Modeling method for radiation transfer and fluorescence effect of underwater coral canopy

Abstract

The invention relates to the technical field of marine ecological remote sensing, in particular to a modeling method for radiation transfer and fluorescence effect of an underwater coral canopy, which comprises the following steps of: establishing an underwater scene three-dimensional model, and constructing a three-dimensional gridding model of an underwater coral target and a substrate; determining environmental parameters; forward simulating a light transmission process in the canopy, constructing an irradiance space distribution model of the underwater scene, and obtaining a fluorescence emission radiance distribution model; simulating a coral fluorescence spectrum through reverse spectral imaging based on a fluorescence emission radiance distribution model; the model is verified and optimized, algorithm parameters are adjusted, and the model accuracy is improved. The invention provides a modeling method for radiation transfer and fluorescence effect of underwater coral canopies, which can comprehensively consider different scales, coral forms, substrate types and water conditions by expanding a BRDF model to a special optical effect containing fluorescence item simulation fluorescence ray propagation and underwater environment. And high-precision underwater coral canopy modeling is realized.

Description

Technical Field

[0001] The invention relates to the field of marine ecological remote sensing technology, and in particular to a modeling method for underwater coral canopy radiation transmission and fluorescence effect. Background Art

[0002] In the protection and research of marine ecosystems, monitoring the health of coral reef ecosystems is of vital importance. Since coral lesions are manifested as changes in the spectral reflectance and fluorescence properties of their surface, fluorescence spectroscopy and hyperspectral imaging technologies can achieve in-situ measurements of the reflectance and fluorescence properties of corals, and are widely used in non-invasive, high-resolution monitoring of coral health at the satellite remote sensing scale.

[0003] In the prior art, there are three-dimensional radiation transfer models that take into account the three-dimensional structure and complex optical properties of the target, but they are mainly used for remote sensing inversion of plant physiological parameters in land and shallow water areas. These technologies simulate the complex propagation process of light in the vegetation canopy by combining the three-dimensional plant model and the optical property model. Commonly used three-dimensional radiation transfer models include DART (Discrete Anisotropic Radiative Transfer, a computer model for simulating the radiation transfer process in a three-dimensional scene) and SAIL (Simulating the Aerosol Layer and the Interaction of Light with leaves, a model for simulating the radiation transfer of the vegetation canopy), etc. However, existing methods perform poorly for achieving higher-resolution coral health detection at the canopy scale. The main reason is that the complex three-dimensional structure of corals leads to an uneven light field within the canopy, resulting in huge differences in readings at different locations of corals in hyperspectral images, making it impossible to obtain the optical properties of corals to analyze coral health. Existing technologies have the disadvantages of being difficult to accurately simulate attenuation processes such as multiple scattering and reabsorption effects of light in underwater environments, failing to effectively integrate the full process simulation of incident light, fluorescence and sensor measurements, and lacking the ability to adapt to different coral species and environmental conditions.

[0004] Therefore, a modeling method that can comprehensively consider the radiation transfer and fluorescence effects of underwater coral canopies is needed. Summary of the invention

[0005] The main purpose of the present invention is to provide a modeling method for underwater coral canopy radiation transmission and fluorescence effect, aiming to solve the problem of insufficient accuracy and practicality of existing technical means.

[0006] To achieve the above object, the present invention proposes a modeling method for underwater coral canopy radiation transmission and fluorescence effect, the method comprising the following steps:

[0007] Establish a 3D model of the underwater scene, construct a 3D grid model of underwater coral targets and bottom, and perform grid preprocessing on the scene;

[0008] Determine environmental parameters and determine the optical properties of corals and substrate through sensor measurement data;

[0009] Forward simulate the light transmission process in the canopy, build the irradiance spatial distribution model of the underwater scene, and obtain the fluorescence emission radiance distribution model;

[0010] Based on the fluorescence emission radiance distribution model, inverse spectral imaging simulates the coral fluorescence spectrum;

[0011] Model verification and optimization, using experimental data collection, adjusting algorithm parameters through experiments to improve model accuracy.

[0012] Furthermore, the steps of establishing a three-dimensional model of the underwater scene, constructing a three-dimensional grid model of the underwater coral target and the bottom, and performing grid preprocessing on the scene include:

[0013] Using structure-from-motion technology, the three-dimensional mesh model of coral targets and bottom is reconstructed through continuous underwater image capture;

[0014] Adjust the seawater in the three-dimensional grid model to a medium with projection and scattering properties;

[0015] Mesh preprocessing of underwater scenes.

[0016] Furthermore, the step of determining the environmental parameters and determining the optical properties of the coral and the optical properties of the substrate through the measurement data of the sensor includes:

[0017] Set the light source and sensor, record the light source type, light source position, light source radiation intensity and sensor parameters, and determine the directional distribution function of the light source radiation intensity;

[0018] Determine the optical properties of corals using bidirectional reflectance functions and fluorescence property extensions;

[0019] By searching the prior database, the optical properties of the substrate are determined;

[0020] The transmittance coefficient, scattering coefficient and fluorescence coefficient of the water body are obtained through field measurements.

[0021] Furthermore, the steps of forward simulating the light transmission process in the canopy, constructing the irradiance spatial distribution model of the underwater scene, and obtaining the fluorescence emission radiance distribution model include:

[0022] Based on the intensity distribution I(ω) of the light source, a probability density function of the direction of the photon is generated;

[0023] For each sampled light, the position x of the photon during its propagation is gradually updated with a step length of t. new , the change of direction ω;

[0024] When a photon intersects with a target, a secondary reflected ray is generated according to the BRDF function at the intersection, and the propagation process is simulated recursively.

[0025] Comprehensively sample photon information and use the KNN algorithm combined with the Monte Carlo integration method to calculate the spatial distribution of irradiance;

[0026] Based on the calculated spatial irradiance distribution and the fluorescence properties of corals, a fluorescence radiance spatial distribution model is constructed.

[0027] Furthermore, the step of forward simulating the light transmission process in the canopy, constructing the irradiance spatial distribution model of the underwater scene, and obtaining the fluorescence emission radiance distribution model also includes:

[0028] When the surfaces interact, the photon information is stored in the KD tree structure;

[0029] The BRDF function f of the target surface at the intersection for wavelength λ r , generating the angle ω of the reflected photon o , calculate the emission direction and energy of the photon after reflection according to BRDF;

[0030] Repeat the iteration for each sampled light until the number of reflections reaches the preset threshold Nn or the photon radiation energy is less than the preset threshold φ when emission occurs. n When the time is cut off, the photon wavelength λ is changed and a new tracking light is regenerated.

[0031] Furthermore, the step of simulating the coral fluorescence spectrum by reverse spectral imaging based on the fluorescence emission radiance distribution model also includes:

[0032] Generate camera rays, starting from the camera position o, and generate reverse tracing rays for each pixel j;

[0033] For each sampling wavelength λ k The tracing ray is built by combining the VCM algorithm with the photon propagation information to establish a connection between the camera position o and the light source x o The incident light propagation path and the paths of fluorescent photons leaving the coral target surface And obtain the energy φ of the photon leaving the coral target surface n .

[0034] Furthermore, the step of simulating the coral fluorescence spectrum by reverse spectral imaging based on the fluorescence emission radiance distribution model also includes:

[0035] The intensity of light entering the camera is calculated, the energy reaching the camera after the attenuation of the radiation energy due to the absorption and scattering effects of the water body during the photon propagation process is simulated, and the contribution of all accumulated paths and wavelengths is calculated for each pixel j.

[0036] The present invention provides a modeling method for underwater coral canopy radiation transmission and fluorescence effect. By expanding the BRDF model to include fluorescence terms to simulate the propagation of fluorescent light and the special optical effects of the underwater environment, it is possible to comprehensively consider different scales, coral morphologies, bottom types and water conditions to achieve high-precision underwater coral canopy modeling. BRIEF DESCRIPTION OF THE DRAWINGS

[0037] In order to more clearly illustrate the embodiments of the present invention or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For ordinary technicians in this field, other drawings can be obtained according to the processes shown in these drawings without paying creative work.

[0038] Figure 1 Schematic diagram of a flow chart of an embodiment of the method for modeling radiation transmission and fluorescence effect of underwater coral canopy. DETAILED DESCRIPTION

[0039] The following will be combined with the drawings in the embodiments of the present invention to clearly and completely describe the technical solutions in the embodiments of the present invention. Obviously, the described embodiments are only part of the embodiments of the present invention, not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of the present invention.

[0040] It should be noted that all directional indications in the embodiments of the present invention (such as up, down, left, right, front, back, etc.) are only used to explain the relative position relationship, movement status, etc. between the components under a certain specific posture (as shown in the accompanying drawings). If the specific posture changes, the directional indication will also change accordingly.

[0041] In addition, the descriptions of "first", "second", etc. in the present invention are only used for descriptive purposes and cannot be understood as indicating or implying their relative importance or implicitly indicating the number of the indicated technical features. Therefore, the features defined as "first" and "second" may explicitly or implicitly include at least one of the features. In addition, the technical solutions between the various embodiments can be combined with each other, but they must be based on the ability of ordinary technicians in the field to implement them. When the combination of technical solutions is contradictory or cannot be implemented, it should be deemed that such a combination of technical solutions does not exist and is not within the scope of protection required by the present invention.

[0042] In the prior art, three-dimensional radiation transfer models that take into account the three-dimensional structure and complex optical properties of the target are mainly used for remote sensing inversion of plant physiological parameters in land and shallow water areas. These technologies can simulate the complex propagation process of light in the vegetation canopy by combining the three-dimensional plant model and the optical property model. Commonly used three-dimensional radiation models include DART (Discrete Anisotropic Radiative Transfer, a computer model for simulating the radiation transfer process in a three-dimensional scene) and SAIL (Simulating the Aerosol Layer and the Interaction of Light with leaves, a model for simulating the radiation transfer of the vegetation canopy), etc.

[0043] However, the existing technology still cannot solve the problem of uneven light field in the canopy caused by the complex three-dimensional structure of the coral, and the photon mapping technology mostly used in the existing three-dimensional radiation transfer modeling requires a large amount of calculation. The existing three-dimensional radiation transfer modeling method does not take into account the unique fluorescence effect of the coral surface and the scattering properties of the surrounding water medium, resulting in insufficient accuracy in describing the radiation transfer process of underwater fluorescence spectral imaging, and the measured fluorescence spectrum cannot reflect the fluorescence properties of the coral.

[0044] Based on this, the present application embodiment provides a modeling method for underwater coral canopy radiation transmission and fluorescence effect, referring to Figure 1 , Figure 1 Schematic diagram of a flow chart of an embodiment of the method for modeling radiation transmission and fluorescence effect of underwater coral canopy.

[0045] In this embodiment, the specific steps of the modeling method for underwater coral canopy radiation transmission and fluorescence effect are as follows:

[0046] Step S10, establish a three-dimensional model of the underwater scene, construct a three-dimensional grid model of the underwater coral target and the bottom, and perform grid preprocessing on the scene; then use the motion recovery structure technology to reconstruct the three-dimensional grid model of the coral target and the bottom through continuous underwater shooting images; adjust the seawater in the three-dimensional grid model to a medium with projection and scattering properties, and perform grid preprocessing on the underwater scene.

[0047] In this step, the structure from motion technology is used to establish a three-dimensional grid model of the coral target and the bottom through continuous underwater image capture. At the same time, the seawater is modeled as a medium with projection and scattering properties in the three-dimensional grid model. In the process of constructing the three-dimensional grid model, the scene is grid preprocessed to accelerate the subsequent calculation of the radiation transfer process.

[0048] In detail, the present invention realizes the modeling of underwater coral fluorescence spectrum imaging process based on the photon path efficient tracking method of VCM (vertex connection and merging, a combination of bidirectional route tracking and photon mapping). This method decouples the incident light from the fluorescence. First, the spatial distribution of the irradiance of the incident light on the coral target is analyzed to obtain the spatial distribution of the radiance of the excited fluorescence. Then, based on the VCM method, the energy of the incident light and the fluorescence captured by the sensor is calculated to complete the simulation of the fluorescence spectrum imaging process. This method comprehensively considers the influence of the fluorescent target and the scattering medium in the process of photon propagation, and realizes the three-dimensional radiation transmission modeling in the process of underwater biomass target fluorescence spectrum imaging.

[0049] Step S20, determining environmental parameters, and determining optical properties of corals and optical properties of the bottom through measurement data of the sensor;

[0050] Step S21, setting the light source and the sensor, recording the light source type, light source position, light source radiation intensity and sensor parameters, and determining the light source radiation intensity directional distribution function;

[0051] Step S22, using the bidirectional reflectance function and the fluorescence property extension term to determine the optical properties of the coral;

[0052] Step S23, determining the optical properties of the substrate by searching the priori database;

[0053] Step S24, obtaining the transmission coefficient, scattering coefficient and fluorescence coefficient of the water body through field measurement.

[0054] In detail, the present invention determines the optical properties of corals through BRDF (bidirectional reflectance function) and fluorescence property extension, determines the optical properties of the substrate through the database corresponding to the substrate, and obtains the transmission coefficient, scattering coefficient and fluorescence coefficient of the water body through field measurement. In this embodiment, the light source type is set to a point light source, and the light source position is set to a three-dimensional coordinate x o , the radiation intensity of the light source is recorded as I o (λ), λ is the wavelength, and the directional distribution function of the radiation intensity of the light source is: R(ω, λ), where ω is the spatial solid angle.

[0055] Step S30, forward simulating the light transmission process in the canopy, constructing an irradiance spatial distribution model of the underwater scene, and obtaining a fluorescence emission radiance distribution model;

[0056] The present invention uses photon mapping technology combined with the Monte Carlo method and importance sampling to construct a spatial distribution model of the irradiance of incident light in the coral canopy and obtain a fluorescence emission radiance distribution model. From the perspective of radiometry, in an underwater environment, the propagation of light follows the RTE (radiative transport equation), and the specific formula is as follows:

[0057]

[0058] Where L(x,ω) is the radiant brightness of the light at position x along the direction ω; c(x) is the attenuation coefficient of the light when it propagates in the water medium; β(x,ω ′ →ω) is the scattering phase function of the water medium; Q(x,ω) is the contribution of the light emitting sources in the environment other than the light source to the radiance of the light;

[0059] Photon mapping technology obtains an approximate solution to RTE by tracking a large number of photons with different wavelengths λ. The energy φ(λ) carried by each photon propagates in the scene according to:

[0060] φ i+1 (λ)=φ i (λ)*R(x i ,λ,ω i →ω i+1 )

[0061] Where R is the BRDF (Bidirectional Reflectance Distribution Function) of the surface or the phase function of the water body.

[0062] Based on the above technical solution, the specific steps of constructing the radiance spatial distribution model are as follows:

[0063] Step S31, generating a probability density function of the direction of the photon based on the intensity distribution I(ω) of the light source;

[0064] Step S32: for each sampling light, the position x of the photon during the photon propagation process is gradually updated with a step length of t. new , the change of direction ω;

[0065] Step S33, when the photon intersects with the target, a secondary reflected light is generated according to the BRDF function at the intersection, and the propagation process is simulated in a recursive manner;

[0066] Step S34, the BRDF function f of the target surface at the intersection for the wavelength λ r , generating the angle ω of the reflected photon o , calculate the emission direction and energy of the photon after reflection according to BRDF;

[0067] Step S35, repeat the iteration for each sampled light until the number of reflections reaches a preset threshold Nn or the photon radiation energy is less than a preset threshold φ when emission occurs. n When the time is cut off, the photon wavelength λ is changed and a new tracking light is regenerated.

[0068] Step S36, when the surfaces interact, storing the photon information in the KD tree structure;

[0069] Step S37, comprehensively sampling photon information, and using KNN algorithm combined with Monte Carlo integration method to calculate the irradiance spatial distribution;

[0070] Step S38, constructing a fluorescence radiance spatial distribution model based on the calculated spatial irradiance distribution and the fluorescence properties of the coral.

[0071] In detail, the probability density function (PDF) generated based on the intensity distribution I(ω) of the light source is as follows:

[0072]

[0073] The initial radiation flux is:

[0074]

[0075] Among them, N is the total number of photons; I0(λ) is the initial intensity of the light source; R(ω,λ) is the directional distribution function of the radiation intensity of the light source.

[0076] In detail, the present invention comprehensively considers the scattering effect of water bodies, calculates the intersection of the light and the coral target and the radiance distribution on the light in an iterative manner, and gradually updates the position x of the photon in the photon propagation process with t as the step size for each sampled light. new And simulate the change of propagation direction ω caused by the scattering properties of water medium during the movement of photons, calculate xnew The specific announcement is as follows:

[0077] x new =x old +t*ω

[0078] Where t is the propagation distance of the sample.

[0079] The specific formula for calculating the change in propagation direction ω is as follows:

[0080] ω new =sample(β(x,ω old →ω new ))

[0081] Among them, β(x,ω old →ω new ) is the scattering phase function of water medium; sample(·) represents the sampling of probability density.

[0082] According to Beer-Lambert's law, the specific formula for simulating the attenuation of radiation energy during photon propagation due to the absorption and scattering effects of water is as follows:

[0083] φ new =Φ old *exp(-σ t *t)

[0084] Among them, v t It is the total attenuation coefficient of radiation intensity taking into account the absorption and scattering effects of the medium.

[0085] When the photon intersects the target, the BRDF sampling technique is used according to the BRDF properties at the intersection to generate secondary reflected light and continue to simulate the propagation process in a recursive manner. For the BRDF function f of the target surface at the intersection for wavelength λ r , generating the angle ω of the reflected photon o The probability density function PDF is:

[0086]

[0087] At the same time, the new direction and energy of the reflected light are calculated according to the BRDF. The specific formula is as follows:

[0088] ω new =sample(f r (x,λ,ω old →ω new ))

[0089]

[0090] where ω i is the direction of the incident light; ωo is the direction of the outgoing light; θ o is the angle between the outgoing ray and the surface normal.

[0091] Then, steps S32 to S34 are repeatedly performed for each sampled light until the number of reflections reaches a preset threshold value Nn, or the radiation energy of the outgoing photon when reflection occurs is less than a preset threshold value Φ n After stopping the repetition, the photon wavelength λ is changed, a new tracing light is repeatedly generated, and steps S31 to S34 are repeatedly executed to simulate the propagation process of photons with different wavelengths.

[0092] At each surface interaction, the photon information (position, incident direction, energy, wavelength) is stored in a KD-tree structure (k-dimensional tree, a tree-shaped data structure that stores instance points in k-dimensional space for fast retrieval).

[0093] In detail, this step needs to consider the spatial distribution analysis of direct illumination irradiance, based on steps S31 to S34, comprehensively sample photon information, and use density estimation methods such as KNN (K-Nearest Neighbor, K nearest neighbor algorithm, for any n-dimensional input vector, each corresponds to a point in the feature space, and the output is the category label or predicted value corresponding to the feature vector) combined with the Monte Carlo integration method to calculate the spatial distribution of irradiance.

[0094] Specifically, for the geometric center x of each grid on the coral surface, the KNN method is used to search for photons with a wavelength of λ and an end point near position x, and then the Monte Carlo integration method is used to calculate the irradiance at position x. The specific formula is as follows:

[0095]

[0096] Among them, r is the preset search radius; k is the preset number of neighbors; Φ i (λ) are the energies of the i-th photon, θ i is the angle between the incident light and the surface normal.

[0097] Based on step S35, the spatial irradiance distribution and the coral surface fluorescence property model are constructed according to the calculation, and the spatial distribution of fluorescence radiance is constructed. The specific calculation method is as follows:

[0098] Assuming that the fluorescence emission is isotropic and the intensity follows the Lambertian distribution, the specific formula for the spatial and angular distribution of the fluorescence emission radiance is:

[0099]

[0100] where λ emis the fluorescence emission wavelength independent variable; α(λ ex ) is the wavelength λ of the coral ex The absorption coefficient at f is the fluorescence quantum yield of the coral material, indicating the proportion of absorbed photons that produce fluorescence; S em (λ em ,λ ex ) is the fluorescence emission spectrum of coral, indicating that ex After excitation, em The relative emission intensity at λ is λ; Λ is the range of all possible excitation wavelengths. The above material property parameters can be obtained through experimental measurement or data search.

[0101] Through steps S31-S35, the light transmission process in the complex three-dimensional structure of the coral canopy can be accurately simulated, while simulating the scattering effect of the seawater medium and the fluorescence effect of the coral. It can be understood that this method combines the efficiency of photon mapping and the unbiasedness of Monte Carlo integration, and can effectively handle complex optical phenomena in underwater coral canopies, such as multiple scattering and fluorescence.

[0102] Step S40, based on the fluorescence emission radiance distribution model, reverse spectral imaging simulates the coral fluorescence spectrum, generates camera light, takes the camera position o as the starting point, generates reverse tracing light for each pixel j; for each sampling wavelength λ k The tracing ray is built by combining the VCM algorithm with the photon propagation information to establish a connection between the camera position o and the light source x o The incident light propagation path and the paths of fluorescent photons leaving the coral target surface And obtain the energy φ of the photon leaving the coral target surface n .

[0103] Step S50, calculate the intensity of light entering the camera, simulate the energy reaching the camera after the radiation energy is attenuated by the absorption and scattering effects of the water body during the photon propagation process, calculate the cumulative contribution of all paths and wavelengths for each pixel j, and then verify and optimize the model, use experimental collection data, adjust the algorithm parameters through experiments, and improve the accuracy of the model.

[0104] Among them, steps S40 to S50 are based on the light transmission process model, photon propagation process model, and fluorescence radiance spatial distribution model constructed in step S30, and use VCM technology to simulate the imaging process of coral fluorescence spectrum. The specific formula is as follows:

[0105] Taking the camera position o as the starting point, the specific formula for generating reverse tracing rays for each pixel j is:

[0106] ray(t)=o+t*ω

[0107] Among them, ω is the direction of the light, which is determined by the camera parameters and the position of the pixel in the image.

[0108] For each ray, the specific formula for adaptive wavelength sampling in the visible spectrum range is:

[0109] λ k =sample(S camera (λ)

[0110] Among them, S camera is the spectral response function of the camera, which can be read in the camera manual; sample(·) represents the sampling of the probability density.

[0111] In detail, for each sampling wavelength λ k The VCM algorithm is used to combine the photon propagation information stored in the KD tree structure in step S30 to establish the incident light propagation path connecting the camera position o and the light source x0. and the paths of fluorescent photons leaving the coral target surface Get the energy of the photon leaving the coral target surface Φ n Among them, the incident light propagation path and fluorescence photon path The specific formula is:

[0112]

[0113] For each incident ray path from the coral target surface to the camera position o, n ,o), according to Beer-Lambert law, the energy reaching the camera after the radiation energy is attenuated by the absorption and scattering effects of the water during the photon propagation process is simulated:

[0114] φ o =Φ n *exp(-σ t *t)

[0115] Among them, σ t It is the total attenuation coefficient of radiation intensity taking into account the absorption and scattering effects of the medium.

[0116] The specific formula for accumulating the contributions of all paths and wavelengths for each pixel is:

[0117]

[0118] Among them, R j is the spectral response function of pixel j.

[0119] It is understandable that in this embodiment, experimental data can also be used to adjust algorithm parameters through experimental data to improve model accuracy. Through the above steps, the spectral imaging of coral fluorescence can be accurately simulated, while considering the particularity of the underwater environment. The present invention combines the efficiency of the VCM algorithm and the robustness of the bidirectional path tracing method, and can effectively handle complex optical phenomena such as water scattering, refraction and fluorescence effects of the target. In particular, it can accurately simulate the propagation and conversion of light of different wavelengths in the underwater environment, thereby obtaining high-quality spectral images.

[0120] In combination with all the above technical solutions, the present invention provides a modeling method for underwater coral canopy radiation transmission and fluorescence effect. By considering the complex three-dimensional structure of the coral canopy and the underwater environmental characteristics, the coral canopy grid model and the ray tracing algorithm based on physical properties are adopted to achieve a significant improvement in the accuracy of radiation transmission simulation. The present invention also introduces the simulation of fluorescence effect in the coral canopy radiation transmission model, expands the BRDF model to include fluorescence terms, and simulates the propagation of fluorescent light separately to achieve the special optical effect of simulating the underwater environment. The Monte Carlo integration algorithm is used to optimize the ray tracing strategy, which significantly improves the calculation efficiency and accuracy, and can monitor coral reefs on a large scale. At the same time, it can adapt to different coral morphologies, bottom types and water conditions. It has wide practicality and can be extended to the study of optical properties of other complex underwater ecosystems.

[0121] The above description is only a preferred embodiment of the present invention, and does not limit the patent scope of the present invention. All equivalent structural changes made by using the contents of the present invention specification and drawings under the inventive concept of the present invention, or directly / indirectly applied in other related technical fields are included in the patent protection scope of the present invention.

Claims

1. A modeling method for underwater coral canopy radiation transfer and fluorescence effects, characterized in that: The following steps are involved: Establish a 3D model of the underwater scene, construct a 3D grid model of underwater coral targets and bottom, and perform grid preprocessing on the scene; Determine environmental parameters and determine the optical properties of corals and substrate through sensor measurement data; Forward simulate the light transmission process in the canopy, build the irradiance spatial distribution model of the underwater scene, and obtain the fluorescence emission radiance distribution model; Based on the fluorescence emission radiance distribution model, inverse spectral imaging simulates the coral fluorescence spectrum; Model verification and optimization, using experimental data collection, adjusting algorithm parameters through experiments to improve model accuracy.

2. The method for modeling underwater coral canopy radiation transmission and fluorescence effect according to claim 1, characterized in that: The steps of establishing a three-dimensional model of an underwater scene, constructing a three-dimensional grid model of underwater coral targets and bottom materials, and performing grid preprocessing on the scene include: Using structure-from-motion technology, the three-dimensional mesh model of coral targets and bottom is reconstructed through continuous underwater image capture; Adjust the seawater in the three-dimensional grid model to a medium with projection and scattering properties; Mesh preprocessing of underwater scenes.

3. The modeling method for underwater coral canopy radiation transmission and fluorescence effect as claimed in claim 2, characterized in that: The step of determining the environmental parameters and determining the optical properties of the coral and the optical properties of the substrate through the measurement data of the sensor includes: Set the light source and sensor, record the light source type, light source position, light source radiation intensity and sensor parameters, and determine the directional distribution function of the light source radiation intensity; Determine the optical properties of corals using bidirectional reflectance functions and fluorescence property extensions; By searching the prior database, the optical properties of the substrate are determined; The transmittance coefficient, scattering coefficient and fluorescence coefficient of the water body are obtained through field measurements.

4. The method for modeling underwater coral canopy radiation transmission and fluorescence effect as claimed in claim 1, characterized in that: The steps of forward simulating the light transmission process in the canopy, constructing the irradiance spatial distribution model of the underwater scene, and obtaining the fluorescence emission radiance distribution model include: Based on the intensity distribution I(ω) of the light source, a probability density function of the direction of the photon is generated; For each sampled light, the position x of the photon during its propagation is gradually updated with a step length of t. new , the change of direction ω; When a photon intersects with a target, a secondary reflected ray is generated according to the BRDF function at the intersection, and the propagation process is simulated recursively. Comprehensively sample photon information and use the KNN algorithm combined with the Monte Carlo integration method to calculate the spatial distribution of irradiance; Based on the calculated spatial irradiance distribution and the fluorescence properties of corals, a fluorescence radiance spatial distribution model is constructed.

5. The modeling method for underwater coral canopy radiation transmission and fluorescence effect as claimed in claim 1, characterized in that: The step of forward simulating the light transmission process in the canopy, constructing the irradiance spatial distribution model of the underwater scene, and obtaining the fluorescence emission radiance distribution model also includes: When the surfaces interact, the photon information is stored in the KD tree structure; The BRDF function f of the target surface at the intersection for wavelength λ r , generating the angle ω of the reflected photon o , calculate the emission direction and energy of the photon after reflection according to BRDF; Repeat the iteration for each sampled light until the number of reflections reaches the preset threshold Nn or the photon radiation energy is less than the preset threshold φ when emission occurs. n When the time is cut off, the photon wavelength λ is changed and a new tracking light is regenerated.

6. The modeling method for underwater coral canopy radiation transmission and fluorescence effect according to claim 1, characterized in that: The step of simulating the coral fluorescence spectrum by reverse spectral imaging based on the fluorescence emission radiance distribution model also includes: Generate camera rays, starting from the camera position o, and generate reverse tracing rays for each pixel j; For each sampling wavelength λ k The tracing ray is built by combining the VCM algorithm with the photon propagation information to establish a connection between the camera position o and the light source x o The incident light propagation path and the paths of fluorescent photons leaving the coral target surface And obtain the energy φ of the photon leaving the coral target surface n .

7. The method for modeling underwater coral canopy radiation transmission and fluorescence effect according to claim 6, characterized in that: The step of simulating the coral fluorescence spectrum by reverse spectral imaging based on the fluorescence emission radiance distribution model also includes: The intensity of light entering the camera is calculated, the energy reaching the camera after the attenuation of the radiation energy due to the absorption and scattering effects of the water body during the photon propagation process is simulated, and the contribution of all accumulated paths and wavelengths is calculated for each pixel j.

Images