Low-Cost UAV for High-Resolution and Large-Scale Coastal Dune Change Monitoring Using Photogrammetry

Quentin Laporte-Fauret,Stéphane Bujan,Bruno Castelle,David Rosebery,Vincent Marieu,Richard Michalet

doi:10.3390/jmse7030063

Abstract

In this paper, coastal dune data are collected at Truc Vert, SW France, using photogrammetry via Unmanned Aerial Vehicles (UAVs). A low-cost GoPro-equipped DJI Phantom 2 quadcopter and a 20 MPix camera-equipped DJI Phantom 4 Pro quadcopter UAVs were used to remotely sense the coastal dune morphology over large spatial scales (4 km alongshore, i.e., approximately 1 km2 of beach-dune system), within a short time (less than 2 h of flight). The primary objective of this paper is to propose a low-cost and replicable approach which, combined with simple and efficient permanent Ground Control Point (GCP) set-up, can be applied to routinely survey upper beach and coastal dune morphological changes at high frequency (after each storm) and high resolution (0.1 m). Results show that a high-resolution and accurate Digital Surface Model (DSM) can be inferred with both UAVs if enough permanent GCPs are implemented. The more recent DJI Phantom 4 gives substantially more accurate DSM with a root-mean-square vertical error and bias of 0.05 m and −0.03 m, respectively, while the DSM inferred from the DJI Phantom 2 still largely meets the standard for coastal monitoring. The automatic flight plan procedure allows replicable surveys to address large-scale morphological evolution at high temporal resolution (e.g., weeks, months), providing unprecedented insight into the coastal dune evolution driven by marine and aeolian processes. The detailed morphological evolution of a 4-km section of beach-dune system is analyzed over a 6-month winter period, showing highly alongshore variable beach and incipient foredune wave-driven erosion, together with wind-driven inland migration of the established foredune by a few meters, and alongshore-variable sand deposition on the grey dune. In a context of widespread erosion, this photogrammetry approach via low-cost flexible and lightweight UAVs is well adapted for coastal research groups and coastal dune management stakeholders, including in developing countries where data are lacking.

Highlights

Photogrammetry using Unmanned Aerial Vehicles (UAVs) has been increasingly used in recent years to remotely sense topographic data in different fields of geoscience like gully erosion [1], beach dune system evolution [2,3,4,5,6], tidal inlet evolution [7], rocky cliff erosion [8], volcanic gas measurements [9] and eroding sub-humid badlands [10]
We develop a low-cost, lightweight and replicable UAV photogrammetry protocol with two different UAVs, one equipped with a fisheye lens camera and the second, more recent, equipped with a high-resolution camera providing weakly-distorted high-resolution images
The second objective is to determine whether a very low-cost UAV equipped with a fisheye-lens action camera can monitor the morphological evolution of beach-dune systems with an accuracy meeting coastal monitoring requirements, or if latest generation off-the-shelf camera-equipped UAVs are necessary. This approach is further used to address the beach-dune morphological changes in SW France driven by the combination of marine and aeolian processes during the winter of 2017/2018. We show that this approach can provide unprecedented insight into beach-dune dynamics across the entire system under the combined action of storm wind and waves

Summary

Introduction

Photogrammetry using Unmanned Aerial Vehicles (UAVs) has been increasingly used in recent years to remotely sense topographic data in different fields of geoscience like gully erosion [1], beach dune system evolution [2,3,4,5,6], tidal inlet evolution [7], rocky cliff erosion [8], volcanic gas measurements [9] and eroding sub-humid badlands [10]. Reference [13] used photogrammetry with Pleiades satellite images to obtain DTMs in mountainous areas, with, after optimization, horizontal and vertical accuracy of 0.5 m and 1.0 m, respectively, but the spatial and temporal resolution remain much larger than those possible with UAVs. High resolution DSM can be obtained by a terrestrial or airborne LiDAR. High resolution DSM can be obtained by a terrestrial or airborne LiDAR These optical remote sensing techniques use the flight time of laser pulses reflected by the surface of the points. The airborne LiDAR allows for monitoring a very large-scale area with high precision and resolution, and vegetation penetration, but the high cost and the long processing time of each survey is prohibitive for monitoring the coast at high frequency (i.e., monthly, seasonally). Contrary to most of these studies [1,2,3,4,5,6,7,8,9,10], our contribution (1) uses high-resolution fish eye lens and regular-angle lens; (2) is based on a permanent GCPs spatial distribution with automatized flight plan and waypoints software for high replicability and (3) covers a large area

Objectives

Methods

Conclusion