be improved by increasing the transmitted power that illuminates the 

 target. At ranges closer to the radar platform, the antenna beam inter- 

 sects the sea surface at larger incident angles and sea returns add 

 to and eventually exceed the basic radar receiver noise, so that target 

 detection becomes clutter limited. The onset of significant sea returns 

 occurs at incidence angles equal to or greater than about 2 below the 

 horizon and rapidly increases with increasing incidence angles (shorter 

 ranges) to greatly degrade ship detection, despite the closer range, 

 unless suitable design measures are taken. 



Increasing transmitter power will not help in 

 clutter-limited zones. Similarly, increasing the number of pulses that 

 are integrated will not increase the target detection process because 

 the physical structure of the sea surface changes very slowly (i.e., of 

 the order o'f 30 s to 2 minutes decorrelation time), and therefore will 

 not average out in short integration intervals. 



The most effective measures employed to reduce the 

 effects of sea clutter are those that decrease the resolution cell size. 

 This is done in two ways: by increasing the range resolution (i.e., 

 shorter effective pulse length), and by decreasing the angular sector 

 width of the resolution cell (i.e., narrower azimuthal beamwidth) . As 

 a practical limit, however, SCRs will not be improved by reducing the 

 resolution cell dimensions to values smaller than the size of the target 

 (viz. ~ 100 ft). The limitations to shortening the effective radar 

 pulse duration are of the order of 0.02 |_is (i.e., ~ 3 m range) because: 

 (1) the receiver video bandwidth must be of the order of the reciprocal 

 of the pulse length so that 50 MHz (i.e., 1/0.02 \is) is about the 

 practical limit of current receiver technology; (2) as the actual pulse 

 transmitted becomes shorter, the power incident on the target diminishes, 

 which produces insufficient signal to noise for reliable detection; 

 (3) pulse compression techniques (which permit a long chirped pulse to 



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