Raymarine RL80CRC PLUS manual Indirect Echoes, Multiple Echoes, Blind Sectors or Shadow Effect

3-6

Identifying False Echo

Returns

hsb2 PLUS Series Color LCD Display

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 True echo True echo

Passing	Mast
ship	or funnel	False echo
			D1641-2

Figure 3-4: Indirect Echoes

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 True echo

Multiple echoes

D1642-1

Figure 3-5: Multiple Echoes

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 8).