A remote sensing inversion method and apparatus for chlorophyll a concentration

Abstract

This application provides a remote sensing inversion method and apparatus for chlorophyll a concentration, relating to the field of remote sensing technology. By removing the influence of bottom effects (such as aquatic plants and bottom sediments), this application significantly improves the accuracy of chlorophyll a concentration inversion in optically shallow water areas, and enables more reliable eutrophication assessment based on more accurate chlorophyll a concentration data. Furthermore, because this application improves upon the overestimation of chlorophyll a concentration caused by the failure to eliminate bottom effects in traditional algorithms, it provides more accurate data support for subsequent water quality monitoring and management. Moreover, this application is applicable to various complex aquatic environments, including waters with abundant aquatic vegetation and sediment distribution, greatly enhancing the effectiveness and applicability of water quality monitoring and management.

Description

Technical Field

[0001] This application relates to the field of remote sensing technology, and in particular to a remote sensing inversion method and apparatus for chlorophyll a concentration. Background Technology

[0002] With the continuous development of industrialization and agriculture, more and more water bodies are being polluted by factors such as industrial and agricultural emissions. The accumulation of pollutants makes the water rich in nutrients, promoting the excessive reproduction of phytoplankton and causing eutrophication. This not only seriously affects water quality and damages the ecological environment, but may also pose a threat to human health and the socio-economic situation.

[0003] To address eutrophication, researchers have developed remote sensing inversion technology. This technology uses remote sensing satellite imagery data to analyze chlorophyll a concentration in water bodies, thereby assessing the health of the water. Existing remote sensing inversion technologies are typically developed for optically deep water areas where bottom matter (such as aquatic plants and sediments) can be disregarded due to the greater depth.

[0004] However, in optically shallow water areas, the underwater material significantly influences the optical properties of the water body, easily leading to an overestimation of chlorophyll a concentration. This, in turn, results in erroneous eutrophication assessments, impacting water quality monitoring and management decisions. Therefore, achieving more accurate chlorophyll a concentration retrieval has become a pressing technical challenge. Summary of the Invention

[0005] To address the aforementioned issues, this application provides a remote sensing inversion method and apparatus for chlorophyll a concentration, which can achieve more accurate chlorophyll a concentration inversion.

[0006] The embodiments of this application disclose the following technical solutions:

[0007] In a first aspect, this application discloses a remote sensing inversion method for chlorophyll a concentration, the method comprising:

[0008] Acquire information on suspended solids concentration and actual water depth of the target water body;

[0009] Based on the suspended matter concentration information, the uplink and downlink radiation attenuation coefficients of the red, green and blue bands are determined respectively using the uplink and downlink radiation attenuation coefficient models of the red, green and blue bands.

[0010] Based on the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information, the underwater optical deep-water remote sensing reflectance of the aquatic plant area and bottom sediment area of ​​the target water body is determined by the formula of underwater remote sensing reflectance.

[0011] Based on the underwater optical deep-water remote sensing reflectance of the aquatic plant area and the bottom sediment area, the underwater optical deep-water remote sensing reflectance of the aquatic plant area is replaced with the underwater optical deep-water remote sensing reflectance of the bottom sediment area, and then the equivalent water depth information is determined by the formula for underwater remote sensing reflectance.

[0012] Based on the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the equivalent water depth information, the underwater remote sensing reflectance of the red, green and blue bands after removing the bottom effect is determined by the formula for underwater remote sensing reflectance.

[0013] Based on the underwater remote sensing reflectance of the red, green, and blue bands after removing the underwater effect, determine the above-water remote sensing reflectance of the red, green, and blue bands after removing the underwater effect.

[0014] The concentration of chlorophyll a was determined based on the water remote sensing reflectance in the red, green, and blue bands after removing the underwater effect.

[0015] Optionally, the formula for the remote sensing reflectance below the water surface is as follows:

[0016]

[0017] in, R represents the subsurface reflectance of the aquatic plant area or bottom sediment area. rs Here, ρ is the water surface remote sensing reflectance, K is the underwater irradiance reflectance, and K is the bottom irradiance. d This is the uplink radiation attenuation coefficient. Let be the downward radiation attenuation coefficient of the water column. Z is the downflow radiation attenuation coefficient at the bottom of the water. B This is the actual water depth information.

[0018] Optionally, replacing the underwater optical deep-water remote sensing reflectance of the aquatic plant area with the underwater optical deep-water remote sensing reflectance of the bottom sediment area includes:

[0019] The underwater optical deep-water remote sensing reflectance of the aquatic plant area is replaced with the underwater optical deep-water remote sensing reflectance of the target sediment area. The target sediment area is a sediment area whose center point is less than a distance threshold from the center point of the aquatic plant area and whose water optical conditions are consistent with those of the aquatic plant area.

[0020] Optionally, the formula for determining the surface remote sensing reflectance of the red, green, and blue bands (after removing the underwater effect) based on the underwater remote sensing reflectance of the red, green, and blue bands is as follows:

[0021]

[0022] in, To remove the underwater underwater effect, the reflectance of the water surface remote sensing is denoted by i, where i is any one of the red, green, or blue bands. To remove the underwater effect, the reflectance of the remote sensing below the water surface.

[0023] Optionally, determining the chlorophyll a concentration based on the water remote sensing reflectance in the red, green, and blue bands after removing the underwater effect includes:

[0024] Based on the actual spectrum corresponding to the water remote sensing reflectance in the red, green and blue bands after removing the bottom effect, a simulated spectrum is determined from the spectral library, wherein the simulated spectrum is the spectrum with the smallest Euclidean distance from the actual spectrum;

[0025] Based on the spectral library, determine the chlorophyll a concentration corresponding to the simulated spectrum.

[0026] Secondly, this application provides a remote sensing inversion device for chlorophyll a concentration, the device comprising: an information acquisition module, a first determination module, a second determination module, a third determination module, a fourth determination module, a fifth determination module, and a sixth determination module;

[0027] The information acquisition module is used to acquire suspended solids concentration information and actual water depth information of the target water body;

[0028] The first determining module is used to determine the uplink and downlink radiation attenuation coefficients of the red, green, and blue bands respectively based on the suspended matter concentration information and the uplink and downlink radiation attenuation coefficient models of the red, green, and blue bands.

[0029] The second determining module is used to determine the underwater optical deep-water remote sensing reflectance of the aquatic plant area and bottom sediment area of ​​the target water body based on the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information, using the underwater remote sensing reflectance formula.

[0030] The third determining module is used to replace the underwater optical deep-water remote sensing reflectance of the aquatic plant area with the underwater optical deep-water remote sensing reflectance of the bottom sediment area based on the underwater optical deep-water remote sensing reflectance of the aquatic plant area and the bottom sediment area, and then determine the equivalent water depth information through the underwater remote sensing reflectance formula.

[0031] The fourth determining module is used to determine the underwater remote sensing reflectance of the red, green and blue bands after removing the bottom effect, based on the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the equivalent water depth information, using the underwater remote sensing reflectance formula.

[0032] The fifth determining module is used to determine the surface remote sensing reflectance of the red, green and blue bands after removing the bottom effect based on the underwater remote sensing reflectance of the red, green and blue bands after removing the bottom effect.

[0033] The sixth determining module is used to determine the chlorophyll a concentration based on the water remote sensing reflectance of the red, green and blue bands after removing the bottom effect.

[0034] Optionally, the formula for the remote sensing reflectance below the water surface is as follows:

[0035]

[0036] in, R represents the subsurface reflectance of the aquatic plant area or bottom sediment area. rs Here, ρ is the water surface remote sensing reflectance, K is the underwater irradiance reflectance, and K is the bottom irradiance. d This is the uplink radiation attenuation coefficient. Let be the downward radiation attenuation coefficient of the water column. Z is the downflow radiation attenuation coefficient at the bottom of the water. B This is the actual water depth information.

[0037] Optionally, the third determining module is specifically used to: replace the underwater optical deep-water remote sensing reflectance of the aquatic plant area with the underwater optical deep-water remote sensing reflectance of the target sediment area, wherein the target sediment area is a sediment area whose center point is less than a distance threshold from the center point of the aquatic plant area, and whose water optical conditions are consistent with those of the aquatic plant area.

[0038] Optionally, the formula for determining the surface remote sensing reflectance of the red, green, and blue bands (after removing the underwater effect) based on the underwater remote sensing reflectance of the red, green, and blue bands is as follows:

[0039]

[0040] in, To remove the underwater underwater effect, the reflectance of the water surface remote sensing is denoted by i, where i is any one of the red, green, or blue bands. To remove the underwater effect, the reflectance of the remote sensing below the water surface.

[0041] Optionally, the sixth determining module is specifically used to: determine a simulated spectrum from a spectral library based on the actual spectrum corresponding to the water remote sensing reflectance in the red, green and blue bands after removing the bottom effect, wherein the simulated spectrum is the spectrum with the smallest Euclidean distance from the actual spectrum; and determine the chlorophyll a concentration corresponding to the simulated spectrum based on the spectral library.

[0042] Compared with the prior art, this application has the following beneficial effects:

[0043] This application provides a remote sensing inversion method and apparatus for chlorophyll a concentration. By removing the influence of bottom effects (such as aquatic plants and bottom sediments), this application not only significantly improves the accuracy of chlorophyll a concentration inversion in optically shallow water areas, but also enables more reliable eutrophication assessment based on more accurate chlorophyll a concentration data. Furthermore, because this application improves upon the overestimation of chlorophyll a concentration caused by the failure to eliminate bottom effects in traditional algorithms, it provides more accurate data support for subsequent water quality monitoring and management. Moreover, this application is applicable to various complex aquatic environments, including waters with abundant aquatic vegetation and sediment distribution, greatly enhancing the effectiveness and applicability of water quality monitoring and management. Attached Figure Description

[0044] To more clearly illustrate the technical solutions in the embodiments of this application or the prior art, the drawings used in the description of the embodiments or the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0045] Figure 1 A flowchart of a remote sensing inversion method for chlorophyll a concentration provided in this application;

[0046] Figure 2 A schematic diagram illustrating the difference in chlorophyll a concentration inversion accuracy between a conventional method and the method of this application, as provided in the embodiments of this application;

[0047] Figure 3 A schematic diagram illustrating the calculation of chlorophyll a concentration distribution and error distribution using a conventional method and the method of this application, as provided in the embodiments of this application;

[0048] Figure 4 A schematic diagram of a remote sensing inversion device for chlorophyll a concentration provided in this application. Detailed Implementation

[0049] As described earlier, in order to address the phenomenon of eutrophication, technicians have developed remote sensing inversion technology. Remote sensing inversion technology refers to the technique of using remote sensing satellite imagery data to analyze the concentration of chlorophyll a in water bodies, thereby assessing the health status of the water. Existing remote sensing inversion technologies are typically developed for optically deep water areas, where bottom materials (such as aquatic plants and bottom sediments) can be ignored due to the greater water depth.

[0050] However, in optically shallow water areas, the underwater material significantly influences the optical properties of the water body, easily leading to an overestimation of chlorophyll a concentration. This, in turn, results in erroneous eutrophication assessments, impacting water quality monitoring and management decisions. Therefore, achieving more accurate chlorophyll a concentration retrieval has become a pressing technical challenge.

[0051] The inventors, through research, proposed a remote sensing inversion method and device for chlorophyll a concentration. The method includes: acquiring suspended matter concentration information and actual water depth information of the target water body; determining the uplink and downlink radiative attenuation coefficients of the red, green, and blue bands respectively, based on the suspended matter concentration information and using uplink and downlink radiative attenuation coefficient models for the red, green, and blue bands; determining the underwater optical deep-water remote sensing reflectance of the aquatic plant area and bottom sediment area of ​​the target water body using the underwater remote sensing reflectance formula, based on the underwater optical deep-water remote sensing reflectance of the aquatic plant area and bottom sediment area; and, based on the underwater optical deep-water remote sensing reflectance of the aquatic plant area and bottom sediment area, determining the underwater optical deep-water remote sensing reflectance of the water body. The subsurface optical deep-water remote sensing reflectance of the grassy area is replaced with the subsurface optical deep-water remote sensing reflectance of the bottom sediment area. The equivalent water depth information is then determined using the subsurface remote sensing reflectance formula. Based on the uplink and downlink radiative attenuation coefficients of the red, green, and blue bands and the equivalent water depth information, the subsurface remote sensing reflectance of the red, green, and blue bands, after removing bottom effects, is determined using the subsurface remote sensing reflectance formula. Based on the subsurface remote sensing reflectance of the red, green, and blue bands, after removing bottom effects, the surface remote sensing reflectance of the red, green, and blue bands, after removing bottom effects, is then determined. Finally, the chlorophyll a concentration is determined based on the surface remote sensing reflectance of the red, green, and blue bands, after removing bottom effects. Therefore, this application, by removing the influence of bottom effects (such as aquatic plants and bottom sediments), not only significantly improves the accuracy of chlorophyll a concentration inversion in optically shallow water areas but also enables more reliable eutrophication assessment based on more accurate chlorophyll a concentration data. Furthermore, because this application improves upon the problem of overestimation of chlorophyll a concentration caused by the failure to eliminate the bottom effect in traditional algorithms, it provides more accurate data support for subsequent water quality testing and management. Moreover, this application is applicable to various complex aquatic environments, including waters with abundant aquatic vegetation and sediment distribution, greatly enhancing the effectiveness and scope of water quality testing and management.

[0052] To enable those skilled in the art to better understand the present application, the technical solutions in the embodiments of the present application will be clearly and completely described below with reference to the accompanying drawings. Obviously, the described embodiments are only some embodiments of the present application, and not all embodiments. Based on the embodiments in the present application, all other embodiments obtained by those of ordinary skill in the art without creative effort are within the scope of protection of the present application.

[0053] See Figure 1This figure is a flowchart of a remote sensing inversion method for chlorophyll a concentration provided in an embodiment of this application. The method includes:

[0054] S101: Based on the suspended matter concentration information, the uplink and downlink radiation attenuation coefficients of the red, green, and blue bands are determined respectively using the uplink and downlink radiation attenuation coefficient models of the red, green, and blue bands.

[0055] Total suspended solids (TSS) refer to aqueous particles larger than 2 micrometers in size in a body of water, including sediments (such as silt particles), plankton (such as algae), and organic debris. Suspended solids can significantly affect the optical properties of water bodies.

[0056] In some specific implementations, suspended solids concentration information can be obtained through remote sensing technology. Specifically, satellite sensors can determine the corresponding suspended solids concentration information by measuring the electromagnetic radiation data reflected from the water surface and based on the known correspondence between electromagnetic radiation data and suspended solids concentration information.

[0057] In the optical environment of water, light propagation is affected by absorption and scattering, resulting in an exponential decrease in radiation intensity with distance. This attenuation can be categorized into upward radiation attenuation and downward radiation attenuation. Upward radiation attenuation refers to the decrease in light intensity propagating from deep water towards the surface, while downward radiation attenuation refers to the decrease in light intensity penetrating downwards from the surface. Upward radiation attenuation further includes upward radiation attenuation from the water column (i.e., the attenuation due to absorption and scattering of light by suspended matter in the water) and upward radiation attenuation from the bottom (i.e., the attenuation due to light being scattered upwards by the bottom).

[0058] In the remote sensing inversion method for chlorophyll a concentration provided in this application embodiment, the uplink and downlink radiative attenuation coefficients of the red, green, and blue bands can be determined based on the suspended matter concentration information using the uplink and downlink radiative attenuation coefficient models for the red, green, and blue bands, respectively. The uplink and downlink radiative attenuation coefficient models for the red, green, and blue bands are shown in Table 1 below:

[0059] Table 1

[0060]

[0061] As shown in Table 1, the radiation attenuation coefficient for each band is a linear function of the suspended matter concentration. For example, assuming a suspended matter concentration of TSS = 10 mg / L, the uplink radiation attenuation coefficient K for the blue band can be calculated using the formula. d,Blue =0.078*10+3.717=4.497(1 / m); Downward radiation attenuation coefficient of water column in blue band Downward radiation attenuation coefficient of underwater blue band

[0062] S102: Based on the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information, the underwater remote sensing reflectance of the aquatic plant area and the bottom sediment area is determined by the formula of underwater remote sensing reflectance.

[0063] Regarding actual water depth information: In some specific implementations, actual water depth information can be obtained through remote sensing technology. Specifically, blue band reflectance and red band reflectance can be obtained through remote sensing, and the actual water depth information can be calculated based on these reflectances. In another specific implementation, actual water depth information can also be obtained through acoustic detection technology. Specifically, the actual water depth information can be retrieved by analyzing the time difference of sound wave signal propagation in the water. In yet another specific implementation, actual water depth information can also be obtained through field measurements (such as using a sounding rod or buoy). This application does not limit the specific method for obtaining actual water depth information.

[0064] Regarding aquatic plant areas and sediment areas: In some specific implementations, aquatic plant areas and sediment areas can be distinguished based on the optical reflectance characteristics of different regions in remote sensing images. Specifically, the reflectance spectra of aquatic plants typically exhibit distinct chlorophyll absorption peaks (low reflectance in the blue and red bands) and reflectance peaks (high reflectance in the green and near-infrared bands), while the reflectance of sediment is usually relatively flat. Therefore, a classification model can be constructed to distinguish aquatic plant areas from sediment areas by analyzing the spectral characteristics of the red, green, blue, and near-infrared bands. In another specific implementation, aquatic plant areas and sediment areas can also be distinguished through field measurements (such as underwater surveys or sampling analysis). This application does not limit the specific methods for distinguishing aquatic plant areas and sediment areas.

[0065] In the remote sensing inversion method for chlorophyll a concentration provided in this application embodiment, the formula for remote sensing reflectance below the water surface can be shown in the following formula (1):

[0066]

[0067] in, R represents the subsurface reflectance of the aquatic plant area or bottom sediment area. rs Here, ρ is the water surface remote sensing reflectance, K is the underwater irradiance reflectance, and K is the bottom irradiance. d This is the uplink radiation attenuation coefficient. Let be the downward radiation attenuation coefficient of the water column. Z is the downflow radiation attenuation coefficient at the bottom of the water. B This refers to the actual water depth. It should be noted that "below the water surface" in this application refers to exactly below the water surface (0...). - ).

[0068] S103: Based on the underwater optical deep-water remote sensing reflectance of the aquatic plant area and the bottom sediment area, replace the underwater optical deep-water remote sensing reflectance of the aquatic plant area with the underwater optical deep-water remote sensing reflectance of the bottom sediment area, and then determine the equivalent water depth information using the underwater remote sensing reflectance formula.

[0069] In areas with aquatic plants, the optical deep-water remote sensing reflectance is affected not only by the optical properties of the water body, but also by the water depth (Z). B The interference from absorption and scattering by aquatic plants at different heights (h) is also considered. In contrast, the optical deep-water remote sensing reflectance in the bottom sediment area is more stable, mainly reflecting a certain water depth (Z). B Under these conditions, the optical interaction between the water body and the bottom sediment is considered. Furthermore, the water depth in the aquatic plant area and the adjacent bottom sediment area is similar or even the same. Therefore, it is necessary to replace the optical deep-water remote sensing reflectance of the aquatic plant area with that of the nearest bottom sediment area to eliminate the interference of aquatic plants on the optical deep-water remote sensing reflectance, thereby enabling more accurate water depth calculations. It should be noted that the adjacent bottom sediment area here refers to a bottom sediment area that is spatially close to the aquatic plant area (e.g., a bottom sediment area where the center point of the aquatic plant area is less than a distance threshold from the center point of the bottom sediment area is defined as an adjacent bottom sediment area) and has the same water depth and similar optical characteristics of water components (e.g., a bottom sediment area with stable spectral characteristics and consistent optical conditions with the aquatic plant area is defined as an adjacent bottom sediment area).

[0070] Subsequently, using the formula for underwater remote sensing reflectance shown in formula (1), the equivalent water depth information Z' corresponding to the optical deep-water remote sensing reflectance of the aquatic plant area (which has been replaced with the optical deep-water remote sensing reflectance of the adjacent bottom sediment area) is obtained by inversion. B It is understandable that the equivalent water depth information Z' B =Z B -h, where h represents the height of the aquatic plants.

[0071] S104: Based on the uplink and downlink radiation attenuation coefficients and equivalent water depth information of the red, green and blue bands, the underwater remote sensing reflectance of the red, green and blue bands after removing the bottom effect is determined by the formula of underwater remote sensing reflectance.

[0072] In the remote sensing inversion method for chlorophyll a concentration provided in this application embodiment, the formula for the remote sensing reflectance below the water surface after removing the bottom effect can be shown in the following formula (2):

[0073]

[0074] in, To remove the underwater effect, the remote sensing reflectance below the water surface, where i is any one of the red, green, and blue bands, and R... rs,i Let ρ(i) be the water surface remote sensing reflectance, and K be the underwater irradiance reflectance.d,i This is the downlink radiation attenuation coefficient. Let be the upward radiation attenuation coefficient of the water column. Z' is the upward radiation attenuation coefficient at the bottom of the water. B This is equivalent water depth information.

[0075] Understandably, the underwater remote sensing reflectance obtained by removing the influence of the bottom effect can more accurately reflect the optical properties of water bodies, more accurately invert chlorophyll a concentration, and thus more accurately assess the health status of various water bodies such as lakes, wetlands, and rivers.

[0076] S105: Determine the surface remote sensing reflectance of the red, green, and blue bands after removing the underwater effect based on the underwater remote sensing reflectance of the red, green, and blue bands.

[0077] In the remote sensing inversion method for chlorophyll a concentration provided in this application embodiment, the remote sensing reflectance above the water surface in the red, green, and blue bands (after removing the bottom effect) can be obtained by the following formula (3):

[0078]

[0079] in, To remove the underwater underwater effect, the reflectance of the water surface remote sensing is denoted by i, where i is any one of the red, green, or blue bands. To remove the underwater effect, the reflectance of the remote sensing below the water surface.

[0080] Understandably, by converting the underwater remote sensing reflectance to the above-water remote sensing reflectance after removing the bottom effect, and making direct comparison of remote sensing images, chlorophyll a concentration can be retrieved more accurately, thereby more accurately assessing the health status of various water bodies such as lakes, wetlands, and rivers.

[0081] S106: Determine the chlorophyll a concentration based on the water surface remote sensing reflectance in the red, green and blue bands after removing the underwater effect.

[0082] In one specific implementation, a bio-optical property model can be used to simulate water spectra in the red, green, and blue bands under different water quality parameters (including chlorophyll a concentration), resulting in a spectral library containing the expected water surface remote sensing reflectance at different chlorophyll a concentrations. Subsequently, the actual spectra corresponding to the water surface remote sensing reflectance in the red, green, and blue bands after removing the bottom effect are compared with the simulated spectra in the spectral library. Specifically, the Euclidean distance between the actual spectrum corresponding to the water surface remote sensing reflectance in the red, green, and blue bands after removing the bottom effect and the simulated spectra in the spectral library can be calculated, and the simulated spectrum with the smallest Euclidean distance is determined as the simulated spectrum closest to the actual observed spectrum. Then, based on the chlorophyll a concentration corresponding to this simulated spectrum, the actual chlorophyll a concentration is determined.

[0083] Therefore, this application can accurately retrieve chlorophyll a concentration without being affected by the bottom effect. This not only improves the accuracy of chlorophyll a concentration retrieval but also makes the assessment of eutrophication levels in water bodies more accurate and reliable.

[0084] In practical applications, using the remote sensing inversion method for chlorophyll a concentration provided in this application, taking Taihu Lake as an example, the remote sensing inversion of chlorophyll a concentration of phytoplankton in the optically shallow water area of ​​Taihu Lake was performed, and compared with traditional chlorophyll a inversion algorithms. The reason for using Taihu Lake as an example is that Taihu Lake is a typical water body with complex optical characteristics, consisting of a highly turbid optically deep water area in the northwest and a clear optically shallow water area in the east with abundant underwater aquatic plants. Due to the significant influence of underwater aquatic plants on water-leaving radiation in the optically shallow water area, traditional chlorophyll a concentration inversion algorithms will inevitably overestimate the chlorophyll a concentration of phytoplankton in the eastern part of Taihu Lake. See also... Figure 2 This figure is a schematic diagram comparing the chlorophyll a concentration inversion accuracy of a conventional method and the method of this application, as provided in an embodiment of this application. See also... Figure 3 This figure is a schematic diagram illustrating the calculation of chlorophyll a concentration distribution and error distribution using a conventional method and the method of this application, as provided in an embodiment of this application. Figure 2 As shown in (b), the root mean square error (RMSE) of chlorophyll a concentration calculated using the traditional inversion algorithm is 45.61 μg / L, and the mean absolute percentage error (MAPE) is 245.12%. Figure 2As shown in (a) of this application, the RMSE of chlorophyll a concentration calculated using the remote sensing inversion method for chlorophyll a concentration proposed in this application is 8.69 μg / L, and the MAPE is 19.58%. Therefore, the remote sensing inversion method for chlorophyll a concentration proposed in this application can effectively remove the contribution of underwater aquatic plants to water-free radiation in the shallow optical water area of ​​East Taihu Lake, greatly reducing the inversion error MAPE of chlorophyll a concentration in East Taihu Lake, which is far superior to the error of traditional inversion algorithms.

[0085] In summary, this application provides a remote sensing inversion method for chlorophyll a concentration. By removing the influence of bottom effects (such as aquatic plants and bottom sediments), this application not only significantly improves the accuracy of chlorophyll a concentration inversion in optically shallow water areas, but also enables more reliable eutrophication assessment based on more accurate chlorophyll a concentration data. Furthermore, because this application improves the problem of overestimation of chlorophyll a concentration caused by the failure to eliminate bottom effects in traditional algorithms, it provides more accurate data support for subsequent water quality monitoring and management. Moreover, this application is applicable to various complex aquatic environments, including waters with abundant aquatic vegetation and sediment distribution, greatly enhancing the effectiveness and applicability of water quality monitoring and management.

[0086] See Figure 4 The figure is a schematic diagram of a remote sensing inversion device for chlorophyll a concentration provided in an embodiment of this application. The remote sensing inversion device 400 for chlorophyll a concentration includes: an information acquisition module 401, a first determination module 402, a second determination module 403, a third determination module 404, a fourth determination module 405, a fifth determination module 406, and a sixth determination module 407.

[0087] The information acquisition module is used to acquire information on the suspended solids concentration and actual water depth of the target water body;

[0088] The first determining module 401 is used to determine the uplink and downlink radiation attenuation coefficients of the red, green and blue bands respectively based on the suspended matter concentration information and the uplink and downlink radiation attenuation coefficient models of the red, green and blue bands.

[0089] The second determining module 402 is used to determine the underwater optical deep-water remote sensing reflectance of the aquatic plant area and bottom sediment area of ​​the target water body based on the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information, using the formula for underwater remote sensing reflectance.

[0090] The third determining module 403 is used to replace the optical deep-water remote sensing reflectance below the water surface of the aquatic plant area with the optical deep-water remote sensing reflectance below the water surface of the bottom sediment area based on the optical deep-water remote sensing reflectance below the water surface of the aquatic plant area and the bottom sediment area, and then determine the equivalent water depth information through the formula of the remote sensing reflectance below the water surface.

[0091] The fourth determining module 404 is used to determine the underwater remote sensing reflectance of the red, green and blue bands after removing the bottom effect, based on the uplink and downlink radiation attenuation coefficients and equivalent water depth information of the red, green and blue bands, and through the formula of underwater remote sensing reflectance.

[0092] The fifth determining module 405 is used to determine the surface remote sensing reflectance of the red, green and blue bands after removing the bottom effect based on the underwater remote sensing reflectance of the red, green and blue bands.

[0093] The sixth determining module 406 is used to determine the chlorophyll a concentration based on the water remote sensing reflectance of the red, green and blue bands after removing the bottom effect.

[0094] In some specific implementation methods, the formula for the remote sensing reflectance below the water surface is shown in formula (4):

[0095]

[0096] in, R represents the subsurface reflectance of the aquatic plant area or bottom sediment area. rs Here, ρ is the water surface remote sensing reflectance, K is the underwater irradiance reflectance, and K is the bottom irradiance. d This is the downlink radiation attenuation coefficient. Let be the upward radiation attenuation coefficient of the water column. Z is the upward radiation attenuation coefficient at the bottom of the water. B This is the actual water depth information.

[0097] In some specific implementations, the third determining module 404 is specifically used to: replace the underwater optical deep-water remote sensing reflectance of the aquatic plant area with the underwater optical deep-water remote sensing reflectance of the target sediment area, wherein the target sediment area is a sediment area whose center point is less than the center point of the aquatic plant area and whose water optical conditions are consistent with those of the aquatic plant area.

[0098] In some specific implementations, the formula for determining the surface remote sensing reflectance of the red, green, and blue bands after removing the underwater effect is as follows: Formula (5):

[0099]

[0100] in, To remove the underwater underwater effect, the reflectance of the water surface remote sensing is denoted by i, where i is any one of the red, green, or blue bands. To remove the underwater effect, the reflectance of the remote sensing below the water surface.

[0101] Optionally, the sixth determining module 407 is specifically used to: determine a simulated spectrum from a spectral library based on the actual spectrum corresponding to the water remote sensing reflectance in the red, green and blue bands after removing the bottom effect, wherein the simulated spectrum is the spectrum with the smallest Euclidean distance from the actual spectrum; and determine the chlorophyll a concentration corresponding to the simulated spectrum based on the spectral library.

[0102] In summary, this application provides a remote sensing inversion device for chlorophyll a concentration. By removing the influence of bottom effects (such as aquatic plants and bottom sediments), this application not only significantly improves the accuracy of chlorophyll a concentration inversion in optically shallow water areas, but also enables more reliable eutrophication assessment based on more accurate chlorophyll a concentration data. Furthermore, because this application improves upon the overestimation of chlorophyll a concentration caused by the failure to eliminate bottom effects in traditional algorithms, it provides more accurate data support for subsequent water quality monitoring and management. Moreover, this application is applicable to various complex aquatic environments, including waters with abundant aquatic vegetation and sediment distribution, greatly enhancing the effectiveness and applicability of water quality monitoring and management.

[0103] It should be noted that the various embodiments in this specification are described in a progressive manner, and the same or similar parts between the various embodiments can be referred to mutually. Each embodiment focuses on describing the differences from other embodiments. In particular, for the device and system embodiments, since they are basically similar to the method embodiments, the description is relatively simple, and the relevant parts can be referred to the description of the method embodiments. The device and system embodiments described above are merely illustrative. The units described as separate components may or may not be physically separate, and the components indicated as units may or may not be physical units, that is, they may be located in one place or distributed across multiple network units. Some or all of the modules can be selected to achieve the purpose of the solution in this embodiment according to actual needs. Those skilled in the art can understand and implement this without creative effort.

[0104] The above description is merely one specific embodiment of this application, but the scope of protection of this application is not limited thereto. Any variations or substitutions that can be easily conceived by those skilled in the art within the technical scope disclosed in this application should be included within the scope of protection of this application. Therefore, the scope of protection of this application should be determined by the scope of the claims.

Claims

1. A remote sensing inversion method for chlorophyll a concentration, characterized in that, The method includes: Acquire information on suspended solids concentration and actual water depth of the target water body; Based on the suspended matter concentration information, the uplink and downlink radiation attenuation coefficients of the red, green and blue bands are determined respectively using the uplink and downlink radiation attenuation coefficient models of the red, green and blue bands. Based on the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information, the underwater optical deep-water remote sensing reflectance of the aquatic plant area and bottom sediment area of ​​the target water body is determined by the formula of underwater remote sensing reflectance. Based on the underwater optical deep-water remote sensing reflectance of the aquatic plant area and the bottom sediment area, the underwater optical deep-water remote sensing reflectance of the aquatic plant area is replaced with the underwater optical deep-water remote sensing reflectance of the bottom sediment area, and then the equivalent water depth information is determined by the formula for underwater remote sensing reflectance. Based on the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the equivalent water depth information, the underwater remote sensing reflectance of the red, green and blue bands after removing the bottom effect is determined by the formula for underwater remote sensing reflectance. Based on the underwater remote sensing reflectance of the red, green, and blue bands after removing the underwater effect, determine the above-water remote sensing reflectance of the red, green, and blue bands after removing the underwater effect. The concentration of chlorophyll a was determined based on the water remote sensing reflectance in the red, green, and blue bands after removing the underwater effect.

2. The method according to claim 1, characterized in that, The formula for the remote sensing reflectance below the water surface is as follows: in, R represents the subsurface reflectance of the aquatic plant area or bottom sediment area. rs Here, ρ is the water surface remote sensing reflectance, K is the water bottom irradiance reflectance, and K is the water surface remote sensing reflectance. d This is the downlink radiation attenuation coefficient. Let be the upward radiation attenuation coefficient of the water column. Z is the upward radiation attenuation coefficient at the bottom of the water. B This is the actual water depth information.

3. The method according to claim 1, characterized in that, The replacement of the underwater optical deep-water remote sensing reflectance of the aquatic plant area with the underwater optical deep-water remote sensing reflectance of the bottom sediment area includes: The underwater optical deep-water remote sensing reflectance of the aquatic plant area is replaced with the underwater optical deep-water remote sensing reflectance of the target sediment area. The target sediment area is a sediment area whose center point is less than a distance threshold from the center point of the aquatic plant area and whose water optical conditions are consistent with those of the aquatic plant area.

4. The method according to claim 1, characterized in that, The formula for determining the surface remote sensing reflectance of the red, green, and blue bands (after removing the underwater effect) based on the underwater remote sensing reflectance is as follows: in, To remove the underwater underwater effect, the reflectance of the water surface remote sensing is denoted by i, where i is any one of the red, green, or blue bands. To remove the underwater effect, the reflectance of the remote sensing below the water surface.

5. The method according to claim 1, characterized in that, The determination of chlorophyll a concentration based on the waterborne remote sensing reflectance in the red, green, and blue bands after removing the underwater effect includes: Based on the actual spectrum corresponding to the water remote sensing reflectance in the red, green and blue bands after removing the bottom effect, a simulated spectrum is determined from the spectral library, wherein the simulated spectrum is the spectrum with the smallest Euclidean distance from the actual spectrum; Based on the spectral library, determine the chlorophyll a concentration corresponding to the simulated spectrum.

6. A remote sensing inversion device for chlorophyll a concentration, characterized in that, The device includes: an information acquisition module, a first determination module, a second determination module, a third determination module, a fourth determination module, a fifth determination module, and a sixth determination module; The information acquisition module is used to acquire suspended solids concentration information and actual water depth information of the target water body; The first determining module is used to determine the uplink and downlink radiation attenuation coefficients of the red, green, and blue bands respectively based on the suspended matter concentration information and the uplink and downlink radiation attenuation coefficient models of the red, green, and blue bands. The second determining module is used to determine the underwater optical deep-water remote sensing reflectance of the aquatic plant area and bottom sediment area of ​​the target water body based on the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information, using the underwater remote sensing reflectance formula. The third determining module is used to replace the underwater optical deep-water remote sensing reflectance of the aquatic plant area with the underwater optical deep-water remote sensing reflectance of the bottom sediment area based on the underwater optical deep-water remote sensing reflectance of the aquatic plant area and the bottom sediment area, and then determine the equivalent water depth information through the underwater remote sensing reflectance formula. The fourth determining module is used to determine the underwater remote sensing reflectance of the red, green and blue bands after removing the bottom effect, based on the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the equivalent water depth information, using the underwater remote sensing reflectance formula. The fifth determining module is used to determine the surface remote sensing reflectance of the red, green and blue bands after removing the bottom effect based on the underwater remote sensing reflectance of the red, green and blue bands after removing the bottom effect. The sixth determining module is used to determine the chlorophyll a concentration based on the water remote sensing reflectance of the red, green and blue bands after removing the bottom effect.

7. The apparatus according to claim 6, characterized in that, The formula for the remote sensing reflectance below the water surface is as follows: in, R represents the subsurface reflectance of the aquatic plant area or bottom sediment area. rs Here, ρ is the water surface remote sensing reflectance, K is the water bottom irradiance reflectance, and K is the water surface remote sensing reflectance. d This is the downlink radiation attenuation coefficient. Let be the upward radiation attenuation coefficient of the water column. Z is the upward radiation attenuation coefficient at the bottom of the water. B This is the actual water depth information.

8. The apparatus according to claim 6, characterized in that, The third determining module is specifically used to: replace the underwater optical deep-water remote sensing reflectance of the aquatic plant area with the underwater optical deep-water remote sensing reflectance of the target sediment area, wherein the target sediment area is a sediment area whose center point is less than a distance threshold from the center point of the aquatic plant area, and whose water optical conditions are consistent with those of the aquatic plant area.

9. The apparatus according to claim 6, characterized in that, The formula for determining the surface remote sensing reflectance of the red, green, and blue bands (after removing the underwater effect) based on the underwater remote sensing reflectance is as follows: in, To remove the underwater underwater effect, the reflectance of the water surface remote sensing is denoted by i, where i is any one of the red, green, or blue bands. To remove the underwater effect, the reflectance of the remote sensing below the water surface.

10. The apparatus according to claim 6, characterized in that, The sixth determining module is specifically used to: determine a simulated spectrum from a spectral library based on the actual spectrum corresponding to the water remote sensing reflectance in the red, green and blue bands after removing the bottom effect, wherein the simulated spectrum is the spectrum with the smallest Euclidean distance from the actual spectrum; and determine the chlorophyll a concentration corresponding to the simulated spectrum based on the spectral library.

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