Strength Of Reflection From The Target; Sea Clutters; False Echoes - JRC JMA-9922-6XA Instruction Manual

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Strength of Reflection from the Targets¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥
The signal intensity reflected from a target depends not only on the height and size of the target
but also on its material and shape. The echo intensity from a higher and larger target is not
always higher in general.
In particular, the echo from a coast line is affected by the geographic conditions of the coast.
If the coast has a very gentle slope, the echo from a mountain on the inland appears on the radar
display.
Therefore, the distance to the coast line should be measured carefully.
Mountain displayed on the radar display
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Sea Clutters¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥
When the sea surface ruffles, bright echo returns spread around the center of the radar display.
The higher the waves are, the echo returns are larger.
Swirling currents may appears as a smooth line like a coastal line.
False Echoes¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥ ¥
The radar observer may be embarrassed with some echoes that do not exist actually. These
false echoes appear by the following caused that are well known:
[I] Shadow
When the radar scanner is installed near a funnel or mast, the echo of a target that exists in the
direction of the funnel or mast cannot appear on the radar display because the radar beam is
reflected on the funnel or mast. Whether there are some false echoes due to shadows can be
checked by monitoring the sea clutter returns, in which there may be a part of weak or no returns.
Such shadows appear always in the same directions, which the operator should have in mind in
radar operation.
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Sea shore line not displayed on the radar display
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Fig. 6.2
6-3
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