Simrad ARGUS FMCW 3G, Руководство пользователя

Страница: 93 / 150

| 91
Tracking | Argus Radar Operator Manual
These effects, when they are an extension of the main echo, can cause momentary errors for
the tracking, course and speed values given by the tracking can become unstable. Normally the
problem can be eliminated or strongly reduced by an accurate adjustment of the sea control.
Blind sectors
Funnels, masts (when located near the radar antenna) may cause blind or shadow sectors,
where the target visibility may be completely lost or strongly reduced. In these sectors the
tracking will be very difficult and targets remaining there for long time (not seen for more
than 10 antenna revolutions) will be lost triggering the “LOST TARGET ALARM”.
Low Signal to Noise Ratio and Signal to Clutter Ratio
In situations where the signal to noise or the signal to clutter ratio of the radar echoes is less
than approximately 3 dB (small vessels in heavy sea or rain clutter, or big vessels close to the
radar horizon), target detection is very poor and the tracking will not see the target at each
antenna revolution, this will cause errors in the tracking, that can range from missed infor-
mation and up to complete loss of the target when it is missed for 10 consecutive antenna
revolutions.
Warning: The speed and course of a radar target are obtained by consecutive measure-
ments 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 manouvre.
Tracking operation in 2
nd
PPI zone and under video combination mode
When operating in the additional PPI, the source and targets are the same as viewed in the
first PPI, given that the main source is the same transmitter of the first PPI. In any case, it is not
possible to operate on tracked targets or AIS.
Using video combination mode, there are two sources and there will be two tracker processes
operating separately on the two single channels. The two sources are then brought together
in a single system track, where the kinematic data represent a combination of the data from
the two individual trackers.
More specifically, the data from the trace where the estimated positioning error is the smallest
is favored. The tracker function evaluates trace quality by using the best number of scans out
of ten when combining the two sets of data.
In the case that one of the trackers has to follow a trace through a blind sector, the position
used to track the radar echo is indicated by the information supplied from the other tracker.
The trace is declared as lost only in the case that both trackers cannot see an echo at the posi-
tion extrapolated by the system track for at least ten scans.
AIS (Automatic Iden tification System)
The AIS (Automatic Identification System) is a shipborne broadcast system that can act like a
transponder, operating in the VHF Maritime band. It is capable of handling over 5000 reports
per minute and updates as often as every two seconds. The information is coded and the sys-
tem allows exchange of the information among all the ships operating in the same area. The