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 1.08-2.27 m/a, the multi-year average sand Drift Potential (DP) was 78.82 VU, and the annual Resultant Drift Potential (RDP) was 25.92 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 57.83°-107.39°, 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=5.616, P=0.045). 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.