Aerospace and Electronic Systems Magazine July 2017 Tutorial XI - 46

Tutorial:

DOI. No. 10.1109/MAES.2017.150178

Weather Radar: Operation and Phenomenology
Jenny L. Reed, Aaron D. Lanterman, John M. Trostel, Georgia Tech Research Institute,
Smyrna, GA, USA

Radar is an indispensable technology in areas of defense, air
traffic control (ATC), and weather surveillance. The usual goal
of defense and air traffic control radars is to detect and track individual targets; in contrast, the "target" of weather radars may
stretch hundreds of kilometers. The meteorology, defense, and
ATC communities typically publish research in different venues,
and each community has a vernacular and characteristic ways of
approaching problems. The goals of this article are twofold. Its
primary goal is to summarize typical weather radar systems and
define associated jargon in terms more familiar to other radar
communities. The second goal is to provide a detailed discussion
of the physical scattering phenomenology exploited specifically
in radar meteorology. Furthermore, while there are a number of
operational weather radars, we focus throughout much of this
article on the most common weather radar, Weather Surveillance Radar 1988 Doppler (WSR-88D), as a canonical example,
because much of the current research and phenomenological
analysis are based on its operational parameters.

I. INTRODUCTION
Radar plays a key part in the observation, analysis, and prediction
of severe weather events and other meteorological phenomena. The
network of Weather Surveillance Radar 1988 Doppler (WSR-88D)
radars spanning the United States is the primary source of weather
radar data used by the National Weather Service (NWS) and other
commercial interests to extrapolate information regarding precipitation and severe weather events. There are 160 WSR-88D sites,
operated by the Departments of Commerce, Transportation, and
Defense [1], in the United States and U.S. territories. These radars
are commonly called the NEXRAD (Next-Generation Radar) network. There are a number of other commercial and experimental
weather radars as well [2]. Most notably, the multifunction phased
Authors' current address: Sensors and Electromagnetics Laboratory, Georgia Tech Research Institute, 7220 Richardson Road,
Smyrna, GA 30080, USA, Email: (jenny.reed@gtri.gatech.edu).
The authors thank the State of Georgia for funding the work
related to this article. The authors whose names are listed on
this article certify that they have no affiliation with or involvement in any organization or entity with any financial interest
or nonfinancial interest in the subject matter or materials
discussed in this manuscript.
Manuscript received August 18, 2016, revised February 20,
2016, May 20, 2017, and ready for publication May 20, 2017.
Review handled by W. D. Blair.
0885/8985/17/$26.00 © 2017 IEEE
46

array radar (MPAR) program [3]-[5] is investigating the potential
of a phased array radar to aid in remote weather observation, air
traffic control, air route surveillance, and homeland defense tasks.

II. BASIC RADAR PHENOMENOLOGY
While many of the concepts and terminology [7] in this section
will be familiar to radar practitioners, we review them to both establish notation and make connections between the jargon of radar
meteorology and that of other radar communities.
A radar transmits radio frequency (RF) electromagnetic (EM)
waves into a region of interest and receives EM waves reflected
back by objects in this region [8]. The signals received by the radar
include energy reflected by objects of interest, which are called targets, and objects that are not of interest, which are called clutter. In
the case of weather radar, the objects of interest are meteorological
scatterers such as raindrops, hail, or even tornadic debris. Clutter often includes backscatter from terrain, trees, and buildings. In
contrast, most other radar practitioners would consider weather to
be the clutter that obscures the desired target.

A. RANGE
A pulsed-wave (PW) radar, also known as a pulse-Doppler radar [7],
the type employed in meteorological applications, periodically transmits a discrete pulse of short duration and then stops transmitting while
waiting to receive the reflected pulse. The time it takes for the pulse to
be received directly relates to the distance traveled by the pulse, i.e.,
twice the range of the reflecting object. Because the pulse travels at
the speed of light, c = 2.998 × 108 m/s, the range may be computed as
R=

cΔt
,
2

(1)

where Δt is the roundtrip time of the pulse between the radar and
the reflecting object. The received data samples for a single pulse
correspond to a series of range bins.

B. RANGE RESOLUTION
Range resolution is the physical separation, in the range dimension, between two objects such that the objects are still resolvable
by the radar. The bandwidth of the transmitted waveform determines the range resolution of the radar:
ΔR =

c
,
2β

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