Remote sensing inversion method and device for chlorophyll concentration

Abstract

The embodiment of the invention provides a remote sensing inversion method and device for chlorophyll a concentration, and relates to the technical field of remote sensing. According to the method, the influence of underwater effects (such as aquatic plants and bottom sediments) is removed, so that the precision of chlorophyll a concentration inversion in the optical shallow water region is remarkably improved, and more reliable eutrophication evaluation can be carried out based on more accurate chlorophyll a concentration data. Moreover, the method improves the problem that the concentration of chlorophyll a is overestimated due to the fact that the underwater effect is not eliminated in a traditional algorithm, so that more accurate data support can be provided for subsequent water quality detection and management. Furthermore, the method is suitable for various complex water environments including water areas with luxuriant aquatic vegetation and sediment distribution, and the effectiveness and the application range of water quality detection and management work are greatly improved.

Description

Technical Field

[0001] The present application relates to the field of remote sensing technology, and in particular to a remote sensing inversion method and device for chlorophyll a concentration. Background Art

[0002] With the continuous development of industrialization and agriculture, more and more water bodies have been polluted by industrial and agricultural emissions. The accumulation of pollutants makes the water rich in nutrients, promotes the excessive reproduction of phytoplankton, and causes eutrophication of water bodies. This not only seriously affects water quality and damages the ecological environment, but also may threaten human health and social economy.

[0003] In order to deal with the phenomenon of eutrophication of water bodies, relevant technicians have developed remote sensing inversion technology. Remote sensing inversion technology refers to the technology of using remote sensing satellite image data to analyze the concentration of chlorophyll a in water bodies to assess the health of water bodies. Existing remote sensing inversion technology is usually developed for optical deep water areas, where the bottom materials (such as aquatic plants and bottom sediments) can be ignored due to the large water depth.

[0004] However, when performing remote sensing inversion in optically shallow water areas, the bottom matter will have a significant impact on the optical properties of the water body, which can easily lead to an overestimation of chlorophyll a concentration, which in turn leads to incorrect eutrophication assessments and affects water quality monitoring and management decisions. Therefore, how to achieve more accurate chlorophyll a concentration inversion has become a technical problem that needs to be solved urgently. Summary of the invention

[0005] Based on the above problems, the present application provides a remote sensing inversion method and device for chlorophyll a concentration, which can achieve more accurate chlorophyll a concentration inversion.

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

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

[0008] Obtain suspended matter concentration information and actual water depth information of the target water body;

[0009] According to the suspended matter concentration information, the uplink and downlink radiation attenuation coefficients of the red, green and blue bands are determined respectively through the uplink and downlink radiation attenuation coefficient models of the red, green and blue bands;

[0010] According to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information, the optical deep-water remote sensing reflectivity below the water surface of the aquatic plant area and the bottom mud area of ​​the target water body is determined by the remote sensing reflectivity formula below the water surface;

[0011] According to the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area and the bottom mud area, the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area is replaced by the optical deep water remote sensing reflectivity below the water surface of the bottom mud area, and then the equivalent water depth information is determined by the formula of the remote sensing reflectivity below the water surface;

[0012] According to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the equivalent water depth information, the remote sensing reflectivity below the water surface of the red, green and blue bands with the bottom effect removed is determined by the remote sensing reflectivity formula below the water surface;

[0013] Determine the above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect according to the sub-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect;

[0014] The chlorophyll a concentration is determined based on the above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect.

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

[0016]

[0017] in, is the remote sensing reflectivity below the water surface in the aquatic plant area or the bottom mud area, R rs is the water remote sensing reflectivity, ρ is the irradiance reflectivity of the bottom, K d is the uplink radiation attenuation coefficient, is the downward radiation attenuation coefficient of the water column, is the downward radiation attenuation coefficient of the water bottom, Z B The actual water depth information.

[0018] Optionally, replacing the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area with the optical deep water remote sensing reflectivity below the water surface of the bottom mud area comprises:

[0019] The optical deep-water remote sensing reflectivity below the water surface of the aquatic plant area is replaced by the optical deep-water remote sensing reflectivity below the water surface of the target bottom mud area, wherein the target bottom mud area is a bottom mud 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 above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect based on the sub-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect is as follows:

[0021]

[0022] in, The reflectivity of water remote sensing is obtained by removing the bottom effect, i is any one of the red, green and blue bands, To remove the bottom effect of the water surface remote sensing reflectivity.

[0023] Optionally, determining the chlorophyll a concentration according to the water remote sensing reflectance of the red, green and blue bands after removing the bottom effect includes:

[0024] Determine a simulated spectrum from a spectrum library according to an actual spectrum corresponding to the water remote sensing reflectance of the red, green and blue bands after removing the bottom effect, wherein the simulated spectrum is a spectrum with the smallest Euclidean distance from the actual spectrum;

[0025] The chlorophyll a concentration corresponding to the simulated spectrum is determined according to the spectrum library.

[0026] In a second aspect, the present 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 obtain the suspended matter concentration information and actual water depth information of the target water body;

[0028] The first determination module is used to determine the uplink and downlink radiation attenuation coefficients of the red, green and blue bands respectively according to the suspended matter concentration information and through the uplink and downlink radiation attenuation coefficient models of the red, green and blue bands;

[0029] The second determination module is used to determine the optical deep-water remote sensing reflectivity below the water surface of the aquatic plant area and the bottom mud area of ​​the target water body through the remote sensing reflectivity formula below the water surface according to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information;

[0030] The third determination module is used to replace the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area with the optical deep water remote sensing reflectivity below the water surface of the bottom mud area according to the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area and the bottom mud area, and then determine the equivalent water depth information by the remote sensing reflectivity formula below the water surface;

[0031] The fourth determination module is used to determine the subsurface remote sensing reflectivity of the red, green and blue bands with the bottom effect removed according to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the equivalent water depth information and through the subsurface remote sensing reflectivity formula;

[0032] The fifth determination module is used to determine the above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect of the water according to the below-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect of the water;

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

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

[0035]

[0036] in, is the remote sensing reflectivity below the water surface in the aquatic plant area or the bottom mud area, R rs is the water remote sensing reflectivity, ρ is the irradiance reflectivity of the bottom, K d is the uplink radiation attenuation coefficient, is the downward radiation attenuation coefficient of the water column, is the downward radiation attenuation coefficient of the water bottom, Z B The actual water depth information.

[0037] Optionally, the third determination module is specifically used to replace the optical deep-water remote sensing reflectivity below the water surface of the aquatic plant area with the optical deep-water remote sensing reflectivity below the water surface of a 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 above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect based on the sub-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect is as follows:

[0039]

[0040] in, The reflectivity of water remote sensing is obtained by removing the bottom effect, i is any one of the red, green and blue bands, To remove the bottom effect of the water surface remote sensing reflectivity.

[0041] Optionally, the sixth determination module is specifically used to: determine a simulated spectrum from a spectral library based on an actual spectrum corresponding to the water remote sensing reflectivity of the red, green and blue bands with the bottom effect removed, wherein the simulated spectrum is a 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] The embodiment of the present application provides a remote sensing inversion method and device for chlorophyll a concentration. By removing the influence of bottom effects (such as aquatic plants and bottom sediments), the present application not only significantly improves the accuracy of chlorophyll a concentration inversion in optical shallow water areas, but also can perform more reliable eutrophication evaluation based on more accurate chlorophyll a concentration data. In addition, because the present application improves the problem of overestimation of chlorophyll a concentration caused by the failure to eliminate bottom effects in traditional algorithms, it can provide more accurate data support for subsequent water quality testing and management. Furthermore, the present application is applicable to a variety of complex water environments, including waters with lush aquatic vegetation and sediment distribution, which greatly improves the effectiveness and scope of water quality testing and management. BRIEF DESCRIPTION OF THE DRAWINGS

[0044] In order to more clearly illustrate the embodiments of the present application or the technical solutions in the prior art, the drawings required for use in the embodiments or the description of the prior art will be briefly introduced below. Obviously, the drawings described below are only some embodiments of the present application. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying creative labor.

[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 of the chlorophyll a concentration inversion accuracy of a traditional method and the method of the present application provided in the embodiments of the present application;

[0047] Figure 3 A schematic diagram of calculating chlorophyll a concentration distribution and error distribution using a conventional method and a method of the present application provided in an embodiment of the present application;

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

[0049] As described above, in order to deal with the phenomenon of eutrophication of water bodies, relevant technicians have developed remote sensing inversion technology. Remote sensing inversion technology refers to the technology of using remote sensing satellite image data to analyze the concentration of chlorophyll a in water bodies to assess the health of water bodies. Existing remote sensing inversion technology is usually developed for optical deep water areas, where the bottom materials (such as aquatic plants and bottom sediments) can be ignored due to the large water depth.

[0050] However, when performing remote sensing inversion in optically shallow water areas, the bottom matter will have a significant impact on the optical properties of the water body, which can easily lead to an overestimation of chlorophyll a concentration, which in turn leads to incorrect eutrophication assessments and affects water quality monitoring and management decisions. Therefore, how to achieve more accurate chlorophyll a concentration inversion has become a technical problem that needs to be solved urgently.

[0051] After research, the inventors proposed a remote sensing inversion method and device for chlorophyll a concentration, which includes: obtaining suspended matter concentration information and actual water depth information of the target water body; according to the suspended matter concentration information, respectively determining the uplink and downlink radiation attenuation coefficients of the red, green and blue bands through the uplink and downlink radiation attenuation coefficient models of the red, green and blue bands; according to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information, determining the optical deep water remote sensing reflectivity of the water grass area and the bottom mud area of ​​the target water body through the remote sensing reflectivity formula below the water surface; according to the optical deep water remote sensing reflectivity of the water grass area and the bottom mud area, the water grass area is inverted into the bottom mud area. The optical deep water remote sensing reflectivity below the water surface in the grass area is replaced by the optical deep water remote sensing reflectivity below the water surface in the bottom mud area, and then the equivalent water depth information is determined by the remote sensing reflectivity formula below the water surface; according to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the equivalent water depth information, the remote sensing reflectivity formula below the water surface is used to determine the remote sensing reflectivity below the water surface of the red, green and blue bands after removing the bottom effect; according to the remote sensing reflectivity below the water surface of the red, green and blue bands after removing the bottom effect, the above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect is determined; according to the above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect, the chlorophyll a concentration is determined. It can be seen from this that the present application not only significantly improves the accuracy of chlorophyll a concentration inversion in optical shallow water areas by removing the influence of bottom effects (such as water grass and bottom sediments), but also can make more reliable eutrophication evaluation based on more accurate chlorophyll a concentration data. Moreover, because the present application improves the problem of overestimation of chlorophyll a concentration caused by failure to eliminate the bottom effect in the traditional algorithm, it can provide more accurate data support for subsequent water quality detection and management. Furthermore, the present application is applicable to a variety of complex water environments, including waters with lush aquatic vegetation and sediment distribution, greatly improving the effectiveness and scope of water quality detection and management.

[0052] In order to enable those skilled in the art to better understand the solution of the present application, the technical solution in the embodiments of the present application will be clearly and completely described below in conjunction with the drawings in the embodiments of the present application. Obviously, the described embodiments are only part of the embodiments of the present application, not all of the embodiments. Based on the embodiments in the present application, all other embodiments obtained by ordinary technicians in this field without creative work are within the scope of protection of this application.

[0053] See also Figure 1, which is a flow chart of a remote sensing inversion method for chlorophyll a concentration provided in an embodiment of the present application. The method comprises:

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

[0055] Total suspended solids (TSS) refers to water particles larger than 2 microns in the water, including sediments (such as silt particles), plankton (such as algae), organic debris, etc. Suspended solids can have a significant impact on the optical properties of water.

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

[0057] In the water optical environment, the propagation of light in water is affected by absorption and scattering, which is manifested as the radiation intensity attenuating exponentially with distance. The attenuation direction can be divided into upward radiation attenuation and downward radiation attenuation. Upward radiation attenuation refers to the attenuation of the radiation intensity of light propagating from the depth of the water body to the water surface, and downward radiation attenuation refers to the attenuation of the radiation intensity of light penetrating downward from the water surface. Among them, upward radiation attenuation includes the upward radiation attenuation of the water column (i.e., the attenuation of the absorption and scattering of light by suspended matter in the water body) and the upward radiation attenuation of the water bottom (i.e., the attenuation of the light scattered upward by the water bottom when it reaches the water bottom).

[0058] In the remote sensing inversion method of chlorophyll a concentration provided in the embodiment of the present application, the uplink and downlink radiation attenuation coefficients of the red, green and blue bands can be determined respectively according to the suspended matter concentration information through the uplink and downlink radiation attenuation coefficient models of the red, green and blue bands. Among them, the uplink and downlink radiation attenuation coefficient models of the three bands of red, green and blue can be shown in the following Table 1:

[0059] Table 1

[0060]

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

[0062] S102: According to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information, the remote sensing reflectivity below the water surface of the aquatic plant area and the bottom mud area is determined by the remote sensing reflectivity formula below the water surface.

[0063] About the actual water depth information: In some specific implementations, the actual water depth information can be obtained through remote sensing technology. Specifically, the blue band reflectivity and the red band reflectivity can be obtained through remote sensing technology, and the actual water depth information can be calculated based on the blue band reflectivity and the red band reflectivity. In another specific implementation, the actual water depth information can also be obtained through acoustic detection technology. Specifically, the actual water depth information can be inverted through the time difference of the sound wave signal propagating in the water body. In another specific implementation, the actual water depth information can also be obtained through field measurements (such as a detection rod or buoy). This application does not limit the specific method for obtaining the actual water depth information.

[0064] Regarding aquatic plants areas and bottom mud areas: In some specific implementations, aquatic plants areas and bottom mud areas can be distinguished based on the optical reflection characteristics of different areas in the remote sensing image. Specifically, the reflection spectrum of aquatic plants usually has obvious chlorophyll absorption peaks (low reflectivity in the blue band and red band) and reflection peaks (high reflectivity in the green band and near-infrared band), while the reflectivity of the bottom mud is usually relatively flat. Therefore, by analyzing the spectral characteristics of the red, green, blue and near-infrared bands, a classification model can be constructed to distinguish between aquatic plants areas and bottom mud areas. In another specific implementation, aquatic plants areas and bottom mud areas can also be distinguished by field measurements (such as diving surveys or sampling analysis). This application does not limit the specific method for distinguishing between aquatic plants areas and bottom mud areas.

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

[0066]

[0067] in, is the remote sensing reflectivity below the water surface in the aquatic plant area or the bottom mud area, R rs is the water remote sensing reflectivity, ρ is the irradiance reflectivity of the bottom, K d is the uplink radiation attenuation coefficient, is the downward radiation attenuation coefficient of the water column, is the downward radiation attenuation coefficient of the water bottom, Z B It should be noted that “below the water surface” in this application refers to just below the water surface (0 - ).

[0068] S103: Based on the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area and the bottom mud area, the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area is replaced by the optical deep water remote sensing reflectivity below the water surface of the bottom mud area, and then the equivalent water depth information is determined by the remote sensing reflectivity formula below the water surface.

[0069] In the aquatic plant area, the optical deep-water remote sensing reflectivity is not only affected by the optical properties of the water body, but also by the water depth (Z B ) and the interference of absorption and scattering of water plants at different heights (h). In contrast, the optical deep-water remote sensing reflectivity of the bottom mud area is more stable, mainly reflecting the water depth (Z B ) under the optical interaction between the water body and the sediment. Moreover, the water depths of the aquatic plant area and the adjacent sediment area are similar or even the same. Therefore, it is necessary to use the optical deep-water remote sensing reflectivity of the nearest sediment area to replace the optical deep-water remote sensing reflectivity of the aquatic plant area, so as to eliminate the interference of aquatic plants on the optical deep-water remote sensing reflectivity, and then calculate the water depth more accurately. It should be noted that the adjacent sediment area here refers to a sediment area that is spatially close to the aquatic plant area (for example, a sediment area whose center point of the aquatic plant area is less than a distance threshold from the center point of the sediment area is determined as a neighboring sediment area) and has the same water depth and similar water component optical properties (for example, a sediment area with stable spectral characteristics and consistent optical conditions with the aquatic plant area is determined as a neighboring sediment area).

[0070] Then, the remote sensing reflectance formula below the water surface shown in formula (1) is used to invert the equivalent water depth information Z' corresponding to the optical deep water remote sensing reflectance of the aquatic plant area (which has been replaced by the optical deep water remote sensing reflectance of the adjacent bottom mud area). B It can be understood that the equivalent water depth information Z' B =Z B -h, where h is the height of the aquatic plants.

[0071] S104: According to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the equivalent water depth information, the remote sensing reflectivity below the water surface of the red, green and blue bands after removing the bottom effect is determined by the remote sensing reflectivity formula below the water surface.

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

[0073]

[0074] in, is the remote sensing reflectance below the water surface to remove the bottom effect, i is any one of the red, green and blue bands, R rs,i is the remote sensing reflectivity above water, ρ(i) is the irradiance reflectivity of the bottom of water, Kd,i is the downlink radiation attenuation coefficient, is the upward radiation attenuation coefficient of the water column, is the uplink radiation attenuation coefficient of the water bottom, Z' B is the equivalent water depth information.

[0075] It is understandable that the remote sensing reflectivity below the water surface obtained by removing the influence of the bottom effect can more accurately reflect the optical properties of the water body, more accurately invert the chlorophyll a concentration, and thus more accurately evaluate the health status of various water bodies such as lakes, wetlands, and rivers.

[0076] S105: Determine the above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect according to the below-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect.

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

[0078]

[0079] in, The reflectivity of water remote sensing is obtained by removing the bottom effect, i is any one of the red, green and blue bands, To remove the bottom effect of the water surface remote sensing reflectivity.

[0080] It can be understood that by converting the remote sensing reflectance below the water surface that removes the bottom effect into the remote sensing reflectance above the water to facilitate direct comparison of remote sensing images, the chlorophyll a concentration can be inverted 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 remote sensing reflectance of the red, green and blue bands after removing the bottom effect.

[0082] In a specific implementation, the water spectra of the red, green and blue bands under different water quality parameters (including chlorophyll a concentration) can be simulated based on the bio-optical property model to obtain a spectrum library, which contains the expected water remote sensing reflectance under different chlorophyll a concentrations. Subsequently, the actual spectrum corresponding to the water remote sensing reflectance of the red, green and blue bands after removing the bottom effect is compared with the simulated spectrum in the spectrum library. Specifically, the Euclidean distance between the actual spectrum corresponding to the water remote sensing reflectance of the red, green and blue bands after removing the bottom effect and the simulated spectrum in the spectrum 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, the actual chlorophyll a concentration is determined based on the chlorophyll a concentration corresponding to the simulated spectrum.

[0083] Therefore, the present application can invert the chlorophyll a concentration with high precision without being disturbed by the bottom effect. This not only improves the inversion accuracy of the chlorophyll a concentration, but also makes the assessment of the eutrophication level of the water body more accurate and reliable.

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

[0085] In summary, the embodiments of the present application provide a remote sensing inversion method for chlorophyll a concentration. By removing the influence of bottom effects (such as aquatic plants and bottom sediments), the present application not only significantly improves the accuracy of chlorophyll a concentration inversion in optically shallow water areas, but also can perform more reliable eutrophication evaluation based on more accurate chlorophyll a concentration data. Moreover, because the present application improves the problem of overestimation of chlorophyll a concentration caused by the failure to eliminate the bottom effect in traditional algorithms, it can provide more accurate data support for subsequent water quality testing and management. Furthermore, the present application is applicable to a variety of complex water environments, including waters with lush aquatic vegetation and sediment distribution, which greatly improves the effectiveness and scope of water quality testing and management.

[0086] See also Figure 4 , which is a schematic diagram of a chlorophyll a concentration remote sensing inversion device provided in an embodiment of the present application. The chlorophyll a concentration remote sensing inversion device 400 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] An information acquisition module is used to obtain suspended matter concentration information and actual water depth information of the target water body;

[0088] The first determination module 401 is used to determine the uplink and downlink radiation attenuation coefficients of the red, green and blue bands respectively according to the suspended matter concentration information and through the uplink and downlink radiation attenuation coefficient models of the red, green and blue bands;

[0089] The second determination module 402 is used to determine the optical deep water remote sensing reflectivity of the aquatic plant area and the bottom mud area of ​​the target water body through the remote sensing reflectivity formula below the water surface according to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information;

[0090] The third determination module 403 is used to replace the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area with the optical deep water remote sensing reflectivity below the water surface of the bottom mud area according to the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area and the bottom mud area, and then determine the equivalent water depth information by the remote sensing reflectivity formula below the water surface;

[0091] The fourth determination module 404 is used to determine the subsurface remote sensing reflectivity of the red, green and blue bands after removing the bottom effect according to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the equivalent water depth information and the subsurface remote sensing reflectivity formula;

[0092] A fifth determination module 405 is used to determine the above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect according to the below-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect;

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

[0094] In some specific implementations, the remote sensing reflectivity formula below the water surface is as shown in the following formula (4):

[0095]

[0096] in, is the remote sensing reflectivity below the water surface in the aquatic plant area or the bottom mud area, R rs is the water remote sensing reflectivity, ρ is the irradiance reflectivity of the bottom, K d is the downlink radiation attenuation coefficient, is the upward radiation attenuation coefficient of the water column, is the uplink radiation attenuation coefficient of the water bottom, Z B The actual water depth information.

[0097] In some specific implementations, the third determination module 404 is specifically used to replace the optical deep-water remote sensing reflectivity below the water surface of the aquatic plant area with the optical deep-water remote sensing reflectivity below the water surface 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.

[0098] In some specific implementations, based on the subsurface remote sensing reflectivity of the red, green and blue bands without the bottom effect, the formula for determining the above-water remote sensing reflectivity of the red, green and blue bands without the bottom effect is as shown in the following formula (5):

[0099]

[0100] in, The reflectivity of water remote sensing is obtained by removing the bottom effect, i is any one of the red, green and blue bands, To remove the bottom effect of the water surface remote sensing reflectivity.

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

[0102] In summary, the embodiments of the present application provide a remote sensing inversion device for chlorophyll a concentration. By removing the influence of bottom effects (such as aquatic plants and bottom sediments), the present application not only significantly improves the accuracy of chlorophyll a concentration inversion in optically shallow water areas, but also can perform more reliable eutrophication evaluation based on more accurate chlorophyll a concentration data. Moreover, because the present application improves the problem of overestimation of chlorophyll a concentration caused by the failure to eliminate the bottom effect in traditional algorithms, it can provide more accurate data support for subsequent water quality testing and management. Furthermore, the present application is applicable to a variety of complex water environments, including waters with lush aquatic vegetation and sediment distribution, which greatly improves the effectiveness and scope of water quality testing and management.

[0103] It should be noted that each embodiment in this specification is described in a progressive manner, and the same or similar parts between the embodiments can be referred to each other, and each embodiment focuses on 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 partial description of the method embodiments. The device and system embodiments described above are merely schematic, wherein the units described as separate components may or may not be physically separated, and the components indicated as units may or may not be physical units, that is, they may be located in one place, or they may be distributed on multiple network units. Some or all of the modules may be selected according to actual needs to achieve the purpose of the scheme of this embodiment. Ordinary technicians in this field can understand and implement it without paying creative labor.

[0104] The above is only a specific implementation of the present application, but the protection scope of the present application is not limited thereto. Any changes or substitutions that can be easily thought of by a person skilled in the art within the technical scope disclosed in the present application should be included in the protection scope of the present application. Therefore, the protection scope of the present application should be based on the protection scope of the claims.

Claims

1. A remote sensing inversion method for chlorophyll a concentration, characterized in that: The method comprises: Obtain suspended matter concentration information and actual water depth information of the target water body; According to the suspended matter concentration information, the uplink and downlink radiation attenuation coefficients of the red, green and blue bands are determined respectively through the uplink and downlink radiation attenuation coefficient models of the red, green and blue bands; According to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information, the optical deep-water remote sensing reflectivity below the water surface of the aquatic plant area and the bottom mud area of ​​the target water body is determined by the remote sensing reflectivity formula below the water surface; According to the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area and the bottom mud area, the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area is replaced by the optical deep water remote sensing reflectivity below the water surface of the bottom mud area, and then the equivalent water depth information is determined by the formula of the remote sensing reflectivity below the water surface; According to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the equivalent water depth information, the remote sensing reflectivity below the water surface of the red, green and blue bands with the bottom effect removed is determined by the remote sensing reflectivity formula below the water surface; Determine the above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect according to the sub-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect; The chlorophyll a concentration is determined based on the above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect.

2. The method according to claim 1, characterized in that: The formula for remote sensing reflectivity below the water surface is as follows: in, is the remote sensing reflectivity below the water surface in the aquatic plant area or the bottom mud area, R rs is the water remote sensing reflectivity, ρ is the irradiance reflectivity of the bottom, K d is the downlink radiation attenuation coefficient, is the upward radiation attenuation coefficient of the water column, is the uplink radiation attenuation coefficient of the water bottom, Z B The actual water depth information.

3. The method according to claim 1, characterized in that The step of replacing the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area with the optical deep water remote sensing reflectivity below the water surface of the bottom mud area comprises: The optical deep-water remote sensing reflectivity below the water surface of the aquatic plant area is replaced by the optical deep-water remote sensing reflectivity below the water surface of the target bottom mud area, wherein the target bottom mud area is a bottom mud 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 above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect based on the subsurface remote sensing reflectivity of the red, green and blue bands after removing the bottom effect is as follows: in, The reflectivity of water remote sensing is obtained by removing the bottom effect, i is any one of the red, green and blue bands, To remove the bottom effect of the water surface remote sensing reflectivity.

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

6. A remote sensing inversion device for chlorophyll a concentration, characterized in that: The device comprises: 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 obtain the suspended matter concentration information and actual water depth information of the target water body; The first determination module is used to determine the uplink and downlink radiation attenuation coefficients of the red, green and blue bands respectively according to the suspended matter concentration information and through the uplink and downlink radiation attenuation coefficient models of the red, green and blue bands; The second determination module is used to determine the optical deep-water remote sensing reflectivity below the water surface of the aquatic plant area and the bottom mud area of ​​the target water body through the remote sensing reflectivity formula below the water surface according to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the actual water depth information; The third determination module is used to replace the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area with the optical deep water remote sensing reflectivity below the water surface of the bottom mud area according to the optical deep water remote sensing reflectivity below the water surface of the aquatic plant area and the bottom mud area, and then determine the equivalent water depth information by the remote sensing reflectivity formula below the water surface; The fourth determination module is used to determine the subsurface remote sensing reflectivity of the red, green and blue bands with the bottom effect removed according to the uplink and downlink radiation attenuation coefficients of the red, green and blue bands and the equivalent water depth information and through the subsurface remote sensing reflectivity formula; The fifth determination module is used to determine the above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect of the water according to the below-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect of the water; The sixth determination module is used to determine the chlorophyll a concentration based on the water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect.

7. The device according to claim 6, characterized in that The formula for remote sensing reflectivity below the water surface is as follows: in, is the remote sensing reflectivity below the water surface in the aquatic plant area or the bottom mud area, R rs is the water remote sensing reflectivity, ρ is the irradiance reflectivity of the bottom, K d is the downlink radiation attenuation coefficient, is the upward radiation attenuation coefficient of the water column, is the uplink radiation attenuation coefficient of the water bottom, Z B The actual water depth information.

8. The device according to claim 6, characterized in that The third determination module is specifically used to replace the optical deep-water remote sensing reflectivity below the water surface of the aquatic plant area with the optical deep-water remote sensing reflectivity below the water surface 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 device according to claim 6, characterized in that The formula for determining the above-water remote sensing reflectivity of the red, green and blue bands after removing the bottom effect based on the subsurface remote sensing reflectivity of the red, green and blue bands after removing the bottom effect is as follows: in, The reflectivity of water remote sensing is obtained by removing the bottom effect, i is any one of the red, green and blue bands, To remove the bottom effect of the water surface remote sensing reflectivity.

10. The device according to claim 6, characterized in that The sixth determination module is specifically used to: determine a simulated spectrum from a spectral library based on an actual spectrum corresponding to the water remote sensing reflectivity of the red, green and blue bands with the bottom effect removed, wherein the simulated spectrum is a 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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