A method for modeling underwater coral canopy radiative transfer and fluorescence effects

Abstract

The present application relates to the technical field of marine ecological remote sensing, and particularly relates to a modeling method for underwater coral canopy radiation transmission and fluorescence effect, comprising the following steps: establishing a three-dimensional model of an underwater scene, and constructing a three-dimensional gridding model of underwater coral targets and substrates; determining environmental parameters; 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; based on the fluorescence emission radiance distribution model, reversely simulating the coral fluorescence spectrum through spectral imaging; model verification and optimization, adjusting algorithm parameters, and improving the accuracy of the model. The present application provides a modeling method for underwater coral canopy radiation transmission and fluorescence effect, which can comprehensively consider different scales, coral morphologies, substrate types and water conditions by extending the BRDF model to contain a fluorescence term to simulate the propagation of fluorescent light and the special optical effects of the underwater environment, so as to realize high-precision underwater coral canopy modeling.

Description

Technical Field

[0001] This invention relates to the field of marine ecological remote sensing technology, and in particular to a modeling method for underwater coral canopy radiative transfer and fluorescence effects. Background Technology

[0002] In marine ecosystem conservation and research, monitoring the health status of coral reef ecosystems is crucial. Since coral disease manifests as changes in its surface spectral reflectance and fluorescence properties, fluorescence spectroscopy and hyperspectral imaging techniques can achieve in-situ measurements of these properties and are widely used for non-invasive, high-resolution coral health monitoring at the satellite remote sensing scale.

[0003] In existing technologies, there are three-dimensional radiative transfer models that consider the three-dimensional structure and complex optical properties of the target. However, these models are mainly used for remote sensing inversion of plant physiological parameters in terrestrial and shallow water areas. These technologies simulate the complex propagation process of light in the vegetation canopy by combining three-dimensional plant models and optical property models. Commonly used three-dimensional radiative transfer models include DART (Discrete Anisotropic Radiative Transfer, a computer model for simulating radiative transfer processes in three-dimensional scenes) and SAIL (Simulating the Aerosol Layer and the Interaction of Light with Leaves, a model for simulating radiative transfer in the vegetation canopy). However, existing methods are not performing well for coral health detection at higher resolution canopy scales. The main reason is that the complex three-dimensional structure of corals leads to non-uniform light fields within the canopy, resulting in significant differences in readings at different locations of the coral in hyperspectral images. This makes it impossible to obtain the optical properties of the coral to analyze its health. Existing technologies also have shortcomings such as difficulty in accurately simulating the attenuation process of light multiple scattering and reabsorption effects in the underwater environment, failure to effectively integrate the simulation of the entire process of incident light, fluorescence, and sensor measurements, and lack of adaptability to different coral species and environmental conditions.

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

[0005] The main objective of this invention is to provide a modeling method for radiative transmission and fluorescence effects in underwater coral canopies, aiming to address the shortcomings in accuracy and practicality of existing technologies.

[0006] To achieve the above objectives, this invention proposes a modeling method for radiative transport and fluorescence effects in underwater coral canopies, comprising the following steps:

[0007] Establish a 3D model of the underwater scene, construct a 3D mesh model of the underwater coral target and the substrate, and perform mesh preprocessing on the scene;

[0008] Environmental parameters were determined, and the optical properties of the coral and the substrate were determined using sensor measurement data.

[0009] By positively simulating the light transmission process within the canopy, a spatial distribution model of irradiance in an underwater scene is constructed, and a fluorescence emission irradiance distribution model is obtained.

[0010] Based on the fluorescence emission radiance distribution model, reverse spectral imaging was used to simulate the fluorescence spectrum of corals;

[0011] Model validation and optimization involve using experimentally collected data to adjust algorithm parameters and improve model accuracy.

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

[0013] Using motion-reconstruction technology, a three-dimensional mesh model of the coral target and the substrate is reconstructed from continuous underwater images;

[0014] Adjust the seawater in the 3D mesh model to be a medium with projection and scattering properties;

[0015] The underwater scene is preprocessed into a grid.

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

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

[0018] The optical properties of corals were determined using bidirectional reflectance function and fluorescence property extension term;

[0019] The optical properties of the substrate are determined by searching a priori database;

[0020] The transmittance, scattering, and fluorescence coefficients of the water body were obtained through on-site measurements.

[0021] Furthermore, the steps of constructing a spatial distribution model of irradiance for an underwater scene by positively simulating the light transmission process within the canopy and obtaining a fluorescence emission irradiance distribution model include:

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

[0023] For each sampled ray, the position x of the photon during its propagation is updated incrementally with a step size of t. new The change in direction ω;

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

[0025] The spatial distribution of irradiance is calculated by comprehensively sampling photon information and using the KNN algorithm combined with the Monte Carlo integration method.

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

[0027] Furthermore, the step of constructing a spatial distribution model of irradiance for an underwater scene by positively simulating the light transmission process within the canopy and obtaining a fluorescence emission radiance distribution model further includes:

[0028] When surfaces interact, photonic information is stored in a KD tree structure;

[0029] The BRDF function f of the target surface at the intersection point with respect to wavelength λ r The angle ω from which the reflected photon is generated o The direction and energy of the photon after reflection are calculated based on the BRDF.

[0030] This process is repeated iteratively for each sampled light beam until the number of reflections reaches a preset threshold Nn or the emitted photon radiation energy is less than a preset threshold φ. n At the cutoff time, after changing the photon wavelength λ, a new tracking ray is generated.

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

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

[0033] For each sampling wavelength λ k By tracking the light ray and using the VCM algorithm combined with photon propagation information, a connection is established between the camera position o and the light source x. o The propagation path of the incident light And the fluorescent photon path leaving the surface of the coral target And obtain the energy φ of the photon leaving the surface of the coral target. n .

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

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

[0036] This invention provides a modeling method for underwater coral canopy radiative transmission and fluorescence effects. By extending the BRDF model to include fluorescence terms to simulate the propagation of fluorescent light and the special optical effects of the underwater environment, it can comprehensively consider different scales, coral morphologies, substrate types and water conditions to achieve high-precision underwater coral canopy modeling. Attached Figure Description

[0037] To more clearly illustrate the technical solutions in the embodiments of the present invention or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present invention. For those skilled in the art, other drawings can be obtained based on the processes shown in these drawings without creative effort.

[0038] Figure 1 This is a flowchart illustrating one embodiment of the modeling method for underwater coral canopy radiative transfer and fluorescence effects. Detailed Implementation

[0039] The technical solutions of the embodiments of the present invention will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only a part of the embodiments of the present invention, and not all of the embodiments. Based on the embodiments of the present invention, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present invention.

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

[0041] Furthermore, the use of terms such as "first" and "second" in this invention is for descriptive purposes only and should not be construed as indicating or implying their relative importance or implicitly specifying the number of technical features indicated. Therefore, a feature defined with "first" or "second" may explicitly or implicitly include at least one of that feature. Additionally, the technical solutions of the various embodiments can be combined with each other, but only on the basis of being achievable by those skilled in the art. When the combination of technical solutions is contradictory or impossible to implement, such a combination of technical solutions should be considered non-existent and not within the scope of protection claimed by this invention.

[0042] In existing technologies, three-dimensional radiative transfer models that consider the three-dimensional structure and complex optical properties of the target are mainly applied to remote sensing inversion of plant physiological parameters in terrestrial and shallow water fields. These technologies, by combining three-dimensional plant models and optical property models, can simulate the complex propagation process of light within the vegetation canopy. Commonly used three-dimensional radiative transfer models include DART (Discrete Anisotropic Radiative Transfer, a computer model for simulating radiative transfer processes in three-dimensional scenes) and SAIL (Simulating the Aerosol Layer and the Interaction of Light with Leaves, a model for simulating radiative transfer in vegetation canopies).

[0043] However, existing technologies still have limitations in addressing the problem of uneven light field within the canopy caused by the complex three-dimensional structure of corals. Furthermore, the photon mapping technique used in most existing three-dimensional radiative transfer modeling methods requires a large amount of computation, and these methods do not consider the unique fluorescence effect on the coral surface or the scattering properties of the surrounding water medium. This results in insufficient accuracy in describing the radiative transfer process in underwater fluorescence spectral imaging, and the measured fluorescence spectra cannot reflect the fluorescence properties of corals.

[0044] Based on this, embodiments of this application provide a modeling method for radiative transfer and fluorescence effects in underwater coral canopies, referring to... Figure 1 , Figure 1 This is a flowchart illustrating one embodiment of the modeling method for underwater coral canopy radiative transfer and fluorescence effects.

[0045] In this embodiment, the specific steps of the modeling method for underwater coral canopy radiative transport and fluorescence effects are as follows:

[0046] Step S10: Establish a three-dimensional model of the underwater scene, construct a three-dimensional mesh model of the underwater coral target and the substrate, and perform mesh preprocessing on the scene; then use motion recovery structure technology to reconstruct the three-dimensional mesh model of the coral target and the substrate through continuous underwater image capture; adjust the seawater in the three-dimensional mesh model to be a medium with projection and scattering properties, and perform mesh preprocessing on the underwater scene.

[0047] In this step, structure from motion (SFO) technology is used to create a three-dimensional mesh model of the coral target and the substrate by continuously capturing underwater images. At the same time, seawater is modeled as a medium with projection and scattering properties in this three-dimensional mesh model. During the construction of the three-dimensional mesh model, the scene is preprocessed into a mesh to accelerate the calculation of the subsequent radiative transfer process.

[0048] In detail, this invention utilizes a highly efficient photon path tracking method based on VCM (vertex connection and merging, combining bidirectional path tracing and photon mapping) to model the underwater coral fluorescence spectral imaging process. This method decouples incident light from fluorescence. First, by analyzing the spatial distribution of irradiance of the incident light on the coral target, the spatial distribution of irradiance for excitation of fluorescence is obtained. Then, based on the VCM method, the energy of incident light and fluorescence captured by the sensor is calculated to simulate the fluorescence spectral imaging process. This method comprehensively considers the influence of the fluorescent target and the scattering medium during photon propagation, achieving three-dimensional radiative transfer modeling in the underwater biomass target fluorescence spectral imaging process.

[0049] Step S20: Determine environmental parameters and determine the optical properties of the coral and the substrate using sensor measurement data;

[0050] Step S21: Set up 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;

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

[0052] Step S23: Determine the optical properties of the substrate by searching a priori database;

[0053] Step S24: Obtain the transmission coefficient, scattering coefficient, and fluorescence coefficient of the water body through on-site measurement.

[0054] In detail, this invention determines the optical properties of corals using BRDF (Bidirectional Reflectance Function) and extended terms of fluorescence properties, determines the optical properties of the substrate using a database corresponding to the substrate, and obtains the transmittance, scattering, and fluorescence coefficients of the water body through field measurements. In this embodiment, the light source type is set as a point light source, and the light source position is set as a three-dimensional coordinate x. o The radiation intensity of the light source is denoted as I. o (λ), where λ is the wavelength, and the directional distribution function of the light source's radiation intensity is: R(ω, λ), where ω is the spatial solid angle.

[0055] Step S30: Simulate the light transmission process within the canopy in a forward manner to construct an irradiance spatial distribution model for the underwater scene and obtain a fluorescence emission irradiance distribution model;

[0056] This invention utilizes photon mapping technology combined with Monte Carlo methods and importance sampling to construct a spatial distribution model of incident light irradiance in the coral canopy, thereby obtaining a fluorescence emission radiance distribution model. From a radiometric perspective, in the underwater environment, light propagation follows the RTE (radiative transport equation), the specific formula of which is as follows:

[0057]

[0058] Where L(x,ω) is the radiance of the light at position x along direction ω; c(x) is the attenuation coefficient of the light propagating in the water medium; β(x,ω) ′ →ω) is the scattering phase function of the water medium; Q(x,ω) is the contribution of 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 the real-time equation (RTE) by tracking a large number of photons with different wavelengths λ. Each photon carries energy φ(λ), and its propagation in the scene follows the following rules:

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

[0061] Where R is the BRDF (two-way reflection distribution function) of the surface or the phase function of the water body.

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

[0063] Step S31: Based on the intensity distribution I(ω) of the light source, generate the probability density function of the photon direction;

[0064] Step S32: For each sampled ray, update the photon position x during photon propagation step by step with step size t. new The change in direction ω;

[0065] Step S33: When the photon intersects with the target, a secondary reflected ray is generated according to the BRDF function at the intersection point, and the propagation process is simulated recursively.

[0066] Step S34, calculate the BRDF function f of the target surface at the intersection point with respect to wavelength λ. r The angle ω from which the reflected photon is generated o The direction and energy of the photon after reflection are calculated based on the BRDF.

[0067] Step S35: Repeat the iterative process for each sampled light beam until the number of reflections reaches a preset threshold Nn or the emitted light beam energy is less than a preset threshold φ. n At the cutoff time, after changing the photon wavelength λ, a new tracking ray is generated.

[0068] Step S36: When the surfaces interact, the photonic information is stored in the KD tree structure;

[0069] Step S37: Integrate the sampled photon information and use the KNN algorithm combined with the Monte Carlo integration method to calculate the spatial distribution of irradiance;

[0070] Step S38: Based on the calculated spatial irradiance distribution and the fluorescence properties of the coral, construct a spatial distribution model of fluorescence irradiance.

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

[0072]

[0073] The initial radiative flux is:

[0074]

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

[0076] In detail, this invention comprehensively considers the scattering effect of water, and calculates the intersection point of the light ray with the coral target and the radiance distribution on the light ray in an iterative manner. For each sampled light ray, the position x of the photon during the photon propagation is updated step by step with a step size of t. new And to simulate the change in the propagation direction ω caused by the scattering properties of the water medium during the motion of photons, and calculate x.new The specific details are 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 the propagation direction ω is as follows:

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

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

[0082] Based on Beer-Lambert's law, the specific formula for simulating the attenuation of radiation energy during photon propagation due to absorption and scattering effects in 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 considering the absorption and scattering effects of the medium.

[0085] When a photon intersects with a target, based on the BRDF properties at the intersection point, BRDF sampling techniques are used to generate secondary reflected rays and recursively simulate the propagation process. The BRDF function f of the target surface at the intersection point with respect to wavelength λ is... r The angle ω from which the reflected photon is generated o The probability density function PDF is:

[0086]

[0087] At the same time, the new direction and energy of the reflected light are calculated based on BRDF, using the following formula:

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

[0089]

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

[0091] Then, steps S32 to S34 are repeated for each sampled light until the number of reflections reaches a preset threshold Nn, or the emitted photon radiation energy is less than a preset threshold Φ when reflection occurs. n Stop when the repetition stops. After stopping, change the photon wavelength λ, generate new tracking rays, and repeat steps S31 to S34 to simulate the propagation process of photons at different wavelengths.

[0092] During each surface interaction, photon information (position, incident direction, energy, wavelength) is stored in a KD tree structure (a tree-like 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 light irradiance. Based on steps S31 to S34, the sampled photon information is comprehensively analyzed, and density estimation methods such as KNN (K-Nearest Neighbor algorithm, for any n-dimensional input vector, each corresponding to a point in the feature space, the output is the category label or predicted value corresponding to the feature vector) are 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 wavelength λ that terminate 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] Where r is the preset search radius; k is the preset number of nearest neighbors; Φ i (λ) represents the energy of the i-th photon, and θ represents the energy of the i-th photon. i Let be the angle between the incident ray and the surface normal.

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

[0098] Assuming the fluorescence emission is isotropic and the intensity follows a Lambertian distribution, the specific formulas for the spatial distribution of its fluorescence emission radiance and emission angle are as follows:

[0099]

[0100] Where λ emIt is the independent variable of fluorescence emission wavelength; α(λ) ex () is the coral at wavelength λ ex Absorption coefficient at Φ f S represents the fluorescence quantum yield of coral materials, indicating the proportion of absorbed photons that produce fluorescence; em (λ em ,λ ex () is the fluorescence emission spectrum of coral, representing the fluorescence emitted by λ. ex After excitation at λ em The relative emission intensity at a given point; Λ represents the range of all possible excitation wavelengths. These material properties can be obtained through experimental measurements or by consulting relevant literature.

[0101] Through steps S31-S35, the light transmission process in the complex three-dimensional structure of the coral canopy can be accurately simulated, while simultaneously simulating the scattering effects of the seawater medium and the fluorescence effect of the coral. Understandably, this method combines the high efficiency of photon mapping with the unbiasedness of Monte Carlo integration, effectively handling 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, generating camera rays. Starting from the camera position o, reverse tracking rays are generated for each pixel j; for each sampling wavelength λ... k By tracking the light ray and using the VCM algorithm combined with photon propagation information, a connection is established between the camera position o and the light source x. o The propagation path of the incident light And the fluorescent photon path leaving the surface of the coral target And obtain the energy φ of the photon leaving the surface of the coral target. n .

[0103] Step S50: Calculate the light intensity entering the camera, simulate the energy of radiation energy reaching the camera after attenuation due to absorption and scattering effects of water during photon propagation, calculate the cumulative contribution of all paths and wavelengths for each pixel j, and then verify and optimize the model by using experimentally collected data and adjusting algorithm parameters through experiments to improve model accuracy.

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

[0105] The specific formula for generating a backtracking ray for each pixel j, starting from camera position o, is as follows:

[0106] ray(t) = o + t*ω

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

[0108] The specific formula for adaptive wavelength sampling in the visible spectrum for each ray is as follows:

[0109] λ k =sample(S camera (λ))

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

[0111] In detail, for each sampling wavelength λ k By tracking the ray, and using the VCM algorithm combined with the photon propagation information stored in the KD tree structure in step S30, an incident ray propagation path connecting the camera position o and the light source x0 is established. And the fluorescent photon path leaving the surface of the coral target The energy Φ of the photon leaving the surface of the coral target is obtained. n Among them, the propagation path of the incident light. With fluorescent photonic pathway The specific formula is:

[0112]

[0113] For each incident ray path, the ray subpath (x) from the coral target surface to the camera position o n Based on Beer-Lambert's law, the energy of the radiated light during photon propagation, after attenuation due to absorption and scattering effects in the water, reaches the camera:

[0114] φ o =Φ n *exp(-σ t *t)

[0115] Where, σ t It is the total attenuation coefficient of radiation intensity considering 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 as follows:

[0117]

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

[0119] It is understood that, in this embodiment, experimentally collected data can also be used to adjust algorithm parameters and improve model accuracy. Through the above steps, the spectral imaging of coral fluorescence can be accurately simulated. Considering the special characteristics of the underwater environment, this invention combines the efficiency of the VCM algorithm with the robustness of the bidirectional path tracing method, effectively handling complex optical phenomena such as water scattering, refraction, and the fluorescence effect 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] Combining all the above technical solutions, this invention provides a modeling method for underwater coral canopy radiative transfer and fluorescence effects. By considering the complex three-dimensional structure of the coral canopy and the characteristics of the underwater environment, it employs a meshed coral canopy model and a ray tracing algorithm based on physical properties, significantly improving the accuracy of radiative transfer simulation. This invention also introduces fluorescence effect simulation into the coral canopy radiative transfer model, extending the BRDF model to include fluorescence terms and separately simulating the propagation of fluorescent light to simulate special optical effects in the underwater environment. Furthermore, it uses a Monte Carlo integral algorithm to optimize the ray tracing strategy, significantly improving computational efficiency and accuracy. This method enables large-scale coral reef monitoring and is adaptable to different coral morphologies, substrate types, and water conditions, possessing broad applicability and can be extended to the study of optical characteristics of other complex underwater ecosystems.

[0121] The above description is merely a preferred embodiment of the present invention and does not limit the patent scope of the present invention. Any equivalent structural transformations made using the contents of the present invention's specification and drawings under the inventive concept of the present invention, or direct / indirect applications in other related technical fields, are included within the patent protection scope of the present invention.

Claims

1. A modeling method for radiative transport and fluorescence effects in underwater coral canopies, characterized in that, Includes the following steps: Establish a 3D model of the underwater scene, construct a 3D mesh model of the underwater coral target and the substrate, and perform mesh preprocessing on the scene; Environmental parameters were determined, and the optical properties of the coral and the substrate were determined using sensor measurement data. By forward simulating the light transmission process within the canopy, a spatial distribution model of irradiance in an underwater scene is constructed, resulting in a fluorescence emission radiance distribution model. The forward simulation of the light transmission process within the canopy is based on the intensity distribution of the light source. Based on this, a probability density function for the direction of photons is generated, and for each sampled ray, the position of the photon during its propagation is updated incrementally with a step size of t. ,direction The changes; when a photon intersects with a target, a secondary reflected ray is generated according to the BRDF function at the intersection point, and the propagation process is simulated recursively. By comprehensively sampling photon information, the spatial distribution of irradiance is calculated using the KNN algorithm combined with the Monte Carlo integration method. Finally, based on the calculated spatial distribution of irradiance and the fluorescence properties of corals, a spatial distribution model of fluorescence emission irradiance is constructed. Based on the fluorescence emission radiance distribution model, reverse spectral imaging was used to simulate the fluorescence spectrum of corals; Model validation and optimization involve using experimentally collected data to adjust algorithm parameters and improve model accuracy.

2. The modeling method for radiative transfer and fluorescence effects in underwater coral canopies as described in claim 1, characterized in that, The steps of establishing a 3D model of the underwater scene, constructing a 3D meshed model of the underwater coral target and the substrate, and performing meshed preprocessing on the scene include: Using motion-reconstruction technology, a three-dimensional mesh model of the coral target and the substrate is reconstructed from continuous underwater images; Adjust the seawater in the 3D mesh model to be a medium with projection and scattering properties; The underwater scene is preprocessed into a grid.

3. The modeling method for radiative transfer and fluorescence effects in underwater coral canopies as described in claim 2, characterized in that, The steps of determining environmental parameters and using sensor measurement data to determine the optical properties of corals and substrate include: Set up the light source and sensor, record the light source type, light source location, light source radiation intensity, and sensor parameters, and determine the directional distribution function of the light source radiation intensity; The optical properties of corals were determined using bidirectional reflectance function and fluorescence property extension term; The optical properties of the substrate are determined by searching a priori database; The transmittance, scattering, and fluorescence coefficients of the water body were obtained through on-site measurements.

4. The modeling method for radiative transfer and fluorescence effects in underwater coral canopies as described in claim 1, characterized in that, The steps of constructing an irradiance spatial distribution model for an underwater scene by simulating the light transmission process within the canopy and obtaining a fluorescence emission irradiance distribution model further include: When surfaces interact, photonic information is stored in a KD tree structure; For the target surface at the intersection point, the wavelength BRDF function The angle at which the reflected photon is generated The direction and energy of the photon after reflection are calculated based on the BRDF. Repeat the iterative process for each sampled light ray until the number of reflections reaches a preset threshold Nn or the photon radiation energy during reflection is less than a preset threshold. Time cutoff, change photon wavelength Then, a new tracking ray is generated.

5. The modeling method for radiative transfer and fluorescence effects in underwater coral canopies as described in claim 1, characterized in that, The step of simulating coral fluorescence spectra using reverse spectral imaging based on a fluorescence emission radiance distribution model further includes: Generate camera rays, starting from camera position o, and generate a reverse tracing ray for each pixel j; For each sampling wavelength By tracking the light ray and using the VCM algorithm combined with photon propagation information, a connection is established between the camera position o and the light source. The incident light propagation path and the fluorescent photon path leaving the coral target surface. And obtain the energy of photons leaving the surface of the coral target. .

6. The modeling method for radiative transfer and fluorescence effects in underwater coral canopies as described in claim 5, characterized in that, The step of simulating coral fluorescence spectra using reverse spectral imaging based on a fluorescence emission radiance distribution model further includes: The intensity of light entering the camera is calculated, simulating the energy of the radiated light reaching the camera after attenuation due to absorption and scattering effects of the water body during photon propagation, and the cumulative contribution of all paths and wavelengths is calculated for each pixel j.

Images