Research Article: Near-Remote Sensing of Water Turbidity Using Small Unmanned Aircraft Systems

Abstract

This report describes the field demonstration of a near-remote sensing method to measure water turbidity over large areas, in a high-resolution, spatial context. Our interdisciplinary method used a novel multispectral imaging sensor deployed by a hand-launched small unmanned aircraft system (sUAS). The measurement of turbidity is a useful indicator of water quality. Current turbidity measurement tools, such as the Secchi disc, are labor-intensive and often limit coverage such that available samples are extrapolated unrealistically when representing large water resources. This handicaps computer models’ ability to predict run-off, and these models produce the best results if supplied with high-resolution, fine time-increment measurements. This first study of the method developed operated the sUAS below 200 m over the surface of a 9.3-ha lake, capturing visible and near-infrared imagery at resolutions of ~0.2 m/pixel and capturing spectral bands matching those captured by the Landsat 4-5 satellites. The study established the spectral sensitivity and spatial coverage of the instrumentation and correlated turbidity estimates against traditional Secchi disc readings taken across the lake. This study also differentiated turbidity contribution from suspended organics vs. suspended sediments. To manage glare, this new technique required strategically positioned sunlight, thus sharing some operational limitations with the Secchi disc method. Plans have been made to extend the technique to be suitable for deeper, clearer lakes. The technique represents an improved monitoring tool for environmental scientists, watershed managers, and civil engineers.Environmental Practice 18: 18–31 (2016)