A new method for deriving glacier centerlines applied to glaciers in Alaska and northwest Canada

摘要

This study presents a new method to derive centerlines for the main branchesand major tributaries of a set of glaciers, requiring glacier outlines and adigital elevation model (DEM) as input. The method relies on a "cost grid–least-cost route approach" that comprises three main steps. First, terminiand heads are identified for every glacier. Second, centerlines are derivedby calculating the least-cost route on a previously established cost grid.Third, the centerlines are split into branches and a branch order isallocated. Application to 21 720 glaciers in Alaska and northwest Canada(Yukon, British Columbia) yields 41 860 centerlines. The algorithm performsrobustly, requiring no manual adjustments for 87.8% of the glaciers. Manualadjustments are required primarily to correct the locations of glacier heads(7.0% corrected) and termini (3.5% corrected). With corrected heads andtermini, only 1.4% of the derived centerlines need edits. A comparison ofthe lengths from a hydrological approach to the lengths from our longestcenterlines reveals considerable variation. Although the average length ratiois close to unity, only ~ 50% of the 21 720 glaciers have the twolengths within 10% of each other. A second comparison shows that ourcenterline lengths between lowest and highest glacier elevations compare wellto our longest centerline lengths. For > 70% of the 4350 glaciers withtwo or more branches, the two lengths are within 5% of each other. Our finalproduct can be used for calculating glacier length, conducting length changeanalyses, topological analyses, or flowline modeling.