Modeling simulation-based water body spectral absorption attenuation sensor design method

Abstract

The invention discloses a water body spectrum absorption attenuation sensor design method based on modeling simulation, and relates to the technical field of ocean, the method comprises the following steps: initializing design parameters and constructing sensor models, the sensor models comprise an absorption flow pipe model, an attenuation flow pipe model, a detector model and a light source model; photons are emitted at the light source model, state parameters are initialized, Monte Carlo simulation is carried out on the transmission process of each photon in the two flow tube models, and a first photon detection result and a second photon detection result reaching the detector model are determined. And calculating an absorption coefficient test value and an attenuation coefficient test value, and calculating a comprehensive measurement error according to the absorption coefficient theoretical value and the attenuation coefficient theoretical value of the target water body. And adjusting design parameters until the comprehensive measurement error meets the design requirement, and designing to obtain the water body spectral absorption attenuation sensor. The stability and the accuracy of the water body spectral absorption attenuation sensor are effectively improved by modeling, simulating and optimizing design parameters.

Description

Technical Field

[0001] The present application relates to the field of marine technology, and in particular to a method for designing a water body spectral absorption attenuation sensor based on modeling and simulation. Background Art

[0002] Spectral absorption coefficient and attenuation coefficient are important intrinsic optical properties of water, which are usually measured using water spectral absorption attenuation sensors. Water spectral absorption attenuation sensors are widely used in fields such as oceanography, hydrology, and environmental science, and can provide key data for researchers to gain a deeper understanding of the optical properties of water.

[0003] The working principle of the spectral absorption attenuation sensor is to generate a parallel light beam through a light source. The parallel light beam passes through the absorption path and attenuation path containing the water body to be tested and then hits the detector. The spectral absorption coefficient and attenuation coefficient of the water body to be tested can be measured based on the detection results of the detector.

[0004] Based on the above working principle, spectral absorption attenuation sensors with different structures can be designed. The structural design of the spectral absorption attenuation sensor directly affects the transmission process of light in the water body to be measured, and then affects the measurement results of the spectral absorption coefficient and attenuation coefficient. At present, the structure of the spectral absorption attenuation sensor is generally designed based on the human experience of the designer. The unreasonable structural design is easy to introduce additional errors, making it difficult to ensure the accuracy and precision of the measurement results of the spectral absorption attenuation sensor, especially when applied in complex water environments, the stability and robustness are not ideal. Summary of the invention

[0005] In response to the above problems and technical requirements, this application proposes a water spectral absorption attenuation sensor design method based on modeling and simulation. The technical solution of this application is as follows:

[0006] A method for designing a water body spectral absorption attenuation sensor based on modeling and simulation includes the following steps:

[0007] Initialize the design parameters of the water spectral absorption attenuation sensor, which include structural parameters and light source parameters;

[0008] A sensor model is constructed according to the structural parameters of the water body spectral absorption attenuation sensor. The sensor model includes a flow tube model, a detector model and a light source model. The flow tube model includes an absorption flow tube model and an attenuation flow tube model arranged in parallel. The light source model is located at one axial end of the flow tube model, and the detector model is located at the other axial end of the flow tube model.

[0009] The photons are emitted at the light source model and the state parameters of the photons are initialized according to the light source parameters of the water body spectrum absorption attenuation sensor;

[0010] According to the state parameters of each photon initialization and the absorption attenuation characteristic parameters of the target water body, combined with the reflection effect of the inner wall of the absorption flow tube model on the photons and the absorption effect of the inner wall of the attenuation flow tube model on the photons, a Monte Carlo simulation is performed on the transmission process of each photon in the two flow tube models to determine the detection result of the first photon that passes through the absorption flow tube model to reach the detector model and the detection result of the second photon that passes through the attenuation flow tube model to reach the detector model;

[0011] Calculate the absorption coefficient test value according to the first photon detection result, and calculate the attenuation coefficient test value according to the second photon detection result; obtain a comprehensive measurement error according to a first error between the absorption coefficient test value and a theoretical value of the absorption coefficient of the target water body, and a second error between the attenuation coefficient test value and the theoretical value of the attenuation coefficient of the target water body;

[0012] The design parameters of the water body spectral absorption attenuation sensor are adjusted until the comprehensive measurement error meets the design requirements, and the water body spectral absorption attenuation sensor is designed.

[0013] Its further technical solution is that the light source parameters include the coverage area of ​​the point light source, the distribution density of the point light source, the spectral wavelength range and the beam divergence angle; the state parameters of the photons include the photon emission position, photon emission direction and photon energy of each photon; the state parameters of the photons initialized according to the light source parameters of the water body spectral absorption attenuation sensor include:

[0014] The position of each point light source is determined according to the coverage area and distribution density of the point light source, and the position of each point light source is taken as a photon emission position;

[0015] According to the beam divergence angle θ max Initializing the photon emission directions of the plurality of photons emitted at each photon emission position;

[0016] The photon energies of the respective plurality of photons emitted at each photon emission location are initialized according to the spectral wavelength range.

[0017] A further technical solution is to perform Monte Carlo simulation on the transmission process of each photon in the two flow tube models, including:

[0018] Simulate the movement process of photons after emission from the photon emission position where each photon is initialized along the initialized photon emission direction, determine that each photon is reflected after colliding with the inner wall of the absorption flow tube model and changes the photon emission direction to continue transmission based on the reflection effect of the inner wall of the absorption flow tube model on the photons, determine the transmission process of each photon in the absorption flow tube model in combination with the structure of the absorption flow tube model, update the photon energy of each photon in the absorption flow tube model according to the number of collisions and reflections of each photon with the inner wall of the absorption flow tube model during the transmission process, the number of scatterings of each photon during the transmission process, and the absorption attenuation characteristic parameters of the target water body, and obtain the first photon detection result including the photon energy of each photon that passes through the absorption flow tube model and reaches the detector model when it reaches the detector model;

[0019] The movement process of the photon after emission is simulated from the photon emission position initialized by each photon along the initialized photon emission direction. Based on the absorption effect of the inner wall of the attenuation flow tube model on photons, it is determined that each photon is absorbed and stops transmitting after colliding with the inner wall of the attenuation flow tube model. The transmission process of each photon in the attenuation flow tube model is determined in combination with the structure of the attenuation flow tube model. The photon energy of each photon in the attenuation flow tube model is updated according to the number of scattering times of each photon in the transmission process and the absorption attenuation characteristic parameters of the target water body. The second photon detection result obtained includes the photon energy of each photon that passes through the attenuation flow tube model and reaches the detector model when it reaches the detector model.

[0020] The further technical solution is to simulate the motion process of each photon after emission, including:

[0021] Initialize the real-time position of each photon to the photon emission position of the photon;

[0022] In each step cycle, the movement step s of each photon is determined according to the absorption attenuation characteristic parameters of the target water body, and each photon is determined to be scattered once in one step cycle. The real-time position, direction and photon energy of each photon in the two flow tube models are updated according to the movement step s in the current step cycle along the photon emission direction of each photon.

[0023] Photons that are still transmitting and whose photon energy reaches the photon energy threshold are screened and retained, and photons whose photon energy does not reach the photon energy threshold are screened again using the roulette mechanism and retained before entering the next step cycle.

[0024] A further technical solution is that the absorption attenuation characteristic parameters of the target water body include the absorption coefficient theoretical value a and the attenuation coefficient theoretical value c of the target water body, and updating the photon energy of each photon in the absorption flow tube model includes:

[0025] Determine the albedo of the target water body based on the absorption attenuation characteristic parameters of the target water body

[0026] Determine the updated photon energy W for each photon in the absorbing flow tube model t =W0·(ω0) m+k , m is the total number of collisions and reflections of photons with the inner wall of the absorbing flow tube model in each step cycle, , k is the total number of scatterings of photons in each step cycle, and W0 is the photon energy of photon initialization;

[0027] Determine the updated photon energy W for each photon that is not absorbed within the decaying flow tube model t =W0·(ω0) k .

[0028] A further technical solution is to determine the movement step length of each photon according to the absorption attenuation characteristic parameters of the target water body, including:

[0029] Determine the step length of each photon in any step period ζ is a random number in the range of 0 to 1.

[0030] A further technical solution is to use the beam divergence angle θ max Initializing the photon emission directions of the plurality of photons emitted at each photon emission position includes:

[0031] The cycle step angle Δθ is used as the interval between [0,θ max ] is divided into multiple zenith angles θ at equal intervals within the range of [0,360°], and the cyclic step angle Δφ is divided into multiple azimuth angles φ at equal intervals within the range of [0,360°];

[0032] The multiple zenith angles θ and the multiple azimuth angles φ are fully arranged and combined, and the photon emission direction (u) of a photon emitted from the photon emission position in the Cartesian coordinate system is obtained according to the zenith angle θ and the azimuth angle φ in each arrangement and combination. x ,u y ,u z ),in The Cartesian coordinate system takes the midpoint of the light source model as its origin, the direction from the origin along the centerline of the flow tube model to the detector model as the positive direction of the z-axis, the plane where the light source model is located as the xy plane, and the horizontal forward direction from the origin along the xy plane as the positive direction of the x-axis. The zenith angle θ is the angle between the photon emission direction and the positive direction of the z-axis of the Cartesian coordinate system, and the azimuth angle φ is the angle between the projection of the photon emission direction on the xy plane of the Cartesian coordinate system and the positive direction of the x-axis.

[0033] A further technical solution is that calculating the absorption coefficient test value and the attenuation coefficient test value includes:

[0034] The total energy of received photons W is obtained by adding the photon energy when arriving at the detector model included in the first photon detection result. detector , calculate the absorption coefficient test value W light It is the total energy of emitted photons obtained by adding the photon energies of the photons emitted at the light source model;

[0035] The total energy of received photons W' is obtained by adding the photon energy when arriving at the detector model included in the second photon detection result. detector , calculate the attenuation coefficient test value W′ light It is the total energy of emitted photons obtained by adding the photon energies of the photons emitted at the light source model.

[0036] A further technical solution is that initializing the photon energy of each of the multiple photons emitted at each photon emission position according to the spectral wavelength range includes:

[0037] The spectral wavelength of the point light source at each photon emission position is randomly initialized within the spectral wavelength range, and the photon energy of all photons emitted at the photon emission position is initialized according to the light source radiation intensity corresponding to the spectral wavelength of the point light source at each photon emission position.

[0038] Its further technical solution is that the Cartesian coordinate system takes the midpoint of the light source model as the origin, the direction from the origin along the central axis of the flow tube model to the detector model as the positive direction of the z-axis, the plane where the light source model is located as the xy plane, and the horizontal forward direction of the origin along the xy plane as the positive direction of the x-axis. Updating the real-time position and direction of each photon in each flow tube model includes:

[0039] Initialize the integer parameter i = 0 and set the photon at the starting position (x i ,y i ,z i ) is initialized to the photon emission position (x0, y0, z0) of the photon;

[0040] when And (x i +su x ) 2 +(y i +su y ) 2 <R 2 , it is determined that the photon does not collide with the inner wall of the flow tube model in the current i-th step cycle, and the step end position (x i+1 ,y i+1 ,z i+1 )and Set the step end position (xi+1 ,y i+1 ,z i+1 ) as the starting position of the step length of the i+1th step length period and update the photon emission direction (u) when the photon is at the end position of the step length of the i-th step length period xi ,u yi ,u zi )and in, is the scattering angle at which the randomly generated photons scatter, is the azimuth angle of the randomly generated photon scattering, and the photon emission direction (u xi ,u yi ,u zi ) as the photon emission direction at the starting position of the step length of the i+1th step length period, the i+1th step length period, until z i+1 ≥L, L is the tube length of the flow tube model;

[0041] when And (x i +su x ) 2 +(y i +su y ) 2 ≥R 2 , determine that the photon collides with the inner wall of the flow tube model in the current i-th step period, and determine the collision position (x t ,y t ,z t )and t is the distance traveled by the photon from the starting position to the collision position in the current i-th step period and

[0042] When it is determined that the photon collides with the inner wall of the flow tube model in the current i-th step period and the flow tube model is an attenuation flow tube model, it is determined that the real-time position of the photon remains at the collision position (x t ,y t ,z t ) remains unchanged and stops updating the real-time position and direction of the photon;

[0043] When it is determined that the photon collides with the inner wall of the flow tube model in the current i-th step cycle and the flow tube model is an absorbing flow tube model, the photon emission direction (u xt ,u yt ,u zt ),in And according to the updated photon emission direction (u xt ,uyt ,u zt ) continues to transmit in the current i-th step cycle, and determines the total number of collisions and reflections n of the photon with the inner wall of the absorption flow tube model in the current i-th step cycle according to the motion step s, and obtains the step end position (x i+1 ,y i+1 ,z i+1 )and (x n ,y n ,z n ) is the collision position of the photon at the nth collision with the flow tube model in the current i-th step period and (u xn ,u yn ,u zn ) is the direction of photon emission after the nth collision and reflection with the flow tube model in the current i-th step period, t n is the distance from the collision position of the photon with the flow tube model for the nth time in the current step cycle to the step end position of the i-th step cycle; the step end position of the i-th step cycle (x i+1 ,y i+1 ,z i+1 ) as the starting position of the step length of the i+1th step length period and update the photon emission direction (u) when the photon is at the end position of the step length of the i-th step length period xi ,u yi ,u zi )and The photon emission direction (u xi ,u yi ,u zi ) as the photon emission direction at the starting position of the step length of the i+1th step length period, the i+1th step length period, until z i+1 ≥L.

[0044] The beneficial technical effects of this application are:

[0045] This application proposes a method for designing a water spectral absorption attenuation sensor based on modeling and simulation. By constructing a sensor model and using Monte Carlo to simulate the transmission process of photons in a flow tube model, it can flexibly simulate the physical process of light beams transmitting in complex water bodies under different conditions, so as to realize the evaluation of the accuracy of water spectral absorption coefficient and attenuation coefficient measured by water spectral absorption attenuation sensors with different design parameters, providing researchers with an efficient and flexible design method, which helps to ensure the stability and accuracy of the designed water spectral absorption attenuation sensor.

[0046] The design method based on modeling and simulation in this application can optimize and adjust the design parameters of the sensor model in a simulation environment according to specific experimental conditions and measurement requirements of the target water body before the actual manufacturing and underwater experiment of the water spectral absorption attenuation sensor. This can ensure that more accurate and reliable measurement results are obtained in subsequent actual underwater experiments while reducing experimental costs and resource investment and improving design efficiency. BRIEF DESCRIPTION OF THE DRAWINGS

[0047] Figure 1 It is a flow chart of the design method of water spectral absorption attenuation sensor.

[0048] Figure 2 It is a schematic diagram of the absorption flow tube model.

[0049] Figure 3 It is a schematic diagram of the attenuation flow tube model.

[0050] Figure 4 It is a flow chart of the photon transmission process in the two flow tube models.

[0051] Figure 5 It is a comparison chart between the absorption coefficient test values ​​and the absorption coefficient theoretical values ​​at different distribution densities.

[0052] Figure 6 It is a comparison chart of the attenuation coefficient test values ​​and the attenuation coefficient theoretical values ​​for different distribution densities.

[0053] Explanation of the numbers in the figure: 101. detector model, 102. reflecting wall, 103. transmitting light beam, 104. light source model, 202. absorbing wall. DETAILED DESCRIPTION

[0054] The specific implementation of the present application is further described below in conjunction with the accompanying drawings.

[0055] This application proposes a water spectral absorption attenuation sensor design method based on modeling and simulation, please refer to Figure 1 The flowchart shown in the figure has the following specific steps:

[0056] Step 1, based on the designer's experience and the data provided in the official user manual of the existing commercial AC-S spectral absorption and attenuation sensor, the design parameters of the water body spectral absorption and attenuation sensor are initialized, and the design parameters include structural parameters and light source parameters.

[0057] The sensor model is constructed according to the structural parameters of the water body spectral absorption attenuation sensor. The structural parameters include the tube length and inner diameter of the absorption flow tube and the attenuation flow tube, the position and diameter of the detector, and the position and diameter of the light source. The sensor model includes a flow tube model, a detector model 101, and a light source model 104. The flow tube model includes an absorption flow tube model and an attenuation flow tube model arranged in parallel. The light source model 104 is located at one axial end of the flow tube model, and the detector model 101 is located at the other axial end of the flow tube model. The flow tube model is a cylinder. The interior of the flow tube model is an optical path. The tube length can be set to 10 cm or 25 cm, and the inner diameter of the flow tube model is set to 8 cm. The light source model 104 is located in the lower bottom surface area of ​​the cylinder, and the detector model 101 is located in the upper bottom surface area of ​​the cylinder. The light source model 104 is composed of a number of point light sources. The area covered by the point light sources is a circular area, and its diameter is equal to the inner diameter of the flow tube model. The detector model 101 is a circular plane, and its diameter is equal to the inner diameter of the flow tube model. The absorption flow tube model constructed in the Cartesian coordinate system is as follows: Figure 2 As shown, the inner wall of the absorption flow tube is a reflection wall 102, which can reflect photons. The attenuation flow tube model constructed in the Cartesian coordinate system is as follows: Figure 3 As shown, the inner wall of the attenuation flow tube is an absorption wall 202, which can absorb photons. The Cartesian coordinate system takes the midpoint of the light source model 104 as the origin, the direction from the origin along the center axis of the flow tube model to the detector model 101 as the positive direction of the z-axis, the plane where the light source model 104 is located as the xy plane, the horizontal forward direction from the origin along the xy plane as the positive direction of the x-axis, and the horizontal rightward direction from the origin along the xy plane as the positive direction of the y-axis.

[0058] According to the light source parameters of the water body spectral absorption attenuation sensor, the light source model 104 is configured with the emission light beam 103 of the light source. The light source parameters include the coverage area of ​​the point light source, the distribution density of the point light source, the spectral wavelength range and the beam divergence angle. According to the spectral wavelength range of the light beam transmitted in the target water body, the spectral wavelength range of the light source model 104 is set to 400nm-730nm. 3024 point light sources are set to be evenly distributed in the circular coverage area, and 64 point light sources are distributed on the diameter of the circular coverage area. The distribution density of the point light sources of the light source model 104 on the coverage area is adjusted by setting the distribution ratio ratio on the simulation software. When ratio=0.000125 is set, the circular coverage area formed by these 3024 point light sources is equal to the area of ​​the detector model 101, and the distribution spacing between two radially adjacent point light sources is 0.000133m. In practical applications, the light beam 103 emitted by the light source along the axis direction has a certain emission angle. The point light source of the light source model 104 constructed in this application is a laser. The laser beam emitted by the laser is in a very small beam divergence angle range [0, θ max ] is used to describe the light-emitting process of the light source.

[0059] Step 2, emit photons at the light source model 104 and initialize the state parameters of the photons according to the light source parameters of the water body spectral absorption attenuation sensor. The state parameters of the photons include the photon emission position, photon emission direction and photon energy of each photon. The angle between the photon emission direction of each photon and the positive direction of the z-axis of the Cartesian coordinate system is the zenith angle θ, and the angle between the projection of the photon emission direction on the xy plane of the Cartesian coordinate system and the positive direction of the x-axis is the azimuth angle φ. In [0,θ max ] is divided equally in the range of [0,360°] to determine the cyclic step angle Δθ of the zenith angle, and the cyclic step angle Δφ of the azimuth angle is divided equally in the range of [0,360°], and one photon is emitted in each step direction at the light source model 104, and a total of The state parameters of each photon are initialized according to the light source parameters, including:

[0060] (1) The position of each point light source is determined according to the coverage area and distribution density of the point light source, and the position of each point light source is taken as a photon emission position.

[0061] (2) According to the beam divergence angle θ max Initialize the photon emission directions of the plurality of photons emitted at each photon emission position.

[0062] In one embodiment, a cyclic step angle Δθ is used as the interval between [0, θ max ] range is divided into multiple zenith angles θ at equal intervals, and multiple azimuth angles φ are divided into multiple azimuth angles φ at equal intervals within the range of [0,360°]. The multiple zenith angles θ and the multiple azimuth angles φ are fully arranged and combined, and the photon emission direction (u) of a photon emitted from the photon emission position in the Cartesian coordinate system is obtained according to the zenith angle θ and the azimuth angle φ in each arrangement and combination. x ,u y ,u z ),in

[0063] (3) Initializing the photon energy of each of the multiple photons emitted at each photon emission position according to the spectral wavelength range.

[0064] In one embodiment, the spectral wavelength of the point light source at each photon emission position is randomly initialized within the spectral wavelength range, and the photon energy of all photons emitted at the photon emission position is initialized according to the light source radiation intensity corresponding to the spectral wavelength of the point light source at each photon emission position. The spectral wavelength of each point light source is set in the simulation software, and the radiation intensity of the point light source can be calculated according to the spectral wavelength, and then the photon energy of the photons emitted from the point light source can be determined. The photon energy W in the direction of the zenith angle θ θ=W'·cosθ, the photon energy of the photon emitted along the normal direction of the light source model 104 at the photon emission position is W'.

[0065] Step 3, based on the initialization state parameters of each photon and the absorption attenuation characteristic parameters of the target water body, combined with the reflection effect of the inner wall of the absorption flow tube model on the photon and the absorption effect of the inner wall of the attenuation flow tube model on the photon, the transmission process of each photon in the two flow tube models is simulated by Monte Carlo to determine the detection result of the first photon that passes through the absorption flow tube model to reach the detector model 101 and the detection result of the second photon that passes through the attenuation flow tube model to reach the detector model 101. The transmission process of the photon in the two flow tube models is as follows:

[0066] (i) The transmission process of photons in the absorption flow tube model is as follows: the movement process of photons after emission is simulated from the photon emission position initialized by each photon along the initialized photon emission direction; based on the reflection effect of the inner wall of the absorption flow tube model on photons, it is determined that each photon is reflected after colliding with the inner wall of the absorption flow tube model and changes the photon emission direction to continue transmission; the transmission process of each photon in the absorption flow tube model is determined in combination with the structure of the absorption flow tube model; the photon energy of each photon in the absorption flow tube model is updated according to the number of collisions and reflections between each photon and the inner wall of the absorption flow tube model during transmission, the number of scatterings of each photon during transmission, and the absorption attenuation characteristic parameters of the target water body; the first photon detection result obtained includes the photon energy of each photon that passes through the absorption flow tube model and reaches the detector model 101 when it reaches the detector model 101.

[0067] Simulate the movement of each photon after it is emitted from the emission position in the absorption flow tube model. Figure 4 (a), the specific steps are:

[0068] (1) Initialize the real-time position of each photon to the photon emission position of the photon. Initialize the integer parameter i = 0, and set the photon's step start position (x i ,y i ,z i ) is initialized to the photon emission position (x0, y0, z0) of the photon.

[0069] (2) In each step cycle, the movement step s of each photon is determined according to the absorption attenuation characteristic parameters of the target water body, and the real-time position, direction and photon energy of each photon in the absorption flow tube model are updated according to the movement step s in the current step cycle along the photon emission direction of each photon.

[0070] The absorption attenuation characteristic parameters of the target water body include the absorption coefficient theoretical value a and the attenuation coefficient theoretical value c of the target water body. In one embodiment, the motion step length of each photon in any step length cycle is determined. ζ is a random number in the range of 0 to 1.

[0071] when And (x i +su x ) 2 +(y i +su y ) 2 <R 2 When the photon is determined to not collide with the inner wall of the flow tube model in the current i-th step cycle, the step end position of the photon in the i-th step cycle is updated. Update the photon emission direction (u xi ,u yi ,u zi )and in, is the scattering angle at which the randomly generated photons scatter, is the azimuth angle at which randomly generated photons are scattered. Each photon is scattered once in one step period. The scattering angle and azimuth angle of randomly generated photons are used to simulate the scattering phenomenon of photons transmitted in water. It is randomly generated with equal probability in [0,360°] According to the principle of Monte Carlo method, a random number R' between 0 and 1 is generated using the formula Calculate the scattering angle in is the probability density function of the scattering angle, g is the asymmetry factor.

[0072] Set the step end position (x i+1 ,y i+1 ,z i+1 ) as the starting position of the step length of the i+1th step length period, and the photon emission direction (u xi ,u yi ,u zi ) as the photon emission direction at the starting position of the step length of the i+1th step length period, and enter the i+1th step length period until z i+1 ≥L, at this time the photon reaches the detector model 101, and L is the tube length of the flow tube model.

[0073] when And (x i +su x ) 2+(y i +su y ) 2 ≥R 2 , determine that the photon collides with the inner wall of the flow tube model in the current i-th step period, and determine the collision position (x t ,y t ,z t )and t is the distance traveled by the photon from the starting position to the collision position in the current i-th step period and According to the motion trajectory equation of the photon in the current i-th step period And the coordinates of the collision position of the photon and the flow tube model satisfy By analytical solution in

[0074] Update the photon emission direction (u xt ,u yt ,u zt ),in And according to the updated photon emission direction (u xt ,u yt ,u zt ) continues to transmit in the current i-th step cycle, and determines the total number of collisions and reflections n that occur between the photon and the inner wall of the absorption flow tube model in the current i-th step cycle according to the motion step s, and obtains the step end position (x i+1 ,y i+1 ,z i+1 )and (x n ,y n ,z n ) is the collision position of the photon with the flow tube model for the nth time in the current i-th step period, (u xn ,u yn ,u zn ) is the direction of photon emission after the nth collision and reflection with the flow tube model in the current i-th step period, t n is the distance from the collision position of the photon with the flow tube model for the nth time in the current step cycle to the step end position of the i-th step cycle; the step end position of the i-th step cycle (x i+1 ,y i+1 ,z i+1 ) as the starting position of the step length of the i+1th step length period and update the photon emission direction (u) when the photon is at the end position of the step length of the i-th step length period xi ,u yi,u zi )and The photon emission direction (u xi ,u yi ,u zi ) as the photon emission direction at the starting position of the step length of the i+1th step length period, and enter the i+1th step length period until z i+1 ≥L.

[0075] The present application combines the accuracy and computational efficiency of updating the photon energy of photons transmitted in the absorption flow tube model, and updates the photon energy of each photon in the absorption flow tube model according to the number of collisions and reflections of each photon with the inner wall of the absorption flow tube model during transmission, the number of scatterings of each photon during transmission, and the absorption attenuation characteristic parameters of the target water body. In one embodiment, the specific method for updating the photon energy of each photon in the absorption flow tube model is: determining the albedo of the target water body according to the absorption attenuation characteristic parameters of the target water body Determine the updated photon energy W for each photon in the absorbing flow tube model t =W0·(ω0) m+k , m is the total number of collisions and reflections of photons with the inner wall of the absorbing flow tube model in each step period, k is the total number of scatterings of photons in each step period, and W0 is the photon energy initialized by the photons.

[0076] (3) Screen and retain photons that are still transmitting and whose photon energy reaches the photon energy threshold, and use the roulette mechanism to perform secondary screening on photons whose photon energy does not reach the photon energy threshold and retain them before entering the next step cycle. The photon energy threshold can be customized according to the target water body in the actual application scenario. The roulette mechanism is used to simulate the random disappearance characteristics of photons during transmission. This application uses the Russian roulette mechanism to determine the survival probability of photons during transmission. The Russian roulette mechanism is a prior art and will not be described in detail in this application.

[0077] (ii) The transmission process of photons in the attenuation flow tube model is as follows: starting from the photon emission position where each photon is initialized, the movement process of the photon after emission is simulated along the initialized photon emission direction; based on the absorption effect of the inner wall of the attenuation flow tube model on photons, it is determined that each photon is absorbed and stops transmitting after colliding with the inner wall of the attenuation flow tube model; the transmission process of each photon in the attenuation flow tube model is determined in combination with the structure of the attenuation flow tube model; the photon energy of each photon in the attenuation flow tube model is updated according to the number of scattering times of each photon in the transmission process and the absorption attenuation characteristic parameters of the target water body; the second photon detection result obtained includes the photon energy of each photon that passes through the attenuation flow tube model and reaches the detector model 101 when it reaches the detector model 101.

[0078] Simulate the motion of each photon after it is emitted from the emission position in the attenuation flow tube model. Figure 4 (b), the specific steps are:

[0079] (1) Initialize the real-time position of each photon to the photon emission position of the photon. Initialize the integer parameter i = 0, and set the photon's step start position (x i ,y i ,z i ) is initialized to the photon emission position (x0, y0, z0) of the photon.

[0080] (2) In each step cycle, the movement step s of each photon is determined according to the absorption attenuation characteristic parameters of the target water body, and the real-time position, direction and photon energy of each photon in the absorption flow tube model are updated according to the movement step s in the current step cycle along the photon emission direction of each photon.

[0081] The same method as the calculation of the motion step length of photons in the absorption flow tube model is used to determine the motion step length of each photon in any step length period. ζ is a random number in the range of 0 to 1.

[0082] when And (x i +su x ) 2 +(y i +su y ) 2 <R 2 , it is determined that the photon does not collide with the inner wall of the flow tube model in the current i-th step cycle, and the step end position (x i+1 ,y i+1 ,z i+1 )and Update the photon emission direction (u xi ,u yi ,u zi )and in, is the scattering angle at which the randomly generated photons scatter, is the azimuth angle at which the randomly generated photons are scattered. Each photon is scattered once in one step period. The randomly generated scattering angle and azimuth angle of the photon are used to simulate the scattering phenomenon of photons in water. It is randomly generated with equal probability in [0,360°] According to the principle of Monte Carlo method, a random number R' between 0 and 1 is generated using the formula Calculate the scattering angle in is the probability density function of the scattering angle, g is the asymmetry factor.

[0083] Set the step end position (x i+1 ,y i+1 ,z i+1 ) as the starting position of the step length of the i+1th step length period, and the photon emission direction (u xi ,u yi ,u zi ) as the photon emission direction at the starting position of the step length of the i+1th step length period, and enter the i+1th step length period until z i+1 ≥L, at this time the photon reaches the detector model 101, and L is the tube length of the flow tube model.

[0084] when And (x i +su x ) 2 +(y i +su y ) 2 ≥R 2 When , it is determined that the photon collides with the inner wall of the flow tube model in the current i-th step period, and the collision position (x t ,y t ,z t )and t is the distance traveled by the photon from the starting position to the collision position in the current i-th step period and According to the motion trajectory equation of the photon in the current i-th step period And the coordinates of the collision position of the photon and the flow tube model satisfy By analytical solution in

[0085] Determine the real-time position of the photon to remain at the collision position (x t ,y t ,z t ) remains unchanged and stops updating the real-time position and direction of the photon.

[0086] For photons that reach the detector model 101 without colliding with the inner wall of the attenuation flow tube model, the photon energy of each photon in the attenuation flow tube model is updated according to the number of scattering times of each photon during transmission and the absorption attenuation characteristic parameters of the target water body. In one embodiment, the updated photon energy W of each photon that is not absorbed in the attenuation flow tube model is determined. t =W0·(ω0) k, k is the total number of scatterings of photons in each step period.

[0087] (3) Screen and retain photons that are still transmitting and whose photon energy reaches the photon energy threshold, and use the roulette mechanism to perform secondary screening on photons whose photon energy does not reach the photon energy threshold and retain them before entering the next step cycle. The photon energy threshold can be customized according to the target water body in the actual application scenario. The roulette mechanism is used to simulate the random disappearance characteristics of photons during transmission. This application uses the Russian roulette mechanism to determine the survival probability of photons during transmission. The Russian roulette mechanism is a prior art and will not be described in detail in this application.

[0088] Step 4: Calculate the absorption coefficient test value according to the first photon detection result, and calculate the attenuation coefficient test value according to the second photon detection result. Obtain a comprehensive measurement error based on a first error between the absorption coefficient test value and a theoretical value of the absorption coefficient of the target water body, and a second error between the attenuation coefficient test value and a theoretical value of the attenuation coefficient of the target water body.

[0089] In one embodiment, the photon energy included in the first photon detection result when arriving at the detector model 101 is added to obtain the total received photon energy W detector , calculate the absorption coefficient test value W light The total energy of the emitted photons is obtained by adding the photon energies of the photons emitted at the light source model 104. The total energy of the received photons is obtained by adding the photon energies of the photons arriving at the detector model 101 included in the second photon detection result. d ' etector , calculate the attenuation coefficient test value W l ' ight It is the total energy of emitted photons obtained by adding the photon energies of the photons emitted at the light source model 104.

[0090] Step 5, adjust the design parameters of the water body spectral absorption attenuation sensor until the comprehensive measurement error meets the design requirements, and the water body spectral absorption attenuation sensor is designed.

[0091] The light source model 104 with two different point light source distribution densities is simulated and the comprehensive measurement errors of the two light source parameters are compared. When ratio = 0.000125 is set, the comparison results of the absorption coefficient test value obtained and the absorption coefficient theoretical value of the target water body are as follows: Figure 5 When ratio = 0.0000125, the comparison between the absorption coefficient test value and the absorption coefficient theoretical value of the target water body is shown in (a). Figure 5 (b) as shown.

[0092] When ratio is set to 0.000125, the comparison results between the attenuation coefficient test value and the theoretical attenuation coefficient of the target water body are as follows: Figure 6 When ratio = 0.0000125, the comparison between the attenuation coefficient test value and the theoretical attenuation coefficient of the target water body is shown in (a). Figure 6 (b) as shown.

[0093] According to the comparison results in the figure, it can be seen that when ratio = 0.000125, the first error between the absorption coefficient test value and the theoretical value of the absorption coefficient of the target water body is smaller, and the second error between the attenuation coefficient test value and the theoretical value of the attenuation coefficient of the target water body when ratio = 0.000125 and ratio = 0.0000125 is similar. It can be concluded that the comprehensive measurement error is smaller when ratio = 0.000125.

[0094] The above is only a preferred embodiment of the present application, and the present application is not limited to the above embodiments. It is understood that other improvements and changes directly derived or associated by those skilled in the art without departing from the spirit and concept of the present application should be considered to be included in the protection scope of the present application.

Claims

1. A method for designing a water spectral absorption attenuation sensor based on modeling and simulation, characterized in that: The water body spectral absorption attenuation sensor design method comprises: Initializing design parameters of a water body spectral absorption attenuation sensor, wherein the design parameters include structural parameters and light source parameters; A sensor model is constructed according to the structural parameters of the water body spectral absorption attenuation sensor, wherein the sensor model includes a flow tube model, a detector model and a light source model, wherein the flow tube model includes an absorption flow tube model and an attenuation flow tube model arranged in parallel, wherein the light source model is located at one axial end of the flow tube model, and the detector model is located at the other axial end of the flow tube model; Emitting photons at the light source model and initializing state parameters of the photons according to light source parameters of the water body spectral absorption attenuation sensor; According to the state parameters of each photon initialization and the absorption attenuation characteristic parameters of the target water body, combined with the reflection effect of the inner wall of the absorption flow tube model on the photons and the absorption effect of the inner wall of the attenuation flow tube model on the photons, a Monte Carlo simulation is performed on the transmission process of each photon in the two flow tube models to determine the detection result of the first photon that passes through the absorption flow tube model to reach the detector model and the detection result of the second photon that passes through the attenuation flow tube model to reach the detector model; Calculate the absorption coefficient test value according to the first photon detection result, and calculate the attenuation coefficient test value according to the second photon detection result; obtain a comprehensive measurement error according to a first error between the absorption coefficient test value and a theoretical value of the absorption coefficient of the target water body, and a second error between the attenuation coefficient test value and the theoretical value of the attenuation coefficient of the target water body; The design parameters of the water body spectral absorption attenuation sensor are adjusted until the comprehensive measurement error meets the design requirements, and the water body spectral absorption attenuation sensor is designed.

2. The method for designing a water body spectral absorption attenuation sensor according to claim 1, characterized in that: The light source parameters include the coverage area of ​​the point light source, the distribution density of the point light source, the spectral wavelength range and the beam divergence angle; the state parameters of the photons include the photon emission position, photon emission direction and photon energy of each photon; The state parameters of the photons initialized according to the light source parameters of the water spectral absorption attenuation sensor include: The position of each point light source is determined according to the coverage area and distribution density of the point light source, and the position of each point light source is taken as a photon emission position; According to the beam divergence angle θ max Initializing the photon emission directions of the plurality of photons emitted at each photon emission position; The photon energies of each of the plurality of photons emitted at each photon emission location are initialized according to the spectral wavelength range.

3. The method for designing a water body spectral absorption attenuation sensor according to claim 2, characterized in that: The Monte Carlo simulation of the transmission process of each photon in the two flow tube models includes: Simulate the movement process of the photon after emission from the photon emission position where each photon is initialized along the initialized photon emission direction, determine that each photon is reflected after colliding with the inner wall of the absorption flow tube model and changes the photon emission direction to continue transmission based on the reflection effect of the inner wall of the absorption flow tube model on the photon, determine the transmission process of each photon in the absorption flow tube model in combination with the structure of the absorption flow tube model, update the photon energy of each photon in the absorption flow tube model according to the number of collisions and reflections of each photon with the inner wall of the absorption flow tube model during transmission, the number of scatterings of each photon during transmission and the absorption attenuation characteristic parameters of the target water body, and obtain the first photon detection result including the photon energy of each photon that passes through the absorption flow tube model and reaches the detector model when it reaches the detector model; The movement process of the photon after emission is simulated from the photon emission position where each photon is initialized along the initialized photon emission direction. Based on the absorption effect of the inner wall of the attenuation flow tube model on photons, it is determined that each photon is absorbed and stops transmitting after colliding with the inner wall of the attenuation flow tube model. The transmission process of each photon in the attenuation flow tube model is determined in combination with the structure of the attenuation flow tube model. The photon energy of each photon in the attenuation flow tube model is updated according to the number of scattering times of each photon in the transmission process and the absorption attenuation characteristic parameters of the target water body. The second photon detection result obtained includes the photon energy of each photon that passes through the attenuation flow tube model and reaches the detector model when it reaches the detector model.

4. The method for designing a water body spectral absorption attenuation sensor according to claim 3, characterized in that: Simulate the motion of each photon after emission, including: Initializing the real-time position of each photon to the photon emission position of the photon; In each step cycle, the movement step s of each photon is determined according to the absorption attenuation characteristic parameters of the target water body, and each photon is determined to be scattered once in one step cycle. The real-time position, direction and photon energy of each photon in the two flow tube models are updated according to the movement step s in the current step cycle along the photon emission direction of each photon. Photons that are still transmitting and whose photon energy reaches the photon energy threshold are screened and retained, and photons whose photon energy does not reach the photon energy threshold are screened again using the roulette mechanism and retained before entering the next step cycle.

5. The method for designing a water body spectral absorption attenuation sensor according to claim 4, characterized in that: The absorption attenuation characteristic parameters of the target water body include the absorption coefficient theoretical value a and the attenuation coefficient theoretical value c of the target water body. The photon energy of each photon in the absorption flow tube model is updated including: Determine the albedo of the target water body based on the absorption attenuation characteristic parameters of the target water body Determine the updated photon energy W for each photon in the absorbing flow tube model t =W0·(ω0) m+k , m is the total number of collisions and reflections of the photons with the inner wall of the absorption flow tube model in each step period, k is the total number of scatterings of the photons in each step period, and W0 is the photon energy of the photon initialization; Determine the updated photon energy W for each photon that is not absorbed within the decaying flow tube model t =W0·(ω0) k .

6. The method for designing a water body spectral absorption attenuation sensor according to claim 5, characterized in that: Determining the motion step length of each photon based on the absorption attenuation characteristic parameters of the target water body includes: Determine the step length of each photon in any step period ζ is a random number in the range of 0 to 1.

7. The method for designing a water body spectral absorption attenuation sensor according to claim 2, characterized in that: According to the beam divergence angle θ max Initializing the photon emission directions of the plurality of photons emitted at each photon emission position includes: The cycle step angle Δθ is used as the interval between [0,θ max ] is divided into multiple zenith angles θ at equal intervals within the range of ], and multiple azimuth angles φ are divided into multiple azimuth angles φ at equal intervals within the range of [0,360°] at intervals of a cyclic step angle Δφ; The multiple zenith angles θ and the multiple azimuth angles φ are fully arranged and combined, and the photon emission direction (u) of a photon emitted from the photon emission position in the Cartesian coordinate system is obtained according to the zenith angle θ and the azimuth angle φ in each arrangement and combination. x ,u y ,u z ),in The Cartesian coordinate system takes the midpoint of the light source model as its origin, the direction from the origin along the centerline of the flow tube model to the detector model as the positive direction of the z-axis, the plane where the light source model is located as the xy plane, and the horizontal forward direction from the origin along the xy plane as the positive direction of the x-axis. The zenith angle θ is the angle between the photon emission direction and the positive direction of the z-axis of the Cartesian coordinate system, and the azimuth angle φ is the angle between the projection of the photon emission direction on the xy plane of the Cartesian coordinate system and the positive direction of the x-axis.

8. The method for designing a water body spectral absorption attenuation sensor according to claim 3, characterized in that: Calculation of absorption coefficient test values ​​and attenuation coefficient test values ​​includes: The first photon detection result includes the photon energy when it reaches the detector model, and the total received photon energy W is obtained by adding detector , calculate the absorption coefficient test value W light It is the total energy of emitted photons obtained by adding the photon energies of the photons emitted at the light source model; The second photon detection result includes the photon energy when it reaches the detector model, and the total received photon energy W' is obtained by adding detector , calculate the attenuation coefficient test value W' light It is the total energy of emitted photons obtained by adding the photon energies of the photons emitted at the light source model.

9. The method for designing a water body spectral absorption attenuation sensor according to claim 2, characterized in that: Initializing the photon energy of each of the plurality of photons emitted at each photon emission position according to the spectral wavelength range comprises: The spectral wavelength of the point light source at each photon emission position is randomly initialized within the spectral wavelength range, and the photon energy of all photons emitted at the photon emission position is initialized according to the light source radiation intensity corresponding to the spectral wavelength of the point light source at each photon emission position.

10. The method for designing a water body spectral absorption attenuation sensor according to claim 4, characterized in that: The Cartesian coordinate system takes the midpoint of the light source model as the origin, the direction from the origin along the center axis of the flow tube model to the detector model as the positive direction of the z-axis, the plane where the light source model is located as the xy plane, and the horizontal forward direction of the origin along the xy plane as the positive direction of the x-axis. The real-time position and direction of each photon in each flow tube model are updated as follows: Initialize the integer parameter i=0, and set the photon at the starting position (x i ,y i ,z i ) is initialized to the photon emission position (x0, y0, z0) of the photon; when And (x i +su x ) 2 +(y i +su y ) 2 <R 2 , it is determined that the photon does not collide with the inner wall of the flow tube model in the current i-th step cycle, and the step end position (x i+1 ,y i+1 ,z i+1 )and Set the step end position (x i+1 ,y i+1 ,z i+1 ) as the starting position of the step length of the i+1th step length period and update the photon emission direction (u) of the photon at the end position of the step length of the i-th step length period xi ,u yi ,u zi )and in, is the scattering angle at which the randomly generated photons scatter, is the azimuth angle of the randomly generated photon scattering, and the photon emission direction (u xi ,u yi ,u zi ) as the photon emission direction at the starting position of the step length of the i+1th step length period, and enter the i+1th step length period until z i+1 ≥L, L is the tube length of the flow tube model; when And (x i +su x ) 2 +(y i +su y ) 2 ≥R 2 , determine that the photon collides with the inner wall of the flow tube model in the current i-th step period, and determine the collision position (x t ,y t ,z t )and t is the distance traveled by the photon from the starting position to the collision position in the current i-th step period and When it is determined that the photon collides with the inner wall of the flow tube model in the current i-th step period and the flow tube model is a decaying flow tube model, it is determined that the real-time position of the photon remains at the collision position (x t ,y t ,z t ) remains unchanged and stops updating the real-time position and direction of the photon; When it is determined that the photon collides with the inner wall of the flow tube model in the current i-th step period and the flow tube model is an absorbing flow tube model, the photon emission direction (u xt ,u yt ,u zt ),in And according to the updated photon emission direction (u xt ,u yt ,u zt ) continues to transmit in the current i-th step cycle, and determines the total number of collisions and reflections n of the photon with the inner wall of the absorption flow tube model in the current i-th step cycle according to the movement step s, and obtains the step end position (x i+1 ,y i+1 ,z i+1 )and (x n ,y n ,z n ) is the collision position of the photon at the nth collision with the flow tube model in the current i-th step period and (u xn ,u yn ,u zn ) is the photon emission direction after the photon collides and reflects with the flow tube model for the nth time in the current i-th step period, t n is the movement distance from the collision position of the photon with the flow tube model for the nth time in the current i-th step cycle to the step end position of the i-th step cycle; the step end position of the i-th step cycle (x i+1 ,y i+1 ,z i+1 ) as the starting position of the step length of the i+1th step length period and update the photon emission direction (u) of the photon at the end position of the step length of the i-th step length period xi ,u yi ,u zi )and The photon emission direction (u xi ,u yi ,u zi ) as the photon emission direction at the starting position of the step length of the i+1th step length period, and enter the i+1th step length period until z i+1 ≥L.

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