Furuno FEA-2107 - Adjusting Radar Overlay to Match Positions of Chart Features; Error Sources of Radar Echo Image and Chart Display Mismatch; Error Sources for Radar Echo Image and ARPA Target Mismatch

22. Radar Overlay
22-9
22.5 Adjusting Radar Overlay to Match Positions of
Chart Features
22.5.1 Error sources of radar echo image and chart display
mismatch
There are several reasons why the radar echo image and chart display do not match exactly. The mismatch is a
combination of several reasons and removing one reason doesn't solve the mismatch perfectly. There is a
fundamental difference between the radar echo image and corresponding chart feature. The radar echo is a reflection
from the real life target and the actual position of the real life target is the front edge of the radar echo. Therefore,
the radar echo should start from the chart feature and extend as far as the radar pulse length goes.
Bearing error sources:
1. Gyro
2. Inaccurate chart
3. Improper installation parameters (radar 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 overlay range
offset, datum chosen for position receiver)
22.5.2 Error sources for radar echo image and ARPA target
mismatch
There are several reasons why the radar echo image and ARPA target symbols do not match exactly.
1. Different gyro value at ARPA radar display and at ECDIS.
2. Improper installation parameters (radar overlay bearing offset, radar overlay range offset, conning position
offset).
The example below shows how different gyro value set at ARPA radar display and at ECDIS affect the display of
the ECDIS.
Different gyro value at ARPA and ECDIS Equal gyro value at ARPA and ECDIS