environmentally safe sources of inexhaustible electric power have not been available. Although 

 the application of solar cells to marine electronic devices is only limited by the imagination 

 of the designer, three specific devices will be discussed in this paper as examples of potential 

 applications for solar cells. 



MARKERS FOR UNDERWATER HAZARDS TO NAVIGATION 



Submerged rock pinnacles, sunken ships, and collapsed offshore oil production plat- 

 forms that are submerged less than 40 ft below the water surface pose a grave danger to 

 shipping. Because of subsurface and surface turbulences associated with these obstacles it 

 is rather difficult to mark such subsurface hazards to navigation with standard surface navi- 

 gational buoys. It would be rather easy, however, to fasten an acoustic transponder to the 

 submerged obstacle which would warn approaching ships of the hidden danger. 



Because of the close proximity to the ocean surface, the batteries in the transponder 

 would always be fully charged by the solar cell array, while at the same time the submerged 

 location of the device would protect it from vandalism and storm damage. Although most 

 ships are not now equipped to interrogate such submerged acoustic transponders, they would 

 rapidly acquire such equipment once it became known that underwater hazards were marked 

 in such a manner. 



UNDERWATER SENTINELS 



A difficult problem facing law enforcement at sea is denying access to restricted areas 

 by casual or intentional trespassers. Such restricted areas may be fishlife refuges, sensitive 

 naval installations, oil fields, or oil shipping terminals. Although restricted areas are generally 

 marked around their perimeter by surface buoys equipped with appropriate warning signs 

 and/or equipment, they are easily avoided, ignored, and often vandalized. Hidden electronic 

 sentinels that respond only to vessels that fail to emit the appropriate sonic password are 

 necessary. 



To be effective, such sentinels would have to be subsurface buoys whose locations 

 could not be ascertained by the intruder with the help of radar or visual observation. The 

 buoy would be equipped with a sensitive hydrophone capable of distinguishing between 

 typical propeller sound and ambient sea noise. If the sound of a rotating propeller was not 

 accompanied by the appropriate acoustic password radiated from a hydrophone on the 

 intruding ship, the sentinel would classify the intruding vessel as a trespasser, extend a whip 

 antenna through the water surface, and alert by radio the central monitor. Since the power 

 consumption of passive listening devices is rather low, the solar cells mounted on top of the 

 buoy would have no difficulty in keeping the batteries charged for round-the-clock operation. 



ROVING PATROL 



Of the major challenges faced by all maritime nations, patrolling the continental 

 shelf is probably the greatest. Patrolling by manned surface vessels and aircraft requires a 

 significant expenditure of funds, not only for construction of ships and aircraft, but also for 



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