CHAPTER 1
INTRODUCTION
BY LOUIS N. RIDENOUR
101. What Radar Does. —Radar is an addition to man’s sensory
equipment which affords genuinely new facilities.
It enables a certain
class of objects to be “seen”
—that is, detected andlocated—at distances
far beyond those at which they could be distinguished by the unaided
eye. This ‘(seeing” is unimpaired by night, fog, cloud, smoke, and most
other obstacles to ordinary vision.
Radar further permits the measure-
ment of the range of the objects it “sees” (this verb will hereafter be used
without apologetic quotation marks) with a convenience and precision
entirely unknown in the past.
It can also measure the instantaneous
speed of such an object toward or away from the observing station in a
simple and natural way.
The superiority of radar to ordinary vision lies, then, in the greater
distances at which seeing is possible with radar, in the ability of radar to
work regardless of light condition and of obscuration of the object being
seen, and in the unparalled ease with which target range and its rate of
change can be measured. In certain other respects radar is definitely
inferior to the eye. The detailed definition of the picture it offers is very
much poorer than that afforded by the eye.
Even the most advanced
radar equipment can on]y show the gross outlines of a large object, such
as a ship; the eye can—if it can see the ship at all—pick out fine details
such as the rails on the deck and the number or character of the flags at
the masthead. Because of this grossness of radar vision, the objects
that can usefully be seen by radar are not as numerous as the objects
that canabe distinguished by the eye.
Radar is at its best in dealing with
isolated targets located in a relatively featureless background, such as
aircraft in the air, ships on the open sea, islands and coastlines, cities in
a plain, and the like. Though modern high-definition radar does afford
a fairly detailed presentation of such a complex target as a city viewed
from the air (see, for example, Fig. 335), the radar picture of such a
target is incomparably poorer in detail than a vertical photograph taken
under favorable conditions would be.
One further property of radar is worth remarking: its freedom from
difficulties of perspective, By suitable design of the equipment, the
picture obtained from a radar set can be presented as a true plan view,
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