Visible light imaging device and monitoring method suitable for underwater monitoring of shallow coral reefs

Abstract

This invention belongs to the field of coral reef ecosystem monitoring technology, and discloses a visible light imaging device and monitoring method suitable for underwater monitoring of shallow-sea coral reefs. The device includes: a central control platform, a spectroscopic camera, a solar irradiance meter, a depth sounding sonar, and a water sampling device. The focal planes of the spectroscopic camera, the solar irradiance meter, and the depth sounding sonar are located on a plane parallel to the sea level. The spectroscopic camera's shooting direction is perpendicular to the sea level, and the solar irradiance meter's measurement direction is opposite to the spectroscopic camera's shooting direction. This invention effectively solves the effects of solar flares and wave lensing by using an underwater imaging device. By simultaneously acquiring the spectra of the seabed coral reef target and the solar irradiance spectrum, remote sensing reflectance data of coral reefs at different depths can be calculated, avoiding differences in imaging brightness caused by the weakening of sunlight at different water depths.

Description

Technical Field

[0001] This invention belongs to the field of coral reef ecosystem monitoring technology, and particularly relates to a visible light imaging device and monitoring method suitable for underwater monitoring of shallow sea coral reefs. Background Technology

[0002] Currently, the purpose of coral reef ecosystem monitoring is to discover and identify coral reefs, classify coral reef species, and assess the health status of coral reefs. Reflectance spectral identification and diagnostic methods based on optical remote sensing are one of the main approaches to coral reef detection, classification, and assessment. The challenges and characteristics of remote sensing monitoring of coral reefs are as follows: First, imaging devices placed on the water surface, such as satellites, drones, and even survey vessels, are often affected by air-sea interface refraction and water surface reflection flares when observing coral reefs. They are also affected by both water and atmospheric radiation transmission, leading to image distortion, contamination, and spectral distortion in the optical imaging results. Second, most coral reefs grow in areas with a deep euphotic zone, primarily in the upper 20m of the euphotic zone. While this area has relatively good light, the light energy decreases exponentially with depth, causing different reflectivities for the same type of target at different depths in the same image during optical measurements above the water surface. Third, areas suitable for and densely growing coral reefs are often also rich in suspended particulate matter, chlorophyll, and nutrients, and do not meet completely clean water conditions, which can negatively impact remote sensing monitoring of coral reefs. Therefore, an underwater optical imaging device for coral reefs needs to be designed to address various distortions and aberrations in surface-level imaging during coral reef remote sensing monitoring, overcome reflectivity errors caused by varying water depths, and resolve image quality degradation due to light energy attenuation caused by poor water quality. To meet the monitoring needs of coral reef ecosystems, further development of methods for coral reef type identification and health assessment is required based on the designed underwater optical imaging device and the images it captures.

[0003] For remote sensing monitoring of coral reef ecosystems, underwater imaging devices have the potential to overcome the aforementioned technical problems in underwater target imaging. However, current underwater optical imaging devices cannot effectively solve these problems for several reasons: firstly, they cannot effectively acquire reflectance spectral imaging data, which is crucial for coral reef detection, classification, and assessment; secondly, they cannot eliminate the absorption and scattering effects caused by water radiation transmission between the lens and the target, especially under low-light conditions due to water depth, where it is difficult to improve the signal-to-noise ratio of the imaging data. Therefore, there is an urgent need for a new visible light imaging device and monitoring method suitable for underwater monitoring of shallow-sea coral reefs.

[0004] Based on the above analysis, the problems and shortcomings of the existing technology are as follows:

[0005] (1) Existing imaging devices placed on the water surface of satellites, drones or even survey ships are often affected by the lens effect caused by the refraction of the sea-air interface and the flare caused by the reflection of the water surface when observing coral reefs due to the presence of waves. They are also affected by the dual effects of water radiation transmission and atmospheric radiation transmission, resulting in image distortion, image contamination and spectral distortion in the optical imaging results.

[0006] (2) Most coral reefs grow in areas with a large euphotic layer and are located in the upper part of the euphotic layer, about 20m below the surface. The light in these areas is good, but as the depth increases, the light energy decreases exponentially. This causes different reflectances for the same type of target in different water depth areas in the same image when optical remote sensing monitoring of coral reefs is carried out above the water surface.

[0007] (3) Areas where coral reefs are suitable for growth and dense growth are often also areas rich in suspended particulate matter, chlorophyll and nutrients. The water quality conditions that are not completely clean will have a certain impact on remote sensing monitoring of coral reefs, resulting in a decrease in imaging quality.

[0008] (4) Current underwater optical imaging devices cannot effectively acquire reflectance spectral imaging data that is crucial for coral reef detection, classification and assessment. They cannot remove the absorption and scattering effects caused by water radiation transmission between the lens and the target. In particular, under low light conditions due to water depth, it is difficult to improve the signal-to-noise ratio of the imaging data.

[0009] The difficulty in solving the above problems and defects is as follows:

[0010] (1) The underwater imaging method is difficult to solve the effects of the lensing effect caused by waves and the influence of solar glare. The randomness and uncertainty of the above-mentioned interference information means that the current correction method cannot guarantee the complete recovery and preservation of the characteristic information of the coral reef.

[0011] (2) The attenuation effect of electromagnetic waves in seawater radiation transmission is significant and strongly correlated with water quality conditions. The imaging method above the water surface cannot be completed in terms of water depth measurement and water quality measurement. Therefore, it cannot correct the imaging spectrum of coral reefs, resulting in large differences in imaging results of the same type of coral reef substrate at different depths, thus distorting the obtained imaging results.

[0012] The significance of solving the above problems and defects is as follows:

[0013] This technology overcomes a series of problems and shortcomings in traditional surface-based coral reef monitoring, solving the distortion and contamination of visible light electromagnetic waves containing coral reef information caused by refraction and reflection at the air-sea interface. It achieves high-precision real-time correction for information attenuation caused by variations in water depth and quality. This results in high-fidelity imaging of the subsurface coral reef substrate type and ecosystem, providing unprecedented high-fidelity, distortion-free optical remote sensing data for monitoring coral reefs and living reef-building corals, as well as for assessing the health of coral reef ecosystems. This is of great significance for the protection of my country's coral reef ecosystems and the maintenance of the security of my country's coral islands and reefs. Summary of the Invention

[0014] To address the problems existing in the prior art, this invention provides a visible light imaging device and monitoring method suitable for underwater monitoring of coral reefs in shallow waters.

[0015] The present invention is implemented as follows: a visible light imaging device suitable for underwater monitoring of shallow sea coral reefs, the visible light imaging device suitable for underwater monitoring of shallow sea coral reefs includes: a central control platform, a spectral camera, a solar irradiance measuring instrument, a depth sounding sonar, and a water sample collection device.

[0016] The focal plane of the spectroscopic camera, the focal plane of the solar irradiance measuring instrument, and the depth sounding sonar are located on a plane parallel to the sea level; the shooting direction of the spectroscopic camera is perpendicular to the sea level, and the measurement direction of the solar irradiance measuring instrument is opposite to the shooting direction of the spectroscopic camera.

[0017] Furthermore, the central control platform is used to provide integrated space, power supply, control, and data storage interaction for the spectroscopic camera, solar down-going irradiance meter, depth sounding sonar, and water sampling device; the central control platform needs to be sealed and waterproof; the integrated DC power supply provides stable power to the spectroscopic camera, solar down-going irradiance meter, depth sounding sonar, and water sampling device; the integrated control unit controls the switching and coordination of all internal devices, and provides storage and retrieval services for the data acquired by the integrated devices.

[0018] Furthermore, the spectroscopic camera internally includes a camera lens assembly, a CCD or CMOS optical recording array, and a storage device; the field of view Φ of the camera should be no less than 40° in air; the spectroscopic camera should include characteristic bands with center wavelengths of 395nm, 430nm, 490nm, 517nm, 575nm, 600nm, and 650nm, all of which are preferred bands for coral reef remote sensing observation, and should include at least three coral reef characteristic bands including 575nm, 600nm, and 650nm; during operation, the lens of the spectroscopic camera is vertically downward to form the field of view; the shooting mode of the spectroscopic camera during operation is frame-type imaging.

[0019] Furthermore, the solar down-going irradiance measuring instrument has the same band setting as the spectroscopic camera, and the light receiving lens is vertically upward; when the solar down-going irradiance measuring instrument is working, the distance between its lens and the sea surface is ≥30cm; the function of the solar down-going irradiance measuring instrument is to measure the remote sensing incident energy with the sun as the light source, and to provide an incident energy metric for the calculation of the remote sensing reflectance of the spectroscopic camera measurement data; when the solar down-going irradiance measuring instrument is working, it should achieve synchronous data acquisition with the spectroscopic camera through the control unit in the overall control platform.

[0020] Furthermore, the depth sounding sonar is connected to the central control platform via a cable, and the direction of acoustic distance measurement should be consistent with the direction of the spectral camera; the function of the depth sounding sonar is to measure the distance between the scene target and the spectral camera at the time the spectral camera is working, and to perform water body radiation transmission correction on the spectral energy received by the spectral camera.

[0021] Furthermore, when the spectral camera is in a stable position, before or shortly after data recording begins, the water sampling device opens its valve to fill the sampling device with water, and then closes the sealing valve to complete the water sampling. The function of the water sampling device is to collect water samples near the scene captured by the spectral camera during operation, for analyzing the water quality parameters of the water at that location and time, and using the parameters to perform water radiative transmission correction on the spectral energy received by the spectral camera.

[0022] Furthermore, the spectral camera, the solar down-facing irradiance meter, and the depth sounding sonar must simultaneously measure and record data during operation.

[0023] Another object of the present invention is to provide a monitoring method based on the visible light imaging device for underwater monitoring of shallow coral reefs, which utilizes the aforementioned visible light imaging device suitable for underwater monitoring of shallow coral reefs. The monitoring method based on the visible light imaging device for underwater monitoring of shallow coral reefs includes the following steps:

[0024] Step 1: Completely submerge the visible light imaging device suitable for underwater monitoring of shallow coral reefs; wherein, h2 is not less than 30cm, to avoid the solar irradiance measuring lens being exposed above the water surface due to waves and other sea surface fluctuations.

[0025] Step two: When photographing coral reefs underwater, the distance to the coral reef is measured in real time by a depth sounding sonar; wherein, the distance h between the device and the seabed is greater than h1;

[0026] Step 3: After the visible light imaging device reaches a certain position in the sea area where coral reefs are distributed, select an appropriate working depth based on the measurement data obtained from the depth sounding sonar.

[0027] Step four: The control platform should stop moving and remain relatively stationary relative to the seabed coral reef target, and the water sampling device should begin collecting water samples until completion;

[0028] Step 5: Once the main control platform reaches and maintains a stable state, the spectral camera and the solar down-side irradiance meter are turned on simultaneously to record measurement data and back it up on the main control platform.

[0029] Furthermore, the monitoring method of the visible light imaging device based on underwater monitoring of shallow coral reefs also includes:

[0030] The light intensity at wavelength λ recorded by the photosensitive element of the solar down-facing irradiance meter is E. λo The light intensity recorded by the spectral camera's image sensor is E. λ1 :

[0031]

[0032] In equation (1), α λ It is the attenuation coefficient of light with wavelength λ per unit optical path in seawater. This attenuation coefficient is obtained from water samples collected by a water sampling device and through water quality analysis, etc.

[0033] Furthermore, the monitoring method of the visible light imaging device based on underwater monitoring of shallow coral reefs also includes:

[0034] Assume that the seawater quality conditions remain constant within a finite measurement space; R λ Let R be the reflectance of a seabed target such as a coral reef to light with wavelength λ. Then, remove the reflectance R from equation (1). λ for:

[0035]

[0036] When considering the spatial position of each pixel within the field of view of the spectral camera, equation (1) is changed to:

[0037]

[0038] In equation (3), (i, j) are the pixel coordinates within the image with the center pixel as the origin, and the number of column pixels of the spectral camera is N, then:

[0039] x=(h 2 +((i*L / 2N) 2 +(j*L / 2N) 2 ) 1 / 2 ) 1 / 2 (4)

[0040] Equation (2) is then changed to a formula for calculating reflectance involving the spatial location of each pixel:

[0041]

[0042] Combining all the above technical solutions, the advantages and positive effects of this invention are as follows: The visible light imaging device and monitoring method provided by this invention, suitable for underwater monitoring of shallow coral reefs, addresses the remote sensing monitoring and assessment needs of shallow coral reef ecosystems in tropical seas. It utilizes the light flux in the visible spectrum provided by solar downdraft radiation, and simultaneously, based on measured water quality parameters, removes the attenuation of electromagnetic wave paths in different bands caused by varying water quality conditions, ultimately obtaining consistent reflectance spectral imaging data for the same type of target under different seawater depths. Based on the aforementioned underwater optical reflectance spectral imaging data of coral reefs, methods for coral reef detection, classification, and health assessment are developed.

[0043] This invention uses an underwater spectral camera to image, effectively solving the problems of solar reflection flares and wave lensing that occur when imaging above the water surface. By using the spectrum of the underwater coral reef target and the solar downslope spectrum acquired simultaneously, remote sensing reflectance data of coral reefs at different depths can be calculated, avoiding differences in imaging brightness caused by the weakening of sunlight at different water depths.

[0044] This invention, through real-time measurement of the distance between the spectral camera and the seabed coral reef target, and water sample analysis data obtained through the water sample collection device, can effectively correct for the influence of radiation transmission of reflected light from the seabed target on the optical path by the water body, thereby improving the accuracy of remote sensing reflectance data and enhancing imaging quality. Furthermore, this invention only requires adjusting the measurement height (i.e., the distance between the spectral camera and the coral reef target) according to the different water depth conditions in the coral reef distribution area; all data acquisition processes can be completed automatically, making it convenient, safe, and reliable. Attached Figure Description

[0045] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the embodiments of the present invention 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 these drawings without creative effort.

[0046] Figure 1 This is a structural diagram of a visible light imaging device suitable for underwater monitoring of shallow coral reefs provided in an embodiment of the present invention;

[0047] In the diagram: 1. Spectroscopic camera; 2. Solar downhill irradiance meter; 3. Depth sounding sonar; 4. Water sampling device; 5. Central control platform; 6. Photosensitive element of solar downhill irradiance meter; 7. Photosensitive element of spectroscopic camera.

[0048] Figure 2This is a flowchart of a monitoring method for a visible light imaging device for underwater monitoring of shallow coral reefs provided in an embodiment of the present invention.

[0049] Figure 3 These are images showing the effect of water reflectance spectrum changes before and after correction in different coral reef distribution areas provided in this embodiment of the invention. (a) Foreshore terrace, with a coral reef coverage of about 15% and a water depth of about 7m; (b) Coral deposition area, with a coral reef coverage of about 35% and a water depth of about 13m. Detailed Implementation

[0050] To make the objectives, technical solutions, and advantages of this invention clearer, the invention will be further described in detail below with reference to embodiments. It should be understood that the specific embodiments described herein are merely illustrative and not intended to limit the invention.

[0051] To address the problems existing in the prior art, the present invention provides a visible light imaging device and monitoring method suitable for underwater monitoring of shallow sea coral reefs. The present invention will be described in detail below with reference to the accompanying drawings.

[0052] like Figure 1 As shown in the figure, the visible light imaging device for underwater monitoring of shallow coral reefs provided in this embodiment of the invention includes: a central control platform, a spectroscopic camera, a solar irradiance measuring instrument, a depth sounding sonar, and a water sample collection device.

[0053] The focal plane of the spectroscopic camera, the focal plane of the solar irradiance measuring instrument, and the depth sounding sonar are located on a plane parallel to the sea level; the shooting direction of the spectroscopic camera is perpendicular to the sea level, and the measurement direction of the solar irradiance measuring instrument is opposite to the shooting direction of the spectroscopic camera.

[0054] like Figure 2 As shown in the figure, the monitoring method of the visible light imaging device based on underwater monitoring of shallow coral reefs provided in this embodiment of the invention includes the following steps:

[0055] S101, The visible light imaging device suitable for underwater monitoring of shallow coral reefs is completely placed underwater; wherein, h2 is not less than 30cm;

[0056] S102, when photographing coral reefs underwater, the distance to the coral reef is measured in real time by a depth sounding sonar; wherein, the distance h between the device and the seabed target is greater than h1;

[0057] S103, When the visible light imaging device reaches a certain position in the sea area where coral reefs are distributed, it selects a suitable working depth based on the measurement data obtained from the depth sounding sonar.

[0058] S104, the control platform should stop moving and remain relatively stationary with respect to the seabed coral reef target, and the water sampling device should begin collecting water samples until completion;

[0059] S105: With the main control platform maintaining a stable state, the spectroscopic camera and the solar down-side irradiance meter are turned on and working simultaneously, recording measurement data at the same time and backing up the data on the main control platform.

[0060] The technical solution of the present invention will be further described below with reference to the embodiments.

[0061] Example 1

[0062] Addressing the need for remote sensing monitoring and assessment of shallow coral reef ecosystems in tropical waters, this invention aims to provide an underwater optical spectral imaging device for coral reefs. Utilizing the luminous flux in the visible spectrum provided by downward solar radiation, and based on measured water quality parameters, it removes electromagnetic wave attenuation caused by varying water quality conditions, ultimately obtaining consistent reflectance spectral imaging data for the same type of target at different seawater depths. Based on this underwater optical reflectance spectral imaging data of coral reefs, methods for coral reef detection, classification, and health assessment can be developed.

[0063] To achieve the above objectives, the technical solution adopted by this invention is as follows:

[0064] An underwater spectral imaging device and monitoring method suitable for monitoring shallow-sea coral reef ecosystems are disclosed. The device includes a central control platform, a spectral camera, a solar-downward irradiance meter, a depth sounding sonar, and a water sampling device. The focal planes of the spectral camera, the solar-downward irradiance meter, and the depth sounding sonar are located on a plane parallel to the sea level. The spectral camera's imaging direction is perpendicular to the sea level, while the solar-downward irradiance meter's measurement direction is opposite to the spectral camera's imaging direction.

[0065] The central control platform provides integrated space, power supply, control, and data storage interaction for the spectroscopic camera, solar down-the-horizontal irradiance meter, depth sounding sonar, and water sampling device. The central control platform must be sealed and waterproof; the integrated DC power supply provides stable power to the spectroscopic camera, solar down-the-horizontal irradiance meter, depth sounding sonar, and water sampling device; the integrated control unit controls the switching and coordination of all internal devices and provides storage and retrieval services for the data acquired by the integrated devices.

[0066] The spectroscopic camera internally includes a camera lens assembly, a CCD or CMOS optical recording array, and a storage device. The camera's field of view Φ in air should be no less than 40°. The spectroscopic camera should include characteristic bands with center wavelengths of 395nm, 430nm, 490nm, 517nm, 575nm, 600nm, and 650nm. These bands are preferred for coral reef remote sensing observation, and at least three characteristic coral reef bands (575nm, 600nm, and 650nm) should be included. During operation, the spectroscopic camera lens points vertically downwards, forming the field of view. The spectroscopic camera operates using frame-based imaging.

[0067] The solar down-facing irradiance meter has the same spectral band settings as the spectroscopic camera, with its light-receiving lens pointing vertically upwards. When the solar down-facing irradiance meter is operating, the distance between its lens and the sea surface should be ≥30cm. The function of the solar down-facing irradiance meter is to measure the remote-sensing incident energy emanating from the sun, providing an incident energy metric for calculating the remote-sensing reflectance of the spectroscopic camera's data. During operation, the solar down-facing irradiance meter should achieve synchronized data acquisition with the spectroscopic camera through the control unit in the central control platform.

[0068] The depth sounding sonar is connected to the central control platform via cable, and the direction of acoustic distance measurement should be consistent with the direction of the spectral camera. The function of the depth sounding sonar is to measure the distance between the scene target and the spectral camera at the time the spectral camera is operating, in order to perform water radiative transmission correction on the spectral energy received by the spectral camera.

[0069] The water sampling device, when the spectral camera is in a stable position, opens its valve shortly before or after data recording begins, allowing water to fill the device. The valve is then closed to complete the water sample collection. The function of the water sampling device is to collect water samples from the vicinity of the scene captured by the spectral camera during operation. This data is used to analyze the water quality parameters at that location and time, and to perform water radiative transfer correction on the spectral energy received by the spectral camera.

[0070] The spectral camera, the solar down-going irradiance meter, and the depth sounding sonar need to measure and record data simultaneously during operation.

[0071] This invention uses an underwater spectral camera to image, effectively solving the problems of solar reflection flares and wave lensing that occur when imaging above the water surface. By simultaneously acquiring the spectrum of the seabed coral reef target and the downward solar spectrum, this invention can calculate the remote sensing reflectance data of coral reefs located at different depths, avoiding the difference in imaging brightness caused by the weakening of sunlight at different water depths.

[0072] This invention, through real-time measurement of the distance between the spectral camera and the seabed coral reef target, and water sample analysis data obtained through the water sample collection device, can effectively correct for the absorption and scattering effects of water bodies in the intermediate optical path on the reflected light from the seabed target, thereby improving the accuracy of remote sensing reflectance data and enhancing imaging quality. This invention only requires adjusting the measurement height (i.e., the distance between the spectral camera and the coral reef target) according to the different water depth conditions in the coral reef distribution area; all data acquisition processes can be completed automatically. It is convenient to operate and safe and reliable.

[0073] Example 2

[0074] like Figure 1 The diagram shown is a structural arrangement diagram of the present invention.

[0075] The device of this invention is completely submerged in water during use. To ensure that the solar irradiance measuring instrument does not emerge from the water surface or is unaffected by sea waves throughout the entire measurement process, such as... Figure 1 As shown in the figure, h2 should be no less than 30cm.

[0076] When the device of this invention is used for underwater coral reef photography, the distance to the coral reef is measured in real time by a 3D depth sounder. To ensure that the device does not touch the bottom and is damaged, and to obtain images of a suitable width, such as... Figure 1 The distance h between the device shown and the seabed should be at least greater than h1.

[0077] like Figure 1 After the device reaches a certain position in the sea area where coral reefs are distributed, it selects an appropriate depth based on the measurement data obtained by the depth sounding sonar. The main control platform should stop moving and remain relatively stationary with respect to the seabed coral reef target. Then, the water sampling device starts collecting water samples until the task is completed.

[0078] With the 5-way master control platform maintaining a stable state, the 1-way spectrometer and the 2-way solar irradiance measuring instruments are simultaneously powered on and start working, recording measurement data at the same time, and backing up the data on the 5-way master control platform.

[0079] At this time, the light intensity at wavelength λ recorded by the photosensitive element of the 6-solar-downward irradiance meter is E. λ0 The light intensity recorded by the 7-spectrum camera's image sensor is E. λ1 ,at this time:

[0080]

[0081] In equation (1), α λ R is the attenuation coefficient of light with wavelength λ per unit optical path in seawater. This attenuation coefficient is obtained from water samples collected by a four-sampling device after water quality analysis. Of course, it is assumed here that the seawater quality conditions are constant within a limited measurement space. λLet R be the reflectance of a seabed target such as a coral reef to light with wavelength λ. Then, remove the reflectance R from equation (1). λ for:

[0082]

[0083] When considering such Figure 1 When considering the spatial positions of each pixel within the field of view of the 1-spectrum camera, equation (1) can be written as:

[0084]

[0085] In equation (3), (i, j) are the pixel coordinates within the image with the center pixel as the origin, and the number of column pixels of the 1-spectrum camera is N, then:

[0086] x=(h 2 +((i*L / 2N) 2 +(j*L / 2N) 2 ) 1 / 2 ) 1 / 2 (4)

[0087] Equation (2) is then changed to a formula for calculating reflectance involving the spatial location of each pixel:

[0088]

[0089] In sea areas with coral reefs, several distinct characteristics emerge: First, the water quality is generally Class I, characterized by chlorophyll as the primary water quality element. However, in coral reef basins with islands and sandbars, suspended particulate matter is a significant water quality factor due to the influence of tides, waves, and the substrate conditions of the coral sand. Therefore, backscattering caused by suspended particulate matter must be considered, while the content of soluble organic salts and their resulting spectral absorption can be disregarded. Second, coral reefs are primarily distributed in tropical seas. In shallow waters, particularly at depths of 20m and below, the coral reefs are most densely and abundantly distributed. Underwater lighting conditions are good in these areas and depths, eliminating the need for additional active light sources when photographing coral reefs. Thirdly, areas with well-grown coral reefs typically have high water flow, especially in front of the reef platform. High-speed currents create waves on the wave-breaking zone of the reef slope, which is also where coral reefs are most densely distributed. Under these conditions, the immersion depth of the solar irradiance meter should be adjusted to a deeper depth depending on the wave conditions.

[0090] The core function and main working method of this invention is to simultaneously observe the reflected light energy and downward-facing solar radiation energy of coral reefs in shallow waters, and then correct for the changes caused by absorption and scattering of light rays during radiative transmission in the seawater to obtain a reflectance spectral image of the coral reef distribution area. A key aspect of obtaining high-quality coral reef reflectance spectral images is the correction of the influence of radiative transmission of observed light rays in the seawater; the feasibility of this correction is crucial to the invention's overall success.

[0091] As shown in equation (2), the reflectance image R is obtained. λ The key is to determine the attenuation coefficient α of light in the seawater of the coral reef monitoring area. λ , and α λ =f(a(λ), b b (λ) can be obtained through water quality analysis parameters obtained by the water quality acquisition device carried by this invention. Wherein, a(λ) is the total absorption coefficient at wavelength λ, and b... b (λ) is the backscattering coefficient at wavelength λ.

[0092] To facilitate experimental derivation and understanding, equation (2) can be further rewritten as:

[0093] R(λ)=R t (λ)-R w (λ)

[0094] Among them, R t (λ) is calculated directly from the measurements of the solar downlink irradiance meter and the spectral camera in this invention. The key next step is to calculate the influence of water reflectance, i.e., to remove R. w (λ). And R w (λ) is again a(λ) and b b A function of (λ). In nearshore waters where chlorophyll and suspended particulate matter are the main water quality conditions, R w (λ) can be expressed as:

[0095]

[0096] Where H is the optical path length of the light from the monitored target in seawater.

[0097] Here, the total absorption coefficient a(λ) and the backscattering coefficient b at wavelength λ are... b (λ) can be obtained by measuring water samples collected by the water sampling device of the present invention, and used as a water radiative transfer parameter within a limited local spatial range to participate in the radiative transfer correction of the coral reef observation spectrum. The scale of this local space can be determined by collecting water samples in the field to measure the water absorption and scattering parameters, and by conducting spatial heterogeneity analysis of the absorption and scattering characteristics.

[0098] like Figure 3 As shown, this diagram illustrates the results before and after spectral correction for water radiative transfer, presented using discrete spectra measured in-situ. The simulation typically includes four spectral bands for commonly used optical remote sensors: blue (490nm), green (575nm), red (650nm), and near-infrared (835nm) light bands, with center wavelengths of 490nm, 575nm, 650nm, and 835nm respectively. Figure 3 It is easy to see that in water, due to the absorption effect of water molecules on electromagnetic waves, the near-infrared band cannot propagate in water. Therefore, underwater optical observation can only utilize electromagnetic waves in the blue to red light range. In the water correction results above, on the one hand, the spectral reflectance is significantly improved after correction; on the other hand, for coral deposition areas with greater water depth, the increase in reflectance spectrum is greater than that in shallower foreland terraces.

[0099] In the above embodiments, implementation can be achieved, in whole or in part, through software, hardware, firmware, or any combination thereof. When implemented, in whole or in part, as a computer program product, the computer program product includes one or more computer instructions. When the computer program instructions are loaded or executed on a computer, all or part of the processes or functions described in the embodiments of the present invention are generated. The computer can be a general-purpose computer, a special-purpose computer, a computer network, or other programmable device. The computer instructions can be stored in a computer-readable storage medium or transmitted from one computer-readable storage medium to another. For example, the computer instructions can be transmitted from one website, computer, server, or data center to another website, computer, server, or data center via wired (e.g., coaxial cable, fiber optic, digital subscriber line (DSL)) or wireless (e.g., infrared, wireless, microwave, etc.) means. The computer-readable storage medium can be any available medium that a computer can access or a data storage device such as a server or data center that integrates one or more available media. The available medium can be a magnetic medium (e.g., floppy disk, hard disk, magnetic tape), an optical medium (e.g., DVD), or a semiconductor medium (e.g., a solid-state drive (SSD)).

[0100] The above description is merely a specific embodiment of the present invention, but the scope of protection of the present invention is not limited thereto. Any modifications, equivalent substitutions, and improvements made by those skilled in the art within the scope of the technology disclosed in the present invention, and within the spirit and principles of the present invention, should be covered within the scope of protection of the present invention.

Claims

1. A monitoring method using a visible light imaging device for underwater monitoring of shallow coral reefs, characterized in that, Includes the following steps: Step 1: Completely submerge the visible light imaging device suitable for underwater monitoring of shallow coral reefs; where h2 is the distance between the visible light imaging device and the water surface, and h2 is not less than 30cm, so as to avoid the observation lens of the solar irradiance measuring instrument being exposed above the water surface due to the undulation of the sea surface caused by waves. Step two: During underwater coral reef photography, the distance to the coral reef is measured in real time by a depth sounding sonar. The focal plane of the spectroscopic camera, the focal plane of the solar irradiance meter, and the depth sounding sonar are all located on a plane parallel to the sea level. The spectroscopic camera's shooting direction is perpendicular to the sea level, and the solar irradiance meter's measurement direction is opposite to the spectroscopic camera's shooting direction. h is the distance between the solar irradiance meter's focal plane and the seabed target, and h1 is the distance between the solar irradiance meter's focal plane and the lower lens of the spectroscopic camera; h > h1. Step 3: After the visible light imaging device reaches a certain position in the sea area where coral reefs are distributed, select an appropriate working depth based on the measurement data obtained from the depth sounding sonar. Step four: The control platform should stop moving and remain relatively stationary relative to the seabed coral reef target, and the water sampling device should begin collecting water samples until completion; Step 5: With the main control platform in a stable state, the spectral camera and the solar down-side irradiance meter are turned on simultaneously to record measurement data and back up the data on the main control platform. The monitoring method of the visible light imaging device based on underwater monitoring of shallow coral reefs further includes: Wavelengths recorded by the photosensitive element of the down-facing solar irradiance meter Light intensity is The light intensity recorded by the spectral camera's image sensor is : (1) In equation (1), It is a wavelength of The attenuation coefficient of light per unit optical path in seawater, which is obtained by water quality analysis of water samples collected by a water sampling device. The monitoring method of the visible light imaging device based on underwater monitoring of shallow coral reefs further includes: Assume that the seawater quality conditions remain constant within a finite measurement space; For underwater targets such as coral reefs, the wavelength is... The reflectivity of light, the reflectivity in equation (1) for: (2) When considering the spatial position of each pixel within the field of view of the spectral camera, equation (1) is changed to: (3) In equation (3), Let N be the pixel coordinates within the image with the center pixel as the origin, and let N be the number of column pixels of the spectral camera. Then: (4) Equation (2) is then changed to a formula for calculating reflectance involving the spatial location of each pixel: (5)。

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