Page 340 - NS-2 Textbook

PHYSICAL SCIENCE 335

where you hear them as an echo. There is a time interval vides a bird's eye view of the area covered by the radal~
between the instant you shout and when you hear the showing the transmitter in the center of the screen. Each
echo. The farther you are away from the cliff, the longer time a target is detected it appears as an intensified spot
the interval before the echo retums. The distance to the on the scope. Thus an observer watching the PPI can tell
cliff is proportional to the length of the time interval. If a the range and bearing to the target. Other radars can tell
dh'ectional device is built to h'ansmit and receive this echo, the altitude of incoming aircraft and missiles.
it can be used to determine the direction and distance to
the cliff, since we know the speed of sotmd.
Radar equipment works on the same principle. Pulse- RADAR IN THE NAVY
modulated radio waves of extremely high frequency are
Radar has many uses in today's Navy. Smface search
beamed out, and the radar set is programmed to receive
and navigational radars are used extensively to assist
its own echo. This out-and-back cycle is repeated up to
Navy ships in navigating through constricted waters and
4,000 times per second. If the outgoing wave is sent into
dming times of poor visibility and stormy weather, as
clear space, no energy is reflected back to the receiver. But
well as tracking other shipping in the area. Air search
if the wave strikes an object-such as an airplane, a ship,
and height-finding radar is used to track both friendly
a bullding, or a hill-some of the energy comes back, at
and potentially threatening aircraft, and fire control
the speed of light, as a reflected wave.
radars of various kinds are used to guide shipboard
In the case of a search radar, the echoes received by
weapons to their targets.
the radar receiver appear as marks of light on a cathode
The information gathered by most shipboard search
ray tube (CRT), a device similar to a TV screen. It is com-
radars is presented and analyzed in a shipboard space
monly called a "scope" or PPI (plan position indicator).
called the Combat Information Center (CIe); in some
The scope is marked with a scale of yards or meters,
more advanced surface warships this space is called the
miles or kilometers (1,000 meters), and degrees. It pro-
Combat Direction Center, 01' CDC. Quite often on today's
ships dming general quarters the commanding officer
(CO) assumes a battle station in the CIC 01' CDC and
leaves the executive officer as the senior officer on the
bridge. As the head evaluator of the information coming
into the center, the CO must decide which targets to en-
gage and with what means-aircraft, guided missiles, or
radar-directed gunfire. The CO must also decide how to
maneuver in order to escape or engage enemy ships, sub-
marines, and aircraft.

PULSE STRIKES TARGET
.Lt1-·H HH

ECHO IS RETURNED AS ORIGINAL PULSE CONTINUES

ECHO RETURNING A.T SPEED OF LIGHT

!~!~O~H~S~CO~P~E OF PRESENCE
OF OTHER SHIP A PPI (plan position indicator) scope presentation. On this scope tar-
gets appear as white dots called pips. Here the inset shows the PPI
The principle of radar operation. scope presentation of the physical targets shown above it.