In addition, ad-hoc tests are conducted with red-emitting off-the-shelf polyethylene particles and a new class of orange-fluorescent particles, formulated to be environmentally-friendly and biodegradable [38], to explore the effects of alternative fluorophores. Experiments are executed by deploying few grams of particles in a custom-built water channel placed in an outdoor environment and by recording the transit of the beads through the sensing station developed in [35]. Specifically, beads’ fluorescence is elicited through commercially available light sources and a miniature digital camera is operated to record the particles’ transit. As compared with [35], the sensing station is enhanced to reduce the effect of camera distortions and light reflections at the water surface.
Such improvements allow for obtaining higher performance while reducing apparatus’ costs. The influence of the following parameters on the system performance is investigated: (i) distance of the light source from the water surface, (ii) presence of a filter at the specific range of emission of the particles, (iii) camera resolution and frame rate, (iv) regime of the investigated flows, and (v) ambient light. Experimental results garnered in this study provide valuable information on the system performance as several key parameters are systematically varied, thus informing implementation guidelines for field studies.The rest of the paper is organized as follows.
In Section 2, the sensing station and the fluorescent particles used for the experiments are presented.
In Section 3, descriptions of the experimental setup and protocol are provided. In Sections 4, experimental results are reported and discussed. Conclusions are summarized in Section 5.2.?Materials and Methods2.1. Experimental Set Up and Sensing SystemThe experimental set up is composed of a 2 m long and 22 cm wide reclinable polyvinyl chloride water channel placed outdoor and a portable sensing station, see Figure 1. The water channel Entinostat cross section is AV-951 concave and its bed is covered with a mixture of soil and bitumen to create a naturally rough surface. Water is injected into the channel through a hose and a valve is used to regulate flow discharge.
Figure 1.Schematic of the instrumented water channel for surface flow measurements.The sensing station is constituted of a 40 cm �� 100 cm wooden plate resting on adjustable steel tripods. The tripods allow for raising and lowering the plate at variable distances from the water surface from a few centimeters up to 70 cm. The bottom side of the plate hosts the light unit whose wavelength range is selected to excite the fluorescence of the specific particle tracer.