坡度和粗糙度对ICESat-GLAS回波特征及其光斑脚点高程误差的影响研究

Characteristics of ICESat-GLAS Full Waveforms and the Errors of GLAS Footprints Elevation Change Influenced by the Surface Slope and Roughness

为评价ICESat-GLAS数据在青藏高原地区冰川表面高程变化中的不确定性,采用GLA01产品和GLA14产品,基于SRTM DEM数据所派生的冰川区和非冰川区表面坡度、粗糙度数据,利用多元线性回归关系模型分析了表面粗糙度、坡度对GLAS光斑脚点高程的不确定误差。结果表明:当GLAS光斑脚点坡度小于10°时,GLAS光斑脚点高程偏差为0.1m,且高程偏差随着坡度的增加而增大。在受坡度和粗糙度影响复杂地形下,GLAS光斑的回波展宽较大,不确定性偏差为0.3m。此外,冰川区GLAS光斑脚点高程误差可通过高斯滤波进行展宽偏差校正,但当冰川表面坡度大于45°时,相应的GLAS光斑脚点高程在冰川表面高程变化估算中不可用。在后续的研究中,需考虑冰川运动、GLAS回波在冰雪表面渗透对冰川DEM高程精度以及GLAS光斑脚点水平位移的高程偏差影响。

To evaluate on the uncertainty of the GLAS footprints elevation change on the glaciers in Tibet Plateau,the GLA01 product and GLA14 product are employed for the error analysis of GLAS footprints elevation.The bias of the centroid of return echo signal in the GLAS waveforms in the glacier surface and non-glacier land surface region are compared based on the SRTM DEM-derived roughness and slope data.Using the multiple linear regression models,the GLAS footprints elevation deviation are significantly related to the land surface roughness and slope of GLAS footprints.The results showed that the errors of GLAS footprints elevation on the glacier surface are 0.1m,while the glacier surface slope value of GLAS footprints are less than 10°.The deviation of GLAS footprints elevation increases with the surface slope categories increased.The GLAS footprints are jointly affected by the slope and roughness,which the overall uncertain error was 0.3m.In addition,if the glacier surface slope is more than 45°,the corresponding GLAS footprints are not available for estimation on the surface elevation change.The GLAS full waveforms are filtered by the Gaussian-Centroid method and the process can reduce the uncertain error of the centroid of the laser returned echo of the GLAS footprints.In future studies,the offset compensation caused by the glacier surface motion and the glacier surface DEM elevation deviation evaluation without considering the penetration effect of GLAS returned echo on the snow/ice surface would be considered.