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Radar designers have
devised all sorts of tricks to further enhance target acquisition and
discrimination. For instance, savvy operators typically switch ranges
frequently because a transceiver reconfigures itself for each range, in
a sense refocusing its "sight." The longer pulses and slower
repetition rate of a desirable larger range may blot out close targets.
Modern displays can often be offset to Look Ahead or even in a variable
direction (perhaps when operating along a shore) to make best use of a
given range’s focus. Some can also zoom into a user-selectable area,
displaying the results in a separate window. Most units have an Expand
function that overrides pulse length for smaller ranges, thus amplifying
the target size, but at the expense of resolution.
New sets from Simrad
and Si-Tex offer dual ranges in side-by-side windows, employing a double
speed scanner that can feed the display two sets of pulse lengths and
repetition rates simultaneously. Several manufacturers also offer optional
3D windows beneath the normal bird’s-eye display. Software interpolates
target echoes into images you might see from a high bridge. They look
decidedly more realistic than possible and should be treated with caution;
apparently their real value is as an advanced form of sea clutter filtering,
looking for and emphasizing the peaks of targets.
Doing classic coastal
navigation in dark or fog, skippers worked hard comparing radar screen
to paper chart–usually with a course track and dead-reckoning position
penciled in–to determine which targets were fixed, confirm position,
and identify traffic. Range rings helped with the cross referencing, and
EBLs (Electronic Bearing Lines), VRMs (Variable Range Markers), and/or
a screen cursor could be used to plot identified land features or aids
to navigation relative to the vessel, or vice-versa.
These techniques are
not completely dead; in fact, a lot of modern machines have added "Floating"
EBLs and VRMs useful for certain advanced double-checking exercises. However,
GPSs are ubiquitous, and a simple NMEA waypoint sentence can be automatically
displayed on a radar as a lollipop icon, both helping to orient the radar
to the chart and perhaps identifying a target if your waypoint happens
to be a buoy. Even simple GPS heading data–especially now with SA
off and WAAS on–can be used to turn the radar image north up or course
up. Either mode makes comparison to a chart easier, while also eliminating
the confusion of a head-up display on which everything swings relative
to your steering.
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