Research On The Characteristics Of Cultivated Land Change In Loess Mining Area Based On Time Series Remote Sensing

The Loess Plateau mining area is one of the major coal producing areas in China.The ground collapse caused by large-scale and high-intensity underground mining inevitably causes continuous damage to the arable land resources in the mining area,which in turn leads to the reduction of the arable land area and quality in the loess mining area,making the human-land conflict increasingly prominent.Therefore,it is of great significance to conduct quantitatively research on the dynamic evolution of arable land resources in coal mining areas for the sustainable development of mining areas.At present,satellite remote sensing technology has become an important means of monitoring land use changes.But the results of time-series remote sensing monitoring for the evolution of arable land resources in mining areas with complex terrain on the Loess Plateau are still insufficient.In this context,this paper takes Dafosi coal mine as the study area,which is a typical loess mining area.Based on the long time series remote sensing image data,the Spatio-temporal segmentation algorithm is used on the GEE platform to extract information on the change of arable land in the Dafosi mining area,analyze the change characteristics of land use,especially arable land use,and explore the influence of topographic factors on the spatial distribution and evolution of arable land to reveal the disturbance effect of coal mining subsidence deformation on the Spatio-temporal evolution characteristics of arable land in the mining area.The main contents and results of the paper are as follows.(1)A multi-featured image extraction technology method based on spatio-temporal segmentation of cropland is constructed,by combining the spatial features of remote sensing images with the time windows of cropland crop growing period.The specific elements of the method are to generate statistics such as median and standard deviation of spectral features in stages according to the critical crop fertility period,add texture features and use the results of principal component analysis as input to the SNIC algorithm to achieve image spatial segmentation;introduce topographic factors and apply the results of feature preference to the random forest classification algorithm.The results show that the method used in this paper achieves better accuracy in extracting the spatial distribution of cultivated land in long time series,small and medium scale complex terrain areas,and the accuracy of the classification results is improved by about 9.81%compared with single time phase images and about 5.6%compared with pixel-based classification method.The terrain correction effectively solves the confusion of image element types caused by uneven illumination in complex terrain areas and reduces the misclassification rate.(2)In this section,the spatial and temporal characteristics of arable land changes in the Dafosi mining area between 2005 and 2020 are quantitatively analysed using dynamic land use indicators,and the influence of topographic factors on the spatial distribution and evolution of arable land is explored.In addition,the spatial location and time of occurrence of arable land evolution in the mining area were obtained on an annual basis based on the LandTrendr timetrajectory breakpoint monitoring model.The results show that the phase change of the arable land use process in the mine area is obvious,and the overall arable land use structure shows a fluctuating upward trend,and the abandonment phenomenon is more common in the mine area,and the length of abandonment is inversely proportional to the area of abandoned arable land.In terms of temporal changes,the intensity of cultivated land transfer during the study period showed a trend of "increasing before decreasing",with the main transfer directions being construction land,forest and grassland and bare land,and the main transfer directions being forest,grassland and bare land;the characteristics of change in cultivated land use changed from a high abandonment rate and a low recovery rate to a low abandonment rate and a high recovery rate.In terms of spatial changes,the distribution of cropland evolution and topographic factors show a strong spatial correlation,which is reflected in the fact that cropland is generally located in areas with higher elevation,gentler slope and higher topographic position,while abandoned cropland is mostly located in areas with obvious topographic changes,among which,the gently sloping areas of high-altitude plateau are the areas where cropland is most likely to be converted.In comparison with the existing classification results,the accuracy of the temporal trajectory model can reach 93.33%,which demonstrates the effectiveness of the GEE platform in extracting the evolutionary features of arable land on a small regional scale in a long time series.(3)The spatial and temporal characteristics of the evolution of arable land in mining subsidence areas and the impact of subsidence disturbance on the change of arable land are analysed by combining the extent of coal mining subsidence disturbance and related indicators.The InSAR technique and the mining subsidence calculation model were used to obtain the extent of mining-induced surface subsidence and to circle the area of arable land destruction.The study area was then divided into different coal mining impact areas according to the degree of mining disturbance,and the spatial and temporal distribution of the reduction in arable land area within each impact area was analysed and statistically calculated,and finally the mechanism of the impact of coal mining subsidence deformation on arable land was analysed in terms of the changes in arable land levelling and soil properties.The results show that the reduction of arable land area is positively correlated with the degree of mining impact.Among them,the change rates of arable land area in the mining subsidence area,indirectly affected area and non-affected area were-24.27%,-19.39%and 24.07%respectively.The uneven subsidence of the surface within the mining subsidence area changed the flatness of the arable land,and the mining cracks damaged the integrity of the arable land,causing excessive loss of soil moisture and fertility and reducing the quality of the arable land in the mine area.