Standard Horizon MDS-9, MDS-8, MDS-10-5, MDS-10-4 manual False echoes, Ghost echoes, Multiple echoes

create a shdow zone behind it and prevent you from seeing targets on the other side. More importantly, if a mast or some part of the boat’s superstructure is in the path of the antenna’s sweep, this will also create a shadow zone. No targets will be recognized behind it and it could create a dangerous situation.

A.1.2 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.

Ghost echoes

Sometimes one large object very near your boat will appear as two different targets on screen. 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, break walls or building along shore.

Target

Direct reflection path

Secondary reflection path

Mast etc.

Direction of ghost echo

3

1

HU

Real echo

Ghost echo

Figure A.1.2 - Ghost Echoes

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.

Radar Installation Manual Page 33