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378 · Radar Echo Overlay
How to adjust radar echo overlay to match positions
of chart features
Error sources of radar echo image and chart display miss match
Mariner should be aware that there are several reasons why the radar echo image and chart display do not match
exactly. One should also be aware that normally the miss match is a combination of several reasons and adjusting
only one feature doesn't solve the miss match all around. There is a fundamental difference between radar echo
image and corresponding chart feature. Radar echo is a reflection from the real life target and the actual position of
the real life target is front edge of the radar echo. Thus radar echo should start from the chart feature and extent as
far as the used radar pulse length goes.
Bearing error sources
1. Gyro
2. Inaccurate chart
3. Improper installation parameters (radar echo overlay bearing offset)
Position error sources
1. Inaccurate position
2. Position offset
3. Inaccurate chart
4. Wrong datum
5. Datum offset with ARCS material
6. Improper installation parameters (conning position offset, position receiver antenna offset,
radar echo overlay range offset, datum selected for position receiver)
Error sources of radar echo image and display of ARPA target miss
match
Mariner should be aware that there are several reasons why the radar echo image and display of ARPA target
symbols do not match exactly.
1. different gyro value at ARPA radar display and at ECDIS
2. improper installation parameters (radar echo overlay bearing offset, radar echo overlay range
offset, conning position offset)
See example below, how different gyro value set at ARPA radar display and at ECDIS effects the display of the
ECDIS.
Different gyro value at ARPA and ECDIS Equal gyro value at ARPA and ECDIS