Locating a groundwater discharge site in a river by measuring water surface temperature with a drone

Abstract

　This report illustrates a novel trial to use a drone equipped with both visible light and infrared cameras to measure river surface temperature to locate a site where groundwater is being directly discharged into the river. The water at the site was distinguished from the surrounding river water by its temperature. It was compared with the water in the middle of the river in terms of physical and chemical properties, including via an examination of stable isotopes. In addition, microbial DNA analysis was applied to estimate the variations in dominant prokaryotes in the water sample. The site where groundwater is discharged directly into the river may provide a unique habitat where temperature does not fluctuate through the seasons. Discharged groundwater may also affect the surrounding water though the area of this effect would be limited. In terms of the hydrological cycle, evaluating the influence of the direct discharge of groundwater into a river system is an essential step in river management. Therefore, measurement of river surface temperature by drones is a useful tool.