基于无人机航测的红树林潮滩地貌高程反演

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

红树林潮滩地貌高程的变化直接影响红树林生长发育。精确快速获取潮滩地貌高程动态变化过程,对实施红树林培育与造林意义重大。然而,受限于潮水涨落、潮滩易陷及红树林区难以深入等因素,红树林潮滩地貌的高程获取成为当前备受关注的难点。基于此,本文以广西北部湾北部北仑河口为例,利用DJI Phantom 4 RTK无人机对区域进行多高度、多架次航测,以Structure from Motion(SFM)算法为核心反演该区域的红树林潮滩地貌高程,探讨影响高程反演精度的因素,进而拟合出一套误差修正关系式,并以钦江与南流江河口红树林潮滩为应用对象验证该关系式的适用性。结果表明:(1)无人机飞行高度直接影响高程提取精度,其中飞行高度越高,提取的地貌高程误差越大,飞行高度约在110 m时更能兼顾航测用时和高程提取精度;(2)无人机航测提取的潮滩地貌高程值与RTK测量值存在较为显著的垂向平移偏差关系,提取值普遍高于RTK测量值,基于此提出了修正关系式,实现了对不同飞行高度的高程提取值的修正,显著提高了其精度,且关系式有较好的适用性和普适性;(3)植被覆盖度是无人机提取潮滩地貌高程的重要影响因子,植被覆盖度越高,提取精度越低,本研究的修正关系式在光滩区域的修正效果优于植被区域。研究结果可为无人机反演红树林潮滩地貌高程变化过程提供部分理论和技术支撑,对提高无人机反演红树林潮滩地貌高程的效率和精度有一定借鉴意义。

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.