The prevention of attacks on marine structures has been an ongoing challenge and hascreated an awareness of the vulnerability of these structures to such attacks. Especiallysince the 9/11 era, it has become crucial for owners and operators of dams to protect themfrom underwater attacks and maintain a constant, secure perimeter that will provideimmediate detection and tracking of all threats. Sonar provides a cost effective andefficient means of underwater security because unlike other methods of surveillance,acoustic waves with low to mid-range frequencies can travel virtually unimpeded throughwater until reflected back to the receiver. The center frequency and power levels arelargely determinant of a sonar's performance, as well as the unique aspects of the marineenvironment where it will be used. This paper presents an evaluation of the uncertaintiesthat exist underwater that can affect sonar performance. These uncertainties include thesound velocity profile (which shows the speed of sound underwater as a function oftemperature, depth, and salinity), the signal-to-noise ratio, and the behavior of soundwaves as they propagate through various mediums. This study determined that factorssuch as depth and variable sound profiles can lead to problems such as reverberation,multipath reflections, and poor range performance. Also, ambient noise associated withdaily dam operation and recreational lake activity can result in false alarms and misseddetections. However, it was concluded that when all of these factors are included in thedeployment considerations, sonar provides adequate warning time to counteractapproaching underwater threats.
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