Global Positioning System Reference
In-Depth Information
campaign, by providing the Allies with the capability to detect U-boat
periscopes from the air during the long and hard-fought Battle of the
Atlantic. By the end of the war, more e√ort and expense had been put into
radar development than into the development of any other technology
apart from nuclear bombs.
The rapid maturing of radar as an independent discipline can be seen in
the many di√erent applications of radar equipment evident today. Most of
these were known, in theory if not in practice, to the early wartime de-
velopers. Nowadays radar is a crucial component of weather prediction,
terrain mapping, airplane altimetry and air tra≈c control, and space mis-
sions. Of course, it still has many military applications, such as missile
guidance and gun-laying, airplane and missile tracking, and air and sea
surveillance. A spin-o√ of radar proper, medical imaging uses remote sens-
ing technology and algorithms that are taken directly from (or which fol-
low on from) radar remote sensing.
Several of these radar fields lend themselves to navigation applications.
The radar equipment and processing techniques used in navigation vary
considerably from one application to the next. The shape and size of radar
antennas (both transmitters and receivers); the transmitted frequencies;
the shape, number, and power of transmitted radar pulses; the detection
range; frequency bandwidth; and display screen attributes—all di√er sig-
nificantly between radar altimeters and synthetic aperture mapping ra-
dars, or between short-range missile trackers and Doppler weather radars,
or between surveillance radars that are designed to look up at airborne
targets and those that are searching for terrestrial targets. 14
I concentrate here on the navigation applications of radar and provide
only a brief summary of radar operation, making no further reference to
the techniques used to process signals or to the wider implications of our
expanding knowledge of this important field. Radar surveillance, tracking,
and mapping impinge on modern electronic navigation capabilities. Argu-
ably, the most important facet of radar for navigators today and in the
future lies with the sensor fusion potential of di√erent electronic remote-
sensing techniques; data obtained from di√erent sources can be displayed
14. In radar terminology, a target is simply the object that a radar operator is looking for,
whether or not he intends to shoot at it. Clutter is everything else that he sees on his radar
display. Thus, rain and other precipitation are clutter to a naval radar operator who is trying
to detect incoming missiles, but these atmospheric phenomena are a target for a meteorolo-
gist who is using radar to gather data for weather forecasts.
 
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