Pond Bathymetry Revealed by a Drone-Echosounder System

A pond system composed of more than 2,800 waterbodies forms a unique landscape in northwestern Taiwan. Those waterbodies were historically used for irrigation and aquacultural purposes. However, owing to the rapid urban development, an increasing demand of land looms the preservation of ponds in the past decades. It has drawn wide attention that some ponds are gradually disappearing or intentionally filled up. In order to capture the current status of the ponds for environmental preservation, we must effectively and accurately measure the hydrological parameters of those waterbodies.

The traditional approach to acquire water area and water volume relies on labor-intensive and high-cost fieldworks. Especially, it is difficult to fathom the detailed pond floor topography. Therefore, we develop a measuring system composed of a drone, a smartphone, and a single beam echosounder to map hundreds of ponds in Taoyuan, Taiwan. First, we validate the measurement of a pond that has an area of ~32,000 square meter and an average depth of ~1.7 m by using an unmanned surface vehicle with a multibeam echosounder. In our validation results, the accuracy in terms of root-mean-square error of depth, is less than 0.5 m and the difference of volume is less than 10%. We further apply this technique to more than two hundreds of ponds to estimate the storage of water for potential drought event. Our advantage is the flexibility and low-cost of measurement as compared against ship surveys. Also, the workflow developed herein is expandable to other remote areas inaccessible to vessel deployment.