific simplification result is set as follows:

[0073] ;

[0074] ;

[0075] Step 5: d Set to 0, d Substituting 0 into the second simplification result yields the simplest result, specifically set as follows:

[0076] ;

[0077] in, depth This indicates the height of the pixel above the water surface. This represents the offset of a pixel under two different conditions: calm sea surface and undulating sea surface.

[0078] Preferably, step S4 specifically includes the following steps:

[0079] S41: Simulate lidar scanning imaging, set the incident light as an array laser beam surface, the array laser beam surface includes multiple uniform rays, the incident direction of the rays is set as perpendicular, the light intensity of the rays is set as 1, and the laser wavelength of the rays is set as 532nm.

[0080] S42: Set the relative refractive index of the air-sea interface to 1.33, the average scattering angle within the seawater channel to an empirical value of 0.03 rad, and the seawater absorption coefficient to 0.089 m. -1 The seawater scattering coefficient was set to 0.610m. -1 ;

[0081] S43: Perform cross-media imaging simulations for different detection depths, sea conditions, and water types.

[0082] Therefore, the present invention employs the above-mentioned cross-medium uplink imaging simulation method based on downlink optical field, which has the following beneficial effects:

[0083] (1) This scheme realizes the first complete cross-medium simulation of two-way optical path coupling and completes the full-link closed-loop simulation of cross-medium “downlink transmission-target reflection-uplink imaging”;

[0084] (2) This scheme is the first to analyze the imaging degradation mechanism in a non-statistical sense from the image level, and has the ability to model multi-dimensional parameterization of detection depth, sea state level, water characteristics, etc.

[0085] (3) The model of this scheme has strong advantages in simulation accuracy and scalability. It provides a model tool for cross-medium underwater imaging simulation in complex marine exploration scenarios, which can optimize the design of imaging detection system parameters and reduce the cost of field tests.

[0086] The method of the present invention will be further described in detail below with reference to the accompanying drawings and embodiments. Attached Figure Description

[0087] Figure 1 This is a flowchart of a cross-medium uplink imaging simulation method based on downlink optical field according to the present invention;

[0088] Figure 2 This is a diagram of the cross-medium closed-loop simulation model architecture of the present invention;

[0089] Figure 3 This is a framework diagram of the cross-medium uplink optical field imaging simulation algorithm of the present invention;

[0090] Figure 4 This is a schematic diagram of the attenuation curve characteristics of the modulation transfer function (MTF) of the present invention, wherein (a) attenuation curve characteristics at different distances, and (b) attenuation curve characteristics under different water body parameters.

[0091] Figure 5 This is a schematic diagram of the imaging distortion under the dynamic sea surface according to the present invention;

[0092] Figure 6 This is a schematic diagram illustrating the refraction of light on a calm sea surface according to the present invention.

[0093] Figure 7 This is a schematic diagram of the refraction of the undulating sea surface according to the present invention;

[0094] Figure 8 This is a schematic diagram of the refraction plane of the wave-like sea surface according to the present invention;

[0095] Figure 9 The images show cross-medium imaging at different detection depths according to the present invention, where (a) is the original image, (b) is 1m, (c) is 3m, (d) is 5m, and (e) is 10m.

[0096] Figure 10 The images are cross-media imaging of different sea state levels according to the present invention, wherein (a) is the original image, (b) is level 2, (c) is level 4, (d) is level 6, (e) is level 8, and (f) is level 10.

[0097] Figure 11 This invention provides cross-media imaging of different water body types, including (a) the original image, (b) water body Jerlov I, (c) water body Jerlov II, (d) water body Jerlov III, and (e) the experimental image. Detailed Implementation

[0098] The method of the present invention will be further described below with reference to the accompanying drawings and embodiments.

[0099] Unless otherwise defined, the methodological or scientific terms used in this invention shall have the ordinary meaning as understood by one of ordinary skill in the art to which this invention pertains.

[0100] The terms "comprising" or "including" as used in this invention mean that the element preceding the term encompasses the element listed after the term, and do not exclude the possibility of encompassing other elements as well. Terms such as "inner," "outer," "upper," and "lower" indicate the orientation or positional relationship based on the orientation or positional relationship shown in the accompanying drawings, and are only for the convenience of describing the invention and simplifying the description, and do not indicate or imply that the device or element referred to must have a specific orientation, or be constructed and operated in a specific orientation. Therefore, they should not be construed as limitations on the invention. When the absolute position of the described object changes, the relative positional relationship may also change accordingly. In this invention, unless otherwise explicitly specified and limited, the term "attached" and similar terms should be interpreted broadly. For example, it can refer to a fixed connection, a detachable connection, or an integral part; it can refer to a direct connection or an indirect connection through an intermediate medium; it can refer to the internal communication of two elements or the interaction relationship between two elements. Those skilled in the art can understand the specific meaning of the above terms in this invention according to the specific circumstances.

[0101] Example

[0102] like Figure 1-3 As shown, this invention provides a cross-medium uplink imaging simulation method based on downlink optical field, comprising the following steps:

[0103] S1: Based on the bidirectional reflection distribution theory, an analytical model for the laser reflection characteristics of underwater targets is established;

[0104] Step S1 specifically includes the following steps:

[0105] S11: Combining the optical properties of microsurfaces with radiative transfer theory, through the bidirectional reflection distribution function Construct a Lambertian model and a two-way reflection distribution function. This model can be used to describe the radiation and reflection characteristics of various target surfaces. It combines the optical properties of micro-surfaces with radiative transfer theory, and is tailored to the microscopic geometric features of underwater targets, including a bidirectional reflection distribution function. Specifically set as follows:

[0106] ;

[0107] in, L r This represents the reflected radiance of light radiation. E i Indicates incident irradiance, Indicates the angle of incidence at the zenith. Indicates the incident azimuth angle. Indicates the reflected zenith angle. Indicates the azimuth angle of the reflection;

[0108] The differential relationship between incident irradiance and reflected radiance is rigorously defined, comprehensively describing the energy distribution characteristics of incident light in hemispherical space after passing through the target surface. The azimuth parameter includes the incident zenith angle. incident azimuth Reflected zenith angle Reflection azimuth angle A four-dimensional coordinate system is formed.

[0109] In step S11, when the ideal Lambertian surface satisfies the ideal diffuse reflection condition, the bidirectional reflection distribution function of the ideal Lambertian surface is specifically set as follows:

[0110] ;

[0111] in, This represents the simplified constant value of the bidirectional reflection distribution function when an ideal Lambertian surface satisfies the ideal diffuse reflection condition. This represents the diffuse reflectance of the surface of an underwater target.

[0112] This stems from the cosine radiation law strictly followed by the Lambert, which exhibits isotropic radiation characteristics in any observation direction. This characteristic makes it an important standard reference in underwater optical detection.

[0113] S12: Perform pixel normalization mapping on the given image grayscale values ​​of the underwater target to obtain the surface reflectance of the underwater target. ;

[0114] S13: Treating the underwater target as an ideal Lambertian surface, construct the initial upward optical field of the laser reflection characteristics of the underwater target based on the Lambertian model, and the isotropic uniform reflection optical field of any incident direction. Specifically set as follows:

[0115] ;

[0116] in, This represents an isotropic, uniformly reflected light field with arbitrary incident directions. This represents the downlink optical field across the medium.

[0117] In step S13, an initial upward optical field for the laser reflection characteristics of the underwater target is constructed. The initial upward optical field is an isotropic uniform reflection optical field with arbitrary incident direction. When the incident direction is perpendicular, the upward optical field with perpendicular incident direction is specifically set as follows:

[0118] .

[0119] When laser light travels through seawater, it is scattered and absorbed by the water and particles suspended in the water. The optical scattering phenomenon in seawater mainly manifests in two forms: forward scattering and backward scattering. Forward scattering is dominant, and its scattering amount usually exceeds 90% of the total scattering amount.

[0120] It is worth noting that under short-range propagation conditions, forward scattering can effectively transmit detailed information and features of underwater targets. However, forward scattering can also lead to a decrease in imaging resolution and cause degradation of underwater target images.

[0121] S2: Based on the imaging simulation angle across the medium, establish an underwater forward scattering imaging model;

[0122] Step S2 specifically includes the following steps:

[0123] S21: Particle light scattering in seawater is generally described using a volume scattering function. When considering multiple scattering, the response of laser imaging transmission in seawater is represented by a point spread function, which further represents the scattering broadening effect in the spatial domain. Specifically set as follows:

[0124] ;

[0125] in, This represents the response light field of laser imaging transmission in seawater, i.e., target imaging on a calm water surface. Represents the point spread function;

[0126] At this point, the seawater channel is considered as a uniform, linear, and invariant system, and the transmission process of laser in the seawater channel is expressed as a convolution with the point spread function.

[0127] S22: Based on the Fourier transform principle, the time-domain convolution is transformed into a product relationship in the frequency domain. Specifically, it is expressed as follows:

[0128] ;

[0129] Among them, F -1 This represents the inverse Fourier transform process;

[0130] S23: The modulation transfer function (MTF) is introduced to obtain the intermediate optical field formed by seawater absorption and scattering. This function serves as the core evaluation parameter of the spatial resolution of the optical system and can quantify the imaging system's ability to transmit signals of different spatial frequencies. The introduction of the MTF function is mainly to focus on describing the impact of the seawater channel on imaging, specifically manifested in the blurring and distortion of underwater target images.

[0131] like Figure 4As shown, with the increase of transmission distance or with the increase of seawater turbidity, the effective frequency band of the MTF curve becomes smaller and smaller, and the loss of high-frequency information becomes more and more serious.

[0132] The evolution of the MTF curve with transmission distance and seawater parameters is actually a comprehensive reflection of the modulation of the light field by the absorption and scattering effects of water. In essence, the MTF process is similar to the attenuation of a low-pass filter in the imaging simulation process.

[0133] S3: Simulate and image local geometric deformation by solving the geometric relationship between pixel offset and surface gradient;

[0134] Step S3 specifically includes the following steps:

[0135] like Figure 5 As shown, when the sea is calm, the laser passes through a fixed point P and is then refracted by the receiving surface above the water to form pixel A. When the sea surface is turbulent, the pixel position will shift to B due to the change in the normal vector.

[0136] Therefore, it can be assumed that the pixel offset is correlated with the gradient of the fixed point on the sea surface in both cases. The local geometric deformation of the imaging can be simulated by solving the geometric relationship between the pixel offset and the surface gradient.

[0137] S31: As Figure 6 As shown, when the sea surface is calm, the incident light... Refracted light rays and any fixed point on the sea surface P normal vector N The plane formed is perpendicular to xOy Pixels on a plane with an upward light field I The local geometric relations in the quiescent state are specifically set as follows:

[0138] ;

[0139] in, Indicates the incident ray The geometric projection point of the virtual extension line on the receiving surface. R This indicates the spatial intersection point of the actual refracted light ray and the receiving surface under calm conditions. D Represents the normal vector in a calm state N orthogonal projection reference point, Indicates the angle of incidence. t Indicates the angle of refraction. express I ’ R The direction vector;

[0140] S32: Let Combining the law of refraction and the small-angle first-order approximation, the local geometric relationships in the calm state are simplified. The simplified local geometric relationships in the calm state are specifically set as follows:

[0141] ;

[0142] in, This represents the refractive index parameter in air. This represents the refractive index parameter in water;

[0143] S33: As Figure 7-8 As shown, when the sea surface fluctuates, the pixel shifts because the undulations of the sea surface affect the normal vector. N No longer parallel z Axis, incident ray Refracted rays and normal vector N The plane in question is , PF Perpendicular to the plane pixels in the uplink light field I The local geometric relationships under wave conditions are specifically set as follows:

[0144] ;

[0145] ;

[0146] ;

[0147] in, The spatial intersection point of the actual refracted ray and the receiving surface under wave-like conditions. F Represents the normal vector under wave state N orthogonal projection reference point, Indicates the angle between the horizontal plane and the wavering sea surface. Indicates the incident ray The horizontal direction vector, N 0 represents the normal vector N The intersection of the extended line and the receiving plane, Normal vector N and z The included angle of the axis;

[0148] S34: Combining the law of refraction and the first-order approximation of small angles, the local geometric relationships in the wave state are simplified. The specific local geometric relationships in the calm state of the wave are set as follows:

[0149] ;

[0150] S35: Obtain the surface gradient at a small angle. Normal vector N and incident light exist z Direction vector of the axis Z Relationship;

[0151] Step S35 specifically includes the following steps:

[0152] Step 1: Calculate any fixed point P gradient arbitrarily fixed point P gradient Specifically set as follows:

[0153] ;

[0154] in, The mathematical representation of gradient data computation. Represents the Laplace operator;

[0155] Step 2: Using the gradient formula, obtain the approximate surface gradient at small angles. Normal vector N and incident light exist z Direction vector of the axis Z The relationship between small-angle surface gradient Normal vector N and incident light exist z Direction vector of the axis Z The relationship is specifically set as follows:

[0156] .

[0157] S36: Obtain the mapping relationship between the offset of the pixel and the surface gradient;

[0158] Step S36 specifically includes the following steps:

[0159] Step 1: Incident light Normal vector N and horizontal direction vector The relationship is specifically set as follows:

[0160] ;

[0161] Step 2: Adjust the incident light... Normal vector N and horizontal direction vector The relationship is derived, and the specific derivation result is set as follows:

[0162] ;

[0163] Step 3: Simplify the derivation result for the first time using a small-angle first-order approximation. The specific settings for the first simplification are as follows:

[0164] ;

[0165] ;

[0166] ;

[0167] ;

[0168] ;

[0169] Step 4: Combining The derivation result is simplified a second time, and the specific simplification result is set as follows:

[0170] ;

[0171] ;

[0172] Step 5: d Setting it to 0 explicitly correlates the displacement with the vertical distance from the pixel to the sea surface. d Substituting 0 into the second simplification result yields the simplest result, specifically set as follows:

[0173] ;

[0174] in, depth This indicates the height of the pixel above the water surface. This represents the offset of a pixel under two different conditions: calm sea surface and undulating sea surface.

[0175] S37: For the discretization of sea surface micro-element, a discrete resolution is introduced into the pixel mapping relationship. l Introducing discrete resolution l The pixel offset is specifically set as follows:

[0176] ;

[0177] in, h eq Indicates the equivalent disturbance height ;

[0178] S38: For the receiving surface pixels Corresponding underwater target original pixel Perform the mapping, and set the mapping result as follows:

[0179] .

[0180] S4: Simulate lidar scanning imaging to obtain cross-medium imaging simulation results.

[0181] Step S4 specifically includes the following steps:

[0182] S41: Simulate lidar scanning imaging, set the incident light as an array laser beam surface, the array laser beam surface includes multiple uniform rays, the incident direction of the rays is set as perpendicular, the light intensity of the rays is set as 1, and the laser wavelength of the rays is set as 532nm.

[0183] S42: Set the relative refractive index of the air-sea interface to 1.33, the average scattering angle within the seawater channel to an empirical value of 0.03 rad, and the seawater absorption coefficient to 0.089 m. -1 The seawater scattering coefficient was set to 0.610m. -1 ;

[0184] S43: Conduct cross-media imaging simulations for different detection depths, sea states, and water types, such as... Figure 9 As shown, when the sea surface wind speed is 5 m / s, the detection depths are set to 1 m, 3 m, 5 m, and 10 m respectively. Figure 10 As shown, the fixed detection depth is 2m, and the sea state levels are 2, 4, 6, 8, and 10 respectively. Figure 11 As shown, the fixed detection depth and sea wind speed are 2m and 5m / s, respectively, and the water body types are Jerlov I, Jerlov II, Jerlov III, and experimental water body parameters.

[0185] Therefore, this invention adopts the above-mentioned cross-medium uplink imaging simulation method based on downlink optical field, uses the ideal Lambert bidirectional reflection distribution function to generate the target uplink optical field, solves the target multiple scattering degradation imaging under calm sea surface conditions through the point spread function model, and completes the dynamic simulation of all elements from laser emission, medium transmission to target imaging by constructing a nonlinear mapping between wavefront gradient field and optical field phase shift.

[0186] Finally, it should be noted that the above embodiments are only used to illustrate the method of the present invention and not to limit it. Although the present invention has been described in detail with reference to preferred embodiments, those skilled in the art should understand that modifications or equivalent substitutions can still be made to the method of the present invention, and these modifications or equivalent substitutions should not cause the modified method to deviate from the spirit and scope of the method of the present invention.

Claims

1. A cross-medium uplink imaging simulation method based on downlink optical field, characterized in that, Includes the following steps: S1: Based on the bidirectional reflection distribution theory, an analytical model for the laser reflection characteristics of underwater targets is established; S2: Based on the imaging simulation angle across the medium, establish an underwater forward scattering imaging model; Step S2 specifically includes the following steps: S21: The response of laser imaging transmission in seawater is represented by the point spread function, which further represents the scattering broadening effect in the spatial domain. Specifically set as follows: ； in, This represents the response light field of laser imaging transmission in seawater, i.e., target imaging on a calm water surface. Represents the point spread function; S22: Based on the Fourier transform principle, the time-domain convolution is transformed into a product relationship in the frequency domain. Specifically, it is expressed as follows: ； Among them, F -1 This represents the inverse Fourier transform process; S23: Introduce the modulation transfer function MTF to obtain the intermediate optical field formed by seawater absorption and seawater scattering; S3: Simulate and image local geometric deformation by solving the geometric relationship between pixel offset and surface gradient; Step S3 specifically includes the following steps: S31: When the sea is calm, the incident light... Refracted light rays and any fixed point on the sea surface normal vector The plane formed is perpendicular to Pixels on a plane with an upward light field The local geometric relations in the quiescent state are specifically set as follows: ； in, Indicates the incident ray The geometric projection point of the virtual extension line on the receiving surface. R This indicates the spatial intersection point of the actual refracted light ray and the receiving surface under calm conditions. D Represents the normal vector in a calm state N orthogonal projection reference point, Indicates the angle of incidence. t Indicates the angle of refraction. express The direction vector; S32: Let Combining the law of refraction and the small-angle first-order approximation, the local geometric relationships in the calm state are simplified. The simplified local geometric relationships in the calm state are specifically set as follows: ； in, This represents the refractive index parameter in air. This represents the refractive index parameter in water; S33: Pixels in the upward light field when the sea surface is fluctuating. The local geometric relationships under wave conditions are specifically set as follows: ； ； ； in, The spatial intersection point of the actual refracted ray and the receiving surface under wave-like conditions. F Represents the normal vector under wave state N orthogonal projection reference point, Indicates the angle between the horizontal plane and the wavering sea surface. Indicates the incident ray The horizontal direction vector, Normal vector N The intersection of the extended line and the receiving plane, Normal vector N and z The included angle of the axis; S34: Combining the law of refraction and the first-order approximation of small angles, the local geometric relationships in the wave state are simplified. The specific local geometric relationships in the calm state of the wave are set as follows: ； S35: Obtain the surface gradient at a small angle. Normal vector N and incident light exist z Direction vector of the axis Z Relationship; S36: Obtain the mapping relationship between the offset of the pixel and the surface gradient; S37: Introducing discrete resolution into pixel mapping relationships Introducing discrete resolution The pixel offset is specifically set as follows: ； in, Indicates the equivalent disturbance height ; S38: For receiving surface pixels Corresponding underwater target original pixel Perform the mapping, and set the mapping result as follows: ； S4: Simulate lidar scanning imaging to obtain cross-medium imaging simulation results.

2. The cross-medium uplink imaging simulation method based on downlink optical field according to claim 1, characterized in that, Step S1 specifically includes the following steps: S11: Combining the optical properties of microsurfaces with radiative transfer theory, through the bidirectional reflection distribution function Construct a Lambertian model and a two-way reflection distribution function. Specifically set as follows: ； in, This represents the reflected radiance of light radiation. Indicates incident irradiance, Indicates the angle of incidence at the zenith. Indicates the incident azimuth angle. Indicates the reflected zenith angle. Indicates the azimuth angle of the reflection; S12: Perform pixel normalization mapping on the given image grayscale values ​​of the underwater target to obtain the surface reflectance of the underwater target. ; S13: Treating the underwater target as an ideal Lambertian surface, construct the initial upward optical field of the laser reflection characteristics of the underwater target based on the Lambertian model, and the isotropic uniform reflection optical field of any incident direction. Specifically set as follows: ； in, This represents an isotropic, uniformly reflected light field with arbitrary incident directions. This represents the downlink optical field across the medium.

3. The cross-medium uplink imaging simulation method based on downlink optical field according to claim 2, characterized in that, In step S11, when the ideal Lambertian surface satisfies the ideal diffuse reflection condition, the bidirectional reflection distribution function of the ideal Lambertian surface is specifically set as follows: ； in, This represents the simplified constant value of the bidirectional reflection distribution function when an ideal Lambertian surface satisfies the ideal diffuse reflection condition. This represents the diffuse reflectance of the surface of an underwater target.

4. The cross-medium uplink imaging simulation method based on downlink optical field according to claim 2, characterized in that, In step S13, an initial upward optical field for the laser reflection characteristics of the underwater target is constructed. The initial upward optical field is an isotropic uniform reflection optical field with arbitrary incident direction. When the incident direction is perpendicular, the upward optical field with perpendicular incident direction is specifically set as follows: 。 5. The cross-medium uplink imaging simulation method based on downlink optical field according to claim 1, characterized in that, Step S35 specifically includes the following steps: Step 1: Calculate any fixed point gradient arbitrarily fixed point gradient Specifically set as follows: ； in, The mathematical representation of gradient data computation. Represents the Laplace operator; Step 2: Using the gradient formula, obtain the approximate surface gradient at small angles. Normal vector N and incident light exist z Direction vector of the axis Z The relationship between small-angle surface gradient Normal vector N and incident light exist z Direction vector of the axis Z The relationship is specifically set as follows: 。 6. The cross-medium uplink imaging simulation method based on downlink optical field according to claim 1, characterized in that, Step S36 specifically includes the following steps: Step 1: Incident light Normal vector N and horizontal direction vector The relationship is specifically set as follows: ； Step 2: Adjust the incident light... Normal vector N and horizontal direction vector The relationship is derived, and the specific derivation result is set as follows: ； Step 3: Simplify the derivation result for the first time using a small-angle first-order approximation. The specific settings for the first simplification are as follows: ； ； ； ； ； Step 4: Combining The derivation result is simplified a second time, and the specific simplification result is set as follows: ； ； Step 5: Set to 0, Substituting 0 into the second simplification result yields the simplest result, specifically set as follows: ； in, This indicates the height of the pixel above the water surface. This represents the offset of a pixel under two different conditions: calm sea surface and undulating sea surface.

7. The cross-medium uplink imaging simulation method based on downlink optical field according to claim 1, characterized in that, Step S4 specifically includes the following steps: S41: Simulate lidar scanning imaging, set the incident light as an array laser beam surface, the array laser beam surface includes multiple uniform rays, the incident direction of the rays is set as perpendicular, the light intensity of the rays is set as 1, and the laser wavelength of the rays is set as 532nm. S42: Set the relative refractive index of the air-sea interface to 1.33, the average scattering angle within the seawater channel to an empirical value of 0.03 rad, and the seawater absorption coefficient to 0.089 m. -1 The seawater scattering coefficient was set to 0.610m. -1 ; S43: Perform cross-media imaging simulations for different detection depths, sea conditions, and water types.

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