User's Manual

ED 3100 G 110 / 02 (2011-10)
Operating Instructions
A-1 General Information
A RADAR.fm / 10.11.11
A-15
NACOS Platinum
- Large targets with good reflection characteristics produce strong echo signals and are displayed with
corresponding clarity on the screen.
- Smaller targets situated in the shadow of large objects are not illuminated by the radar pulses and
are therefore not displayed.
- Flat coasts have an unfavourable reflection cross-section and cannot be recognized until they have
been approached more closely. On the other e , high coastlines and mountainous regions further
inland are recognised at a very early stage.
- In the coastal approaches, the tide rip lines and surf areas are displayed similarly to coastlines.
However, this rather irritating display can be a valuable orientation aid for the coastal navigator.
- The reflections of radar waves from ice depend largely on the surface structure of the areas illumi-
nated by the radar. Rough and jagged surfaces produce good echo displays, whereas smoothly
frozen-over surfaces, rounded surfaces and surfaces at an oblique angle generally reflect the trans-
mitted pulses away from the ship. Thus, for example, the echo display of large icebergs can fluc-
tuate extremely severely, depending on the existing aspect.
- The detection of low-lying blocks of ice (growlers) probably presents the greatest uncertainty:
1.4.3 Distortions of the RADAR Video
Because of the physical characteristics of the radar principle used, the video displayed does not corre-
spond exactly to the position and form of the reflecting target. A distinction must be drawn between
radial distortions (in the direction of the target) and azimuthal distortions (perpendicular to the target
direction) - see figure on next page.
Radial Distortions
Radial distortions in the direction of transmission are caused by the fact that a target reflects the trans-
mitted pulse for as long as the pulse is moving past the target
1)
. Thus, radial lengthening depending on
the pulse duration occurs on the screen. In the case of range measurements, it must be noted that the
echo edge facing own ship corresponds to the true front edge of the target.
If there are several targets behind one another with small (radial) distances between them, they are
shown separately on the screen if, and only if, their distance apart is so large that the radial lengthened
echoes do not overlap.
Azimuthal Distortions
Azimuthal distortions are caused by the width of the beam radiated by the antenna. A point target
appears wider the further away it is. At a distance of 10 NM with a horizontal antenna-beamwidth of
1.5°, an individual target is displayed as an arc with a length of 480 m. Because of this effect, individual
targets situated beside one another can merge to form a single target.
Even if the anticlutter facilities are operated carefully, the echoes from growlers
can no longer be definitely identified if moderate disturbances from the sea
surface are present.
1)
The pulse length setting Long Pulse thus generates larger radial distortions than Short Pulse.