of the passive reflector lies in the many directions
in which its radar cross section is low, resulting
in a minimal return.
The polar plot shows that Sea-me
has a much more even response pattern and suffers
from none of the gaps so typical of a passive
1. Greater detection range.
The strength of a radar signal falls off rapidly
with distance. In the case of a passive reflector
this degradation takes place over a distance equal
to double the range (radar to target and back)
whereas in the case of an active device, which
is itself a transmitter, it only falls off over
the return distance - and from a much higher amplified
signal level. This means that Sea-me,
an active device, has a greater detection range
than the typical passive reflector.
2. A more consistent return.
Ships today use a system known as ARPA (Automatic
Radar Plotting Aid). This enables the radar to
emit an alarm when it acquires a target within
its guard zones and thus to alert the watchkeeper.
Target acquisition will only take place if the
radar receives returns on at least 50% of scans.
Two factors contribute to a consistent return
- the strength of the returned signal and, because
small boats yaw and heel, particularly in rough
seas, the evenness of the return.
3. Better performance
Performance in clutter (rain and wave) is all
about signal strength. The single fact that Sea-me
emits a stronger signal means that it performs
better in clutter.
4. Better performance
The effectiveness of a passive reflector falls
off rapidly as the boat heels, as you would expect
of a device which is effectively a mirror reflecting
in a single direction. The Sea-me
device shapes the beam to provide an effective
return even when the boat is heeled.
5. Ship detection alert.
Passive reflectors cannot give you any warning
that you have been struck by a radar signal indicating
that there is a ship in your area.
Sea-me, being active,
knows when it has received a signal and can alert
you with a flashing light, and if required, audibly.
Sea-me thus enables
you to sharpen up your lookout when necessary.