CN109710718B - Method for quickly estimating plant coverage factor - Google Patents
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Abstract
The invention discloses a method for quickly estimating a plant covered factor. The method comprises the steps of judging the stability of the land use type grid to obtain a stable land use type grid and an unstable land use type grid. And secondly, determining the grid value range of the vegetation coverage factor on the stable land use type grid by utilizing meta analysis. And thirdly, dynamically simulating the vegetation coverage factor on the unstable land use type grid by using the linear model. And finally, obtaining a complete vegetation coverage factor spatial distribution map through spatial combination. The method quantitatively analyzes the space-time variation characteristics of the vegetation cover factors on the land use types at the same position and different time, dynamically simulates the change of the vegetation cover factors in the process of converting the land use types, overcomes the defect that the dynamic change of the vegetation cover factors in the process of changing the land use cannot be estimated by the traditional method, and provides a new idea for simulating the soil erosion in a large regional scale.
Description
Technical Field
The invention relates to the technical field of soil erosion methods, in particular to a method for quickly estimating a plant coverage factor.
Background
In the soil erosion estimation model, the vegetation coverage factor is the ratio of the amount of soil loss on the land with vegetation coverage to the amount of soil loss on the clear-ploughed continuous fallow land in a certain period of time under the same conditions. Vegetation coverage factors reflect the inhibitory effect of vegetation coverage on soil erosion (Wischmeier et al, 1965). In general, the estimation of the vegetation coverage factor needs information such as a plant canopy, ground coverage, ground roughness, soil water content and the like, and the estimation value of the vegetation coverage factor can only represent a simulation result on a point location scale or a standard cell scale, and the estimation of a large area scale cannot be realized, so that a new method needs to be found to establish a simple algorithm suitable for the vegetation coverage factor of the large area scale.
At present, the method for researching the large-area scale vegetation coverage factor at home and abroad is mainly a land utilization type direct value assigning method. Namely, the vegetation coverage factors on different land use types are subjected to empirical value assignment. The direct valuation method of the land utilization types considers that the vegetation coverage factors on the same land utilization type are the same and are a constant. However, the vegetation coverage factor value is gradually changed during the change of the land use type. For example, in the process of changing forest land into grassland, the vegetation coverage degree is continuously decreased from high to low until a stable state is reached, and in the process of the change, the value of the vegetation coverage factor is gradually increased along with the decrease of the vegetation coverage degree. The traditional valuation method ignores the dynamic variability characteristics of the vegetation coverage factor in the process of changing the land utilization types at different time in the same place, so that errors exist.
The land utilization type and the vegetation coverage information are comprehensively utilized, a model relation between the land utilization type and the vegetation coverage information is established, and the rapid quantitative estimation and the drawing of the large-area scale vegetation coverage factor are facilitated.
Disclosure of Invention
The invention aims to solve the problems in the existing method and provide a method for quickly estimating the plant covered factor.
The technical scheme adopted by the invention comprises the following steps:
a method for rapidly estimating a plant coverage factor comprises the following steps:
step (1), data acquisition: acquiring land use type grid data and MODIS vegetation grid data in a time span range according to the time span range to be estimated;
step (2), primarily judging the stability of the land utilization type grid: carrying out multi-temporal primary judgment on the stability of the land use type grid on the land use type grid data acquired in the step (1) to obtain a long-term stable land use type grid and a long-term unstable land use type grid;
and (3) further judging the stability of the land utilization type grid: further judging the long-term unstable land utilization type grid obtained in the step (2) to obtain a short-term stable land utilization type grid and a short-term unstable land utilization type grid;
step (4), land utilization type grid conversion and identification: analyzing the short-term unstable land use type grids obtained in the step (3), and identifying and tracking the conversion form of the land use type grids in the land use type grids;
and (5) carrying out assignment on vegetation coverage factors of cultivated land: directly assigning the cultivated land grid in the long-term stable land utilization type obtained in the step (2) and the cultivated land grid in the short-term stable land utilization type obtained in the step (3);
and (6) assigning the value range of the vegetation coverage factor of the land utilization type except cultivated land: determining grid value ranges of vegetation coverage factors of different land utilization types except cultivated land according to the land utilization type grid data obtained in the step (1);
and (7) determining the vegetation coverage factor value of the stable land utilization type grid: obtaining vegetation cover factor values except cultivated land on the two types of stable land use type grids by establishing a linear model between a vegetation cover factor grid threshold value obtained in the step (5) and MODIS vegetation grid data obtained in the step (1) for the two types of stable land use type grids, namely the long-term stable land use type grid obtained in the step (2) and the short-term stable land use type grid obtained in the step (3), and carrying out grid assignment;
step (8) vegetation coverage factor value determination of the short-term unstable land utilization type grid: for the conversion form of the land use type grid identified in the step (4), a vegetation coverage factor value on the short-term unstable land use type grid data is obtained by establishing a linear model between the vegetation coverage factor grid threshold obtained in the step (5) and the MODIS vegetation grid data obtained in the step (1);
combining vegetation coverage factors in the step (9): and (3) merging the cultivated land vegetation coverage factor value obtained in the step (6), the vegetation coverage factor value of the stable land utilization type grid obtained in the step (7) and the vegetation coverage factor value of the short-term unstable land utilization type grid obtained in the step (8) by using a space merging method to obtain a complete vegetation coverage factor space distribution map.
Preferably, the preliminary determination of the grid stability of the land use type in the step (2) is performed through primary classification of the land use type; the land utilization types comprise 4 primary classifications and 16 secondary classifications of cultivated land, forest land, grassland and unused land; the MODIS vegetation grid data are MOD44B data, time resolution is year, space resolution is 250 meters, and each grid comprises tree coverage, non-tree coverage and bare soil coverage.
Preferably, the long-term stable land use type grid in the step (2) refers to a grid in which the land use type does not change within the time span to be estimated; a long term unstable land use type grid is a grid in which the land use type changes over the time span to be estimated.
Preferably, in the step (3), the short-term stable land use type grid refers to a grid which divides the time span range to be estimated into a plurality of sub-span ranges, and the land use type does not change in any two adjacent sub-span ranges; the short-term unstable land use type grid refers to a grid with a land use type changed in all the adjacent two sub-span ranges.
Preferably, the transformation of the land use type grid in step (4) includes forest land-to-grass land interconversion and grass land-to-arable land interconversion.
Preferably, the vegetation cover factor value of the cultivated land in the step (5) and the vegetation cover factor value range of the land use type other than the cultivated land in the step (6) include a maximum value and a minimum value, and the values are obtained by meta analysis.
Preferably, the vegetation coverage factor value of the stable land utilization type grid in the step (7) is simulated by three linear models, namely simulation of vegetation coverage factor on stable forest land, simulation of vegetation coverage factor on stable grassland and simulation of vegetation coverage factor on stable unutilized land, wherein the simulation formula is as follows:
Cforest (forest)＝MinForest (forest)+(MaxForest (forest)-MinForest (forest))×(100-TC)×0.01
Wherein, CForest (forest)Is to stabilize the vegetation coverage factor value, Max, on the forest landForest (forest)Is the maximum value of the vegetation coverage factor, Min, on the stable forest landForest (forest)The minimum value of the vegetation coverage factor on the stable forest land, and TC is the tree-containing coverage value of MODIS vegetation grid data;
Cgrass (Haw)＝MinGrass (Haw)+(MaxGrass (Haw)-MinGrass (Haw))×NVS×0.01
Wherein, CGrass (Haw)Is a value of the vegetation coverage factor, Max, on stable grasslandsGrass (Haw)Is the maximum value of the vegetation coverage factor, Min, on stable grasslandsGrass (Haw)Is the minimum value of the vegetation coverage factor on the stable grassland, and NVS is the bare soil coverage value of MODIS vegetation grid data;
Cis prepared from＝MinIs prepared from+ (Max not-Min)Is prepared from)×NVS×0.01
Wherein, CIs prepared fromIs the stable vegetation cover factor value on the unused land, MaxIs prepared fromIs the maximum value of the vegetation coverage factor, Min, on the stable unutilized groundIs prepared fromIs the minimum value of the stable unused land vegetation coverage factor, and NVS is the bare soil coverage value of MODIS vegetation grid data.
Preferably, the determining of the vegetation coverage factor value of the short-term unstable land utilization type grid in the step (8) is simulated by two linear models, namely a short-term unstable forest land and grassland interconversion vegetation coverage factor model and a short-term unstable grassland and farmland interconversion vegetation coverage factor model, and the specific formula is as follows:
Cforest and grass＝MinForest and grass+(MaxForest and grass-MinForest and grass)×NVS×0.01
Wherein, CForest and grassIs a vegetation cover factor value, Max, of short-term unstable woodland and grassland interconversionForest and grassIs the maximum value of the vegetation coverage factor, Max, of the short-term unstable woodland and grassland interconversionForest and grass-minimum value of vegetation coverage factor on grassland; minForest and grassIs the minimum value of the vegetation coverage factor, Min, of the short-term unstable woodland and grassland interconversionForest and grassMaximum value of vegetation coverage factor on forest land; NVS is the bare soil coverage value of MODIS vegetation grid data;
Cgrass plough＝MinGrass plough+(MaxGrass plough-MinGrass plough)×NVS×0.01
Wherein, CGrass ploughIs the vegetation cover factor value, Max, of the mutual conversion between the short-term unstable grassland and the cultivated landGrass ploughIs the maximum value of the vegetation coverage factor, Max, of the interconversion between the short-term unstable grassland and the cultivated landGrass ploughThe minimum value of vegetation coverage factors on the farmland; minGrass ploughIs the minimum value of the vegetation coverage factor, Min, of the interconversion between the short-term unstable grassland and the cultivated landGrass ploughMaximum value of vegetation coverage factor on grasslands; NVS is bare soil coverage value of MODIS vegetation grid data.
Compared with the prior art, the invention has the beneficial effects that:
the invention estimates the vegetation cover factor in a large-scale area, can quantitatively analyze the variability characteristics of the vegetation cover factor on the land utilization types of the same place at different time, and can also dynamically simulate the vegetation cover factor change caused in the mutual conversion process between woodland, grassland and cultivated land. The method overcomes the defect that the traditional assignment method ignores the dynamic variability characteristics of the vegetation cover factor in the process of changing the land use types at different places and different times, provides a new method for dynamically estimating the vegetation cover factor in large regional scales, and has reference significance for making the water and soil conservation policy in the large regional scales.
Drawings
Fig. 1 is a spatial distribution diagram of the coverage factor of the young tibetan plateau according to the embodiment 2015.
Detailed Description
The invention is further illustrated with reference to the following figures and examples.
The method for rapidly estimating the vegetation coverage factor comprises the following steps:
step (1), data acquisition: and acquiring land use type grid data and MODIS vegetation grid data in the time span range according to the time span range to be estimated.
Step (2), primarily judging the stability of the land utilization type grid: carrying out multi-temporal primary judgment on the stability of the land use type grid on the land use type grid data acquired in the step (1) to obtain a long-term stable land use type grid and a long-term unstable land use type grid;
the primary judgment of the grid stability of the land utilization type is carried out through the primary classification of the land utilization type; the land use types include 4 primary classifications and 16 secondary classifications of cultivated land, woodland, grassland, and unused land. The MODIS vegetation grid data adopted in the invention is MOD44B data, the time resolution is year, the space resolution is 250 meters, and each grid comprises three layers of data of tree coverage, non-tree coverage and bare soil coverage.
The specific methods for discriminating the long-term stable land use type grid and the long-term unstable land use type grid are as follows: the long-term stable land use type grid refers to a grid in which the land use type is not changed all the time within the time span range to be estimated; a long term unstable land use type grid is one in which the land use type has changed over the time span to be estimated.
And (3) further judging the stability of the land utilization type grid: and (3) further judging the long-term unstable land use type grid obtained in the step (2) to obtain a short-term stable land use type grid and a short-term unstable land use type grid, wherein the specific judgment method comprises the following steps:
the short-term stable land use type grid refers to a grid which divides a time span range to be estimated into a plurality of sub-span ranges, and the land use type does not change in any two adjacent sub-span ranges; while unsatisfactory ones are classified as short-term unstable land use type grids, i.e. grids in which the land use type changes in all adjacent subspans.
Step (4), land utilization type grid conversion and identification: analyzing the short-term unstable land use type grids obtained in the step (3), and identifying and tracking a conversion form of the land use type grids in the land use type grids. The conversion form of the land use type grid includes forest land and grassland interconversion and grassland and arable land interconversion.
And (5) carrying out assignment on vegetation coverage factors of cultivated land: and (3) directly assigning the cultivated land grid in the long-term stable land utilization type obtained in the step (2) and the cultivated land grid in the short-term stable land utilization type obtained in the step (3). The vegetation coverage factor value of cultivated land is obtained by meta analysis.
And (6) assigning the value range of the vegetation coverage factor of the land utilization type except cultivated land: and (2) determining the grid value range of the vegetation coverage factors of different land utilization types except cultivated land according to the land utilization type grid data obtained in the step (1). The value range of the vegetation coverage factor of the land utilization type except cultivated land comprises the maximum value and the minimum value of the grid, and the values are obtained through meta analysis.
And (7) determining the vegetation coverage factor value of the stable land utilization type grid: and (3) for the two types of stable land utilization type grids, namely the long-term stable land utilization type grid obtained in the step (2) and the short-term stable land utilization type grid obtained in the step (3), obtaining vegetation coverage factor values except cultivated land on the two types of stable land utilization type grid data by establishing a linear model between the vegetation coverage factor grid threshold obtained in the step (6) and the MODIS vegetation grid data obtained in the step (1), and carrying out grid assignment. The specific calculation method is as follows:
the vegetation cover factor value of the stable land utilization type grid is simulated through three linear models, namely the simulation of the vegetation cover factor on a stable forest land, the simulation of the vegetation cover factor on a stable grassland and the simulation of the vegetation cover factor on a stable unused land, wherein the simulation formula is as follows:
Cforest (forest)＝MinForest (forest)+(MaxForest (forest)-MinForest (forest))×(100-TC)×0.01
Wherein, CForest (forest)Is to stabilize the vegetation coverage factor value, Max, on the forest landForest (forest)Is the maximum value of the vegetation coverage factor, Min, on the stable forest landForest (forest)The minimum value of the vegetation coverage factor on the stable forest land, and TC is the tree-containing coverage value of MODIS vegetation grid data;
Cgrass (Haw)＝MinGrass (Haw)+(MaxGrass (Haw)-MinGrass (Haw))×NVS×0.01
Wherein, CGrass (Haw)Is a value of the vegetation coverage factor, Max, on stable grasslandsGrass (Haw)Is the maximum value of the vegetation coverage factor, Min, on stable grasslandsGrass (Haw)Is the minimum value of the vegetation coverage factor on the stable grassland, and NVS is the bare soil coverage value of MODIS vegetation grid data;
Cis prepared from＝MinIs prepared from+(MaxIs prepared from-MinIs prepared from)×NVS×0.01
Wherein, CIs prepared fromIs the stable vegetation cover factor value on the unused land, MaxIs prepared fromIs the maximum value of the vegetation coverage factor, Min, on the stable unutilized groundIs prepared fromIs the minimum value of the stable unused land vegetation coverage factor, and NVS is the bare soil coverage value of MODIS vegetation grid data.
Step (8) vegetation coverage factor value determination of the short-term unstable land utilization type grid: for the conversion form of the land use type grid identified in the step (4), a vegetation coverage factor value on the short-term unstable land use type grid data is obtained by establishing a linear model between the vegetation coverage factor grid threshold obtained in the step (6) and the MODIS vegetation grid data obtained in the step (1);
the vegetation coverage factor value determination of the short-term unstable land utilization type grid is simulated by two linear models, namely a vegetation coverage factor simulation of the mutual transformation of the short-term unstable forest land and the grassland and a vegetation coverage factor simulation of the mutual transformation of the short-term unstable grassland and the cultivated land, wherein the specific formulas are as follows respectively:
Cforest and grass＝MinForest and grass+(MaxForest and grass-MinForest and grass)×NVS×0.01
Wherein, CForest and grassIs a vegetation cover factor value, Max, of short-term unstable woodland and grassland interconversionForest and grassIs the maximum value of the vegetation coverage factor, Max, of the short-term unstable woodland and grassland interconversionForest and grass-minimum value of vegetation coverage factor on grassland; minForest and grassIs the minimum value of the vegetation coverage factor, Min, of the short-term unstable woodland and grassland interconversionForest and grassMaximum value of vegetation coverage factor on forest land; NVS is the bare soil coverage value of MODIS vegetation grid data;
Cgrass plough＝MinGrass plough+(MaxGrass plough-MinGrass plough)×NVS×0.01
Wherein, CGrass ploughIs the vegetation cover factor value, Max, of the mutual conversion between the short-term unstable grassland and the cultivated landGrass ploughIs the maximum value of the vegetation coverage factor, Max, of the interconversion between the short-term unstable grassland and the cultivated landGrass ploughThe minimum value of vegetation coverage factors on the farmland; minGrass ploughIs the minimum value of the vegetation coverage factor, Min, of the interconversion between the short-term unstable grassland and the cultivated landGrass ploughMaximum value of vegetation coverage factor on grasslands; NVS is bare soil coverage value of MODIS vegetation grid data.
Combining vegetation coverage factors in the step (9): and (3) merging the cultivated land vegetation coverage factor value obtained in the step (5), the vegetation coverage factor value of the stable land utilization type grid obtained in the step (7) and the vegetation coverage factor value of the short-term unstable land utilization type grid obtained in the step (8) by using a space merging method to obtain a complete vegetation coverage factor space distribution map.
The technical effects of the present invention will be further explained based on the method and with reference to specific embodiments.
Examples
Selecting the Qinghai-Tibet plateau as a research area, quickly estimating vegetation coverage factors on different land utilization types in year 2000-2015, and finally obtaining a Qinghai-Tibet plateau vegetation coverage factor distribution characteristic diagram with the spatial resolution of 1 km:
(1) the method comprises the steps of obtaining land utilization type grid data with 1km spatial resolution within 2000-2015 years in the Qinghai-Tibet plateau range, wherein the data are obtained from a Chinese multi-period land utilization coverage remote sensing monitoring data set (CNLUCC) (http:// www.resdc.cn/doi/doi.aspx. The land use types include 4 primary classifications and 16 secondary classifications of cultivated land, woodland, grassland, and unused land. Obtaining MODIS (Moderate Resolution imaging spectrometer) vegetation grid data product MOD44B data with time Resolution of years and spatial Resolution of 250 meters between 2000-2015 years in Qinghai-Tibet plateau range, wherein each grid comprises three layers of data including tree coverage, non-tree coverage and bare soil coverage. Under the influence of climate change and human activities, there are certain changes in the utilization types of Qinghai-Tibet plateau land between 2000-2015, including interconversion between woodland and grassland and interconversion between grassland and cultivated land. These land use type variations will affect the surface vegetation coverage (e.g., tree coverage, non-tree coverage, and bare soil coverage) and thereby change the value of the vegetation coverage factor across different years of the same grid. Therefore, the stability and the change of the land utilization type need to be judged and tracked, and the change process of the vegetation coverage factor needs to be simulated.
(2) Primarily judging the stability of the land utilization type grid: and (3) carrying out land use type stability judgment on the land use type grid data of the 2000-year 2015 acquired in the step (1) to obtain a land use type grid stable for a long time in the 2000-year 2015 and a land use type grid unstable for a long time in the 2000-year 2015. The land use type grid which is stable for a long time is the grid which has no change in land use type between 2000-2015, and the change of the vegetation coverage factor value on the grids does not exceed the threshold range of the vegetation coverage factor value on the land use type; a long term unstable land use type grid is one in which the land use type changes between 2000-2015, and the vegetation coverage factor values on these grids change within different vegetation coverage factor value thresholds on different land use types.
(3) Further judging the stability of the land utilization type grid: the year 2000-charge 2015 is divided into three stages of 2000-charge 2005, 2005-charge 2010 and 2010-charge 2015, and the long-term unstable land utilization type grid obtained in the step (2) in the year 2000-charge 2015 is further judged to obtain a short-term stable land utilization type grid and a short-term unstable land utilization type grid respectively. The short-term stable land use type grid refers to a grid with unchanged land use types of two adjacent stages (2000-2005 and 2005-2010, 2005-2010 and 2010-2015) in three stages of 2000-2005, 2005-2010 and 2010-2015; the short-term unstable land use type grid refers to a grid in which the land use types of two adjacent stages change in the three stages of 2005-, 2005-2010-and 2010-2015, the land use types on the grids change drastically, and the vegetation coverage factor values on the grids change significantly within different vegetation coverage factor value thresholds of different land use types.
(4) Land utilization type grid conversion recognition: analyzing the short-term unstable land use type grid in the step (3), and identifying and tracking a land use type grid conversion form. The grid transformation form of the land utilization type determined in the period of 2000-2015 mainly comprises the interconversion between woodland and grassland and the interconversion between grassland and cultivated land.
(5) And (3) assigning a vegetation coverage factor of the cultivated land: and (3) directly assigning values to the cultivated land grids in the long-term stable land utilization type obtained in the step (2) and the cultivated land grids in the short-term stable land utilization type obtained in the step (3) according to the land utilization type grid data obtained in the step (1). The vegetation coverage factor value of cultivated land is obtained by meta analysis.
(6) Assigning a value of a vegetation coverage factor value range of a land utilization type except cultivated land: and (2) determining the grid value range of the vegetation cover factors of different land utilization types according to the land utilization type grid data acquired in the step (1). The value range of the vegetation coverage factor of the land utilization type except cultivated land comprises the maximum value and the minimum value of the grid, and the values are obtained through meta analysis.
(7) Determining a vegetation coverage factor value of the stable land use type grid: and (3) for the long-term stable land use type grid mentioned in the step (2) and the short-term stable land use type grid mentioned in the step (3), obtaining a vegetation coverage factor value on the stable land use type grid data by establishing a linear model between the vegetation coverage factor grid threshold mentioned in the step (6) and the MODIS vegetation grid data mentioned in the step (1). The range of values of the vegetation coverage factor corresponding to different land use types is shown in table 1. The linear models comprise three types, namely simulation of vegetation coverage factors on stable forest lands, simulation of vegetation coverage factors on stable grasslands and simulation of vegetation coverage factors on stable unutilized lands, and the simulation formula is as follows:
Cforest (forest)＝MinForest (forest)+(MaxForest (forest)-MinForest (forest))×(100-TC)×0.01
Wherein, CForest (forest)Is to stabilize the vegetation coverage factor value, Max, on the forest landForest (forest)Is the maximum value of the vegetation coverage factor, Min, on the stable forest landForest (forest)The minimum value of the vegetation coverage factor on the stable forest land, and TC is the tree-containing coverage value of MODIS vegetation grid data;
Cgrass (Haw)＝MinGrass (Haw)+(MaxGrass (Haw)-MinGrass (Haw))×NVS×0.01
Wherein, CGrass (Haw)Is a value of the vegetation coverage factor, Max, on stable grasslandsGrass (Haw)Is the maximum value of the vegetation coverage factor, Min, on stable grasslandsGrass (Haw)Is the minimum value of the vegetation coverage factor on the stable grassland, and NVS is the bare soil coverage value of MODIS vegetation grid data;
Cis prepared from＝MinIs prepared from+(MaxIs prepared from-MinIs prepared from)×NVS×0.01
Wherein, CIs prepared fromIs the stable vegetation cover factor value on the unused land, MaxIs prepared fromIs the maximum value of the vegetation coverage factor, Min, on the stable unutilized groundIs prepared fromIs the minimum value of the stable unused land vegetation coverage factor, and NVS is the bare soil coverage value of MODIS vegetation grid data.
(8) Determining short-term unstable land utilization type vegetation coverage factors: and (3) for the land use type conversion form mentioned in the step (4), obtaining the relation between the vegetation coverage factor threshold mentioned in the step (6) and the MOD44B data mentioned in the step (1) through a linear model, and obtaining the vegetation coverage factor value of each grid on the short-term unstable land use type. The linear model comprises two types, namely a short-term unstable forest land and grassland interconversion vegetation coverage factor simulation and a short-term unstable grassland and farmland interconversion vegetation coverage factor simulation, and the specific formula is as follows:
Cforest and grass＝MinForest and grass+(MaxForest and grass-MinForest and grass)×NVS×0.01
Wherein, CForest and grassIs a vegetation cover factor value, Max, of short-term unstable woodland and grassland interconversionForest and grassIs the maximum value of the vegetation coverage factor, Min, of the short-term unstable woodland and grassland interconversionForest and grassThe minimum value of the vegetation coverage factor of the short-term unstable forest land and the grassland which are mutually converted is obtained, and NVS is the bare soil coverage value of MODIS vegetation grid data;
Cgrass plough＝MinGrass plough+(MaxGrass plough-MinGrass plough)×NVS×0.01
Wherein, CGrass ploughIs the vegetation cover factor value, Max, of the mutual conversion between the short-term unstable grassland and the cultivated landGrass ploughIs the maximum value of the vegetation coverage factor, Min, of the interconversion between the short-term unstable grassland and the cultivated landGrass ploughThe minimum value of the vegetation coverage factor of the short-term unstable grassland and cultivated land interconversion is obtained, and the NVS is the bare soil coverage value of MODIS vegetation grid data.
(9) And (3) vegetation coverage factor combination: combining the cultivated land vegetation coverage factor value obtained in the step (5), the vegetation coverage factor value of the stable land utilization type grid obtained in the step (7) and the vegetation coverage factor value of the short-term non-stable land utilization type grid obtained in the step (8) by using a space combination method, wherein the spatial distribution characteristic of the 2015 Qinghai-Tibet plateau vegetation coverage factor calculated based on the method is shown in fig. 1.
TABLE 1 Vegetation coverage factor value ranges corresponding to Qinghai-Tibet plateau land utilization types
The method can quantitatively analyze the space-time variation characteristics of the vegetation cover factors on the land use types at the same position and at different times, dynamically simulate the change of the vegetation cover factors in the conversion process of the land use types, overcome the defect that the dynamic change of the vegetation cover factors in the process of the change of the land use cannot be estimated by the traditional method, and provide a new idea for simulating the soil erosion in a large regional scale.
Claims (8)
1. A method for rapidly estimating a plant coverage factor is characterized by comprising the following steps:
step (1), data acquisition: acquiring land use type grid data and MODIS vegetation grid data in a time span range according to the time span range to be estimated;
step (2), primarily judging the stability of the land utilization type grid: carrying out multi-temporal primary judgment on the stability of the land use type grid on the land use type grid data acquired in the step (1) to obtain a long-term stable land use type grid and a long-term unstable land use type grid;
and (3) further judging the stability of the land utilization type grid: further judging the long-term unstable land utilization type grid obtained in the step (2) to obtain a short-term stable land utilization type grid and a short-term unstable land utilization type grid;
step (4), land utilization type grid conversion and identification: analyzing the short-term unstable land use type grids obtained in the step (3), and identifying and tracking the conversion form of the land use type grids in the land use type grids;
and (5) carrying out assignment on vegetation coverage factors of cultivated land: directly assigning the cultivated land grid in the long-term stable land utilization type obtained in the step (2) and the cultivated land grid in the short-term stable land utilization type obtained in the step (3);
and (6) assigning the value range of the vegetation coverage factor of the land utilization type except cultivated land: determining grid value ranges of vegetation coverage factors of different land utilization types except cultivated land according to the land utilization type grid data acquired in the step (1);
and (7) determining the vegetation coverage factor value of the stable land utilization type grid: obtaining vegetation cover factor values except cultivated lands on the two types of stable land use type grids by establishing a linear model between the grid value range of the vegetation cover factor obtained in the step (6) and the MODIS vegetation grid data obtained in the step (1) for the two types of stable land use type grids, namely the long-term stable land use type grid obtained in the step (2) and the short-term stable land use type grid obtained in the step (3), and carrying out grid assignment;
step (8) vegetation coverage factor value determination of the short-term unstable land utilization type grid: for the conversion form of the land use type grid identified in the step (4), a vegetation cover factor value on the short-term unstable land use type grid data is obtained by establishing a linear model between the grid value range of the vegetation cover factor obtained in the step (6) and the MODIS vegetation grid data obtained in the step (1);
combining vegetation coverage factors in the step (9): and (3) merging the cultivated land vegetation coverage factor value obtained in the step (5), the vegetation coverage factor value of the stable land utilization type grid obtained in the step (7) and the vegetation coverage factor value of the short-term unstable land utilization type grid obtained in the step (8) by using a space merging method to obtain a complete vegetation coverage factor space distribution map.
2. The method for rapidly estimating vegetation coverage factor according to claim 1, wherein said preliminary determination of land use type grid stability in step (2) is made by a primary classification of land use type; the land utilization types comprise 4 primary classifications and 16 secondary classifications of cultivated land, forest land, grassland and unused land; the MODIS vegetation grid data are MOD44B data, time resolution is year, space resolution is 250 meters, and each grid comprises tree coverage, non-tree coverage and bare soil coverage.
3. The method for rapidly estimating a vegetation coverage factor as claimed in claim 1, wherein said long-term stable grid of land use type in step (2) means a grid in which the land use type does not change within a time span to be estimated; a long term unstable land use type grid is a grid in which the land use type changes over the time span to be estimated.
4. The method for rapidly estimating vegetation coverage factor according to claim 1, wherein in step (3), said short term stable land use type grid is a grid which divides the time span range to be estimated into several sub-span ranges, and the land use type does not change in any two adjacent sub-span ranges; the short-term unstable land use type grid refers to a grid with a land use type changed in all the adjacent two sub-span ranges.
5. The method for rapidly estimating plant coverage factor according to claim 1, wherein the transformation form of the land use type grid in the step (4) comprises forest land-to-grass land interconversion and grass land-to-arable land interconversion.
6. The method of claim 1, wherein the vegetation cover factor value of the cultivated land in step (5) and the vegetation cover factor value range of the land use type other than the cultivated land in step (6) comprise a maximum value and a minimum value, and the values are obtained by meta analysis.
7. The method according to claim 1, wherein the vegetation coverage factor of the land use stabilization grid in step (7) is simulated by three linear models, namely a vegetation coverage factor simulation on stabilized forest land, a vegetation coverage factor simulation on stabilized grassland, and a vegetation coverage factor simulation on stabilized non-utilized land, wherein the simulation formula is as follows:
Cforest (forest)＝MinForest (forest)+(MaxForest (forest)-MinForest (forest))×(100-TC)×0.01
Wherein, CForest (forest)Is to stabilize the vegetation coverage factor value, Max, on the forest landForest (forest)Is the maximum value of the vegetation coverage factor, Min, on the stable forest landForest (forest)The minimum value of the vegetation coverage factor on the stable forest land, and TC is the tree-containing coverage value of MODIS vegetation grid data;
Cgrass (Haw)＝MinGrass (Haw)+(MaxGrass (Haw)-MinGrass (Haw))×NVS×0.01
Wherein, CGrass (Haw)Is a value of the vegetation coverage factor, Max, on stable grasslandsGrass (Haw)Is the maximum value of the vegetation coverage factor, Min, on stable grasslandsGrass (Haw)Is the minimum value of the vegetation coverage factor on the stable grassland, and NVS is the bare soil coverage value of MODIS vegetation grid data;
Cis prepared from＝MinIs prepared from+(MaxIs prepared from-MinIs prepared from)×NVS×0.01
Wherein, CIs prepared fromIs the stable vegetation cover factor value on the unused land, MaxIs prepared fromIs the maximum value of the vegetation coverage factor, Min, on the stable unutilized groundIs prepared fromIs the minimum value of the vegetation coverage factor on the stable unused land, and NVS is the bare soil coverage value of MODIS vegetation grid data。
8. The method of claim 1, wherein the determining of the vegetation coverage factor of the short term unstable land use type grid in step (8) is simulated by two linear models, namely a short term unstable forest land and grassland interconverting vegetation coverage factor simulation and a short term unstable grassland and farmland interconverting vegetation coverage factor simulation, which are respectively expressed by the following formulas:
Cforest and grass＝MinForest and grass+(MaxForest and grass-MinForest and grass)×NVS×0.01
Wherein, CForest and grassIs a vegetation cover factor value, Max, of short-term unstable woodland and grassland interconversionForest and grassIs the maximum value of the vegetation coverage factor, Max, of the short-term unstable woodland and grassland interconversionForest and grass-minimum value of vegetation coverage factor on grassland; minForest and grassIs the minimum value of the vegetation coverage factor, Min, of the short-term unstable woodland and grassland interconversionForest and grassMaximum value of vegetation coverage factor on forest land; NVS is the bare soil coverage value of MODIS vegetation grid data;
Cgrass plough＝MinGrass plough+(MaxGrass plough-MinGrass plough)×NVS×0.01
Wherein, CGrass ploughIs the vegetation cover factor value, Max, of the mutual conversion between the short-term unstable grassland and the cultivated landGrass ploughIs the maximum value of the vegetation coverage factor, Max, of the interconversion between the short-term unstable grassland and the cultivated landGrass ploughThe minimum value of vegetation coverage factors on the farmland; minGrass ploughIs the minimum value of the vegetation coverage factor, Min, of the interconversion between the short-term unstable grassland and the cultivated landGrass ploughMaximum value of vegetation coverage factor on grasslands; NVS is bare soil coverage value of MODIS vegetation grid data.
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