Method for quickly classifying loess plateau landform types

Abstract

The invention discloses a loess plateau landform type rapid classification method, which comprises the following steps: S1, determining a minimum processing unit data set: cutting basic raster data of a target drainage basin by taking a single sub-drainage basin as a boundary, and obtaining the basic raster data of a sub-drainage basin range as the minimum processing unit data set for landform classification; s2, sub-basin landform classification: for each minimum processing unit data set, simulating river network traceability one by one, and preliminarily dividing sub-basin grids into valley types, gully types and gully types; respectively merging and / or correcting the island type, the source gully type and the abnormal gully in the preliminary division result; and from the source of the river network grid, correcting the upstream gully-tableland river network to realize sub-basin landform classification. The method has the advantages that the upstream and downstream hydraulic connection among the extracted gully tableland-gully slope-gully types can be ensured, and the method can be better applied to distributed water and sediment model unit division.

Description

Technical Field

[0001] The invention relates to the technical field of landform type recognition, and in particular to a method for quickly classifying landform types on the Loess Plateau. Background Art

[0002] The geomorphology of the Loess Plateau is an important underlying surface for studying gully erosion in the Loess Plateau, and is also an important factor affecting the simulation accuracy of the distributed water-sediment model. Different geomorphologies such as gullies, gully slopes, and gullies have different effects on the water-sediment process and need to be distinguished in the water-sediment model.

[0003] Existing studies mainly use ultra-high-precision DEM and other data to identify landform types, which is difficult to apply to large watersheds on the Loess Plateau. The main reasons are the difficulty in obtaining ultra-high-precision DEM data covering the entire area and the computational dimensionality disaster caused by the large amount of data. On the other hand, most existing algorithms divide landforms based on the morphological characteristics of a single grid, which cannot reflect the upstream and downstream connections between landform types (for example, it may divide the situation where gullies and slopes flow to gullies and plateaus), and cannot meet the needs of using hydrological models. Summary of the invention

[0004] The purpose of the present invention is to provide a method for quickly classifying landform types of the Loess Plateau, thereby solving the above-mentioned problems existing in the prior art.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A method for quickly classifying landform types of the Loess Plateau comprises the following steps:

[0007] S1. Determination of the minimum processing unit data set:

[0008] The basic raster data of the target basin is clipped with a single sub-basin as the boundary, and the basic raster data of the sub-basin range is obtained as the minimum processing unit data set for landform classification;

[0009] S2. Sub-basin geomorphology classification:

[0010] For each minimum processing unit data set, the river network is traced back to the source by simulating one by one, and the sub-basin grid is preliminarily divided into gully, gully slope, and gully-tableland types; the island type, source gully-valley type, and abnormal gully-tableland in the preliminary division results are merged and / or corrected respectively; and starting from the source of the river network grid, the upstream gully-tableland river network is corrected to achieve sub-basin landform classification.

[0011] Preferably, step S2 specifically includes the following contents:

[0012] S21, trace back the simulated river network grids, and divide the sub-basin grids into three types: gully valley, gully slope, and gully plateau;

[0013] S22, using the GIS software's mesh filter to merge the island types smaller than the area threshold in the preliminary classification results into the surrounding types, and tracing the river network one by one, and processing the corrected types so that the slope grid connection satisfies the upstream and downstream relationship of gully plateau-gully slope-gully valley;

[0014] S23, modify the sub-basin watershed grid of gully type to gully-plateau type, and recursively move down along the grid flow direction until the simulated river network grid, and modify the grid types of all gully-type grids in the middle to gully-plateau type; trace the source grid by grid from the simulated river network, and if a gully-slope type is encountered, change the gully-plateau type to a gully-slope type along the grid flow direction;

[0015] S24, distinguishing the watershed grid of the gully-plateau type, and modifying the watershed grid of the surrounding grids of the gully-valley or gully-slope type to the gully-valley type;

[0016] S25. Starting from the source of the river network grid, change the river network grid without gully-slope type in the upstream to gully-plateau type, and end at the river network grid with gully-slope type in the upstream.

[0017] Preferably, step S21 specifically includes marking the river network grid as a gully type, tracing the source according to the flow direction, marking the slope grid with a slope less than the slope-valley slope threshold as a gully type, continuing to trace upward, marking the slope grid with a slope greater than the plateau slope threshold as a gully-slope type, and marking the slope grid with a slope less than the plateau slope threshold as a gully-plateau type;

[0018] If there is an area with a gentle slope in the middle of the gully slope type, it needs to be marked as the gully slope type, that is, to ensure that the division result is distributed as gully plateau-gully slope-gully valley from top to bottom.

[0019] Preferably, after step S2, the method further includes: after all the landforms in the sub-basins are classified, integrating the sub-basin classification results according to the relative positions of the sub-basins in the target basin to obtain a complete landform classification result of the target basin.

[0020] Preferably, GIS software is used to calculate the basic grid data of the target watershed, such as the grid flow direction, runoff accumulation, simulated river network, slope and sub-basin unit of the target watershed, based on the DEM data of the target watershed.

[0021] Preferably, the grid flow direction is extracted using the D8 algorithm.

[0022] Preferably, the simulated river network is extracted from the cumulative number of confluence according to a given river network threshold, and the values ​​greater than the threshold are defined as 1, indicating a river network grid, and the rest are defined as 0, indicating a slope grid; the river network threshold is determined by trial calculation according to the basin conditions.

[0023] Preferably, the sub-basin unit divides the area belonging to the same river section into the same sub-basin according to the simulated river network confluence control range.

[0024] The beneficial effects of the present invention are as follows: 1. The present invention divides the raster data of a large watershed into numerous relatively independent sub-watersheds for landform type classification, and can use a parallel algorithm to simultaneously calculate different sub-watersheds, effectively improving the classification rate. 2. Compared with the existing algorithms, the present invention can use a relatively low-precision DEM for landform type classification, and can ensure a certain degree of correctness of the classification results. 3. The gully-slope-gully-valley types extracted by the present invention can ensure the upstream and downstream hydraulic connection between the three, and can be better applied to the division of distributed water and sediment model units. BRIEF DESCRIPTION OF THE DRAWINGS

[0025] Figure 1 It is a principle flow chart of the method in the embodiment of the present invention;

[0026] Figure 2 Schematic diagram of dividing cases in an embodiment of the present invention. DETAILED DESCRIPTION

[0027] In order to make the purpose, technical solution and advantages of the present invention more clearly understood, the present invention is further described in detail below in conjunction with the accompanying drawings. It should be understood that the specific implementation methods described herein are only used to explain the present invention and are not used to limit the present invention.

[0028] like Figure 1 As shown, in this embodiment, a method for rapid classification of landform types of the Loess Plateau is provided, including the following three parts:

[0029] 1. Basic raster data acquisition

[0030] GIS software is used to calculate the basic grid data of the target watershed, such as grid flow direction, confluence accumulation, simulated river network, slope and sub-basin unit, based on the DEM data of the target watershed.

[0031] The grid flow direction is extracted using the D8 algorithm; the simulated river network is extracted from the cumulative number of confluence according to the given river network threshold, and the value greater than the threshold is set to 1 (indicating the river network grid), and the rest is set to 0 (indicating the slope grid). The river network threshold is determined by trial calculation according to the watershed conditions. The sub-basin unit is divided into the same sub-basin according to the simulated river network confluence control range.

[0032] 2. Determination of the minimum processing unit data set:

[0033] The basic raster data of the target basin is clipped with a single sub-basin as the boundary, and the basic raster data of the sub-basin range is obtained as the minimum processing unit dataset for landform classification.

[0034] 3. Sub-basin landform classification:

[0035] For each minimum processing unit data set, simulate the river network traceback one by one, and preliminarily divide the sub-basin grid into gully, gully slope, and gully plateau types; merge and / or correct the island type, source gully type, and abnormal gully plateau in the preliminary division results; and correct the upstream gully plateau river network starting from the source of the river network grid to achieve sub-basin landform classification. Specifically, the following five steps need to be performed in each minimum processing unit data set:

[0036] 2.1. Tracing back from each simulated river network grid, the sub-basin grids are divided into three types: gully, gully slope, and gully-plateau. The specific division process is to mark the river network grid as the gully-valley type, trace the source according to the flow direction, mark the slope grid with a slope gradient less than the slope-valley threshold as the gully-valley type, continue to trace upwards and mark the slope grid with a slope gradient greater than the plateau slope threshold as the gully-slope type, and mark the slope grid with an upstream slope gradient less than the plateau slope threshold as the gully-plateau type. It should be noted that if there is a gentle slope area in the gully-slope type, it needs to be marked as the gully-slope type, that is, to ensure that the division result is a gully-plateau-gully-slope-gully type distribution from top to bottom.

[0037] 2.2. Use the sieve filter of GIS software to merge the island types with an area threshold smaller than the initial classification results into the surrounding types, and simulate the river network tracing one by one to process the corrected types so that the slope grid connection satisfies the upstream and downstream relationship of gully plateau-gully slope-gully valley.

[0038] 2.3. Change the sub-basin watershed grid of gully type to gully-plateau type, and recursively move down along the grid flow direction until the simulated river network grid, and change the grid type of all gully-type grids in the middle to gully-plateau type; start from the simulated river network and trace the source grid by grid. If a gully-slope type is encountered, change the gully-plateau type to a gully-slope type along the grid flow direction.

[0039] 2.4. Identify the watershed grids of gully-plateau type, and modify the watershed grids whose surrounding grids are all gully or gully-slope type to gully type.

[0040] 2.5. Starting from the source of the river network grid, change the river network grid without gully-slope type in the upstream to gully-plateau type, and end at the river network grid with gully-slope type in the upstream.

[0041] In this embodiment, after all the landforms in the sub-basins are classified, the sub-basin classification results are integrated according to the relative positions of the sub-basins in the target basin to obtain the complete landform classification results of the target basin. Figure 2 .

[0042] In this embodiment, a parallel algorithm may be used to simultaneously calculate different sub-basins, thereby increasing the classification rate.

[0043] By adopting the above technical solution disclosed in the present invention, the following beneficial effects are obtained:

[0044] The present invention provides a method for rapid classification of landform types on the Loess Plateau. The present invention classifies landform types by splitting raster data in a large watershed into numerous relatively independent sub-watersheds. A parallel algorithm can be used to simultaneously calculate different sub-watersheds, thereby effectively improving the classification rate. Compared with existing algorithms, the present invention can use a relatively low-precision DEM to classify landform types, and can ensure a certain degree of correctness of the classification results. The gully-valley-gully slope-gully type extracted by the present invention can ensure the upstream and downstream hydraulic connection between the three, and can be better applied to the division of distributed water and sediment model units.

[0045] The above is only a preferred embodiment of the present invention. It should be pointed out that for ordinary technicians in this technical field, several improvements and modifications can be made without departing from the principle of the present invention. These improvements and modifications should also be considered as the scope of protection of the present invention.

Claims

1. A method for rapid classification of landform types on the Loess Plateau, characterized by: The following steps are included: S1. Determination of the minimum processing unit data set: The basic raster data of the target basin is clipped with a single sub-basin as the boundary, and the basic raster data of the sub-basin range is obtained as the minimum processing unit data set for landform classification; S2. Sub-basin geomorphology classification: For each minimum processing unit data set, the river network is traced back to the source by simulating one by one, and the sub-basin grid is preliminarily divided into gully, gully slope, and gully-tableland types; the island type, source gully-valley type, and abnormal gully-tableland in the preliminary division results are merged and / or corrected respectively; and starting from the source of the river network grid, the upstream gully-tableland river network is corrected to achieve sub-basin landform classification.

2. The method for rapid classification of landform types of the Loess Plateau according to claim 1 is characterized by: Step S2 specifically includes the following contents: S21, trace back the simulated river network grids, and divide the sub-basin grids into three types: gully valley, gully slope, and gully plateau; S22, using the GIS software's mesh filter to merge the island types smaller than the area threshold in the preliminary classification results into the surrounding types, and tracing the river network one by one, and processing the corrected types so that the slope grid connection satisfies the upstream and downstream relationship of gully plateau-gully slope-gully valley; S23, modify the sub-basin watershed grid of gully type to gully-plateau type, and recursively move down along the grid flow direction until the simulated river network grid, and modify the grid types of all gully-type grids in the middle to gully-plateau type; trace the source grid by grid from the simulated river network, and if a gully-slope type is encountered, change the gully-plateau type to a gully-slope type along the grid flow direction; S24, distinguishing the watershed grid of the gully-plateau type, and modifying the watershed grid of the surrounding grids of the gully-valley or gully-slope type to the gully-valley type; S25. Starting from the source of the river network grid, change the river network grid without gully-slope type in the upstream to gully-plateau type, and end at the river network grid with gully-slope type in the upstream.

3. The method for rapid classification of landform types of the Loess Plateau according to claim 2 is characterized by: Step S21 specifically includes marking the river network grid as a gully type, tracing the source according to the flow direction, marking the slope grid with a slope less than the slope-valley slope threshold as a gully type, and continuing to trace upwards, marking the slope grid with a slope greater than the plateau slope threshold as a gully-slope type, and marking the slope grid with a slope less than the plateau slope threshold as a gully-plateau type; If there is an area with a gentle slope in the middle of the gully slope type, it needs to be marked as the gully slope type, that is, to ensure that the division result is distributed as gully plateau-gully slope-gully valley from top to bottom.

4. The method for rapid classification of landform types of the Loess Plateau according to claim 2 is characterized by: The step S2 also includes, after all the landforms in the sub-basins are classified, integrating the sub-basin classification results according to the relative positions of the sub-basins in the target basin to obtain a complete landform classification result of the target basin.

5. The method for rapid classification of landform types of the Loess Plateau according to any one of claims 1 to 4, characterized in that: GIS software is used to calculate the basic grid data of the target watershed, such as grid flow direction, confluence accumulation, simulated river network, slope and sub-basin unit, based on the DEM data of the target watershed.

6. The method for rapid classification of landform types of the Loess Plateau according to claim 5 is characterized by: The grid flow direction is extracted using the D8 algorithm.

7. The method for rapid classification of landform types of the Loess Plateau according to claim 5 is characterized by: The simulated river network is extracted from the cumulative number of confluence according to a given river network threshold, and the values ​​greater than the threshold are set to 1, representing the river network grid, and the rest are set to 0, representing the slope grid; the river network threshold is determined by trial calculation based on the basin conditions.

8. The method for rapid classification of landform types of the Loess Plateau according to claim 5 is characterized by: The sub-basin unit divides the area belonging to the same river section into the same sub-basin according to the simulated river network confluence control range.

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