Abstract The past two decades have been prolific in production of global or near-global Digital Elevation Models (DEMs) derived from satellite data. The most recent addition to the family of global DEMs is the TanDEM-X DEM with resolution of 0.4 arc sec. DEMs are essential for a wide range of environmental applications, many of which are related to mountains including studies on natural hazards, forestry or glacier mass changes. However, synthetic aperture radar interferometry used for acquisition of TanDEM-X DEM is especially challenging over steep and irregular mountain surfaces due to shadowing and foreshortening effects. In this study, we assessed the absolute vertical accuracy of TanDEM-X DEM in European mountains. We compared it with both a Digital Terrain Model (DTM) and a Digital Surface Model (DSM) derived from airborne laser scanning data. Our results indicate that the height error of TanDEM-X DEM expressed as absolute deviation at the 90% quantile is consistent with the 10 m mission specification benchmark. We further concentrated on the absolute height error with respect to environmental characteristics (i.e. forested and non-forested areas, slope, and aspect). The comparison of TanDEM-X DEM with a reference DTM showed a positive vertical offset; however, the mean error differed greatly between forested and non-forested areas. When compared to reference DSM, our results showed a slight underestimation. We observed the highest underestimation in deciduous forests, followed by coniferous forests and non-forested areas. A significant decrease in accuracy was observed with increasing slope, especially for slopes above 10°. In mountains where the imagery was acquired only in one orbit direction (i.e. ascending for Northern hemisphere), the largest TanDEM-X DEM error when compared to DSM was recorded for the west-facing slopes (i.e. slopes facing the sensor); however, the association with terrain orientation diminished in mountains, the imagery of which was acquired from both the ascending and descending orbit. Finally, we evaluated the effect of data acquisition characteristics provided with TanDEM-X DEM as auxiliary data. Our results show that two coverages might not be sufficient in mountain environment. Additional acquisitions, especially those with different acquisition geometry, improved the absolute vertical accuracy of TanDEM-X DEM and eliminated areas of inconsistency. We discourage from using the Height Error Map (HEM) to estimate the error magnitude. On the other hand, auxiliary data (COM, COV) provide valuable information that should be always used in pre-analyses to identify possible problematic areas.

中文翻译：

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山地环境下全球TanDEM-X数字高程模型精度评估

摘要 过去二十年来，从卫星数据中衍生出的全球或近全球数字高程模型 (DEM) 的产生非常多。全球 DEM 系列的最新成员是分辨率为 0.4 弧秒的 TanDEM-X DEM。DEM 对于广泛的环境应用至关重要，其中许多与山脉有关，包括对自然灾害、林业或冰川质量变化的研究。然而，由于阴影和透视效应，用于采集 TanDEM-X DEM 的合成孔径雷达干涉测量在陡峭和不规则的山地表面上尤其具有挑战性。在这项研究中，我们评估了 TanDEM-X DEM 在欧洲山区的绝对垂直精度。我们将其与基于机载激光扫描数据的数字地形模型 (DTM) 和数字表面模型 (DSM) 进行了比较。我们的结果表明，以 90% 分位数绝对偏差表示的 TanDEM-X DEM 的高度误差与 10 m 任务规范基准一致。我们进一步关注与环境特征（即森林和非森林区域、坡度和坡向）相关的绝对高度误差。TanDEM-X DEM 与参考 DTM 的比较显示出正垂直偏移；然而，森林和非森林地区的平均误差差异很大。与参考 DSM 相比，我们的结果略有低估。我们观察到落叶林的低估程度最高，其次是针叶林和非林区。观察到随着坡度的增加，精度显着降低，尤其是对于 10° 以上的坡度。在仅在一个轨道方向（即北半球上升）获取图像的山脉中，与 DSM 相比，最大的 TanDEM-X DEM 误差记录在面向西的斜坡（即面向传感器的斜坡）；然而，与地形方向的关联在山区减弱，其图像是从上升轨道和下降轨道获得的。最后，我们评估了以 TanDEM-X DEM 作为辅助数据提供的数据采集特性的效果。我们的结果表明，在山区环境中，两个覆盖范围可能不够。额外的采集，尤其是那些具有不同采集几何形状的采集，提高了 TanDEM-X DEM 的绝对垂直精度并消除了不一致的区域。我们不鼓励使用高度误差图 (HEM) 来估计误差幅度。另一方面，辅助数据（COM、COV）提供了有价值的信息，应始终用于预分析以识别可能存在问题的区域。