Simrad R2009 User Manual page 25

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Showing a target's past positions
The Past position option is used to visualize the previous positions of a tracked target or an
activated AIS target.
The time defines the length of time for which each target's past positions should be
displayed on the PPI, while the interval defines interval between each past position indicator.
Warning: Trails build-up starts when exiting from the standby condition.
Trails or past position length will be reached only after the selected time
duration.
Possible target tracking errors
Some factors can generate tracking errors or make the radar image difficult to read, and
therefore reduce target detection capability:
• Sea, rain, snow and low clouds returns
• Radar Interference
• Sidelobe echoes
• Blind sectors
• Low signal to noise ratio and signal to clutter ratio
Warning: The speed and course of a radar target are obtained by
consecutive measurements of the echo position. The data is then filtered to
reach the required precision. This means, that every abrupt change of speed
and direction will be recognized with a certain delay to reach absolute
certainty that the target is moving in a different way. The confirmation delay
is about five scans and after that some additional time is needed to reach
the same data precision as from before the maneuver.
Sea, rain, snow and low clouds returns
Radar echoes in sea, rain or weather clutter areas may be masked by the clutter. The effects
of such errors appear as continuous big changes of the target course and speed vectors.
Sometimes the symbol of a target that has been acquired at high speed can slip away from
the real target position after a certain time, and this might generate the lost target alarm.
These errors can be avoided or at least minimized by proper manual adjustments of sea and
rain controls, or by selecting the automatic control option. For more details, see "Adjusting the
radar image" on page 19.
Radar interference
Other radars operating in the same frequency band can generate interference. Normally this
is seen on the radar screen as a series of spirals. When the interference falls on the tracked
target, it can cause a deformation of the size of the echo, and consequently a small error in
the target's course and speed values.
Adjustment option is available in the Advanced menu. See "Rejecting radar interference" on page
34.
Sidelobe echoes
Radar antennas have a radiation pattern consisting of a main lobe and several very small
sidelobes. Most of the energy transmitted by the radar is radiated and received back on the
main lobe, and a very small part on the sidelobes. This has no effect in case of distant or small
targets, but the returns from a large target at short range (less than 3 NM) can generate, on
both sides of the main echo and at the same range, arcs or series of small echoes. These
effects, when they are an extension of the main echo, can cause momentary errors for the
tracking, and course and speed values given by the tracking can become unstable.
The problem can usually be eliminated or strongly reduced by an accurate adjustment of the
Sea control. Refer "Sea anti-clutter" on page 19.
Target tracking | R2009/R3016 User manual