Elevation Inversion of Mangrove Tidal Flat Geomorphology Based on UAV Aerial Survey

Changes in the topography of mangrove tidal flats directly influence the growth and development of mangroves. Accurately and rapidly acquiring the dynamic variation process of tidal flat surface elevation is crucial for mangrove cultivation and afforestation. However, obtaining the elevation of mangrove tidal flat effectively is challenging due to periodic tide fluctuations, muddy sedimentary conditions, and dense mangrove roots. In this study, a high-precision Unmanned Aerial Vehicle (UAV), the DJI Phantom 4 RTK, is used for elevation inversion in the mangrove tidal flat of the Beilun Estuary, Beibu Gulf, China. The investigation aims to uncover potential influencing factors and assess its applicability to mangrove tidal flats in the estuaries of Qinjiang River and Nanliu River. The results indicate a direct correlation between UAV flight height and the accuracy of elevation inversion, where higher flight heights lead to larger Root Mean Square Error (RMSE). When the UAV flight height reaches approximately 110 m, both efficiency and accuracy can be achieved. There are significant vertical shifting deviations between the elevation measurements from UAV and GPS-RTK, with UAV-based surveys of mangrove tidal flat generally showing higher elevations than GPS-RTK. Therefore, a correction equation is proposed to improve the accuracy of UAV-based surveys. The significant improvement in measurement accuracy verifies the applicability and universality of the equation. The accuracy of elevation inversion through UAV is predominantly influenced by vegetation coverage. Increased vegetation coverage leads to decreased accuracy in elevation inversion. Moreover, the elevation correction equation exhibits reduced reliability in vegetated areas compared to bare flats. The obtained results not only offer theoretical and technical support for UAV-based geomorphology surveys in mangrove tidal flats but also provide valuable references for enhancing the accuracy and efficiency of elevation inversion.