基于无人机技术黄河沿岸沙丘移动速度监测及影响因素分析

为更便捷地监测乌兰布和沙漠黄河沿岸沙丘移动速度并解析其影响因素,该研究以乌兰布和沙漠沿黄段沙丘为研究对象,应用无人机航拍技术开展沿岸沙丘的季节性地貌过程和影响因素研究。结果表明:1)研究区沙丘年移动速率1.08～2.27 m/a,多年平均输沙势为78.82 VU,年合成输沙势为25.92 VU,处于低风能环境,8～12 m/s等级风输沙势是年输沙势的主要部分,约占73.24%。方向变率(合成输沙势(Resultant Drift Potential,RDP)与输沙势(Drift Potential,DP)的比值)RDP/DP保持在0.30～0.46之间,属于中等变率。合成输沙方向RDD为57.83°～107.39°,与沙丘移动方向较为一致,西风组占全年输沙势的52.09%,是沙丘年移动的主要驱动力。2)沙丘移动速率具有明显的季节特征,整体呈现春季移动速率快,冬末-春初次之,秋季与秋末-冬末相近,夏季移动速率最慢。其中,秋末-冬末、春季和秋季输沙势DP 8.48～20.49 VU,合成输沙势方向在90.02°～95.54°之间,RDP/DP值均在0.3～0.8之间,属于中等变率,西风组作用显著,这与年合成输沙方向及沙丘走向较为一致;冬末-春初和春末-夏季分别受东北风(NE)和南风组(SSE、S、SSW)作用,沙丘通过形态变化适应风向,移动速度降缓。季节输沙势主要集中在8～10m/s风速等级,约占整个季节输沙势的40.76%～56.93%。3)综合各季节和年际输沙势与沙丘移动距离呈线性正相关,拟合方程为y=1.02+0.006 62x(R~2=0.339,F=5.616,P=0.045),方程总体显著,输沙势可以表征该地区沙丘移动距离。基于无人机监测的沙丘运动研究综合显示,风况是该地区影响该地区沙丘移动的主要动力,其中西风组8 m/s以上风速是研究区沙丘移动的主要驱动力。风向变率和合成输沙势方向与沙丘移动方向一致时沙丘移动则快,不一致时则缓;无人机可在较大尺度上为沙丘移动提供更为便捷的监测服务,研究结果可为同类地区沙丘移动的无人机监测提供参考依据。

Monitoring and influencing factors of dune movement speed along the Yellow River using UAV technology

A highly urgent need has been concerned to more conveniently monitor the moving speed of dunes along the Yellow River in the Ulan Buh Desert. Taking the coastal dune in Ulan Buh Desert as the research object, the seasonal geomorphological process and influencing factors were investigated using image data acquisition through UAV in this study. Results showed that: 1) The annual movement speed of dune was 1.08-2.27m/a, the multi-year average sand Drift Potential (DP) was 78.82 VU, and the annual Resultant Drift Potential (RDP) was 25.96 VU. It indicated that the study area was in a low wind energy environment. The 8-12 m/s level of sand DP accounted for 73.24% of annual sand DP. The intermediate directional wind variability (i.e. RDP/DP) was around 0.30-0.46. The average Resultant Drift Direction (RDD) was 88.40°, which was consistent with the dune movement direction. The westerly wind contributed 52.09% of the variation of the annual sand DP, indicating the main driving force for the annual movement of dunes. 2) The dune movement speed presented obvious seasonal characteristics. Specifically, the fastest was observed in spring, followed by late winter to early spring, and the slowest in summer. In late autumn to late winter, spring and autumn, the sand DP was around 8.48-20.49 VU, the RDD was 90.02°-95.54°, and the RDP/DP was 0.3-0.8, indicating an intermediate rate of directional wind variability. The westerly wind presented a significant effect on dune movement, particularly compatible with the annual RDD and dune movement direction. In late winter to early spring and late spring to summer, the dune with a relatively low movement speed usually adapted to the wind direction through morphological changes under the northeasterly wind (NE) and southerly wind (SSE, S, and SSW). The seasonal sand DP was mainly composed of 8-10 m/s level wind speed, accounting for 40.76%-56.93% of the whole season. 3) Overall, the seasonal and inter-annual sand DP was linearly positively correlated with dune movement distance. The fitting equation was y=1.02+0.006 62x (R2=0.339, F=5.615 9, P=0.045 26). The fitting equation reached a significant level, indicating that the sand DP can be used to characterize the dune movement distance in the area. The comprehensive landscape was achieved for the dune movement monitored by UVA. Consequently, the wind speed above 8 m/s in the Westerly Group was the main driving force for dune movement in the study area. When the wind direction variability and the RDP were consistent with the movement direction of dunes, the dunes moved faster, otherwise, the dunes moved slowly. Anyway, UAVs can provide more convenient monitoring services for the movement of dunes on a larger scale. This finding can also provide a strong reference for UVA monitoring of dune movement in similar areas.