image. If the width of the swath is taken at 60 nmi (~100 km for the 

 SEASAT L-band SAR) and a surface scan velocity of 6.8 km/s, the maximum 

 usable coverage per orbit (~100 minutes) will be at best a 60-nmi swath 

 along a north-south coastline (~1000 nmi assuming a polar orbit). This 

 is equivalent to covering a path one degree wide on the earth's surface 

 (i.e., 1° = 60 nmi). 



NASA estimates of the performance of the Full 

 Capability Operational SEASAT, planned for the late 1980s, indicate 

 that eight satellites would be required to provide twice daily imaging 

 of the U.S. 200-nmi fishing zone at a resolution of 25 x 25 m, 



(3) Beacon Aiding 



Equipping targets with a transponder or beacon that 

 responds to interrogation by a microwave radar with coded signals (often at 

 a frequency other than the radar frequency) simplifies target detection 

 in sea clutter. Not only can targets be located by this means but other 

 information about the target (identify, status, intentions, etc.) can be 

 provided by coding the beacon replies. The successful use of beacons 

 obviously requires a cooperative vessel. Transponder beacons of various 

 kinds exist that can respond to radar interrogation (on a selective basis 

 in some cases) and that can be coded to provide identification and status 

 information in addition to contributing to accurate position fixing. The 

 Discrete Address Beacon System (DABS) program sponsored by FAA and the 

 joint FAA-DoD AIMS program exemplify the capability of transponder beacon 

 technology, although many other beacon developments have led to opera- 

 tional hardware that is in widespread use. The USCG is presently 

 examining beacon approaches for application to the fisheries enforcement 

 and search and rescue missions.. 



The benefits of radar-beacon operation range from 

 unambiguous target identification and accurate position fixing, which 

 are obtainable with simple and low-cost beacons, to quite elaborate 

 status and intention reporting using more elaborate and expensive beacons. 



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