CHAPTER 12
WEATHER RADAR
This chapter will be devoted to the discussion of
various types of radar, their characteristics, principles,
and elements.
The first portion of our discussion will deal with
characteristics and principles of nondoppler radar,
followed by a discussion of principles, characteristics,
and phenomena associated with doppler radar. Finally,
we will look at the Next Generation Weather Radar
(NEXRAD) system, principally the WSR-88D.
NONDOPPLER RADAR
LEARNING OBJECTIVES: Interpret the
effects of wavelength on nondoppler radar.
Recognize principles of wavelength on
nondoppler weather radars.
Evaluate
nondoppler radar beam characteristics.
Now let’s begin our discussion of nondoppler radar.
For additional information, refer to the Federal
Meteorological Handbook No. 7, Weather Radar
Observations, Part B, NAVAIR 50-1D-7.
EFFECTS OF WAVELENGTH AND
FREQUENCY ON RADAR PERFORMANCE
The concept of energy moving as waves through a
medium such as water is easily understood because we
can observe the oscillation of the material. Both
electrical and magnetic energy are transmitted by these
waves. Viewed along the direction of transmission, the
envelope containing vectors representing an
electromagnetic field appears in wave form. Figure
12-1 shows the common method for representing
waves. The radio energy waves have some semblance
to water waves in that they retain their size while all
traveling at the same speed. Therefore, they could also
be represented as concentric circles about the generating
device, as seen in figure 12-2. In this case, we could say
that the circles represent wave fronts that move away
from the source. In the case of focused waves, such as
we have with weather radars, we could show the wave
fronts moving along the beam path, as in figure 12-3. In
all three illustrations, the distance from wave front to
wave front, and from any part of a wave to the
corresponding part of the next wave, remains constant.
This distance is determined by two factors, the speed
with which the waves move and the rapidity with which
the generating device operates. The generating device
is said to oscillate, and could be thought of as moving
up and down, or back and forth. Each complete
oscillation produces one complete wave. The waves
move away from the oscillator as they are being
generated so that the wave front will be 1 wavelength
away from the oscillator when the next wave front is just
being formed.
Because the speed of wave travel
remains constant, there is a constant, inverse
relationship between the frequency of the oscillation
and the length of the wave; the faster the oscillation
(higher frequency), the shorter the wavelength.
Figure 12-1.-Energy wave represented as oscillations. These are 5 cm long.
12-1
