Figure 3. Tomographic scanning process. 



In the final contract report from AMETEK Offshore Research and 

 Engineering Division (Ref 9), the feasibility of developing a CAT system 

 capable of operating in an underwater environment was documented. Under- 

 water application of tomography is technically feasible. To minimize 

 development risks, it was determined that a specialized system should be 

 designed specifically for inspecting submerged timber structures rather 

 than modifying an existing laboratory or "dry" CAT system. Results of 

 the detailed analyses of the conceptual design, system performance, 

 operational scenarios, and identification of critical issues for under- 

 water CAT inspection of wood pier pilings can be found in References 9 

 and 10. The proposed prototype CAT system, inspection criteria for the 

 CAT system, and scan time considerations are discussed briefly below. 



The prototype CAT design consists of four basic subsystems shown in 

 the block diagram of Figure 5. The scanner subsystem is composed of the 

 source, detectors, and the necessary support and enclosures for under- 

 water use. The telemetry subsystem consists of the electronic leads 

 necessary to connect the scanner subsystem to the data acquisition and 

 control subsystem. The raw data acquired at each incremental angle of 

 rotation are formed into a matrix by the data acquisition and system 

 control subsystem. The data conditioning, reconstruction, and display 

 subsystem consists of the computer algorithms and the associated hard- 

 ware required to reconstruct the tomogram from the data collected. 



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