基于高分七号立体影像提取松嫩典型黑土区切沟和浅沟的精度分析

Accessing accuracy of extracting gully and ephemeral gully in the Songnen typical black soil region based on GF-7 satellite images

沟蚀作为一种极端形式的土地退化现象,对东北黑土区生态安全和粮食安全都构成潜在危险。为探索高分七号立体影像监测东北黑土区沟蚀的适用性,在沟蚀严重的黑龙江省宾县选取典型小流域,以无人机数据为参照,分析使用高分七号提取浅沟和切沟参数的精度。结果表明:1)高分七号解译小流域浅沟数量和密度的误差在50%以上,存在多种情况的误判;而解译切沟线密度和面密度的精度很高,误差分别为1.00%和5.62%。2)基于高分七号影像解译浅沟单沟沟长的平均误差为4.54 m,相对误差在10%以下的浅沟占40.48%,但与无人机测量值在统计上无显著差异,且具有良好的线性关系(R^(2)=0.93)。3)高分七号提取切沟单沟沟长、沟宽和面积的可靠性较高,平均误差分别为2.89%,14.92%和16.02%。切沟平均沟深的平均误差为1.24 m,相对误差24.46%,纵比降误差多在7%左右。切沟体积解译的平均相对误差为69.95%。高分七号切沟单沟二维参数、小流域尺度切沟密度测量方面都具有较高精度,但提取三维切沟参数存有较大误差,难以用于切沟侵蚀量的测量。

[Background]Gully erosion,as an extreme form of land degradation,causes a potential danger for both local ecological security and food security.Gully measurement with high-efficiency and high-precision has important significance for gully erosion monitoring in the black soil area of Northeast China.This study aims to explore the applicability of satellite remote imagery Gaofen-7 for monitoring gully erosion in the black soil area.[Methods]A typical watershed with area of 4.2 km^(2)in Binxian county,Heilongjiang province,was selected as the study area to analyze the accuracy of extracting ephemeral gully(EG)and permanent gully(PG)parameters by visually interpretation using GF-7 stereoscopic satellite images(multispectral data of 0.8 m resolution and panchromatic data of 0.65 m resolution)with unmanned aerial vehicle(UAV)measurement data as a reference.[Results]1)The 64 ephemeral gullies were interpreted from UAV imagery,with a density of 15.23 gullies/km^(2)and an average length of 83.43 m.The 80 ephemeral gullies were extracted from GF-7 with only 42 were the same as those from UAV images.The error in the number and density of ephemeral gullies interpreted using GF-7 images was larger than 50%,with many cases of misinterpretation.Using GF-7 images,the water flow paths,plot boundaries,and field roads may be misidentified as ephemeral gullies.It is inappropriate to be used for monitoring EG erosion at the small watershed scale.The 17 permanent gullies were interpreted from UAV images,with a density of 4.04 gullies/km^(2)and a gully density of 2.02 km/km^(2).The measurement in linear and areal density of the permanent gullies with GF-7 was reliable with the errors were 1.00%and 5.62%,respectively.2)Comparing the length of the 42 EGs interpreted from both GF-7 and UAV images,the average error of gully length using GF-7 images was 4.54 m,with the relative error below 10%accounted for 40.48%.However,there was no statistically significant difference(P>0.05)between the gully length measurements of the GF-7 and UAV and a good linear relationship was fitted(R^(2)=0.93).3)There was high reliability of gully length,width and area of permanent gullies extracted using the GF-7 images with the mean errors were 2.89%,14.92%and 16.02%,respectively.The average error of the gully depth of the permanent gullies was 1.24 m,with a relative error of 24.46%,and the average error of gully gradient was around 7%,and the average relative errors of the permanent gullies volumes were 69.95%,indicating the three-dimensional morphological parameters of permanent gullies from GF-7 were not reliable.[Conclusions]There is high accuracy in the measurement of density and two-dimensional parameters of permanent gullies at the scale of small watershed using GF-7 images,while there is a large error in extraction of three-dimensional parameters of permanent gully.This study may provide an important reference for the investigation and monitoring of gullies in Chinese black soil area.