Document Type
Thesis
Abstract
The development of the Acoustic-Doppler Velocimeter was initiated under contract by the U.S. Army Engineer Waterways Experiment Station in 1992 to satisfy the need for an accurate current meter that can measure 3D dynamic flow in physical models (Lohrmann et al., 1994). The Acoustic-Doppler Velocimeter (ADV) developed by the SonTek environmental company was designed to record and measure instantaneous velocity at relatively high frequencies. The instrument performs velocity measurements in a remote sampling volume (2.0 cm3) at a fixed distance (5, 10, or 18 cm) away from the source probe (SonTek, 2001). An ADV operates by emitting a burst of sound waves with known duration and frequency from a source transducer and using three receiving transducers to measure the backscatter waves. Since the backscatter wave frequency is shifted by moving particles available in the target area, the magnitude of this frequency shift (Doppler Shift) is proportional to the flow velocities (Ha et al., 2009). Since the time of its creation, the ADV has become a very popular and useful apparatus in field and lab experiments for measuring velocity. Although ADVs were originally designed for velocity measurement only, the backscatter associated with the acoustic returns can be successfully calibrated for suspended sediment concentration (Cartwright et al., 2009). ADV measurements are far from perfect and require much post-processing before the data can be used. Acoustic backscatter generally increases in intensity with increases in the amount of sediment in the water. Some research has also found that acoustic backscatter increases with grain size of sediment present in the sampling volume. If this is true, then the ADV will give different backscatter measurements for water with different concentrations of sand as opposed to clay. Because sand is larger and more rigid than clay, the ADV will give a higher backscatter reading for sand and less backscatter for clay sediments, if backscatter is proportional to grain size. If the data show that the above hypothesis is correct, then ADVs in the field and lab can be appropriately calibrated to the grain size of the sampling volume in order to give more precise estimates of concentration.
Date Awarded
2010
Department
Geology
Advisor 1
Carl Friedrichs
Advisor 2
Grace Cartwright
Recommended Citation
Newbill, Donte Deron, "How Accurate is Your ADV? An Investigative Analysis on the Effect of Grain Size on Acoustic Doppler Velocimeter Backscatter" (2010). Geology Senior Theses. William & Mary. Paper 235.
https://scholarworks.wm.edu/geologyseniors/235
