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Welcome to this video produced by the National Weather Service office in Las Vegas, NV.
This video will give you a very brief introduction on how a weather radar works.
The National Weather Service operates a nationwide network of weather radars in conjunction with
the Department of Defense and the FAA. These weather radars are used to help forecasters
determine the location, intensity, type and movement of precipitation. The radars also
give forecasters insight about the speed and direction of the wind. More on that later.
Here is a brief introduction to how radar works: The radar emits a very short pulse
of radio frequency radiation and then listens for a return signal. The pulse of radiation
travels away from the radar at approximately the speed of light (186 282 miles per second).
As the radiation encounters a target a portion of the radiation is scattered back to the
radar. The radar is able to calculate how far the target is from the radar using the
time it takes for the radiation to return back to radar. The radar software also notes
the direction the antenna was pointing when the signal was received back at the radar.
By combining the direction the antenna was pointing with the distance away from the radar
the software is able to calculate the exact location of a target. The intensity of the
radar echo is directly related to the strength of the returning signal. The strength of the
return signal is in turn related to the size and quantity of targets in a given area.
The software in the radar system uses all of this information to generate a reflectivity
map like the one shown in the image. This is a question we often get asked. Generally
speaking, the answer to this question is that there is most likely nothing wrong with the
radar. Lets take a look at what is actually going on.
The radar is actually sampling the environment above the ground. As the radar emits a pulse
of radiation the antenna is pointed at a slight angle. The height above ground level sampled
by the radar increases as you go farther away from the radar due to the elevation angle
of the antenna combined with the curvature of the earth. Just because the radar is sampling
precipitation above the surface does not necessary mean that the precipitation is actually making
it to the ground. It is also possible that the radar is sampling non-meteorological targets
such as birds, bats, insects, smoke, dust or chaff (small, thin metal straps released
by military aircraft). This is a bit of a tricky question. The current
radar system can sense radial motion or the targets either towards or away from the radar
along the radar beam; however it can’t sense any motion across the radar beam. The ability
of the radar to measure radial helps forecasters to gain insight about wind conditions above
the surface. Weather Service meteorologists undergo intense training on how to interpret
velocity signatures. The velocity capabilities of radar are particularly useful in identifying
areas of rotation that may be associated with tornados as well as areas of very strong straight
line winds. The image shows a rotational signature associated with a very strong tornado near
Greensburg, KS back in 2007.
Thank you for watching this video.