(1) Capabilities and Limitations 



One of the most challenging microwave radar design 

 problems is the detection of small objects (vessels) on the surface of 

 the ocean in the presence of returns from the ocean itself, called sea 

 clutter. A fundamental figure of merit for a radar designed for ocean 

 surveillance is therefore the extent to which wanted returns (signal) 

 can be made to exceed unwanted returns (clutter). This figure of merit 

 is the signal-to-clutter ratio (SCR); a SCR somewhat greater than one 

 in a given set of circumstances is required to give reliable detection 

 and to avoid excessive false alarms, i.e., instances of identifying an 

 unwanted clutter return as a target. 



Factors that influence the detection of targets in 

 sea clutter are generally related to the resolution cell size (i.e., 

 the smallest area element of sea surface for which the radar returns 

 can be processed independently). Signal processing compares the total 

 reflected signal (the target reflection plus the sea surface "reflection) 

 in one resolution cell to the total signal in adjacent cells (sea sur- 

 face only). If a cell containing a target produces a substantially 

 greater return (~10 dB) than adjacent cells, then the target in the cell 

 will be detected with a probability of about 507o for that transmitted 

 pulse. Typical radars have pulse repetition rates sufficient to obtain 

 about 10 to 12 hits on a given target each time an antenna beam 'scans 

 the target location. The integration of multiple hits increases the 

 cumulative detection probability to about 907o, depending on the signal 

 to noise ratio (SNR) and the target scintillation characteristics. 



Sea clutter effects exhibit a viewing angle dependence, 

 For an elevated radar platform, such as from an aircraft, sea clutter 

 limitations on target detection do not occur for grazing incidence angles 

 when the radar beam is near the radar horizon. In this case, target 

 detection is essentially radar system noise-limited, and performance can 



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