An Automatic Extraction Method Of Glacier Length Based On Voronoi Algorithm

Glacier length is one of the central parameter representing the glacier geometry,but glacier inventory data sets are mostly lacking length information.In the past,glacier length was relied on time-consuming and labor-intensive manual digitization.Therefore,there is an urgent need to calculate centerlines for large numbers of glaciers from automated methods The automatic extraction of glacier length is a challenge.In recent years,some foreign scholars have proposed several automatic extraction methods for glacier length.However,there is no mature automatic extraction method for glacier length in China.This paper proposes a new method to glacier centerline extraction based on satellite data,and compared with other methods of extraction of glacier centerline.In addition,this paper applied the method to glaciers located in Sanjiangyuan region and analyzed the glacier length distribution and variation characteristics in Sanjiangyuan region This paper presents a new,Voronoi algorithm-based and automated algorithm to calculateglacier centerline,requiring a set of glacier outlines and a digital elevation model(DEM)as input.The method comprises three main steps.First,the lowest point and local highest points for each glacier are identified.Second,the Voronoi is constructed based on the points of the glacier outlines.Third,centerlines are derived by calculating the least route and smoothing the centerlines.To compare with the two existing methods of automatic extraction of glacier centerline,this paper have applied the method to 1125 glaciers located in Southern Alaska This paper compared and analyzed the average length of three extraction methods and the length ratio between different methods.In addition,this paper applied the automatic extraction method of glacier centerline proposed in this paper to glacier located in Sanjiangyuan region,the glacier lengths of 2009 and 2016 were extracted in Sanjiangyuan region,and the glacier length distribution and variation characteristics in Sanjiangyuan area were analyzed.The main conclusions are as follows First,the average lengths of the 1125 glaciers in Southern Alaska measured by the threemethods do not differ much,lie within a range of 1.789 km2 to 1.833 km2.The average value of Rx/m is 1.05,and the average value of Rx/k is 1.01,showing a small positive deviations between the three methods compared with a perfect agreement(R=1.00).In total 92%of all Rx/k lie within a range of 0.9 to 1.1,and 84.2%of all Rx/m is between 0.9 and 1.1.The automatic extraction method of glacier length based on Voronoi algorithm in this paper is comparable with other automatic extraction methods,and the extraction results are reliableSecondly,characteristics of glacier length distribution in sanjiangyuan Region.in 2009 and 2016,the average length of glaciers in the Sanjiangyuan region increased with the increasing scale of glaciers..From 2009 to 2016,the average length of glaciers of different sizes decreased over time.The average length was 1.48 km in 2009 and 1.44 km in 2016,which also reflects the fact that the glaciers in the study area are shrinking.According to mountain system,the study area can be divided into five mountain systems:Amne Machin,Quagajima,Tanggula,Bayan Har and Kunlun,among which Bayan Har has no the distribution of the glaciers.The average glacier length of Amne Machin,Quagajima,Tanggula and Kunlun mountains is 1.31 km,0.91 km,1.50 km and 1.80 km respectivelyThirdly,characteristics of glacier length variation in Sanjiangyuan Area.glacier area and glacier length of different size classes have shrunk trend to different degrees.From 2009 to 2016,the annual shrinkage rate of glacier area was 0.43%,and the average length of glacier retreated 5 m per year.The length of glaciers in the four regions of Animaqen,Zaduo North,Tanggula and Kunlun mountains were statistically analyzed.From 2009 to 2016,the average length of glaciers in the four mountain systems in the Sanjiangyuan region decreased.From 2009 to 2016,the rate of glacier area shrinkage and the rate of glacier length change corresponded to each other in the four regions divided by mountain system in the study area Among them,the glacier in the Quagajima has the fastest change rate in length,shrinking 8 m per year,and its area shrinkage rate is 8.35%,which is the fastest among the four regionsFourth,there is a correlation between glacier area and glacier length.The empirical equation,L?k·A?,(k=[0.92,1.70],??[0.467,0.606]).In this paper,the relationship formulas of the glacier length and glacier area in the Sanjiangyuan region are y?1.65x0.53(2009)and y?1.62x0.53(2016)respectively.