PART V: OPERATING PARAMETERS 



68. Side-scan sonar is a potentially useful tool for the reconnaissance 

 and inspection of coastal structures. As noted earlier, there are still 

 equipment and physical limitations on present systems which prohibit quantita- 

 tive data collection such as structure slope, condition of individual armor 

 units, and percentage of armor units displaced. Side-Scan sonar use is 

 applicable mainly in monitoring programs to qualitative assessments of gross 

 changes. Other types of acoustic imaging systems, such as scanning sonars, 

 have the potential to overcome some of these problems. While detailed discus- 

 sions of these other acoustic imaging systems is beyond the scope of this 

 report, they are briefly described at the end of Part VI. The reader may con- 

 sult a recent report from the REMR Program (Howell, Kurcharski, and Clausner 

 in press) which discusses them in more detail. 



69. The limitations of side-scan sonar have to be taken into account 

 when planning a survey. Probably the most important item to consider is wave 

 and current conditions. Other limitations include the survey vessel and speed 

 of the survey; site limitations; coastal structure type, including armor mate- 

 rial nature, size, and condition; expected reflectivity contrast between the 

 structure and the bottom; instrument setting and behavior; position control; 

 and the experience of the operator. These limitations will be discussed 

 briefly to give the engineer or planner an appreciation of their effect on 

 side-scan sonar operations. Kurcharski and Clausner (in preparation) discuss 

 these limitations in detail. 



70. Proper planning and execution should revolve around the intent of 

 the survey and the nature of the structure. The maximum value of side-scan 

 sonar is often realized after some experimentation and imaginative tailoring 

 for the particular location and structure. The clarity of the record and its 

 usefulness are very sensitive to the operating techniques mentioned above 

 which affect the vessel, the site, the instrument and the operator. The 

 following discussions are based on the premise of using a 500-kHz system for 

 coastal structure evaluation. Figures 37 and 38 demonstrate the increased 

 resolution of a 500-kHz system over a 100-kHz system in calm conditions. The 

 greater resolution obtained with the 500-kHz towfish is evident in comparing 

 features A, B, C (Figure 37), and the overall finer detail evident in the 

 500-kHz portion in Figure 38. In cases of a more severe wave climate, for 



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