Sediment Flux Measurement at High Concentration Based on Image Analysis with Combined Illumination

Abstract

An improved measurement system was developed to quantify the sediment flux on the basis of two image-based techniques for sediment concentration and velocity measurement respectively. Motion images of sediment particles in target flow are recorded by a high-speed camera with an electro luminescence sheet as a backlight source. A stroboscope is synchronized with the camera through a time delay generator at half of the frame rate. Normal (backlight only) and strobo-illuminated images are alternatively obtained for image analysis. Sediment concentration is estimated from normal images according to a pre-calibrated relationship between concentration and light attenuation based on the Lambert-Beer law. Velocities of sediment particles are obtained by applying PIV to each set of the normal and strobo-illuminated motion images. Sediment flux can be figured out by multiplying the concentration and velocity at respective locations. Simple verification tests were conducted to demonstrate the feasibility of the improved system. The results suggest that the system is capable of measuring sediment concentration over 190g/L with errors of no more than 10%.