■Blind and Shadow sectors
Blind or Shadow sectors may exist because of ob- structions such as masts, derricks or stacks. An ob- struction may throw either a complete or partial shadow as shown in the diagram below. If a target is in a shadow sector, target echoes may not appear on the screen.
Shadow sector
Mast or similar obstruction
■Target resolution
Target resolution is determined by the horizontal beam width and transmit pulse width. Sometimes it is difficult to detect two targets which are separated by short dis- tances or which are in the same direction.
DDistance resolution
When two targets are separated by more than the pulse width, they appear as two echoes.
When two targets are not separated by more than the pulse width, they appear as 1 echo.
Target 1
Target 1 Target 2
Transmit Echoes pulse
Target 2
Target 1,2
Transmit Echo pulse
Target 1, 2
BASIC RADAR THEORY | 8 |
When tall and massive targets such as a large island are located at close range also shadowed without pro- ducing any echoes. This phenomenon is called blind sector. It is very important to know the bearings and widths of all shadow sectors caused by your own ship’s obstructions.
Blind sector
Own ship | Large | Small |
| island | island |
DDirection resolution
When two targets are separated by more than the horizontal beam width, they appear as two echoes.
When two targets are not separated by more than the horizontal beam width, they appear as one echo.
Target 1
Target 1
Target 2
Scanner
Target 2
Target 1
Target 2
Scanner
Target 1, 2
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