Radar Fundamentals
Meteorology 415
Fall 2012
Name: _______________
Radar principles
University of Illinois
The active sensor with radar is generally a 10cm microwave emitter that transmits at a rapid rate an
envelope of high energy waves at various elevation angles. Since the WSR-88D era, the return signal can
now be ‘listened’ to for any phase shift that is related to the velocity of the air along that radius of
transmission. The new dual polarized Doppler radar is equipped to send out simultaneously a second
signal at a 90 degree angle to the existing beam. The return signal (echoes) now contains a plethora of
information about the size, shape, orientation and density of the hydrometeors and other objects in its
path. It is strongly recommended that you review the following:
http://www.wdtb.noaa.gov/courses/dualpol/outreach/
Term definition – PRF (pulse repetition frequency): _________________________________________
____________________________________________________________________________________
Defining Products:
There are many current products of the WSR-88D and there will soon be a host of new radar products
from the Dual-Polarization Radar when deployment is completed in 2013. The most common products
can be seen below.
Composite Reflectivity
What is the difference between base reflectivity and composite reflectivity?
___________________________________________________________________________________
Reading Velocity Data
The colors indicate warm colors are objects moving toward the radar and cool colors away from the
radar with the wind direction being at a right angle to the gray line separating the two regions. Indicate
how the winds are shifting from the surface to higher up at this location.
Surface wind direction: ___________________
Wind direction above the surface: ________
Differences between Aliasing and Range Folding:
There are limits to the WSR 88D’s capability in both reflectivity and velocity detection.
On the right panel is an example of Range Folding –define this term:
On the left panel contains some Velocity Aliasing – define this term:
The Radar attributes
Cone of Silence
Under what circumstances might this cone be a problem for short-range forecasters?
___________________________________________________________________________________
Estimated Rainfall
One of the improvements in radar technology that has benefitted flood forecasters the most is the QPE
or quantitative precipitation estimates. The new Dual-Pol should even provide better estimates.
However, consider the situations that would lead to incorrect rainfall estimates and list at least two for
each:
-
Underestimating factors:
-
1.________________________________________________________________________
2. ________________________________________________________________________
-
Overestimating factors
1. ________________________________________________________________________
2. ________________________________________________________________________
Precipitation Type
In principle, it has been known for many years that radar has the capability of discerning
precipitation types and in practice, the technology has been available for a few decades. But
now the implementation of this tool is occurring and a new series of products will soon be at
each forecasters’ disposal.
Define the following new terms of Dual-Pol:
CC: ________________________________________________
ZDR: ________________________________________________
KDP: _________________________________________________
HC: ___________________________________________________
ML: _______________________________________________
Anomalous Propagation:
Occasionally, the thermal structure of the lower troposphere can cause the radar beam to
bend in unusual ways leading to phenomena known as AP.
What period of the day is ‘AP’ most common? ________________________________