基于CryoSat-2测高数据的全南极冰盖DEM的建立与精度评估

DEM development and precision analysis for Antarctic ice sheet using CryoSat-2 altimetry data

数字高程模型(DEM)是南极冰盖变化研究的基础,由于现场实测数据的稀缺,卫星测高数据是南极地区构建DEM的'主要数据来源.CryoSat-2是新一代用于极地冰盖、海冰监测的测高卫星,本文利用2012-12-2015-01两个完整周期的CryoSat-2测高数据建立一个新的南极冰盖DEM.坡度是影响卫星测高精度的重要因素之一,利用改进的重定位方法对CryoSat-2数据进行坡度改正.插值方法是影响DEM精度的重要因素,通过对几种常用插值方法的比较,最后选用克里金插值方法对测高数据进行插值,建立了1km分辨率的南极DEM.在88°S以南的CryoSat-2数据空白区,利用南极数字数据库(ADD)的等高线数据对DEM进行填补,建立了全南极冰盖DEM.利用ICESat卫星测高数据、IceBridge航空测高数据以及GPS地面实测数据对新建立的CryoSat-2 DEM进行精度验证,并与Bamber 1 km DEM、ICESat DEM、RAMPv2 DEM以及JLB97 DEM等四种国际上常用的南极DEM进行比较.结果表明:新建立的CryoSat-2 DEM的整体精度约为0.730±8.398 m;在冰弯顶部区域,DEM精度优于1 m;在冰架上,DEM精度约为4 m;在内陆冰盖大部分地区,DEM精度优于10 m;在地形复杂的山区和沿海边缘地区,DEM误差超过150 m.

Digital elevation models are of fundamental importance to many geoscientific and environmental studies in Antarctic, and due to relatively poor coverage by ground based surveys, the main data source for constructing an Antarctic DEM is satellite altimetry. The newest operating satellite-borne altimeter with ice applications is the ESA satellite CryoSat-2, which was launched in April 2010. CryoSat-2 provides altimetry data up to a latitude of 88°S/N, which is a significant improvement to previous satellite borne altimeters. Based on two full cycles of CryoSat-2 observations acquired between December 2012 and January 2015 we derived a new DEM for the Antarctic Ice Sheet. The accuracy of generated DEM depends largely on the interpolation method adopted and five commonly used interpolation methods were compared using the Cross Validation method. The Kriging method yielded better estimates for the Antarctic Ice Sheet and was adopted when constructing the final DEM. For the CryoSat-2 LRM data we followed an iterative approach to correct for the surface slope, and the slope correction was applied to each data point using the relocation method. Data gap beyond the latitudinal limit of the CryoSat-2 mission （88°S） was filled by contour data from ADD. Finally, we present a new Antarctic DEM with a pixel size of 1 km×1 km.The accuracy of the final DEM was assessed by using ICESat data, IceBridge data and GPS data and compared with four common used Antarctic DEMs namely Bamber 1 km DEM, ICESat DEM, RAMPv2 DEM and JLB97 DEM. The results show that the CryoSat-2 DEM has an uncertainty of 0.73±8.398 m. The vertical accuracy of the DEM is better than 1 m at domes, better than 4 m for the ice shelves, better than 10 m for the interior ice sheet and over 150 m for the rugged mountainous and coastal areas.