Doppler radar
Definition A system that utilizes the Doppler
effect to measure the velocity of moving objects
The development of Doppler radar systems during the
1980’s led to myriad applications, ranging from improved
weather prediction to improved air defense systems.
The primary use of Doppler radar is to distinguish be-
tween stationary and moving objects by using the
Doppler effect, which occurs whenever there is rela-
tive motion between a radar wave’s source and an
observer. During the late 1970’s and into the 1980’s,
computer systems and processing techniques im-
proved, gaining the ability to analyze the frequency
content of radar signals using mathematical opera-
tions known as fast Fourier transforms. As a result, co-
herent pulsed Doppler radar systems were developed
that could determine the velocity of moving targets.
Pulsed radar systems use one antenna that alternately
transmits pulses and receives their reflections. These
reflected waves are shifted from their initial fre-
quency by the Doppler effect. If the object from
which they are reflected is moving away from the
transmitter, the waves’ frequency is lowered. If the ob-
ject is moving toward the transmitter, the frequency is
increased. Thus, by comparing the initial and re-
flected frequencies of radar waves, computers can de-
termine the velocity and direction of movement of
target objects. In the 1980’s, improved Doppler radar
systems led to improvements in weather forecasting,
air traffic control, and air defense.
During the 1980’s and 1990’s, the National
Weather Service installed Doppler radar systems
throughout the United States. Radar waves transmit-
ted from these systems were scattered and reflected
by objects in the air, including raindrops, snow crys-
tals, hailstones, and dust. Improved computer sys-
tems could use Doppler frequency-shift information
to determine the speed and direction of winds blow-
ing around these airborne objects. During the mid-
to late 1980’s, the Next Generation Weather Radar
program (NEXRAD), or Weather Service Radar 1988
Doppler (WSR-88D), advanced Doppler radar to the
forefront of efforts to detect severe weather events
that could threaten life and property. The presence,
speed, and direction of severe weather elements,
such as turbulence, violent thunderstorms, torna-
does, hurricanes, and lightning, were determined
from Doppler radar measurements.
Impact The advancements made in Doppler radar
systems during the 1980’s provided meteorologists
with the ability to ascertain flight conditions and
make weather forecasts taking into account atmo-
spheric flow patterns and wind motions in storms.
They also increased their ability to determine the
location and intensity of precipitation. Improved
Doppler radar technology could detect low-level
windshear and microburst hazards in the vicinity of
airports, as well as detecting and monitoring the
movement and development of severe storms. The
new technology improved air traffic control systems
and brought them to higher levels of automation.
During the 1980’s, meteorologists extended their
ability to predict weather to about a week in advance.
Continued improvements in the precision of Dopp-
ler radar systems would increase the forecast interval
to fourteen weeks and longer. In addition, Doppler
radar laser guns, used to help enforce roadway speed
limits, were added to the law-enforcement arsenal in
the late 1980’s.Further Reading
Doviak, Richard J., and Dusan S. Zrnic.Doppler Radar
and Weather Observations. 2d ed. Mineola, N.Y.: Do-
ver, 2006.
Schetzen, Martin.Airborne Doppler Radar. Reston, Va.:
American Institute for Aeronautics and Astronau-
tics, 2006.
Winslow, Jennifer L.Comparisons of Observations by
WSR-88D and High Resolution Mobile Doppler Radar
in Tornadoes and a Hurricane. Washington, D.C.:
Storming Media, 1998.
Alvin K. BensonSee also Astronomy; Computers; Science and tech-
nology.Douglas, Michael
Identification American actor and producer
Born September 25, 1944; New Brunswick, New
JerseyDouglas in the 1980’s proved that he could come back from
years of career inactivity and that he had acting talent as
well as film-production skills. He starred in several films
that came to define both the cinema and the American cul-
ture of the 1980’s.The Eighties in America Douglas, Michael 297