Merging Unmanned Aerial Systems (UAS) Imagery and Echo Soundings with an Adaptive Sampling Technique for Bathymetric Surveys

Abstract

Bathymetric surveying to gather information about depths and underwater terrain is increasingly important to the sciences of hydrology and geomorphology. Submerged terrain change detection, water level, and reservoir storage monitoring demand extensive bathymetric data. Despite often being scarce or unavailable, this information is fundamental to hydrodynamic modeling for imposing boundary conditions and building computational domains. In this manuscript, a novel, low-cost, rapid, and accurate method is developed to measure submerged topography, as an alternative to conventional approaches that require significant economic investments and human power. The method integrates two types of Unmanned Aerial Systems (UAS) sampling techniques. The first couples a small UAS (sUAS) to an echosounder attached to a miniaturized boat for surveying submerged topography in deeper water within the range of accuracy. The second uses Structure from Motion (SfM) photogrammetry to cover shallower water areas no detected by the echosounder where the bed is visible from the sUAS. The refraction of light passing through air–water interface is considered for improving the bathymetric results. A zonal adaptive sampling algorithm is developed and applied to the echosounder data to densify measurements where the standard deviation of clustered points is high. This method is tested at a small reservoir in the U.S. southern plains. Ground Control Points (GCPs) and checkpoints surveyed with a total station are used for properly georeferencing of the SfM photogrammetry and assessment of the UAS imagery accuracy. An independent validation procedure providing a number of skill and error metrics is conducted using ground-truth data collected with a leveling rod at co-located reservoir points. Assessment of the results shows a strong correlation between the echosounder, SfM measurements and the field observations. The final product is a hybrid bathymetric survey resulting from the merging of SfM photogrammetry and echosoundings within an adaptive sampling framework.

Microorganisms Collected from the Surface of Freshwater Lakes Using a Drone Water Sampling System (DOWSE)

“…However, the temperature ranges from their study did not include distance from shore or depth of measurement. Alvarez et al [19] generated a bathymetric map of Finn Creek Site 21 Reservoir in McCain County, Central Oklahoma, USA using a small unmanned aerial system (sUAS), and attached a floating data collector similar to the system used in our study. The coupling of aerial drone and bathymetric data collectors provides a quick and accurate means to map lakes [19].…”

“…Alvarez et al [19] generated a bathymetric map of Finn Creek Site 21 Reservoir in McCain County, Central Oklahoma, USA using a small unmanned aerial system (sUAS), and attached a floating data collector similar to the system used in our study. The coupling of aerial drone and bathymetric data collectors provides a quick and accurate means to map lakes [19]. Perhaps unmanned systems could be tuned to predict concentrations of bacteria in lakes, provided parameters such as temperature and depth can be measured remotely.…”

Remote sensing of river corridors: A review of current trends and future directions

“…Alongside solely airborne techniques, the combination of USVs and UAVs has become more prominent. Although there are examples of UAVs being used to “tether” USVs (Alvarez et al, ; Bandini et al, ), the majority of studies operate the platforms separately. By combining the two techniques, it is possible to collate information on either the topographic and bathymetric or the above and below canopy nature of a river corridor.…”

“…Young et al () utilised a low‐cost system to survey storage tanks in Bangalore with submetre accuracy. A more advanced set‐up by Alvarez et al () obtained correlation results to ground truth data of R > .98 by combining echo sounder and SfM techniques. Alternatively, UAV and USV platforms can both collect imagery in addition to acoustics to improve estuarine mapping when compared with UAV imagery alone (Mancini, Frontoni, Zingaretti, & Longhi, ), although both methods are limited by vegetation shadowing.…”

Quantification of bedform dynamics and bedload sediment flux in sandy braided rivers from airborne and satellite imagery

“…in many of the world's largest rivers), may be more challenging unless there are future significant technological advances (e.g. UAVs tethered to miniaturised, boat-mounted, echo-sounders as illustrated by Alvarez et al (2018); Bandini et al (2018)).…”