Date of Award

5-2011

Level of Access Assigned by Author

Campus-Only Thesis

Degree Name

Doctor of Philosophy (PhD)

Department

Physics

Advisor

Emmanuel S. Boss

Second Committee Member

Ali Abedi

Third Committee Member

Kate Beard-Tisdale

Abstract

The ability to quantify suspended sediment concentrations in marine environments is invaluable; mass concentration plays an important role in many applications, e.g., in turbulence modeling and in underwater communication. Marine particles have optical and acoustical properties that can be used to quantify particle mass concentration, and can provide information regarding the dynamics of particles (e.g., aggregation, settling/resuspension). Both methods have inherent ad-vantages and disadvantages: in-situ optical sensors are very sensitive to biofouling as where acoustical sensors are not, but the effects of ambient noise on higher frequency acoustics is less known. Previous studies have been performed that tested the validity of an acoustic approach to measuring suspended sediment concentration in-situ. While it is generally accepted that acoustic backscatter systems are adept at measuring the first order variability (due to suspended mass) in marine environments, there is less agreement over how well the second-order variability (due to changes in: particle size, composition, and aggregation) can be ascertained with an acoustic approach. The work presented in this dissertation explores the use of acoustic backscatter sensors in the study of particle dynamics, in-situ, and experiments were performed in the laboratory and in the field to assess the acoustic backscattering to dynamical events. The first chapter describes a laboratory calibration of an Acoustic Doppler Velocimeter (ADV) that was performed in order to characterize the signal strength to changes in suspended mass, and then to characterize the mass-normalized backscat-tering to particle size. The second chapter describes laboratory and field investiga-tions of optical and acoustic backscattering responses to aggregation events. The third chapter investigates: the correlation between co-deployed optical and acoustic backscatter measurements, the predictability of one method from the other, and the possible causes for de-correlation between the two methods. The results from each of these studies suggest that the interactions between marine particulates during dynamic events can affect the optical and acoustical properties of particles which can, in turn, affect the predictability of suspended sediment concentration. Because each method is affected differently by dynamical events, judicious co-deployments of optical and acoustical instrumentation can provide complimentary measurements.

Download

Share