For the classification requirements of fisheries law enforcement, these 

 benefits can be most satisfactorily obtained if specialized beacons 

 are used and if all of the vessels subject to enforcement, i.e., foreign 

 fishing vessels, and only those vessels are equipped with beacons. The 

 design of suitable beacons is a straightforward engineering development 

 project, but establishing a mechanism to distribute the beacons, insure 

 their reliable operation, and prevent illegal fishing by vessels that 

 do not carry (or that disable) the beacons involves many questions that 

 are not technical in nature and that were not addressed in this survey. 



c. Cost Analysis 



For comparison purposes, estimates were made of the costs 

 of microwave radars and beacons and of representative costs of aircraft 

 operation. No independent determination of aircraft related costs was 

 made for the survey. Instead, the estimates made in Reference 7 were 

 used. Table 7 summarizes the cost data. 



2. HF Qver-The-Horizon Radar (OTHR) Techniques 



a. Description 



Remote sensing using electromagnetic energy at microwave 

 and higher frequencies is constrained by the essentially line-of-sight 

 propagation in the atmosphere at these frequencies. Practically, this 

 means that at the higher frequencies sensors must be elevated to achieve 

 significant operating ranges. 



However, as the frequency is lowered, atmospheric refrac- 

 tion increases until at very low frequencies (VLF) (a few tens of kilo- 

 hertz) energy can propagate completely around the earth. In the high 

 frequency (HF) region, roughly 3 to 30 MHz, energy propagates both in 

 a ground wave mode that follows the curvature of the earth out to several 

 hundred miles in a skywave mode in which the energy is refracted in the 



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