Spatial structure, temporal variability, and dynamical features of small river plumes observed by aerial drones

We use optical imagery and video of ocean surface acquired from aerial drones (quadcopters) to study small river plumes formed in the northeastern part of the Black Sea. Quadcopters can continuously observe small river plumes with high spatial resolution from relatively low altitude. It provides unprecedented ability to study spatial structure of small river plumes, detect and measure their temporal variability, register various dynamical features of these plumes. In this work we describe and analyze strongly inhomogeneous structure of small river plumes manifested by complex and dynamically active internal frontal zones; undulate form of sharp front between small river plume and ambient sea and energetic lateral mixing across this front caused by frontal baroclinic instability; internal waves generated by river discharge near a river estuary and propagating within inner part of a plume; internal waves generated by vortex circulation of a river plume and propagating within outer part of a plume. The issues reported in this study remained mainly unaddressed before due to low spatial and/or temporal resolution of in situ measurements and satellite imagery used in previous related studies. We show that usage of aerial drones, first, strongly enhance in situ and satellite observations of structure and variability of small plumes, second, provides ability to perform accurate, continuous, and high-resolution measurements of their spatial characteristics and current velocity fields and, finally, significantly improves organization of operational field measurements. As a result, aerial drones are effective tools to obtain new qualitative insights and quantitative assessments of structure, variability, and dynamics of small river plumes.