3-6 hsb
2
PLUS Series LCD Display
Identifying False Echo
Returns
Indirect Echoes
Thereareseveraltypesofindirectechoesorghostimages-someexamplesare
shown in Figure 3-4. These sometimes have the appearanceof true echoes,
but ingeneral they are intermittentand poorlydefined.
Figure 3-4: Indirect Echoes
Multiple Echoes
Multiple echoes appear if there is a large targetwith a wide vertical surface at
acomparativelyshortrange. Thetransmittedsignalwillbe reflectedback and
forth between the targetand your own ship. Multipleechoes therefore appear
beyondthe true target’s echo on the same bearing,as shown in Figure 3-5.
This is not very common.
Figure 3-5: Multiple Echoes
Blind Sectors or Shadow Effect
Funnelsand masts locatednear the antenna,may cause shadows. In shadow
areasbeyond the obstruction there will be areduction of the beam intensity,
althoughnot necessarily a completecut-off. However, there will be a blind
sectorif the subtendedangle is more than a fewdegrees.There may also be
multipleechoeswhichextend behind the obstruction.This should beavoided
by careful selectionof thescanner site prior to installation(Chapter 8).
False echo
True echo
Passing
ship
True echo
False echo
D1641-2
Mast
or funnel
Indirect (false) echoes
D1642-1
True echo
Multiple echoes
MULTIPLE ECHOES
81186_3.book Page 6 Thursday, August 22, 2002 8:23 AM
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