by Terti Prickett, U.S. Army Engineer Waterways Experiment Station

Most damage to coastal structures, es-pecially rubble-mound breakwaters and jetties, occurs to the submerged portion of the structure. Underwater damage such as that caused by scour, settlement, or scattering and breakage of armor units is not readily visible on the sur-face. If undetected, it can progress until a major structural collapse occurs. Early detection of structural deterioration is therefore essential for cost-effective man-agement of coastal structures over their lifetimes. Diver inspections provide some infor-mation about the condition of underwa-ter structures, but these surveys are Sea Bat sonar head being deployed often difficult and risky, hampered by the normal occurrence of waves and cur-rents and limited visibility around the structure. The information obtained from diver surveys is subjective, and spatial detail is sparse. Additionally, results from side-scan sonars, a viable tool for structural surveys (Kucharski and Causner 1990), are semi-quantitative and often sketchy and distorted because of ener-getic wave and current conditions around the structure. In response to the need for better pro-cedures and equipment for underwater in-spections, research was initiated under the REMR Research Program to identify and evaluate hardware and software tools that would produce useful, high-quality results and yet require a mini-mum level of operator skill, training, and experience. One product developed in the initial investigations was th