Indirect Echoes; Multiple Echoes - Raymarine SL70M Owner's Handbook Manual

3-6

Indirect Echoes

There are several types of indirect echoes or ghost images - some examples are
shown in Figure 3-4. These sometimes have the appearance of true echoes,
but in general they are intermittent and poorly defined.
Indirect (false) echoes
False echo
Passing
ship
Figure 3-4:

Multiple Echoes

Multiple echoes appear if there is a large target with a wide vertical surface at
a comparatively short range. The transmitted signal will be reflected back and
forth between the target and your own ship. Multiple echoes therefore appear
beyond the true target's echo on the same bearing, as shown in Figure 3-5.
This is not very common.
MULTIPLE ECHOES
Figure 3-5:
Blind Sectors or Shadow Effect
Funnels and masts located near the antenna, may cause shadows. In shadow
areas beyond the obstruction there will be a reduction of the beam intensity,
although not necessarily a complete cut-off. However, there will be a blind
sector if the subtended angle is more than a few degrees. There may also be
multiple echoes which extend behind the obstruction. This should be avoided
by careful selection of the scanner site prior to installation (Chapter 6).
SL70M & SL70C PLUS Pathfinder Radar Displays
True echo
Indirect Echoes
Multiple echoes
Multiple Echoes
Mast
or funnel
True echo
D1642-1
True echo
False echo
D1641-2