Bathymetry is considered an important component in marine applications as several coastal erosion monitoring and engineering projects are carried out in this field. It is traditionally acquired via shipboard echo sounding, but nowadays, multispectral satellite imagery is also commonly applied using different remote sensing-based algorithms. Satellite-Derived Bathymetry (SDB) relates the surface reflectance of shallow coastal waters to the depth of the water column. The present study shows the results of the application of Stumpf and Lyzenga algorithms to derive the bathymetry for a small area using an Unmanned Aerial Vehicle (UAV), also known as a drone, equipped with a multispectral camera acquiring images in the same WorldView-2 satellite sensor spectral bands. A hydrographic Multibeam Echosounder survey was performed in the same period in order to validate the method’s results and accuracy. The study area was approximately 0.5 km² and located in Tuscany (Italy). Because of the high percentage of water in the images, a new methodology was also implemented for producing a georeferenced orthophoto mosaic. UAV multispectral images were processed to retrieve bathymetric data for testing different band combinations and evaluating the accuracy as a function of the density and quantity of sea bottom control points. Our results indicate that UAV-Derived Bathymetry (UDB) permits an accuracy of about 20 cm to be obtained in bathymetric mapping in shallow waters, minimizing operative expenses and giving the possibility to program a coastal monitoring surveying activity. The full sea bottom coverage obtained using this methodology permits detailed Digital Elevation Models (DEMs) comparable to a Multibeam Echosounder survey, and can also be applied in very shallow waters, where the traditional hydrographic approach requires hard fieldwork and presents operational limits.

中文翻译：

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无人机衍生的多光谱测深法

测深法被认为是海洋应用中的重要组成部分，因为该领域已进行了一些海岸侵蚀监测和工程项目。传统上是通过船上回声探测获得的，但是如今，多光谱卫星图像也通常使用不同的基于遥感的算法来应用。卫星衍生的测深法（SDB）将沿海浅水的表面反射率与水柱深度相关联。本研究显示了应用Stumpf和Lyzenga算法以使用无人飞行器（UAV）（也称为无人驾驶飞机）获得小范围测深的结果，该无人机配备了在同一WorldView-2中采集图像的多光谱相机卫星传感器光谱带。为了验证该方法的结果和准确性，在同一时期进行了水文Multibeam Echosounder调查。研究区域约为0.5公里²并位于意大利的托斯卡纳。由于图像中水的百分比很高，因此还采用了一种新方法来生成地理参考正射镶嵌图。对无人机多光谱图像进行处理，以获取测深数据，以测试不同的波段组合并根据海底控制点的密度和数量评估精度。我们的结果表明，UAV衍生的测深仪（UDB）允许在浅水区的测深仪测绘中获得约20 cm的精度，从而最大程度地减少了操作费用，并为进行沿海监测测绘活动提供了可能性。使用这种方法获得的整个海底覆盖范围可提供与多波束回声测深仪相当的详细数字高程模型（DEM），也可用于非常浅的水域，