Estimating open channel surface flow velocities under low luminosity conditions, using fluorescent quinine-based tracing techniques and UAS imagery

This study discusses the application of innovative fluorescent quinine-based tracer techniques to estimate surface flow velocities under low luminosity conditions. Quinine is known for its luminescent properties when exposed to ultraviolet A (UVA) light. This research involves fieldwork measurements conducted in open channels with varying hydraulic characteristics. The application of quinine solutions in liquid and solid (ice cubes) states into the water flow allows the recording of the movement of the tracers. This movement is registered by tracking the leading edge of the liquid tracer plume or solid particles over specific time intervals. An Unmanned Aerial System (UAS) equipped with a camera was used to record the movement of the tracers in the channels. To benchmark the performance of the quinine-based tracers, flowmeter-based velocity maps and a thermal tracer technique were employed in the experiments. Results indicated that both liquid and solid quinine solution tracers successfully estimated open channel surface flow velocities under low luminosity conditions. The quinine solid tracer can be used as a dual (fluorescent-thermal) tracer and, despite its smaller volume used in the experiments compared to the liquid tracer, the solid form was easier to track. This was attributed to the conservation of a higher quinine concentration for longer periods of time in the solid tracers, resulting in a higher contrast easier to identify. On the other hand, the liquid tracer faded earlier due to diffusion in the turbulent flow. Nonetheless, the main advantage of using the liquid over the solid tracer was its easier availability for the experiments. This study highlights the applicability and reliability of quinine-based tracers in estimating surface flow velocities, in low luminosity conditions. The use of the UAS in the measurements’ set-up facilitated and enhanced data collection, contributing to the accuracy of the results. The observational approach allowed for capturing the inherent luminescent properties of quinine when exposed to UVA light using minimal tracer quantities.