Extraction And Analysis Of Ephemeral Gully In Loess Plateau Based On Directional Edge Detection

Ephemeral gully is an important member of gully system in the Loess Plateau,which is also one of the main drivers for severe soil loss.Previous studies were usually carried out at micro scale,and lack in spatial distribution analysis at macro scale.So there is an imperative need for detailed mapping ephemeral gully in a large scale,which is basis of above studies.Based on high resolution remote sensing image and DEM data,this paper proposed an automatic extraction method for ephemeral gullies in the Loess Plateau using directional edge detection,and the morphological eharacteristics and spatial distribution pattern were analyzed by statistieal methods.The main work and conclusions of this study are as follows:(1)Study of the automatic extraction for ephemeral gulliesThe automatic segmentation method of hillslope was proposed.Due to there is weak information of ephemeral gullies in the image,the irrelevant image should be removed as possible before the extraction.Firstly,the shoulder lines were extracted quickly on the basis of the DEM surface radiation model.Secondly,the boundry of hillslope within ephemeral gullies was determined by combining shoulder lines with topographic structure lines(watershed boundary and main gully line)derived from DEM.Finally,the hillslopes were gained automatically by mask segmentation from high resolution remote sensing image.After that,automatic extraction for ephemeral gullies based high resolution image was carried out.Firstly,the main direction of the ephemeral gully was determined by manual interpretation based on the RS image.Then,the directional edge detection rules were set up by determined main direction.Finally,a search algorithm was designed for mapping and coding ephemeral gullies.The extraction accuracy ranged from 56%to 86%,which means the proposed extraction method is of high accuracy and efficiency.(2)Analysis of the ephemeral gullies characteristicsTaken Zizhou county,Dingbian county,Huan county and Dingxi city as four typical study areas,this paper analyzed the morphological characteristics and spatial distribution of ephemeral gullies in loess hilly and gully region.The results show:The average length of ephemeral gullies is 38-50 meters;the average slope of ephemeral gullies is 19°-27° and the mean interval of ephemeral gullies is 15 meters.The critical slope degree of ephemeral gullies is 20°.There shows a significant spatial difference in slope aspect for ephemeral gullies,which the amount of ephemeral gullies in sunlit slope is 2-3 times the sunless slope.When soil erosion is intensified,more ephemeral gullies develops into the young gullies,resulting in the popluaration proportion of ephemeral gullies declines in the whole gully system,and its quantitive and spatial characteristic show an increasing trend from the east to west.