基于RTK-GPS的北极Austre Lovénbreen冰川表面高程变化研究

STUDY ON SURFACE ELEVATION CHANGES OF ARCTIC GLACIER AUSTRE LOVéNBREEN USING RTK-GPS

基于多期RTK-GPS(Real Time Kinematic-Global Position System)高精度测量数据,通过冰面高程变化开展北极Austre Lovénbreen冰川物质变化研究。首先基于冰面GPS测点开展多种空间插值方法的比对,兼顾冰面DEM(Digital Elevation Model)的平滑特性以及插值结果的准确性,优选自然邻域法作为冰面地形的插值算法;继而利用2013—2015年3期RTK-GPS数据,通过冰面地形内插和测线交叉点比对两种方式开展了Austre Lovénbreen冰川表面高程变化的分析,结果表明交叉点方法的精度更高,而地形内插法在测线之间的空白区域存在较大误差。最后通过冰雪密度估计将高程变化转化为水当量,计算相应时段的冰川物质平衡:积累区密度取500 kg·m^-3,消融区密度取900 kg·m^-3,得到2013—2014年和2014—2015年的物质平衡分别为–0.277m w.e.和0.065m w.e.。该物质平衡结果相较于传统的冰面物质平衡而言存在一定的差异,主要源于测量时段的不一致,以及可能存在的冰川内部物质变化。此外,将RTK-GPS交叉点高程的年际变化与所在高程进行联合分析,发现冰川物质变化与冰川高程分布既有较强的相关性,部分区域也存在一些差异。总体而言,冰川物质年变化的海拔梯度为2.67‰,在海拔越低的区域冰川消融得越快,随海拔上升消融减慢,在高海拔或冰川边缘区域还存在少量物质积累。

Mass changes of the Austre Lovénbreen Arctic valley glacier have been studied using elevation changes based on high-precision RTK-GPS measurements.Using RTK-GPS data,several spatial interpolation methods were compared to produce a digital elevation model (DEM) of the glacier surface.Considering the smoothness of the glacier surface,the natural neighbor method was considered most suitable for generating the DEM.Two approaches were compared for evaluating the elevation changes of the glacier during 2013–2015:using DEMs generated from direct surface interpolation of RTK-GPS points and calculating the elevation bias of crossover points from RTK-GPS profiles of different years.The results showed that elevation changes calculated from crossover points were much more accurate than using the direct surface interpolation method,which had obvious errors in GPS empty areas.A density assumption for ice and snow was used to convert elevation change to water equivalent to study the mass balance.Assuming density of 900 and 500 kg m^-3 in the ablation and accumulation zones,respectively,the corresponding mass balance in 2013–2014 and 2014–2015 was -0.277 and 0.065 m w.e.,respectively.These results differed slightly from classical glaciological mass balances primarily because of the discrepancy of the observation period and potential subglacial mass changes.The correlation between the elevation changes of crossover points and their corresponding altitude was determined.Despite some anomalies in certain regions,strong correlation was found between mass change and altitude,i.e.,some mass accumulation occurred in high-altitude areas,while mass loss increased with decreasing altitude.The annual mean gradient of mass change versus altitude was approximately 2.67‰.