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gradient system of coloring is also employed. The lighter colors are used to show lower areas while a
gradual increase in density (darkness) is used to portray the higher terrain.
6.10.2. Military operations require the analysis of contour-labeled charts to visualize the land. In
operational planning, this is of the utmost importance, whether it is planning a route for a safe flight or
in determining the best escape from enemy territory.
6.11. Summary. Map reading is a critical skill for navigators in many aircraft, but it takes time to
become proficient. Keep a good DR, work from chart to ground, and remember the effect varying
conditions have on what you see outside your window.
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Chapter 7
RADAR NAVIGATION
Section 7A— Radar Principles
7.1. Introduction. In the hands of the skilled operator, radar provides precise updates to dead reckoning
(DR) for navigation and airborne delivery operators. At cruising altitudes, it provides information on
land and water characteristics as well as hazardous weather conditions over hundreds of miles around
the aircraft. At low-level, it provides detailed terrain information used to navigate at high speed over
changing courses. It is adapted to terrain-avoidance and terrain-following equipment. Radar is a source
of track and drift angle (DA) information for wind computations and can be used with beacons for
intercept, rendezvous, airdrop, and bombing operations.
7.1.1. The basis of the system has been known theoretically since the time of Heinrich Hertz who, in
1888, successfully demonstrated the transfer of electromagnetic energy in space and showed that such
energy is capable of reflection. The transmission of electromagnetic energy between two points was
developed as radio, but it was not until 1922 that practical use of the reflection properties of such energy
was conceived. The idea of measuring the elapsed time between the transmission of a radio signal and
receipt of its reflected echo from a surface originated nearly simultaneously in the United States and
England. In the United States, two scientists working with air-to-ground signals noticed that ships
moving in the nearby Potomac River distorted the pattern of these signals. In 1925, the same scientists
were able to measure the time required for a short burst, or pulse, of radio energy to travel to the
ionosphere and return. Following this success, it was realized the radar principle could be applied to the
detection of other objects, including ships and aircraft.
7.1.2. By the beginning of World War II, the Army and Navy had developed equipment appropriate to
their respective fields. During and following the war, the rapid advance in theory and technological skill
brought improvements and additional applications of the early equipment. It is now possible to measure
accurately the distance and direction of a reflecting surface in space, whether it is an aircraft, a ship, a
hurricane, or a prominent feature of the terrain, even under conditions of darkness or restricted visibility.
For these reasons, radar has become a valuable navigational tool.
7.1.3. As noted previously, the fundamental principle of radar may be likened to that of relating sound to
its echo. Thus, a ship sometimes determines its distance from a cliff at the water's edge by blowing its
whistle and timing the interval until the echo is received. The same principle applies to radar, which uses
the reflected echo of electromagnetic radiation traveling at the speed of light. This speed is
approximately 162,000 NM per second; it may also be expressed as 985 feet per microsecond. If the
interval between the transmission of the signal and return of the echo is 200 microseconds, the distance
to the target is:
Section 7B— Radar Set Components
7.2. Overview. The principle of radar is accomplished by developing a pulse of microwave energy that
is transmitted from the aircraft and is reflected by objects in its path. The reflected pulse is amplified and
174 AFPAM11-216 1 MARCH 2001
converted by the receiver for display on the cathode-ray tube (CRT). The timing unit or synchronizer
synchronizes all the actions in the set. To this basic unit, improvements are added for special purposes,
such as weather avoidance, filtering, and terrain following.
7.3. Components:
7.3.1. The receiver and transmitter are usually one unit (the R/T) with separate functions that, for this
description, are dealt with separately (Figure 7.1).
Figure 7.1. Radar System Components.
7.3.2. The transmitter produces the radio frequency (RF) energy using magnetrons. A magnetron
generates radar pulses by bunching electrons using alternately charged grids the electrons travel past.
The spurts of energy are of high power and short duration. The energy is released at intervals (the pulse
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