Seiwa MDS-18910R User Manual

Page 9

MDS-1R/8R/9R/10R Installation

False echoes

Sometimes radar will display targets on screen that do not exist in the real world. You should
be aware of how and why this happens.

A. Ghost echoes

Sometimes one large object very near your boat will appear as two different targets onscreen.
One is the actual radar echo. The other is a ghost echo generated by a re-reflection of the
original signal. It comes back to your own boat, bounces back to the target, and then is picked
up by the antenna on the second bounce. The actual echo appears at the correct distance
and bearing on the screen. The ghost echo appears somewhere behind your boat. This type
of false echo is also generated by re-reflection of waves from bridges, quay walls or building
along shore.

Target

Direct
reflection path

Secondary
reflection path

Mast etc.

Direction of ghost echo

Real echo

Ghost echo

Fig.2-5 False echoes of radar (Ghost echoes)

B. Multiple echoes

If there is a large vertical reflecting surface near your boat, as in the case when you pass
alongside a large ship, radar signals are repeatedly bounced back and forth between your boat
and the other object. Two to four images appear on the screen at equal intervals in the same
bearing. This is called a multiple echo. The image appearing closest to you is the real echo.
Multiple echoes will disappear as you move away from the reflecting object or its bearing
changes.

Real echo

Multiple
echoes

Fig.2-6 False echoes of radar (Multiple echoes)