Ridge-valley separation-based drainage basin and slope unit GIS (Geographic Information System) optimal division method

Abstract

The invention discloses a ridge-valley separation-based drainage basin and slope unit GIS (Geographic Information System) optimization division method, which comprises the following steps of: 1, obtaining a digital elevation model (DEM) of a research area, and performing inversion to obtain an inverted FDEM; 2, local confluence segmentation is carried out on the DEM and the FDEM respectively, and confluence boundaries of a local concave inner drainage basin and a local convex inner drainage basin are obtained and serve as potential ridge vector lines and valley vector lines respectively; 3, in the DEM, the grid of the valley path is moved downwards by a large distance to obtain a V-DEM, and in the FDEM, the grid of the ridge path is moved downwards by a large distance to obtain an R-FDEM; and 4, sub-basin segmentation is carried out on the V-DEM and the R-FDEM respectively, confluence boundaries of the concave sub-basin and the convex sub-basin are obtained, and the confluence boundaries are combined to obtain slope units. According to the drainage basin and slope unit optimization extraction model originally supported by the GIS, generation of parallel boundaries of the drainage basin and the slope unit is avoided, and compared with an existing algorithm, the method only depends on the GIS, and multiple scales are reserved.

Description

Technical Field

[0001] The invention belongs to the field of GIS image processing, and in particular relates to a GIS optimization division method of watershed and slope units based on ridge-valley separation. Background Art

[0002] Considering that landslides usually occur on slopes, scholars have focused on using slope units as units for landslide susceptibility mapping. The classical approach to slope units is based on a watershed segmentation method constructed from hydrological analysis. However, when the flow direction method is used to extract the drainage network, the presence of depressions constitutes an obstacle to flow routing. It is necessary to raise the internal elevation to the level of the lowest outlet so that the water in each pixel can flow to the outlet. In this process, the depressions are filled and the original low-lying areas are converted into completely flat surfaces. Especially in relatively flat landscapes with limited topographic relief, very large areas can be converted into completely flat surfaces. Parallel river networks are extracted in flat areas (whether primary or secondary), resulting in parallel sub-basin boundaries. Slope units are formed by merging the concave sub-basin boundaries extracted from the original DEM with the convex sub-basin extracted from the inverted DEM, inheriting the parallel boundary characteristics of the sub-basin, which contradicts the geomorphic environment in some local areas. In particular, the inverted DEM converts the original mountain tops into depressions, and then a large number of large flat areas are generated after filling the depressions.

[0003] Previous studies have made different improvements and optimizations to slope units. A more representative method is the curvature watershed segmentation algorithm, which bypasses the filling process by segmenting the watershed on the average curvature. This method can be implemented only by relying on common GIS tools and has been referenced and used by a large number of scholars. However, the size of the extracted slope units is difficult to adjust, that is, the multi-scale characteristics of the slope units are missing. Other scholars have also tried to optimize slope units with the help of other software tools, but due to being separated from ArcGIS, it is difficult to be promoted and used. This article will introduce a new GIS optimization division method for watersheds and slope units. This method can retain the multi-scale characteristics of slope units and is completely dependent on common GIS tools. Summary of the invention

[0004] Purpose of the invention: The purpose of the present invention is to provide a GIS optimization division method for watershed and slope units based on ridge-valley separation, which limits the filling range of depressions by separating the ridges and valleys of DEM, suppresses the parallel boundaries of watershed and slope units, and thus optimizes the watershed and slope units.

[0005] Technical solution:

[0006] A GIS optimization division method for watershed and slope units based on ridge-valley separation includes the following steps:

[0007] Step 1, obtain the digital elevation model (DEM) of the study area, invert the DEM to obtain the inverted digital elevation model FDEM;

[0008] Step 2: Perform local confluence segmentation on DEM and FDEM respectively to obtain the confluence boundaries of the local concave inner basin and the convex inner basin as potential ridge and valley vector lines respectively;

[0009] Step 3, convert the potential ridge and valley vector lines into ridge and valley candidate path grids, superimpose the valley candidate path in the DEM, move the grid of the valley candidate path downward to obtain the V-DEM, and superimpose the ridge candidate path in the FDEM, move the grid of the ridge candidate path downward to obtain the R-FDEM;

[0010] Step 4: Perform sub-basin segmentation on V-DEM and R-FDEM respectively to obtain the confluence boundaries of the concave sub-basin and the convex sub-basin, and merge them to obtain the slope unit.

[0011] Furthermore, the specific steps of step 1 are:

[0012] (11) Obtain DEM data of the study area;

[0013] (12) Construct inverse FDEM data of the study area.

[0014] Furthermore, the specific steps of step 2 are:

[0015] (21) Calculate the flow direction on DEM and FDEM;

[0016] (22) Extract water collection grids on DEM and FDEM;

[0017] (23) Extract the concave and convex inner watersheds of DEM and FDEM.

[0018] Furthermore, the specific steps of step 3 are:

[0019] (31) converting the raster data of the concave inner watershed and the convex inner watershed into vector data of the concave inner watershed and the convex inner watershed;

[0020] (32) converting the vector data of the concave inner watershed and the convex inner watershed into ridge and valley vector line data;

[0021] (33) converting ridge and valley vector line data into raster data of ridge and valley candidate paths;

[0022] (34) In DEM, the valley alternative path grid is superimposed and the grid at the valley position is moved downward to obtain V-DEM. In FDEM, the ridge alternative path grid is superimposed and the grid at the ridge position is moved downward to obtain R-FDEM.

[0023] Furthermore, the specific steps of step 4 are:

[0024] (41) Fill the depressions of V-DEM and R-FDEM;

[0025] (42) Calculate the flow direction and flow on V-DEM and R-FDEM after filling;

[0026] (43) Extract the concave and convex sub-basins on V-DEM and R-FDEM after filling;

[0027] (44) The concave and convex sub-basin raster data are converted into concave and convex sub-basin area vector data, and the slope unit area vector data are obtained by superposition.

[0028] Furthermore, the inner watershed boundary of the DEM is taken as the raster extraction basis for the ridge alternative path, and the inner watershed boundary of the inverted DEM is taken as the raster extraction basis for the valley alternative path.

[0029] Furthermore, by superimposing the valley and ridge alternative path grids to include the valley and ridge target grids, the valley grid of the DEM and the ridge grid of the FDEM are moved downward by a certain distance to form a significant drop. This distance should be greater than the depth of the depression, and a larger value (greater than 30m) can also be set to limit the filling of the depression to the valley and ridge alternative path grids. The generation of parallel river networks requires a certain amount of lateral space. Since the grid width of the path is one grid, the conditions for the generation of parallel river networks are eliminated.

[0030] Furthermore, the watershed and slope unit extraction follows the conventional sub-watershed segmentation method, but the starting data is the digital elevation model after valley-ridge separation produced by the present invention: V-DEM and R-FDEM.

[0031] Furthermore, native analysis tools of ArcGIS or ArcGIS Pro are used, which can be integrated, such as using the ModelBuilder tool, or can be performed in steps.

[0032] Beneficial effects: The method of the present invention can avoid the generation of parallel boundaries and retain the multi-scale characteristics of slope units. Compared with existing algorithms, this method only relies on GIS and retains multi-scale properties, and has broad prospects for promotion and application. BRIEF DESCRIPTION OF THE DRAWINGS

[0033] Figure 1 is a flow chart of the method of the present invention.

[0034] Figure 2 Schematic diagram of the ridge-valley separation model of the present invention, wherein a is the DEM or FDEM before separation, and b is the V-DEM or R-FDEM after separation.

[0035] Figure 3 The following are the step-by-step results of the valley-separated V_DEM and the ridge-separated R_FDEM, where a is the inner watershed on the DEM, b is the inner watershed on the FDEM, c is the grid of the ridge alternative path, d is the grid of the valley alternative path, e is the valley-separated V_DEM, and f is the ridge-separated R_FDEM.

[0036] Figure 4 This is the extraction result map of river network, ridge, concave sub-basin, convex sub-basin and slope unit based on V_DEM and R_FDEM, where a is the river network grid based on V_DEM, b is the river network grid based on R_FDEM, c is the concave sub-basin based on V_DEM, d is the convex sub-basin based on R_FDEM, and e is the slope unit based on ridge-valley separation.

[0037] Figure 5 It is the slope unit map extracted by this method, the traditional sub-basin segmentation method and the curvature basin segmentation method, among which ac is the slope unit extracted by this method, and the catchment area thresholds are 400, 800 and 1600 respectively; df is the slope unit extracted by the traditional sub-basin segmentation, and the catchment area thresholds are 400, 800 and 1600 respectively; gi is the slope unit extracted by the curvature basin segmentation, and the grid sizes are 30, 90 and 180m respectively. DETAILED DESCRIPTION

[0038] The technical solution of the present invention is further described below in conjunction with the accompanying drawings.

[0039] The present invention proposes a GIS optimization partitioning method for watershed and slope units based on ridge-valley separation, such as Figure 1 As shown, the specific steps include:

[0040] Step 1, obtain the digital elevation model (DEM) of the study area, invert the DEM to obtain the inverted digital elevation model FDEM;

[0041] This application is a new understanding of the positive and negative terrain features in DEM. The continental surface is always uneven and produces vertices. Around a vertex, a raised geomorphic entity unit is formed, and the vertex can be regarded as the core of the raised unit. Therefore, the continental surface can be divided into raised units. The boundaries of the raised units are connected and continuous throughout the study area, and are regarded as alternative valley paths, showing the landscape of the drainage system extending to the watershed, and are therefore used to pre-set the possible paths of the water system.

[0042] The ASTER GDEM V3 data was downloaded from the website "Geospatial Data Cloud". The tile is N36E107. The data covers the terrain of the Loess Plateau. The raster data is projected to 30×30 meters. The terrain is generally low in the center and high around, with an altitude between 1820-1043 meters. Figure 3 As shown in a. Since the research area is too large to be displayed in a limited space, an internal sub-area is selected to display the extraction process and results.

[0043] Construct the inverse FDEM data of the study area. The steps are:

[0044] Use the GIS raster calculator "Raster Calculation" tool to invert the original DEM. The calculation formula is:

[0045] FDEM=-DEM

[0046] Step 2: Perform local confluence segmentation on DEM and FDEM respectively to obtain the confluence boundaries of the local concave inner basin and the convex inner basin as ridges and valleys respectively;

[0047] The core of this step is the raster extraction of ridge and valley alternative paths. The inner watershed boundary of DEM is used as the ridge alternative path. The inner watershed is different from the sub-watershed. The inner watershed uses depressions as water collection points and does not need to be filled, while the sub-watershed uses river network branches as water collection points and needs to be filled. The inner watershed boundary of the inverted FDEM is used as the valley alternative path, with the mountain top point as the water collection point;

[0048] The steps to calculate the flow direction on DEM and FDEM are:

[0049] 1) Based on the flow direction calculation "Flow Direction" tool, take DEM as input to obtain the flow direction Flowdir_DEM;

[0050] 2) Based on the flow direction calculation “Flow Direction” tool, with FDEM as input, the flow direction Flowdir_FDEM is obtained.

[0051] The steps to extract the water collection grid Sink on DEM and FDEM are:

[0052] 1) Based on the “Sink” tool, the water collection grid Sink_DEM of DEM is obtained with Flowdir_DEM as input;

[0053] 2) Based on the “Sink” tool, the FDEM water collection grid Sink_FDEM is obtained using Flowdir_FDEM as input.

[0054] The steps to extract the concave and convex inner watersheds of DEM and FDEM are as follows:

[0055] 1) Based on the “Watershed” tool, the inner watershed Watershed_DEM of DEM is obtained with Flowdir_DEM and Sink_DEM as input, such as Figure 3 As shown in a;

[0056] 2) Based on the “Watershed” tool, Flowdir_FDEM and Sink_FDEM are used as input to obtain the inner watershed Watershed_FDEM of FDEM, such as Figure 3 As shown in b.

[0057] Step 3: In DEM, superimpose the valleys and move the grids at the valley positions downward to obtain V-DEM. In FDEM, superimpose the ridges and move the grids at the ridge positions downward to obtain R-FDEM. The valleys in DEM are moved downward to obtain the separated V_DEM, so that in the process of V_DEM filling depressions, only the elevation values ​​in the valleys are changed, while the terrain on both sides remains the same, thereby limiting the width of the filled depressions and the generation of flat land, such as Figure 2 As shown;

[0058] The steps for making vector data of concave inner watershed and convex inner watershed are as follows:

[0059] 1) Based on "Raster to Polygon", the concave watershed raster data Watershed_DEM is converted into the concave watershed vector data Watershed_DEM_toPolygon;

[0060] 2) Based on “Raster to Polygon”, the convex inner watershed raster data Watershed_FDEM is converted into the convex inner watershed area vector data Watershed_FDEM_toPolygon.

[0061] The steps for making ridge and valley vector line data are:

[0062] 1) Based on "Polygon to Polyline", the concave watershed vector data Watershed_DEM_toPolygon is converted into ridge vector data Ridgeline;

[0063] 2) Based on "Polygon to Polyline", the convex watershed area vector data Watershed_FDEM_toPolygon is converted into valley vector data Valleyline.

[0064] The steps to create the raster data for the ridge and valley alternative paths are:

[0065] 1) Based on "Polyline to Raster", convert the ridge vector line data Ridgeline into the raster data Ridge of the ridge alternative path, such as Figure 3 As shown in c;

[0066] 2) Based on "Polyline to Raster", convert the valley vector line data Valleyline into the raster data Valley of the valley alternative path, such as Figure 3 As shown in d.

[0067] The steps of ridge-valley separation are:

[0068] 1) Based on the raster calculator "Raster Calculation", superimpose the Valley and move the DEM grid at the valley position downward to obtain the V-DEM, such as Figure 3 As shown in e;

[0069] 2) Based on the raster calculator “Raster Calculation”, superimpose Ridge and move the FDEM grid at the ridge position downward to obtain R-FDEM, such as Figure 3 f.

[0070] Step 4: Perform sub-basin segmentation on V-DEM and R-FDEM respectively to obtain the concave sub-basin and convex sub-basin confluence boundaries;

[0071] The steps for filling depressions in V-DEM and R-FDEM are as follows:

[0072] 1) Based on the “Fill” tool, fill the V-DEM to obtain Fill_V_DEM;

[0073] 2) Based on the "Fill" tool, fill the R-FDEM to obtain Fill_R_FDEM

[0074] The steps for flow direction and flow calculation are:

[0075] 1) Calculate the flow direction Flowdir_V_DEM of Fill_V_DEM based on “Flow Direction”, and then calculate the flow Flowacc_V_DEM based on “Flow_Accumulation”;

[0076] 2) Calculate the flow direction Flowdir_R_FDEM of Fill_R_FDEM based on “Flow Direction”, and then calculate the flow Flowacc_R_FDEM based on “Flow_Accumulation”.

[0077] The steps for extracting concave sub-basins and convex sub-basins are as follows:

[0078] 1) Extract the river network Stream_V_DEM from Flowacc_V_DEM based on "Raster Calculation" ( Figure 4a) Generate the local confluence node StreamLink_V_DEM from Stream_V_DEM and Flowdir_V_DEM based on “Stream Link”; then obtain the concave subbasin raster data Subbasin_V_DEM from Flowdir_V_DEM and StreamLink_V_DEM based on “Watershed”;

[0079] 2) Extract the river network Stream_R_FDEM from Flowacc_R_FDEM based on "Raster Calculation" ( Figure 4 b) Based on “Stream Link”, generate the local confluence node StreamLink_R_FDEM from Stream_R_FDEM and Flowdir_R_FDEM; then based on “Watershed”, obtain the convex subbasin raster data Subbasin_R_FDEM from Flowdir_R_FDEM and StreamLink_R_FDEM.

[0080] The steps for extracting vectors of sub-basins and slope units are as follows:

[0081] 1) Based on “Raster to Polygon”, the concave subbasin raster data Subbasin_V_DEM is converted into the concave subbasin area vector data Concave_Subbasin, such as Figure 4 As shown in c;

[0082] 2) Based on “Raster to Polygon”, the convex subbasin raster data Subbasin_R_FDEM is converted into the convex subbasin area vector data Convex_Subbasin, such as Figure 4 As shown in d;

[0083] 3) Based on “Feature to Polygon”, the concave subbasin Concave_subbasin and the convex subbasin Convex_Subbasin are merged into the slope unit area vector data Slopeunit, such as Figure 4 As shown in e.

[0084] like Figure 5 As shown in the figure, the slope unit map extracted by this method, the traditional sub-basin segmentation method and the curvature basin segmentation method is shown. As can be seen from the figure, this method can solve the problem of parallel slope unit boundaries extracted by the traditional sub-basin segmentation method and retain multi-scale features. However, the curvature basin segmentation method can only adjust the slope unit size by adjusting the grid size. In comparison, this method is the best.

Claims

1. A GIS optimization method for watershed and slope unit division based on ridge-valley separation, It is characterized in that The steps include: Step 1, obtain the digital elevation model (DEM) of the study area, and invert the DEM to obtain the inverted digital elevation model (FDEM); Step 2: Perform local confluence segmentation on DEM and FDEM respectively to obtain the confluence boundaries of the local concave inner basin and the convex inner basin as potential ridge and valley vector lines respectively; Step 3, convert the potential ridge and valley vector lines into ridge and valley candidate path grids, superimpose the valley candidate path in the DEM, move the grid of the valley candidate path downward to obtain the V-DEM, and superimpose the ridge candidate path in the FDEM, move the grid of the ridge candidate path downward to obtain the R-FDEM; Step 4: Perform sub-basin segmentation on V-DEM and R-FDEM respectively to obtain the confluence boundaries of the concave sub-basin and the convex sub-basin, and merge them to obtain the slope unit.

2. The GIS optimization division method of watershed and slope units based on ridge-valley separation according to claim 1, It is characterized in that The specific steps of step 1 are: (11) Obtain DEM data of the study area; (12) Construct inverse FDEM data of the study area.

3. The GIS optimization division method of watershed and slope units based on ridge-valley separation according to claim 1, It is characterized in that The specific steps of step 2 are: (21) Calculate the flow direction on DEM and FDEM; (22) Extract water collection grids on DEM and FDEM; (23) Extract the concave and convex inner watersheds of DEM and FDEM.

4. The GIS optimization division method of watershed and slope units based on ridge-valley separation according to claim 1, It is characterized in that The specific steps of step 3 are: (31) converting the raster data of the concave inner watershed and the convex inner watershed into vector data of the concave inner watershed and the convex inner watershed; (32) converting the vector data of the concave inner watershed and the convex inner watershed into potential ridge and potential valley vector line data; (33) Convert potential ridge and valley vector line data into raster data as candidate paths for ridges and valleys; (34) In DEM, the valley alternative path is superimposed and the grid of the valley path is moved downward to obtain V-DEM. In FDEM, the ridge alternative path is superimposed and the grid of the ridge path is moved downward to obtain R-FDEM.

5. The GIS optimization division method of watershed and slope units based on ridge-valley separation according to claim 1, It is characterized in that The specific steps of step 4 are: (41) Fill the depressions of V-DEM and R-FDEM; (42) Calculate the flow direction and flow on V-DEM and R-FDEM after filling; (43) Extract the concave and convex sub-basins on V-DEM and R-FDEM after filling; (44) converting the concave and convex sub-basin raster data into concave and convex sub-basin area vector data; (45) The vector data of the slope unit area are obtained by superimposing the vector data of the concave and convex sub-basin areas.

6. The GIS optimization division method of watershed and slope units based on ridge-valley separation according to claim 1, It is characterized in that The inner watershed boundary of DEM is used as the raster extraction basis for the ridge alternative path, and the inner watershed boundary of inverted DEM is used as the raster extraction basis for the valley alternative path.

7. The GIS optimization division method of watershed and slope units based on ridge-valley separation according to claim 1, It is characterized in that By superimposing the valley and ridge alternative path grids including the valley and ridge target grids, the valley grid of the DEM and the ridge grid of the FDEM are moved downward by a certain distance to form a significant drop; this distance is greater than the depth of the depression, or the set value is greater than 30m, thereby limiting the filling of the depression to the valley and ridge alternative path grids.

8. The GIS optimization division method of watershed and slope units based on ridge-valley separation according to claim 1, It is characterized in that The extraction of watershed and slope units follows the conventional sub-watershed segmentation method, but the starting data is the digital elevation model after valley-ridge separation obtained in step 3: V-DEM and R-FDEM.

9. The GIS optimization division method of watershed and slope units based on ridge-valley separation according to claim 1, It is characterized in that ArcGIS or ArcGIS Pro native analysis tools can be used, which can be integrated, such as using ModelBuilder tools and ModelBuilder integrated tools, or they can be performed in steps.

Images