Snow avalanche detection and mapping in multitemporal and multiorbital radar images from TerraSAR-X and Sentinel-1
Snow avalanche detection and mapping in multitemporal and multiorbital radar images from TerraSAR-X and Sentinel-1
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DOI：
10.5194/nhess-20-1783-2020
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发表时间：
2020-06
影响因子：
4.6
通讯作者：
S. Leinss;Raphael Wicki;Sämi Holenstein;Simone Baffelli;Y. Bühler
中科院分区：
文献类型：
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作者：
S. Leinss;Raphael Wicki;Sämi Holenstein;Simone Baffelli;Y. Bühler
抽象。雪崩可能危及人员和基础设施，特别是在人口稠密的山区。在瑞士，公众在冬季每天发布两次雪崩公告，该公告是根据天气信息以及观察员网络的降雪和雪崩报告发布的。然而，在恶劣天气期间，有关雪崩发生的信息可能很少，甚至完全缺失。为了评估与天气无关的雷达卫星的潜力，我们比较了手动和自动变化检测雪崩映射结果，从高分辨率TerraSAR-X（TSX）条带图像和中等分辨率哨兵-1（S1）干涉宽测绘带图像的研究地点在瑞士中部。还将TSX的结果与SPOT-6高分辨率光学卫星图像的现有绘图结果进行了比较。我们发现TSX和S1的雪崩轮廓彼此吻合得很好。截止阈值映射雪崩面积被发现与500平方米的TSX和2000平方米的S1。S1提供了更高的空间和时间覆盖范围，并允许至少每6天免费采集一次整个阿尔卑斯山的地图。使用昂贵的SPOT-6图像，阿尔卑斯山甚至可以在一天内以米的分辨率覆盖，至少在晴朗的天空条件下。对于SPOT-6和TSX的测绘结果，我们发现了一个公平的协议，但从雷达变化检测的时间信息，可以更好地分离重叠雪崩。尽管如此，绘制的雪崩总面积至少相差3倍，因为雷达主要探测到雪崩沉积区，而释放区在SPOT-6数据中已经非常明显。通过自动雪崩映射，我们检测到大约70%的手动映射的新雪崩，至少在旧雪崩数量较少的情况下。为了进一步提高雷达测绘能力，我们结合了多个轨道和极化的S1图像，并获得了显着的分辨率和斑点噪声抑制的增强，使得所获得的测绘结果几乎可以与单轨道TSX变化检测结果相媲美。在覆盖整个瑞士的多轨道S1镶嵌图中，我们手动统计了2018年1月4日左右极端雪崩期间发生的7361次新雪崩。
Abstract. Snow avalanches can endanger people and infrastructure, especially in densely populated mountainous regions. In Switzerland, the public is informed by an avalanche bulletin issued twice a day during winter which is based on weather information and snow and avalanche reports from a network of observers. During bad weather, however, information about avalanches that have occurred can be scarce or even be missing completely. To assess the potential of weather-independent radar satellites, we compared manual and automatic change detection avalanche mapping results from high-resolution TerraSAR-X (TSX) stripmap images and medium-resolution Sentinel-1 (S1) interferometric wide-swath images for a study site in central Switzerland. The TSX results were also compared to available mapping results from high-resolution SPOT-6 optical satellite images. We found that avalanche outlines from TSX and S1 agree well with each other. Cutoff thresholds of mapped avalanche areas were found with 500 m 2 for TSX and 2000 m 2 for S1. S1 provides a much higher spatial and temporal coverage and allows for mapping of the entire Alps at least every 6 d with freely available acquisitions. With costly SPOT-6 images the Alps can even be covered in a single day at meter resolution, at least for clear-sky conditions. For the SPOT-6 and TSX mapping results, we found a fair agreement, but the temporal information from radar change detection allows for a better separation of overlapping avalanches. Still, the total mapped avalanche area differed by at least a factor of 3 because with radar mainly the avalanche deposition zone was detected, whereas the release zone was very visible already in SPOT-6 data. With automatic avalanche mapping we detected around 70 % of manually mapped new avalanches, at least when the number of old avalanches is low. To further improve the radar mapping capabilities, we combined S1 images from multiple orbits and polarizations and obtained a notable enhancement of resolution and speckle reduction such that the obtained mapping results are almost comparable to the single-orbit TSX change detection results. In a multiorbital S1 mosaic covering all of Switzerland, we manually counted 7361 new avalanches which occurred during an extreme avalanche period around 4 January 2018.