possible to take advantage of a real-time high bandwidth data link; use exist- 

 ing, relatively inexpensive data sensors, such as television cameras and sonar 

 systems; and not suffer the disadvantages of high cable drag experienced in 

 tethered submersibles. For the application of a pipeline survey and inspec- 

 tion vehicle, where the submersible will be deployed from a compact canister 

 along relatively straight-line runs for long distances, this approach is quite 

 feasible and attractive. Up to 5 km of cable can be stored on a coil which is 

 approximately 3 in long with an outside diameter of 8 in and an inside dia- 

 meter of 5 in. For the application of structures inspection, this approach is 

 promising but not without fault. Cable entanglement within the structure can 

 break a fiber-optic link with a 6-1 b tensile strength; however, with some 

 autonomous capability the free-swimming submersible could conceivably navigate 

 out of the structure. Use of a fiberglass-sheathed, fiber-optic cable with a 

 100-1 b tensile strength is also being investigated for potentially reducing 

 the risk of breakage due to entanglement. 



Components of the fiber-optic link are shown in figure 14. Subtechnolo- 

 gies to this investigation are listed below: 



1. A method involving a high signal-to-noise ratio (SNR) for modulating 

 large bandwidth signals for transmission of the uplink. NOSC's approach has 

 been to use pulse frequency modulation (PFM) (see reference 9). 



2. A duplex operation for sending relatively low bandwidth command sig- 

 nals to the vehicle and for receiving relatively high bandwidth visual sensor 

 information at the operator console. 



3. Penetration of the fiber-optic link into the underwater containers; 

 the penetration method must be easily disconnected and operate at a depth of 

 2200 ft or greater. 



4. Deployment of the fiber-optic cable from the submersible without ex- 

 ceeding the maximum tension of the cable and without causing vehicle drag. 



5. Precision winding of the cable in the laboratory for installation in 

 the deployment canister. The resulting coil must incorporate pretwisted wind- 

 ing to allow deployment without creating kinks. 



6. A way to avoid cable entanglement in the vehicle propellers. 



The results of the investigation of item 1 are discussed in reference 1. The 

 investigation of the remaining items and inspection of pipelines and struc- 

 tures are discussed in reference 10. 



Approximately 80 percent of the work required for complete demonstration 

 of a deployed, fiber-optic link on the EAVE WEST vehicle has been completed. 

 This includes the PFM techniques, duplex operation, penetration to the vehicle 

 housing, and a precision fiber-optic winding machine. Preliminary tests of 

 possible deployment methods have been made, and the vehicle has been operated 



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