Acoustics

This research presents findings from an in-situ experiment utilizing a hydrophone line array to capture the sound production of the Goliath grouper. Analysis revealed that Goliath grouper calls exhibit multiple frequency components, including one high-amplitude component and 2 to 3 low-amplitude components. The primary high-amplitude component is concentrated in the 30 to 70 Hz band, peaking around 50 Hz, while low-amplitude components span 20 to 30 Hz, 70 to 115 Hz, and 130 to 200 Hz. Comparison between in-situ data and results from a normal modes transmission loss model identified regions where echo level increased with propagation distance. This suggests that the loudness of the call may not necessarily indicate proximity, indicating the Goliath grouper might rely on other cues for localization, such as changes in the frequency profile of its call. Two methods for estimating call distance are presented. The first method vi utilized a transmission loss model and measured transmission loss across a hydrophone line array. This method could also determine the source level of the calls, yielding source level estimates ranging from 124.01 to 144.83 dB re 1 μPa. The second method employed match field filtering, validating the accuracy of the transmission loss model. Both methods produced similar call distance estimations, ranging from 11.5 to 17.1 meters, placing the grouper inside or near its typical habitat.

The detection of rebar corrosion in reinforced concrete is important due to the high costs of corrosion related damages to infrastructure. One such method of rebar corrosion lies in the use of non-destructive ultrasonic testing. To date, acoustic methods require either the training of an artificial neural network or a theory of acoustic wave propagation. Using a more complete acoustic model such as the Biot-Stoll model avoids algorithm training requirements by directly modeling the acoustic environment. A problem with this method lies in the complexity of the model and the selection of free parameters. The problem of parameter selection is addressed by a series of targeted measurements using ultrasonic transducers on a set of existing reinforced concrete samples placed in a saltwater solution. This data can then be analyzed by a non-linear least squares solver to produce a better fit for the acoustic signal.

Wetland loss and degradation have led to the development of restoration programs worldwide, many of which monitor wading bird populations as indicators of wetland quality. Therefore, efficient, standardized monitoring is integral to restoration progress. I tested the use of passive acoustic monitoring to estimate nest abundances and provisioning rates in wading bird colonies and examined regional nesting dynamics in the Florida Everglades, where a long monitoring record enables analysis of nesting patterns relative to hydrologic changes. I found that call rates can serve as indices of colony nest abundances and begging call rate and timing are indicative of provisioning events. Nesting dynamics suggested that resource availability is asynchronous between regions of the Everglades, but the degree of asynchrony varies with species. The conclusions of this study will facilitate the long-term monitoring of wading bird nesting trends, which are important measures of wetland restoration in Florida and worldwide.