A method and device for constructing a model for retrieving concentration of suspended matter

Abstract

The application provides a method and device for constructing a suspended matter concentration inversion model. The method comprises the following steps: obtaining a simulation spectrum of a target water body; performing normalization processing on the simulation spectrum to obtain normalized reflectivity data; analyzing the correlation degree between the normalized reflectivity data and the concentrations of multiple components in the target water body; the multiple components include suspended matter and other components; selecting a combination factor whose correlation degree with the suspended matter is greater than a first threshold value and whose correlation degree with the other components is less than a second threshold value to construct a suspended matter concentration inversion model of the target water body. The device comprises a simulation spectrum acquisition module, a reflectivity acquisition module, a correlation degree analysis module and a model construction module. In this way, a suspended matter inversion model suitable for SDGSAT-1 satellite images in Taihu Lake area is established, which can provide a reference for evaluating the suspended matter of Taihu Lake and provide strong evidence for the unique application ability of SDGSAT-1 satellite in monitoring the water quality of lakes.

Description

Technical Field

[0001] This specification relates to the field of suspended matter concentration inversion technology, and in particular to a method for constructing a suspended matter concentration inversion model. Background Technology

[0002] Currently, the sustainable development of the water environment faces enormous challenges. Suspended solids in water bodies are an important indicator for measuring water quality and the degree of water pollution. Terrestrial nutrients can adhere to the surface of suspended particles, leading to water pollution. Therefore, monitoring the concentration of suspended solids in water bodies is an important means of reflecting the current status and development trend of water quality, and also an important foundation for improving water quality and controlling water pollution.

[0003] The Sustainable Development Satellite-1 (SDGSAT-1) is the world's first scientific satellite dedicated to serving the United Nations 2030 Agenda for Sustainable Development. Developed and operated by the China Center for Big Data for Sustainable Development (CBAS), the satellite is equipped with a Thermal Infrared Spectrometer (TIS), a Glimmer Imager for Urbanization (GIU), and a Multispectral Imager for Inshore (MII). Through various observation modes, it can achieve all-weather, multi-payload collaborative observation. The Multispectral Imager has seven spectral channels in the 380-900 nm wavelength range, with a spatial resolution of 10 m and a swath width of 300 km. In addition to blue, green, red, and near-infrared channels, it also includes two deep blue channels and one red-edge channel. This spectral configuration allows for better identification of water turbidity and more targeted detection of suspended matter in inland waters.

[0004] Taihu Lake, located in the Yangtze River Delta region (30°55'40"N~31°32'58"N, 119°52'32"E~120°36'10"E), has a water area of ​​2338.1 square kilometers and is the third largest freshwater lake in China. The lake water is turbid year-round, with significant suspended solids. The concentration of suspended solids is closely related to the water environment quality and economic development of the Taihu Lake region, making the monitoring of suspended solids concentration in Taihu Lake of great significance.

[0005] The optical properties of inland water bodies are jointly influenced by chlorophyll a, colored soluble organic matter (CDOM), and suspended matter in the water. However, current inversion studies on suspended matter mainly use bands that are more sensitive to suspended matter, and most models ignore the optical contributions of chlorophyll a and colored soluble organic matter (CDOM) to water bodies.

[0006] Therefore, how to construct a suspended matter concentration inversion model for the Taihu Lake region suitable for the SDGSAT-1 satellite has become an urgent problem to be solved. Summary of the Invention

[0007] This invention describes a method and apparatus for constructing a suspended matter concentration inversion model, which can solve the above-mentioned technical problems.

[0008] According to the first aspect, a method for constructing a suspended solids concentration inversion model is provided. The method includes:

[0009] The remote sensing reflectance of the measured water quality parameters of the target water body is simulated using a radiative transfer model to obtain the simulated spectrum of the target water body. The simulated spectrum is normalized using the center wavelength of the third band of the satellite as the normalization base to obtain normalized reflectance data. The correlation between the normalized reflectance data and the concentrations of multiple components in the target water body is analyzed. These multiple components include suspended matter and other components. A combination factor with a correlation greater than a first threshold and a correlation less than a second threshold with the suspended matter is selected to construct a suspended matter concentration inversion model for the target water body suitable for the satellite.

[0010] In one embodiment, the inputs to the radiative transfer model include the absorption and scattering characteristics of suspended solids, pure water, chlorophyll a, and colored soluble organic matter (CDOM) in the target water body.

[0011] In one embodiment, the other components include at least one of the following: chlorophyll a and colored soluble organic compound CDOM.

[0012] In one embodiment, the first threshold is greater than the second threshold.

[0013] In one embodiment, the radiative transfer model is the Hydrolight radiative transfer model.

[0014] According to a second aspect, this application provides an apparatus for constructing a suspended solids concentration inversion model. The apparatus includes:

[0015] The simulated spectrum acquisition module is configured to use a radiative transfer model to simulate the remote sensing reflectance of the measured water quality parameters of the target water body, thereby obtaining the simulated spectrum of the target water body.

[0016] The reflectance acquisition module is configured to use the center wavelength of the third band of the satellite as the normalization base to normalize the simulated spectrum and obtain normalized reflectance data.

[0017] The correlation analysis module is configured to analyze the correlation between the normalized reflectance data and the concentrations of multiple components in the target water body; the multiple components include suspended matter and other components.

[0018] The model building module is configured to select a combination factor whose correlation with the suspended matter is greater than a first threshold and whose correlation with the other components is less than a second threshold, and to build a suspended matter concentration inversion model for the target water body applicable to the satellite.

[0019] In one embodiment, the inputs to the radiative transfer model include the absorption and scattering characteristics of suspended solids, pure water, chlorophyll a, and colored soluble organic matter (CDOM) in the target water body.

[0020] In one embodiment, the other components include at least one of the following: chlorophyll a and colored soluble organic compound CDOM.

[0021] In one embodiment, the first threshold is greater than the second threshold. For example, the first threshold is greater than 0.75, and the second threshold is less than 0.1.

[0022] In one embodiment, the radiative transfer model is the Hydrolight radiative transfer model.

[0023] In the methods and apparatus provided in the embodiments of this specification, a satellite water suspended matter concentration inversion model based on the Hydrolight model is constructed, which can provide a reference for evaluating suspended matter in water bodies and provide strong evidence for the unique application capability of satellites in monitoring lake water quality. Attached Figure Description

[0024] To more clearly illustrate the technical solutions of the embodiments of the present invention, the drawings used in the following description of the embodiments will be briefly introduced. 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.

[0025] Figure 1 This diagram illustrates a comparison between the simulated and measured spectra of water radiative transfer provided in an embodiment of the present invention.

[0026] Figure 2 This diagram illustrates the correlation between normalized reflectance and the concentration of the three elements provided in an embodiment of the present invention.

[0027] Figure 3 A schematic diagram of the inversion model constructed according to an embodiment of the present invention is shown;

[0028] Figure 4 This diagram illustrates the results of suspended matter concentration inversion from SDGSAT-1 images in the Taihu Lake region, as provided in an embodiment of the present invention.

[0029] Figure 5 This diagram illustrates a process flow of a method for constructing a suspended solids concentration inversion model according to an embodiment of the present invention.

[0030] Figure 6 The diagram shows a schematic of the structure of an apparatus for constructing a suspended solids concentration inversion model according to an embodiment of the present invention. Detailed Implementation

[0031] The solution provided in this specification will now be described with reference to the accompanying drawings.

[0032] To make the objectives, technical solutions, and advantages of the embodiments of this application clearer, the technical solutions in the embodiments of this application will be described below with reference to the accompanying drawings.

[0033] In the description of the embodiments of this application, the words "exemplary," "for example," or "for instance" are used to indicate examples, illustrations, or explanations. Any embodiment or design described as "exemplary," "for example," or "for instance" in the embodiments of this application should not be construed as being more preferred or advantageous than other embodiments or designs. Specifically, the use of the words "exemplary," "for example," or "for instance" is intended to present the relevant concepts in a specific manner.

[0034] In the description of the embodiments of this application, the term "and / or" is merely a description of the relationship between related objects, indicating that three relationships can exist. For example, A and / or B can represent: A existing alone, B existing alone, and A and B existing simultaneously. Furthermore, unless otherwise stated, the term "multiple" means two or more.

[0035] Furthermore, the terms "first" and "second" are used for descriptive purposes only and should not be construed as indicating or implying relative importance or implicitly specifying the indicated technical features. Thus, a feature defined as "first" or "second" may explicitly or implicitly include one or more of that feature. The terms "comprising," "including," "having," and their variations all mean "including but not limited to," unless otherwise specifically emphasized.

[0036] The practical application of the method provided in the embodiments of the present invention will be described from the following aspects.

[0037] (I) Simulation of Water Radiative Transfer

[0038] To simulate the spectral reflectance under different water quality parameters in the Taihu Lake area, the study first simulates the scattering and absorption of sunlight when it passes through the water body, based on the absorption and scattering characteristics of four components in the water body: pure water, chlorophyll a, suspended solids, and colored dissolved organic matter (CDOM), combined with environmental conditions.

[0039] The measured spectra of Taihu Lake were acquired using an ASD spectrometer via above-water measurement. The water surface remote sensing reflectance was calculated using the following formula:

[0040]

[0041] R rs (λ) represents the remote sensing spectral reflectance of the water surface, and λ is the wavelength; L t (λ), L sky (λ), L p (λ) represents the measured spectral values ​​of the water surface, sky light, and gray panel, respectively; ρ p (λ) is the gray board reflectance calibrated in the laboratory; ρ sky (λ) represents the reflectivity of the sky-air-water interface.

[0042] Chlorophyll a concentration was determined according to the national standard (SL 88-2012); total suspended solids concentration was determined according to the national standard (GB11901-89); colored soluble organic matter (CDOM) was determined by spectrophotometry, and the absorption coefficient at 440 nm was used to characterize CDOM concentration.

[0043] The process of radiative transfer simulation in water involves establishing the relationship between apparent optical properties and inherent optical properties, that is, establishing the remote sensing reflectance R of water. rs With the total absorption coefficient a(λ) and the total backscattering coefficient b of the water body b The relationship between (λ) and the water body of Taihu Lake conforms to the following formula:

[0044]

[0045] In the formula, f is an empirical parameter, f≈0.32~0.37; Q is the light field distribution parameter, which is affected by the solar altitude angle and the observation angle; t is the interface transmission coefficient from water to atmosphere, usually taken as 0.98; n is the refractive index of water, usually taken as 1.34; the total absorption coefficient of water a(λ) can be regarded as the sum of the absorption coefficients of pure water, chlorophyll a, suspended matter, and CDOM in the water body, and the total backscattering coefficient b b (λ) can be considered as the sum of the backscattering coefficients of pure water, chlorophyll a, and suspended matter in the water body, and the relationship is expressed by the following formula:

[0046] a(λ)=a w(λ)+a chl (λ)+a cdom (λ)+a tsm (λ) (3)

[0047] b b (λ)=b b，w (λ)+b b，chl (λ)+b b，tsm (λ) (4)

[0048] a w (λ) is the absorption coefficient of pure water, b w (λ) is the scattering coefficient of pure water, b b，w (λ) is the backscattering coefficient of pure water; a chl (λ), a tsm (λ), a cdom (λ) represents the absorption coefficients of chlorophyll a, suspended matter, and CDOM, respectively; b b，chl (λ), b b，tsm (λ) are the backscattering coefficients of chlorophyll a and suspended matter, respectively.

[0049] Figure 1 This diagram illustrates a comparison between the simulated and measured spectra of water radiative transfer provided in an embodiment of the present invention.

[0050] (II) Band Correlation Analysis

[0051] To improve the correlation between reflectance and measured water quality parameters, the simulated reflectance data was normalized using the center wavelength of the third band of the SDGSAT-1 satellite.

[0052] Then, a correlation analysis was performed on the normalized reflectance and the concentrations of the three elements. The most commonly used correlation analysis is the Pearson correlation analysis, which uses the correlation coefficient r to represent the degree of correlation. The value of r is between -1 and 1. A correlation coefficient r > 0 indicates a positive correlation, and r < 0 indicates a negative correlation.

[0053] Figure 2 This diagram illustrates the correlation analysis between normalized reflectance and the concentrations of the three elements provided in an embodiment of the present invention. Figure 2 As shown, the normalized reflectance with an absolute correlation coefficient greater than 0.75 (P<0.01) with suspended solids concentration and a weak correlation (r<0.1) with chlorophyll a concentration and colored soluble organic matter (CDOM) concentration is R. rs (660 / 490).

[0054] (III) Construction of Inversion Model

[0055] The band combination R was selected that showed a significant and strong correlation with suspended solids concentration and a weak correlation with chlorophyll a concentration and CDOM concentration. rs (660 / 490). Using this factor as the independent variable and suspended solids concentration as the dependent variable, a suspended solids inversion model (R²) was constructed. 2 =0.81), Figure 3 This diagram illustrates the inversion model constructed according to an embodiment of the present invention, such as... Figure 3 As shown, the model formula is as follows:

[0056]

[0057] (iv) SDGSAT-1 Image Suspended Object Inversion

[0058] First, the image is preprocessed by converting the DN value into remote sensing reflectance through radiometric calibration and atmospheric correction. Then, the vector file of Taihu Lake is obtained using the water index. Finally, the SDGSAT-1 image of Taihu Lake is obtained by mask extraction.

[0059] The model was applied to SDGSAT-1MII imagery to obtain the inversion results of suspended matter in Taihu Lake. Figure 4 This diagram illustrates the results of suspended matter concentration inversion from SDGSAT-1 images of the Taihu Lake region, as provided in an embodiment of the present invention.

[0060] Figure 5 This invention provides a method for constructing a suspended solids concentration inversion model, as illustrated in an embodiment of the present invention. Figure 5 As shown, the method includes the following steps:

[0061] Step S510: Use the radiative transfer model to simulate the remote sensing reflectance of the measured water quality parameters of the target water body to obtain the simulated spectrum of the target water body;

[0062] Step S520: Using the center wavelength of the satellite's third band as the normalization base, normalize the simulated spectrum to obtain normalized reflectance data.

[0063] Step S530: Analyze the correlation between normalized reflectance data and the concentrations of multiple components in the target water body; these components include suspended matter and other components.

[0064] Step S540: Select a combination factor whose correlation with suspended matter is greater than a first threshold and whose correlation with other components is less than a second threshold, and construct a suspended matter concentration inversion model for the target water body suitable for satellite.

[0065] The method provided in this embodiment of the invention can be applied to SDGSAT-1 satellite imagery of the Taihu Lake region. The following description uses SDGSAT-1 satellite imagery of the Taihu Lake region as the execution subject. It should be understood that the method provided in this embodiment of the invention can also be applied to other satellites and other regions; the method provided by this invention can still be used on other water bodies and other satellite imagery.

[0066] 1) The simulated spectrum of the Taihu Lake region was obtained by simulating the remote sensing reflectance of measured water quality parameters using the Hydrolight radiative transfer model. The simulated spectrum of the Taihu Lake region was obtained by simulating the absorption and scattering characteristics of four components in the water body: pure water, chlorophyll a, suspended solids, and CDOM using the Hydrolight radiative transfer model.

[0067] As a feasible approach, the measured spectra were acquired using an ASD spectrometer via a surface-to-water measurement method. Chlorophyll a concentration was measured according to the national standard (SL 88-2012), and total suspended solids concentration was determined according to the national standard (GB11901-89). Colored soluble organic matter (CDOM) was measured using a spectrophotometer, with the absorption coefficient at 440 nm used to characterize CDOM concentration. In one example, based on the absorption and scattering characteristics of the four components—pure water, chlorophyll a, suspended solids, and CDOM—simulated spectral data for the Taihu Lake region were obtained using the Hydrolight radiative transfer model.

[0068] 2) Obtain normalized reflectance data based on simulated spectral data.

[0069] The normalized reflectance data includes simulated spectral data that has been normalized using the center wavelength of the third band of the SDGSAT-1 satellite as the normalization base.

[0070] 3) Analyze the correlation between normalized reflectance data and the concentrations of suspended matter, chlorophyll a, and CDOM.

[0071] In one embodiment, correlation analysis was performed using normalized reflectance data with the concentrations of three elements: chlorophyll a, suspended matter, and colored soluble organic matter (CDOM). The normalized reflectance with the suspended matter concentration had an absolute value greater than 0.75 (P<0.01) and a weak correlation with the concentrations of chlorophyll a and colored soluble organic matter (CDOM) (r<0.1), which was R_rs(660 / 490).

[0072] 4) Selecting combination factors that are significantly strongly correlated with suspended matter concentration and weakly correlated with chlorophyll a concentration and colored soluble organic matter (CDOM) concentration, a single-element inversion model for suspended matter in the Taihu Lake region suitable for SDGSAT-1 satellite was constructed.

[0073] In one embodiment, the model factor R_rs(660 / 490) is used to construct a suspended matter inversion model for the Taihu Lake region using the SDGSAT-1 satellite with a correlation coefficient greater than 0.75 (P<0.01) and a weak correlation (r<0.1) with chlorophyll a concentration and colored soluble organic matter (CDOM) concentration. This model is then applied to SDGSAT-1 satellite imagery.

[0074] This invention fully considers water quality parameters affecting the spectral characteristics of Taihu Lake. Using simulation data from the Hydrolight radiative transfer model and measured data, and through experimental and theoretical analysis, a suspended matter inversion model for the Taihu Lake region, applicable to SDGSAT-1 satellite imagery, is established. This model provides a reference for evaluating suspended matter in Taihu Lake and strongly demonstrates the unique and powerful application capabilities of the SDGSAT-1 satellite in monitoring lake water quality. This suspended matter inversion model can also be applied to other satellite imagery and water bodies.

[0075] Corresponding to the method provided by the present invention, the present invention also provides an apparatus. Figure 6 This diagram illustrates the structure of an apparatus for constructing a suspended solids concentration inversion model, as provided in an embodiment of this specification.

[0076] like Figure 6 As shown, the device 600 includes:

[0077] The simulated spectrum acquisition module 610 is configured to use a radiative transfer model to simulate the remote sensing reflectance of the measured water quality parameters of the target water body, and obtain the simulated spectrum of the target water body.

[0078] The reflectance acquisition module 620 is configured to use the center wavelength of the third band of the satellite as the normalization base to normalize the simulated spectrum and obtain normalized reflectance data.

[0079] The correlation analysis module 630 is configured to analyze the correlation between normalized reflectance data and the concentrations of multiple components in the target water body; these components include suspended matter and other components.

[0080] The model building module 640 is configured to select a combination factor with a correlation greater than a first threshold and a correlation with other components less than a second threshold to build a suspended matter concentration inversion model for the target water body suitable for satellite.

[0081] In one embodiment, the inputs to the radiative transfer model include the absorption and scattering characteristics of suspended solids, pure water, chlorophyll a, and colored soluble organic matter (CDOM) in the target water body.

[0082] In one embodiment, the radiative transfer model is the Hydrolight radiative transfer model.

[0083] In one embodiment, the other components include at least one of the following: chlorophyll a and colored soluble organic compound CDOM.

[0084] In one embodiment, the first threshold is greater than 0.75; the second threshold is less than 0.1.

[0085] It needs to be explained that, for Figure 6 For a description of the apparatus, see also the description of the aforementioned method.

[0086] According to another embodiment, a computer-readable storage medium is also provided, on which a computer program is stored, which, when executed in a computer, causes the computer to perform a combination Figure 5 The method described.

[0087] According to another embodiment, a computing device is also provided, including a memory and a processor, wherein the memory stores executable code, and when the processor executes the executable code, it implements a combination... Figure 5 The methods described herein. Those skilled in the art will recognize that, in one or more of the examples above, the functions described in this invention can be implemented using hardware, software, firmware, or any combination thereof. When implemented in software, these functions can be stored in a computer-readable medium or transmitted as one or more instructions or code on a computer-readable medium.

[0088] The specific embodiments described above further illustrate the purpose, technical solution, and beneficial effects of the present invention. It should be understood that the above description is only a specific embodiment of the present invention and is not intended to limit the scope of protection of the present invention. Any modifications, equivalent substitutions, improvements, etc., made on the basis of the technical solution of the present invention should be included within the scope of protection of the present invention.

Claims

1. A method for constructing a suspended solids concentration inversion model, characterized in that, The method includes: The remote sensing reflectance of the measured water quality parameters of the target water body is simulated using a radiative transfer model to obtain the simulated spectrum of the target water body; Using the center wavelength of the satellite's third band as the normalization base, the simulated spectrum is normalized to obtain normalized reflectance data. The correlation between the normalized reflectance data and the concentrations of multiple components in the target water body was analyzed; these multiple components include suspended matter and other components. By selecting combination factors whose correlation with the suspended matter is greater than a first threshold and whose correlation with the other components is less than a second threshold, a suspended matter concentration inversion model for the target water body suitable for the satellite is constructed. The construction of the suspended matter concentration inversion model for the target water body suitable for the satellite includes: selecting band combinations that are significantly and strongly correlated with suspended matter concentration and have weak correlations with chlorophyll a concentration and CDOM concentration. (660 / 490), with the combined factor as the independent variable and the suspended solids concentration as the dependent variable, the suspended solids inversion model is constructed, and the formula of the suspended solids inversion model is as follows:

2. The method according to claim 1, characterized in that, The inputs to the radiative transfer model include the absorption and scattering characteristics of suspended solids, pure water, chlorophyll a, and colored soluble organic matter (CDOM) in the target water body.

3. The method according to claim 1, characterized in that, The radiative transfer model is the Hydrolight radiative transfer model.

4. The method according to any one of claims 1-3, characterized in that, The other components include at least one of the following: chlorophyll a and colored soluble organic compound CDOM.

5. The method according to any one of claims 1-3, characterized in that, The first threshold is greater than the second threshold.

6. An apparatus for constructing a suspended solids concentration inversion model, characterized in that, The device includes: The simulated spectrum acquisition module is configured to use a radiative transfer model to simulate the remote sensing reflectance of the measured water quality parameters of the target water body, and obtain the simulated spectrum of the target water body. The reflectance acquisition module is configured to use the center wavelength of the third band of the satellite as the normalization base to normalize the simulated spectrum and obtain normalized reflectance data. The correlation analysis module is configured to analyze the correlation between the normalized reflectance data and the concentrations of multiple components in the target water body; the multiple components include suspended matter and other components. The model building module is configured to select combination factors whose correlation with the suspended matter is greater than a first threshold and whose correlation with the other components is less than a second threshold, to construct a suspended matter concentration inversion model for the target water body suitable for the satellite; and to select band combinations that are significantly strongly correlated with suspended matter concentration and weakly correlated with chlorophyll a concentration and CDOM concentration. (660 / 490), with the combined factor as the independent variable and the suspended solids concentration as the dependent variable, the suspended solids inversion model is constructed, and the formula of the suspended solids inversion model is as follows:

7. The apparatus according to claim 6, characterized in that, The inputs to the radiative transfer model include the absorption and scattering characteristics of suspended solids, pure water, chlorophyll a, and colored soluble organic matter (CDOM) in the target water body.

8. The apparatus according to claim 6, characterized in that, The radiative transfer model is the Hydrolight radiative transfer model.

9. The apparatus according to claim 6, characterized in that, The other components include at least one of the following: chlorophyll a and colored soluble organic compound CDOM.

10. The apparatus according to claim 6, characterized in that, The first threshold is greater than the second threshold.

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