Ultrasonic measurements of clays and silts suspended in water

Ongoing work at the National Center for Physical Acoustics is aimed at using acoustics to provide monitoring for fine sediments suspended in water. The ultimate goal of the work is to field an acoustic instrument that can monitor fine particle concentration in rivers and streams. Such an instrument would have several advantages over currently available technologies. Expanding upon work from Carpenter et. al (2009), two immersion transducers were placed at a fixed distance to measure attenuation and backscatter from acoustic signals at 10 MHz and 20 MHz propagated through clays (bentonite, illite, and kaolinite) and silt. The resulting data set encompasses a wide range of concentrations (0.01 - 14 g/L) and particle sizes (0.1 - 64 micron diameter particles). Backscatter and attenuation curves for each material across the range of concentrations will be shown and compared to the theoretical attenuation curves developed by Urick (1948). This work has produced a data set for model development using a combination of backscatter and attenuation to allow for single-frequency discrimination between clay and silt particles suspended in water.