Hydrological frequency analysis method based on remote sensing

Abstract

The invention discloses a hydrological frequency analysis method based on remote sensing, and the method comprises the steps: obtaining DEM data of a to-be-analyzed region, generating a confluence accumulation grid map, recognizing an equal-flux river reach based on the confluence accumulation grid map, determining a first reference water surface area and a second reference water surface area of a typical river reach in the equal-flux river reach, and performing hydrological frequency analysis on the river reach with the hydrological stations in the equal-flux river reaches based on the first reference water surface area to obtain a first hydrological frequency analysis result, and performing hydrological frequency analysis on the river reach without the hydrological stations in the equal-flux river reaches based on the second reference water surface area to obtain a second hydrological frequency analysis result. According to the method, the multi-time-sequence water surface area data is obtained by using the remote sensing image, accurate inversion of the flow and frequency distribution characteristic analysis are realized by establishing the relation model of the water surface area and the flow, and hydrological frequency analysis can be realized without depending on a ground station.

Description

Technical Field

[0001] The invention belongs to the technical field of water conservancy engineering, and in particular relates to a hydrological frequency analysis method based on remote sensing. Background Art

[0002] In the field of hydrological research and engineering practice, hydrological frequency analysis is the key foundation for flood warning, flood control project design, and water resources management in river basins. Traditional hydrological frequency analysis methods are highly dependent on long-term historical data such as flow and water level from ground hydrological stations, but these stations are often not densely distributed, especially in remote mountainous areas and high mountain canyon areas with complex terrain. It is difficult to accurately obtain the frequency characteristics of hydrological events in such areas, which makes the hydrological frequency estimation based on traditional methods have significant limitations and difficult to fully reflect the characteristics of hydrological events in various regions within the basin. In addition, hydrological sequences often show inconsistency under changing environments, and it is difficult to track dynamic changes in the basin in real time using traditional hydrological monitoring methods. Summary of the invention

[0003] To solve the above problems, the present invention provides a hydrological frequency analysis method based on remote sensing to solve the problems that the existing hydrological frequency analysis methods have significant limitations, such as difficulty in comprehensively reflecting the characteristics of hydrological events in various regions within the basin and difficulty in tracking dynamic changes within the basin in real time.

[0004] A hydrological frequency analysis method based on remote sensing, comprising:

[0005] Obtain DEM data of the area to be analyzed and generate a runoff accumulation grid map;

[0006] Identify isoflux river sections based on the flow accumulation grid map;

[0007] Determine the first reference water surface area and the second reference water surface area of ​​a typical river section in an isoflux river section;

[0008] Based on the first reference water surface area, a hydrological frequency analysis is performed on the river sections with hydrological stations in the equal flux river sections to obtain the first hydrological frequency analysis results, and

[0009] Based on the second benchmark water surface area, a hydrological frequency analysis is performed on the river section without hydrological stations in the equal-flux river section to obtain a second hydrological frequency analysis result.

[0010] According to a specific embodiment of the present invention, obtaining DEM data of the area to be analyzed and generating a flow accumulation grid map includes:

[0011] Obtain the DEM data of the area to be analyzed and perform depression-filling processing on the DEM data to obtain DEM processed data;

[0012] The flow direction analysis method is used to determine the water flow direction of the DEM processed data and calculate the runoff accumulation to generate a runoff accumulation grid map.

[0013] According to a specific embodiment of the present invention, identifying isoflux stable river sections based on the confluence accumulation grid map includes:

[0014] Calculate the water intensity of each grid based on the water accumulation grid map;

[0015] Determine the grid where the reference point is located in the confluence accumulation grid map to obtain the first grid;

[0016] Taking the first grid as the starting point, search for the second grid with a water catchment intensity change of 5% along the upstream of the first grid;

[0017] Taking the first grid as the starting point, search for the third grid with a 5% change in water catchment intensity along the downstream of the first grid;

[0018] Based on the position information of the second grid and the position information of the third grid, an isoflux river section corresponding to the reference point is determined.

[0019] According to a specific embodiment of the present invention, calculating the water intensity of each grid based on the water accumulation grid map includes:

[0020] The cumulative flow and grid area of ​​each grid in the grid flow accumulation grid map are counted, and the grid water catchment area is calculated. The calculation formula is:

[0021] A i，j =N×S i，j

[0022] In the formula, A i，j is the catchment area of ​​the grid, m 2 , N is the cumulative number of confluence, S i，j is the grid area;

[0023] Obtain rainfall data for the area to be analyzed, and use the inverse distance weighted method to interpolate the rainfall data to generate a surface rainfall distribution map. The rainfall calculation formula for the interpolation point in the surface rainfall distribution map is:

[0024]

[0025] Where P (x，y) is the rainfall at the point to be interpolated, mm, P i is the rainfall at the ith observation station, mm, d i is the distance between the point to be interpolated and the i-th observation station, m and p represent the power of the distance;

[0026] The rainfall distribution map is normalized to obtain the rainfall weight, which is calculated as follows:

[0027]

[0028] Where W i，j is the normalized rainfall weight, G i，j The average annual rainfall of the grid, P min and P max are the minimum and maximum rainfall in the rainfall distribution map, respectively;

[0029] Calculate the rainfall per unit area P based on the surface rainfall distribution map i，j , and its calculation formula is:

[0030] P i，j =W i，j ×R×A i，j

[0031] Where R is the multi-year average maximum rainfall depth in the region, mm;

[0032] Using the aspect raster map and unit area rainfall P i，j Calculate the total flow Q of the grid i，j , and its calculation formula is:

[0033]

[0034]

[0035] Among them, U i，j is the total grid G i，j The upstream grid collection of the confluence; Q m,n is the upstream grid G m，n The cumulative flow of m，n is the aspect weight, n is the number of outlet grids;

[0036] Based on the total flow Q i，j Calculate the water catchment intensity of each grid, and the calculation formula is:

[0037]

[0038] Where H is the water intensity of each grid, Q i，j is the grid G i，j The total sink flow, Q i±1 is the grid G i，j The total flow of adjacent grids.

[0039] According to a specific embodiment of the present invention, determining the first reference water surface area and the second reference water surface area of ​​a typical river section in an isoflux river section includes:

[0040] The frequency of occurrence of each flow data is calculated based on the daily flow data of the hydrological stations, and the flow data corresponding to the frequencies of 95%, 90%, 85%, ... 10%, 5%, 1%, 0.1%, and 0.01% are selected. The corresponding remote sensing images are matched based on the flow data, and the water surface area of ​​the typical river section is extracted from the remote sensing images to obtain the water surface area data set with different recurrence periods, namely the first benchmark water surface area;

[0041] Acquire long-term monitoring data of remote sensing images and extract the water surface area of ​​each unit river section every ten days, calculate the average water surface area of ​​each unit river section every ten days every 10 years, and obtain a multi-year average water surface area dataset, namely the second benchmark water surface area.

[0042] According to a specific embodiment of the present invention, the typical river section is a non-vertical river section with a length of 5 times or more of the unit river section in the isoflux river section.

[0043] According to a specific embodiment of the present invention, a hydrological frequency analysis is performed on a river section with a hydrological station in an equal-flux river section based on a first reference water surface area, and the first hydrological frequency analysis result includes:

[0044] Obtain the water surface area of ​​the river section with hydrological stations in the real-time remote sensing image and match it with the first benchmark water surface area.

[0045] If the match is successful, the corresponding remote sensing image date is obtained, and the hydrological frequency analysis is performed on the hydrological station flow on the remote sensing image date to obtain the hydrological frequency corresponding to the flow;

[0046] If the matching fails, the water surface area of ​​the real-time remote sensing image is compared with that of the remote sensing image corresponding to the flow rate at different recurrence periods to obtain the hydrological frequency corresponding to the water surface area of ​​the real-time remote sensing image.

[0047] According to a specific embodiment of the present invention, the corresponding remote sensing image date is obtained, and the hydrological frequency analysis is performed on the flow of the hydrological station on the remote sensing image date to obtain the hydrological frequency corresponding to the flow, including:

[0048] Calculate the empirical frequency of the hydrological station flow data on the date of the remote sensing image using the empirical frequency method;

[0049] Based on the empirical frequency, the Pearson III distribution method is used to perform frequency analysis on the hydrological station flow data on the remote sensing image date to obtain a Pearson III frequency distribution curve;

[0050] Based on the Pearson III frequency distribution curve, the hydrological station flow data of the remote sensing image date is fitted to obtain the hydrological frequency under different hydrological events.

[0051] According to a specific embodiment of the present invention, comparing the water surface area of ​​the real-time remote sensing image with the remote sensing image corresponding to the flow rate at different recurrence periods to obtain the hydrological frequency corresponding to the water surface area of ​​the real-time remote sensing image further includes:

[0052] Obtain the return period flows of different frequencies based on the daily flow history data recorded at the hydrological stations;

[0053] Extract the water surface area of ​​different frequency flows of typical river sections from the remote sensing images corresponding to the return period flows;

[0054] The water surface area of ​​the remote sensing image corresponding to the return period flow is compared with the water surface area extracted from the real-time remote sensing image to obtain the hydrological frequency corresponding to the water surface area of ​​the real-time remote sensing image.

[0055] According to a specific embodiment of the present invention, a hydrological frequency analysis is performed on a river section without a hydrological station in an equal-flux river section based on a second reference water surface area, and the second hydrological frequency analysis result includes:

[0056] The flow of the river section without hydrological stations in the equal flux river section is estimated to obtain the estimated flow value;

[0057] The regression analysis method is used to fit the data of the second benchmark water surface area and the estimated flow rate to generate a relationship curve between flow rate and water surface area;

[0058] Obtain real-time remote sensing images and extract the water surface area of ​​the river section without hydrological stations in the stable river section, and invert the relationship curve between flow and water surface area to obtain the corresponding flow value;

[0059] Conduct hydrological frequency analysis on the flow value to obtain the corresponding hydrological frequency.

[0060] According to a specific embodiment of the present invention, flow estimation is performed on a river section without a hydrological station in an equal flux river section, and the flow estimation value obtained includes:

[0061] Extract the water surface area of ​​the river section without hydrological stations in the isoflux river section;

[0062] The water surface gradient, wetted perimeter and cross-sectional area are obtained based on the water surface area, and the estimated flow value of the river under different water surface area conditions is calculated according to the Manning formula. The calculation formula is:

[0063]

[0064]

[0065]

[0066] Where Q is the flow rate, n is the Manning roughness coefficient, R is the hydraulic radius, A is the cross-sectional area of ​​the river channel, P is the wetted perimeter, S is the water surface gradient, ΔH is the water surface height difference between the two end points of the river channel, and L is the length of the typical river section.

[0067] Compared with the prior art, the present invention has the following advantages:

[0068] The present invention provides a remote sensing-based hydrological frequency analysis method, which uses remote sensing images to obtain multi-time series water surface area data of equal-flux river sections, and performs fine processing and analysis on the multi-temporal remote sensing image data in the watershed. In river sections with hydrological stations, hydrological frequency analysis is performed in combination with hydrological station data. In river sections without hydrological stations, the water surface area of ​​equal-flux river sections is obtained through remote sensing images, and the change in water surface area is used to replace the fluctuation of flow. By establishing a relationship model between flow and water surface area, accurate inversion of flow and analysis of frequency distribution characteristics are achieved. The present invention can perform hydrological frequency analysis without relying on dense ground stations, and provides reliable technical support for watershed management and flood control planning. BRIEF DESCRIPTION OF THE DRAWINGS

[0069] In order to more clearly illustrate the embodiments of the present disclosure 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 some embodiments of the present disclosure. For ordinary technicians in this field, other drawings can be obtained based on these drawings without paying any creative work.

[0070] Figure 1 It is a flow chart of a hydrological frequency analysis method based on remote sensing provided according to an embodiment of the present invention.

[0071] Figure 2 It is a flow chart of a method for generating a flow accumulation grid map according to an embodiment of the present invention.

[0072] Figure 3 It is a flow chart of a method for identifying equal-flux river sections based on a confluence accumulation grid map provided according to an embodiment of the present invention.

[0073] Figure 4 It is a flow chart of a method for constructing a three-dimensional river topography of an isoflux river section provided according to an embodiment of the present invention.

[0074] Figure 5 It is a flow chart of a method for determining a reference water surface area of ​​a typical river section based on the three-dimensional topography of a river channel provided according to an embodiment of the present invention.

[0075] Figure 6 It is a flow chart of a method for performing hydrological frequency analysis on a first river section in an equal flux river section provided according to an embodiment of the present invention.

[0076] Figure 7 It is a flow chart of a method for comparing the water surface area of ​​a first river section of a real-time remote sensing image with remote sensing images corresponding to flows with different recurrence periods provided in accordance with an embodiment of the present invention.

[0077] Figure 8 It is a flow chart of a method for performing hydrological frequency analysis on a second river section in an equal flux river section provided according to an embodiment of the present invention.

[0078] Fig. 9 It is a cross-sectional diagram of water volume in a classic river section during flood and non-flood periods provided according to an embodiment of the present invention.

[0079] Fig.10 It is a schematic diagram of the water surface area of ​​a classic river section during flood period and non-flood period provided according to an embodiment of the present invention. DETAILED DESCRIPTION

[0080] In order to make those skilled in the art understand the concept and thought of the present invention more clearly, the present invention is described in detail below in conjunction with specific embodiment.It should be understood that the embodiment provided herein is only a part of all embodiments that the present invention may have.Those skilled in the art, after reading the specification of the application, have the ability to make improvements, transformations, or replacements to part or the whole of the following embodiments, and these improvements, transformations, or replacements are also included in the scope of the present invention.

[0081] In this article, the terms "first", "second" and other similar words are not intended to imply any order, quantity and importance, but are only used to distinguish different elements. In this article, the terms "one", "an" and other similar words are not intended to indicate that there is only one thing, but to indicate that the relevant description is only for one of the things, and the thing may have one or more. In this article, the terms "comprise", "include" and other similar words are intended to indicate logical mutual relations, and cannot be regarded as indicating spatial structural relations. For example, "A includes B" is intended to indicate that B belongs to A logically, but does not mean that B is located inside A in space. In addition, the meanings of the terms "comprise", "include" and other similar words should be regarded as open, rather than closed. For example, "A includes B" is intended to indicate that B belongs to A, but B does not necessarily constitute the whole of A, and A may also include other elements such as C, D, and E.

[0082] In this document, the terms "embodiment", "this embodiment", "one embodiment", and "an embodiment" do not mean that the relevant description is only applicable to a specific embodiment, but rather that the description may also be applicable to one or more other embodiments. Those skilled in the art should understand that in this document, any description of a certain embodiment can be replaced, combined, or combined in other ways with the relevant descriptions in one or more other embodiments, and the new embodiments generated by the replacement, combination, or combination in other ways are easily conceivable by those skilled in the art and fall within the scope of protection of the present invention.

[0083] Example 1

[0084] Additional aspects and advantages of embodiments of the present invention will be described in part in the following description, and will become apparent from the following description, or will be learned through practice of embodiments of the present invention. Figure 1-Figure 10 The embodiment of the present invention provides a hydrological frequency analysis method based on remote sensing, including:

[0085] S1: Obtain the DEM data of the area to be analyzed and generate a runoff accumulation grid map.

[0086] S2: Identify isoflux river sections based on the runoff accumulation grid map.

[0087] S3: Determine the first reference water surface area and the second reference water surface area of ​​a typical river section in the isoflux river section.

[0088] S4: Based on the first benchmark water surface area, a hydrological frequency analysis is performed on the river section with hydrological stations in the equal flux river section to obtain a first hydrological frequency analysis result.

[0089] S5: Based on the second benchmark water surface area, a hydrological frequency analysis is performed on the river section without hydrological stations in the equal-flux river section to obtain a second hydrological frequency analysis result.

[0090] Specifically, step S1 of acquiring DEM data of the area to be analyzed and generating a flow accumulation grid map further includes:

[0091] S11: Obtain DEM data of the area to be analyzed and perform depression-filling processing on the DEM data to obtain DEM processed data.

[0092] The embodiment of the present invention uses the Copernicus DEM (global digital elevation model dataset) with a resolution of 30m provided by the European Space Agency to extract the DEM (digital elevation model) data of the basin, and uses the neighborhood analysis method to fill the DEM data to eliminate the influence of depressions and generate DEM processed data without depressions.

[0093] S12: Use the flow direction analysis method to determine the water flow direction of the DEM processed data and calculate the runoff accumulation, and generate a runoff accumulation grid map.

[0094] The water flow direction is calculated by the flow direction analysis method to reflect the slope and shape of the terrain. Preferably, the present invention adopts a single flow direction method (such as the D8 method) to determine the water flow direction, and then calculates the cumulative runoff based on the water flow direction data. The embodiment of the present invention calculates the cumulative runoff of each grid cell based on the boundaries of each watershed based on the water flow direction data, and displays the calculation results in the form of a grid map, where the value of each grid cell represents the cumulative runoff of the point.

[0095] Specifically, step S2 of identifying equal flux river sections based on the confluence accumulation grid map includes:

[0096] S21: Calculate the water intensity of each grid based on the runoff accumulation grid map.

[0097] The water collection intensity is used to indicate the water collection capacity of the corresponding grid. In the embodiment of the present invention, the product of the accumulated flow of the grid and the area of ​​the grid can be determined as the water collection intensity of the grid, or the product of the accumulated flow of the grid, the area, and the rainfall can be determined as the water collection intensity of the grid.

[0098] Step S21 calculates the water intensity of each grid based on the water accumulation grid map, and specifically includes:

[0099] a. Count the cumulative number of confluence and the grid area of ​​each grid in the confluence accumulation grid map, and calculate the grid's catchment area, the calculation formula is:

[0100] A i，j =N×S i，j (1)

[0101] In the formula, A i，j is the catchment area of ​​the grid, m 2 , N is the cumulative number of confluence, S i，j is the grid area.

[0102] b. Obtain rainfall data for the area to be analyzed, and use the inverse distance weighted method to interpolate the rainfall data to generate a surface rainfall distribution map. The rainfall calculation formula for the interpolation point in the surface rainfall distribution map is:

[0103]

[0104] Where P (x，y) is the rainfall at the point to be interpolated, mm, P i is the rainfall at the ith observation station, mm, d i is the distance between the point to be interpolated and the i-th observation station, and m and p represent the power of the distance.

[0105] In the embodiment of the present invention, satellite remote sensing rainfall data (such as TRMM or GPM) can be used to perform spatial interpolation of large-scale rainfall to obtain rainfall data in the area to be analyzed. And the satellite remote sensing rainfall data is corrected by collecting rainfall station data in the area to be analyzed through the China Meteorological Network to ensure more accurate rainfall data. In the embodiment of the present invention, the inverse distance weighted method (Inverse Distance Weight, IDW) is used to spread the point rainfall to the entire river network to generate a surface rainfall distribution map. And the rainfall data generated by IDW interpolation is saved in raster format to generate a spatial distribution map of multi-year average rainfall.

[0106] c. Normalize the rainfall distribution map to obtain the rainfall weight, which is calculated as follows:

[0107]

[0108] Where W i，j is the normalized rainfall weight, G i，j The average rainfall over many years in the grid, P min and P max They are the minimum and maximum rainfall in the rainfall distribution map, respectively.

[0109] A rainfall distribution map is generated based on rainfall data, and the normalized rainfall weight of each grid is obtained using the rainfall distribution map, and the initial runoff of the corresponding grid is calculated based on the normalized rainfall weight. The generated rainfall distribution map is normalized so that it can be used as a weight file for runoff accumulation calculation, so that the rainfall data has a unified dimension in spatial distribution, and the obtained normalized rainfall distribution map is used as a weight file for runoff accumulation calculation.

[0110] The area of ​​each cell is the same, and this area is the unit area, and the unit is, for example, m2.

[0111] In the embodiment of the present invention, the rainfall data is the multi-year average rainfall, and the multi-year average rainfall is matched with the DEM data through spatial interpolation to ensure the consistency of spatial resolution. The obtained multi-year average rainfall distribution map needs to be normalized to serve as a weight file for the runoff accumulation calculation.

[0112] d. Calculate the rainfall per unit area P based on the surface rainfall distribution map i，j , and its calculation formula is:

[0113] P i，j =W i，j ×R×A i，j (4)

[0114] Where R is the multi-year average maximum rainfall depth in the region, mm.

[0115] e. Perform slope analysis based on DEM data and generate a slope raster map.

[0116] Slope calculation: Perform slope analysis based on DEM data to generate slope raster data for simulating water flow paths and determining confluence relationships.

[0117] The DEM data is used to perform slope analysis to obtain the flow direction of each grid. The commonly used D8 algorithm (each grid flows to one of the eight adjacent grids around it) is used to calculate the slope and generate a slope grid map.

[0118] f. Using the aspect grid map and unit area rainfall P i，j Calculate the total flow Q of the grid i，j , the total flow rate is calculated from the upstream grid to the downstream grid according to the slope aspect map. The total flow rate Q of each grid i，j Including its own rainfall sink P i，j The flow rate transmitted from the upstream grid is calculated as follows:

[0119]

[0120] Aspect weight f m，n :

[0121] Determine the flow ratio: If there are more than one downstream grids flowing from each upstream grid, you need to allocate the flow ratio. Assume that the flow is evenly distributed to all downstream grids:

[0122]

[0123] Among them, U i，j is the total grid G i，j The upstream grid collection of the confluence; Q m,n is the upstream grid G m，n The cumulative flow of m，n is the aspect weight, and n is the number of outlet grids.

[0124] g. Based on the total sink flow Q i，j Calculate the water catchment intensity of each grid, and the calculation formula is:

[0125]

[0126] Where H is the water intensity of each grid, Q i，j is the grid G i，j The total sink flow, Q i±1 is the grid G i，j The total flow of adjacent grids.

[0127] S22: Determine the grid where the reference point is located in the confluence accumulation grid map to obtain a first grid.

[0128] S23: Starting from the first grid, search for a second grid upstream of the first grid where the water harvesting intensity changes by 5%.

[0129] The variation range of the water collection intensity of the second grid is the same as that of the first grid and the preset range. For example, assuming the preset range is 5%, the water collection intensity of the first grid is 100, and the water collection intensity of the second grid is 95 or 105.

[0130] In this step, starting from the first grid, the second grid is searched along the upstream of the first grid, that is, along the upstream of the river section. For example, a grid with a water collection intensity change of 5% can be searched along the upstream direction of the first grid, and the grid is determined as the second grid.

[0131] S24: Starting from the first grid, search for a third grid downstream of the first grid where the water harvesting intensity variation is 5%.

[0132] The variation range of the water collection intensity of the third grid and the water collection intensity of the first grid is the same as the preset range.

[0133] S25: Based on the position information of the second grid and the position information of the third grid, determine the isoflux river section corresponding to the reference point.

[0134] Specifically, step S3 of determining the first reference water surface area and the second reference water surface area of ​​a typical river section in an isoflux river section includes:

[0135] S31: Calculate the frequency of occurrence of each flow data based on the daily flow data of the hydrological station, select the flow data corresponding to the frequency of 95%, 90%, 85%, ... 10%, 5%, 1%, 0.1%, 0.01%, and match the corresponding remote sensing image based on the flow data, extract the water surface area of ​​the typical river section from the remote sensing image, and obtain the water surface area data set with different recurrence periods, that is, the first benchmark water surface area. The typical river section is a non-vertical river section with 5 times or more of the unit river section length in the equal flux river section.

[0136] For river sections with hydrological stations, the daily flow and water level data recorded by the hydrological stations are used to divide the flood period and the non-flood period through flow frequency analysis. And in the confirmed non-flood period, the remote sensing images of the corresponding period are selected to obtain the water surface area of ​​the stable flux section, and then a long-term series of benchmark water surface area data sets are constructed, which is used as the benchmark water surface area for flood process identification. The embodiment of the present invention first arranges the daily flow and hourly flow data recorded by the hydrological station in order, and uses the empirical analysis method to calculate the frequency and cumulative probability of occurrence of each flow data, and then uses the Pearson III curve distribution to fit the sorted daily flow and hourly flow frequency data, selects 95%, 90%, 85%, ... 10%, 5%, 1%, 0.1%, 0.01% corresponding flow data, matches the corresponding remote sensing images, and obtains the water surface area at this time, determines the benchmark water surface area of ​​different recurrence periods, and obtains the first benchmark water surface area.

[0137] Determination of typical river sections:

[0138] 1. Determine the typical river section: Select the typical river section within the equal flux river section. First, make it clear that the length of the typical river section should be more than 5 times the length of the unit river section.

[0139] 2. The typical river section is divided into 5 unit sections. The water volume of the typical river section under normal conditions is V0, and the water surface area of ​​the river section is A0. When a flood comes, the water volume of the typical river section will rise. At this time, the water volume of the typical river section increases to V1, and the water surface area of ​​the river section will also increase to A1.

[0140] Normal state: the amount of water in a unit river section is V 01 、V 02 、V 03 、V 04 、V 05 , the water surface area corresponding to a unit river section is A 01 , A 02 , A 03 , A 04 , A 05 .

[0141] When a flood occurs: the amount of water in a unit river section is V 11 、V 12 、V 13 、V 14 、V 15 , the water surface area corresponding to a unit river section is A 11 , A 12 , A 13 , A 14 , A 15 .

[0142] In a unit river section, when a flood occurs, the amount of water that changes is ΔVi , the changing water surface area is ΔA i Then we have:

[0143] ΔV i =V 1i -V 0i (8)

[0144] ΔA i =A 1i -A 0i (9)

[0145] In the formula, i=1, 2, 3, 4, 5.

[0146] Since the topography of the river section is known, there is a definite correlation between the water volume per unit section and the water surface area per unit section:

[0147] ΔV i =f(ΔA i ) (10)

[0148] 3. Determination of unit river section length: The water surface area of ​​a unit river section is related to the length of the unit river section. According to the correlation between the volume of water in the river section and the water surface area of ​​the river section, there is a unit river section length l such that:

[0149]

[0150] The length l at this time is taken as the unit river section length.

[0151] 4. Basis for selection of typical river sections: Hydrological frequency analysis based on water surface area should avoid selecting vertical river sections. The flow pattern is shaped according to the river section shape. In order to realize river flow monitoring based on remote sensing, the river section can be divided into vertical river section, single-side vertical single-side open river section, and double-side open river section according to the vertical and open form of the river bank.

[0152] Vertical river section: Based on the water surface vector of the river water body, the corresponding water level water edge lines in different time periods are extracted (multi-period remote sensing extraction of river water body boundaries). The water edge line morphology exists in that the moving distance of the water edge lines on both sides along the river section throughout the year is less than 10% of the minimum river width.

[0153] Measurement of water surface width: Draw a vertical line of the cross section based on the center line of the river channel, and the length of the part that intersects with the water edge line is the water surface width of the cross section.

[0154] S32: Obtain long-term monitoring data of remote sensing images and extract the water surface area of ​​each unit river section every ten days, calculate the average water surface area of ​​each unit river section every ten days every 10 years, and obtain a multi-year average water surface area data set every ten days, i.e., the second benchmark water surface area.

[0155] For river sections without hydrological stations, the water surface area of ​​isoflux river sections is obtained through remote sensing images. The embodiment of the present invention uses the long-term monitoring data of remote sensing images to obtain the water surface area of ​​the unit river section every ten days, and takes the average water surface area of ​​the unit river section every ten days for every 10 years as the benchmark water surface area to form a multi-year average water surface area dataset, i.e., the second benchmark water surface area. The second benchmark water surface area can be used to identify and analyze the hydrological frequency of river sections without hydrological stations by constructing the second benchmark water surface area.

[0156] Specifically, step S4 performs a hydrological frequency analysis on a river section with a hydrological station in an equal-flux river section based on the first reference water surface area to obtain a first hydrological frequency analysis result, which specifically includes the following steps:

[0157] S41: Obtain the water surface area of ​​the river section with the hydrological station in the real-time remote sensing image, and match it with the first reference water surface area. If the match is successful, execute step S42; if the match fails, execute step S43.

[0158] S42: Obtain the corresponding remote sensing image date, and perform hydrological frequency analysis on the flow of the hydrological station on the remote sensing image date to obtain the hydrological frequency corresponding to the flow.

[0159] S43: Compare the water surface areas of the real-time remote sensing image and the remote sensing image corresponding to the flow rates at different recurrence periods to obtain the hydrological frequency corresponding to the water surface area of ​​the real-time remote sensing image.

[0160] The embodiment of the present invention divides equal flux river sections into river sections with hydrological stations and river sections without hydrological stations according to the conditions of hydrological stations in the river basin. In the case of hydrological stations, the corresponding remote sensing image is matched by the first reference water surface area, and the flow data is extracted to perform hydrological frequency analysis. The embodiment of the present invention matches the water surface area extracted from the real-time remote sensing image with the first reference water surface area. If a water surface area similar to the first reference water surface area is matched, that is, the match is successful, the corresponding remote sensing image date is obtained, and the hydrological frequency analysis is performed using the hydrological station flow data of the date. If a water surface area similar to the first reference water surface area is not matched, that is, the match fails, the water surface areas of the remote sensing images corresponding to the flows of different recurrence periods are compared to determine the corresponding hydrological frequency.

[0161] In the case of matching similar water surface areas, step S42 further includes:

[0162] S421: Calculate the empirical frequency of the flow data of the hydrological stations on the date of the remote sensing image using the empirical frequency method.

[0163] S422: Based on the empirical frequency, the Pearson III distribution method is used to perform frequency analysis on the hydrological station flow data on the remote sensing image date to obtain the Pearson III frequency distribution curve;

[0164] S423: Based on the Pearson III frequency distribution curve, the flow data of the hydrological stations on the remote sensing image date are fitted to obtain the hydrological frequency under different hydrological events.

[0165] The embodiment of the present invention uses an empirical frequency analysis method to arrange the daily flow data or the hourly flow data in descending order, and applies the empirical frequency method to calculate the empirical frequency. The calculation formula of the empirical frequency is:

[0166]

[0167] In the formula, P is the empirical frequency, expressed as a percentage; m is the serial number corresponding to each value when the series is sorted from large to small; n is the capacity of the time series.

[0168] According to the empirical frequency of sorted daily flow data or hourly flow, the Pearson III distribution is used to fit the hydrological station flow data of the remote sensing image date to generate flow values ​​with different return periods. The flow values ​​corresponding to 95%, 90%, 85%, ... 10%, 5%, 1%, 0.1%, and 0.01% are selected to match the water surface area of ​​the remote sensing image corresponding to the flow value for subsequent comparison and analysis.

[0169] The calculation expression of Pearson type III curve is:

[0170]

[0171] in,

[0172]

[0173]

[0174] Where Γ(α) is the gamma function of α; α, β, and a0 are three parameters that characterize the shape, scale, and location of the Pearson III distribution, α>0, β>0; is the sample mean; x i is the i-th sample value; is the median value; C s is the skewness coefficient; C v is the coefficient of dispersion.

[0175] If no similar water surface area is matched, step S43 further includes:

[0176] S431: Obtain the recurrence flow of different frequencies based on the daily flow history data recorded by the hydrological station.

[0177] S432: Extract the water surface area of ​​different frequency flows of a typical river section from the remote sensing image corresponding to the return period flow.

[0178] S433: Compare the water surface area of ​​the remote sensing image corresponding to the return period flow with the water surface area extracted from the real-time remote sensing image to obtain the hydrological frequency corresponding to the water surface area of ​​the real-time remote sensing image.

[0179] In the embodiment of the present invention, if there is no similar match for the reference water surface area, a frequency analysis is performed based on the historical records of daily flow to obtain the return period flow of different frequencies (such as once in ten years, once in fifty years, etc.). Based on the remote sensing images corresponding to these return period flows, the water surface area of ​​the typical river section at different frequency flows is extracted. The water surface area extracted from the real-time remote sensing image is compared with the water surface area of ​​the remote sensing image corresponding to the return period flow, thereby obtaining the hydrological frequency range corresponding to the water surface area of ​​the newly acquired remote sensing image.

[0180] Specifically, step S5 performs a hydrological frequency analysis on a river section without a hydrological station in an equal-flux river section based on the second reference water surface area to obtain a second hydrological frequency analysis result, further comprising:

[0181] S51: Estimating the flow of the river section without hydrological stations in the equal flux river section to obtain the estimated flow value, specifically including:

[0182] S511: Extract the water surface area of ​​the river section without hydrological stations in the isoflux river section.

[0183] S512: Based on the water surface area, the water surface gradient, wetted perimeter (i.e., the perimeter of the water flow in contact with the riverbed) and cross-sectional area (the area through which the water flows on the cross section of the river) are obtained, and the estimated flow value of the river under different water surface area conditions is calculated according to the Manning formula. The calculation formula is:

[0184]

[0185]

[0186]

[0187] Where Q is the flow rate, n is the Manning roughness coefficient, which is estimated based on the riverbed material, vegetation cover, etc., R is the hydraulic radius, A is the cross-sectional area of ​​the river, P is the wetted perimeter, S is the water surface gradient, ΔH is the water surface height difference between the two end points of the river, and L is the length of the typical river section.

[0188] In the embodiment of the present invention, in the river terrain model, the water surface gradient and wetted perimeter are extracted based on each water surface area. The embodiment of the present invention collects the data required to generate the river terrain, divides the river terrain into the terrain above the highest water level, the terrain below the lowest water level, and the terrain between the highest water level and the lowest water level, and extracts the waterside line, center line and flow section; calculates the relative stability index of the flow section, identifies the stable river sections in the river channel, and divides the stable river sections into curved river sections and straight river sections; assigns elevation values ​​to the waterside lines of the curved river sections and the straight river sections to obtain contour lines; constructs the terrain above the highest water level, the terrain between the lowest water level and the highest water level, and the terrain below the lowest water level, and splices the three terrains to form a complete river terrain.

[0189] S52: Using regression analysis method to perform data fitting on the second reference water surface area and the estimated flow rate, generating a relationship curve between flow rate and water surface area, which is used for flow rate estimation under different water surface area conditions. The relationship curve between flow rate and water surface area can be expressed as:

[0190] Q = f(A 水 ) (19)

[0191] Where, Q is the flow rate mm / s; A 水 is the water surface area, m 2 .

[0192] S53: Acquire real-time remote sensing images and extract the water surface area of ​​the river section without hydrological stations in the stable river section, and obtain the corresponding flow value based on the relationship curve between flow and water surface area.

[0193] The embodiment of the present invention utilizes remote sensing images to extract the actually observed water surface area, and inverts the corresponding flow value based on the established water surface area-flow relationship curve.

[0194] S54: Perform hydrological frequency analysis on the flow value to obtain the corresponding hydrological frequency.

[0195] In river sections without hydrological stations, the relationship curve between water surface area and flow is used to conduct frequency analysis after obtaining flow data to determine the flow and hydrological event probabilities at different recurrence periods.

[0196] Flow-based hydrological frequency analysis is mainly used to assess the probability of occurrence of extreme and typical hydrological events in a river basin, including peak flow, annual runoff, low flow during the dry season, and short-term runoff events caused by rainfall. By analyzing the flow characteristics of different return periods, it can provide scientific support for flood control project design, river basin water resources management, drought and flood warning, etc., thereby achieving optimal allocation of river basin water resources and effective risk management.

[0197] In summary, the hydrological frequency analysis method based on remote sensing described in the present invention has the following advantages:

[0198] The present invention provides a remote sensing-based hydrological frequency analysis method, which uses remote sensing images to obtain multi-time series water surface area data of equal-flux river sections, and performs fine processing and analysis on the multi-temporal remote sensing image data in the watershed. In river sections with hydrological stations, hydrological frequency analysis is performed in combination with hydrological station data. In river sections without hydrological stations, the water surface area of ​​equal-flux river sections is obtained through remote sensing images, and the change in water surface area is used to replace the fluctuation of flow. By establishing a relationship model between flow and water surface area, accurate inversion of flow and analysis of frequency distribution characteristics are achieved. The present invention can perform hydrological frequency analysis without relying on dense ground stations, and provides reliable technical support for watershed management and flood control planning.

[0199] The above describes in detail the concepts, principles and ideas of the present invention in conjunction with specific implementation methods (including embodiments and examples). Those skilled in the art should understand that the implementation methods of the present invention are not limited to the forms given above. After reading this application document, those skilled in the art can make any possible improvements, substitutions and equivalent forms to the steps, methods, systems and components in the above implementation methods. These improvements, substitutions and equivalent forms should be deemed to fall within the scope of the present invention, and the protection scope of the present invention is subject only to the claims.

Claims

1. A hydrological frequency analysis method based on remote sensing, characterized in that: include: Obtain DEM data of the area to be analyzed and generate a runoff accumulation grid map; Identifying isoflux river sections based on the flow accumulation grid map; Determine a first reference water surface area and a second reference water surface area of ​​a typical river section in the isoflux river section; Based on the first reference water surface area, a hydrological frequency analysis is performed on the river section with hydrological stations in the isoflux river section to obtain a first hydrological frequency analysis result; and Based on the second reference water surface area, a hydrological frequency analysis is performed on the river section without hydrological stations in the isoflux river section to obtain a second hydrological frequency analysis result.

2. The hydrological frequency analysis method based on remote sensing according to claim 1, characterized in that: The method of obtaining DEM data of the area to be analyzed and generating a flow accumulation grid map comprises: Obtaining DEM data of the area to be analyzed and performing depression-filling processing on the DEM data to obtain DEM processed data; The flow direction analysis method is used to determine the water flow direction of the DEM processed data and calculate the runoff accumulation, thereby generating a runoff accumulation grid map.

3. The hydrological frequency analysis method based on remote sensing according to claim 1, characterized in that: The identifying of isoflux stable river sections based on the confluence accumulation grid map comprises: Calculating the water confluence intensity of each grid based on the confluence accumulation grid map; Determine the grid where the reference point is located in the confluence accumulation grid map to obtain a first grid; Taking the first grid as the starting point, searching for a second grid upstream of the first grid where the water harvesting intensity changes by 5%; Taking the first grid as the starting point, searching for a third grid with a water harvesting intensity variation of 5% along the downstream of the first grid; Based on the position information of the second grid and the position information of the third grid, an isoflux river section corresponding to a reference point is determined.

4. The hydrological frequency analysis method based on remote sensing according to claim 3 is characterized in that: The calculating of the water confluence intensity of each grid based on the confluence accumulation grid map includes: The cumulative number of confluence and the grid area of ​​each grid in the confluence accumulation grid map are counted, and the grid catchment area is calculated. The calculation formula is: A i,j =N×S i,j In the formula, A i,j is the catchment area of ​​the grid, m 2 , N is the cumulative number of confluence, S i,j is the grid area; The rainfall data of the area to be analyzed is obtained, and the rainfall data is interpolated using the inverse distance weighted method to generate a surface rainfall distribution map. The rainfall calculation formula for the interpolation point in the surface rainfall distribution map is: Where P (x,y) is the rainfall at the point to be interpolated, mm, P i is the rainfall at the ith observation station, mm, d i is the distance between the point to be interpolated and the i-th observation station, m and p represent the power of the distance; The rainfall distribution map is normalized to obtain the rainfall weight, which is calculated as follows: Where W i,j is the normalized rainfall weight, G i,j The average rainfall over many years in the grid, P min and P max are the minimum and maximum rainfall in the rainfall distribution map, respectively; Calculate the rainfall per unit area P based on the surface rainfall distribution map i,j , and its calculation formula is: P i,j =W i,j ×R×A i,j Where R is the multi-year average maximum rainfall depth in the region, mm; Using the aspect raster map and unit area rainfall P i,j Calculate the total flow Q of the grid i,j , and its calculation formula is: Among them, U i,j is the total grid G i,j The upstream grid collection of the confluence; Q m,n is the upstream grid G m,n The cumulative flow of m,n is the aspect weight, n is the number of outlet grids; Based on the total sink flow Q i,j Calculate the water catchment intensity of each grid, and the calculation formula is: Where H is the water intensity of each grid, Q i,j is the grid G i,j The total sink flow, Q i±1 is the grid G i,j The total flow of adjacent grids.

5. The hydrological frequency analysis method based on remote sensing according to claim 1, characterized in that: Determining the first reference water surface area and the second reference water surface area of ​​the typical river section in the isoflux river section comprises: The frequency of occurrence of each flow data is calculated based on the daily flow data of the hydrological station, and the flow data corresponding to the frequencies of 95%, 90%, 85%, ... 10%, 5%, 1%, 0.1%, and 0.01% are selected, and the corresponding remote sensing images are matched based on the flow data, and the water surface area of ​​the typical river section is extracted from the remote sensing images to obtain the water surface area data set with different recurrence periods, that is, the first benchmark water surface area; Acquire long-term monitoring data of remote sensing images and extract the water surface area of ​​each unit river section every ten days, calculate the average water surface area of ​​each unit river section every ten days for every 10 years, and obtain a multi-year average water surface area data set, i.e., the second benchmark water surface area, wherein the typical river section is a non-vertical river section with a length of 5 times or more of the unit river section in the isoflux river section.

6. The hydrological frequency analysis method based on remote sensing according to claim 1, characterized in that: The performing of hydrological frequency analysis on the river section with hydrological stations in the isoflux river section based on the first reference water surface area to obtain the first hydrological frequency analysis result includes: Obtain the water surface area of ​​the river section with the hydrological station in the real-time remote sensing image, and match it with the first benchmark water surface area, If the match is successful, the corresponding remote sensing image date is obtained, and the hydrological frequency analysis is performed on the hydrological station flow on the remote sensing image date to obtain the hydrological frequency corresponding to the flow; If the matching fails, the water surface areas of the real-time remote sensing image and the remote sensing images corresponding to flows with different recurrence periods are compared to obtain the hydrological frequency corresponding to the water surface area of ​​the real-time remote sensing image.

7. The hydrological frequency analysis method based on remote sensing according to claim 6, characterized in that: The obtaining of the corresponding remote sensing image date and performing hydrological frequency analysis on the hydrological station flow on the remote sensing image date to obtain the hydrological frequency corresponding to the flow includes: Calculate the empirical frequency of the hydrological station flow data on the date of the remote sensing image using the empirical frequency method; Based on the empirical frequency, the Pearson III distribution method is used to perform frequency analysis on the hydrological station flow data on the remote sensing image date to obtain a Pearson III frequency distribution curve; Based on the Pearson III frequency distribution curve, the hydrological station flow data of the remote sensing image date is fitted to obtain the hydrological frequency under different hydrological events.

8. The hydrological frequency analysis method based on remote sensing according to claim 6, characterized in that: The step of comparing the water surface areas of the real-time remote sensing image with those of the remote sensing image corresponding to flows with different return periods to obtain the hydrological frequency corresponding to the water surface area of ​​the real-time remote sensing image further comprises: Obtain the return period flows of different frequencies based on the daily flow history data recorded at the hydrological stations; Extracting water surface areas of different frequency flows of typical river sections from remote sensing images corresponding to the return period flows; The water surface area of ​​the remote sensing image corresponding to the recurrence period flow is compared with the water surface area extracted from the real-time remote sensing image to obtain the hydrological frequency corresponding to the water surface area of ​​the real-time remote sensing image.

9. The hydrological frequency analysis method based on remote sensing according to claim 1, characterized in that: The performing of the hydrological frequency analysis on the river section without the hydrological station in the isoflux river section based on the second reference water surface area to obtain the second hydrological frequency analysis result includes: Estimating the flow of the river section without a hydrological station in the isoflux river section to obtain a flow estimation value; Using regression analysis method to perform data fitting on the second reference water surface area and the estimated flow rate to generate a relationship curve between flow rate and water surface area; Acquire real-time remote sensing images and extract the water surface area of ​​a stable river section without a hydrological station, and obtain a corresponding flow value based on the relationship curve between the flow and the water surface area; A hydrological frequency analysis is performed on the flow value to obtain a corresponding hydrological frequency.

10. The hydrological frequency analysis method based on remote sensing according to claim 9, characterized in that: The flow estimation of the river section without hydrological stations in the isoflux river section to obtain the flow estimation value comprises: Extract the water surface area of ​​the river section without hydrological stations in the isoflux river section; Based on the water surface area, the water surface gradient, wetted perimeter and water-passing cross-sectional area are obtained, and the estimated flow value of the river under different water surface area conditions is calculated according to the Manning formula, and the calculation formula is: Where Q is the flow rate, n is the Manning roughness coefficient, R is the hydraulic radius, A is the cross-sectional area of ​​the river channel, P is the wetted perimeter, S is the water surface gradient, ΔH is the water surface height difference between the two end points of the river channel, and L is the length of the typical river section.

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