Coastal dunes are fragile ecosystems emerging at the interface between marine and continental environments. They provide multiple services, among which are the protection against the impact of storms and the hosting of diverse and unique species of fauna and flora. However, changes in the topography or biological component of these systems may endanger the perpetuation of service provision. Topographic changes within dunes can significantly differ in magnitude depending on the type of process (i.e., marine or aeolian) and the temporal scale of analysis (event to annual scale), making their monitoring a challenging task. In recent years, unmanned aerial vehicles (UAVs) have been increasingly used to monitor coastal dunes, proving to be a cost-efficient methodology for the collection of topographic data. Yet, the application of UAVs in combination with the structure from motion approach to obtain digital surface models (DSMs) presents some limitations related to the level of accuracy provided for the evaluation of topographical changes in dunes with low sedimentation rates. This work explores different survey configurations using UAVs flying at low altitudes with the aim of obtaining high-quality DSMs with vertical accuracies preferably around or lower than 0.04 m. Several tests were performed to evaluate the influence of different parameters on the accuracy of the DSM, including flight altitude and orientation, density and spatial distribution of ground control points (GCPs), terrain slope, vegetation cover, and sun-related parameters. The results indicate that the intended accuracies can be obtained by combining overlapped perpendicular flights, GCPs distributed regularly following a diamond grid, with densities of at least 6 GCPs per hectare, sun altitudes between 30 and 40 deg, and a total solar radiation per hour between 1750 and 2250 KJ / m2. In addition, better results were obtained across gentle slope areas, suggesting the eventual need to adapt to the particularities of each site to ensure the accuracy.

中文翻译：

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测量参数对无人机衍生地形用于海岸沙丘监测的影响

海岸沙丘是在海洋和大陆环境交界处出现的脆弱生态系统。它们提供多种服务，其中包括抵御风暴的影响以及托管各种独特的动植物物种。然而，这些系统的地形或生物成分的变化可能会危及服务提供的永久化。根据过程类型（即海洋或风成）和分析的时间尺度（事件到年度尺度），沙丘内的地形变化在幅度上可能存在显着差异，这使得它们的监测成为一项具有挑战性的任务。近年来，无人机（UAV）越来越多地用于监测沿海沙丘，被证明是一种具有成本效益的地形数据收集方法。然而，无人机与结构运动方法相结合以获得数字表面模型 (DSM) 的应用存在一些限制，这些限制与为评估低沉降率沙丘的地形变化提供的准确度水平有关。这项工作探索了使用在低空飞行的无人机的不同测量配置，目的是获得垂直精度最好在 0.04 m 左右或低于 0.04 m 的高质量 DSM。进行了多项测试以评估不同参数对 DSM 精度的影响，包括飞行高度和方向、地面控制点 (GCP) 的密度和空间分布、地形坡度、植被覆盖和太阳相关参数。结果表明，通过组合重叠的垂直飞行可以获得预期的精度，GCP 按照菱形网格规则分布，密度至少为每公顷 6 个 GCP，太阳高度在 30 到 40 度之间，每小时总太阳辐射在 1750 到 2250 KJ/m2 之间。此外，在缓坡区域获得了更好的结果，这表明最终需要适应每个站点的特殊性以确保准确性。