Figure 2-3.—Horizontally and vertically polarized electromagnetic waves.
Wavelength
The distance from wave crest to wave crest (or
trough to trough) along an electromagnetic wave’s
direction of travel is called wavelength. Each
measurement equals one complete wave, or wave
cycle, and is typically expressed in centimeters. Each
wavelength can also be described in terms of degrees,
with one wavelength equal to 360° (fig. 2-4). This
concept will become very important later, when we
discuss Doppler radar.
As radar energy is emitted into the atmosphere, it
encounters particles of dust, dirt, and salts, in addition
to water vapor and precipitation. Collectively, these
are known as scatterers, and they have an important
effect on radar effectiveness. Wavelength plays a
critical role in a weather radar’s ability to see scatterers,
that is, water droplets. Shorter wavelengths provide
more detail and allow detection of small droplets,
while longer wavelengths are best for larger targets,
such as precipitation from rain showers and
thunderstorms. It is important that a radar wavelength
Figure 2-4.—Wavelength of an electromagnetic wave.
2-3
