Severe Weather

The Weather Radar

Radars have an important role in the field of meteorology. These devices send out and receive signals providing valuable information about the location and intensity of precipitation and estimated velocity data.

Conventional Weather Radar

	The radar creates an electromagnetic energy pulse which is focused by an antenna and transmitted through the atmosphere. Objects in the path of this electromagnetic pulse, called targets, scatter the electromagnetic energy. Some of that energy is scattered back toward the radar.
	The receiving antenna (which is normally also the transmitting antenna) gathers this back-scattered radiation and feeds it to a device called a receiver.
	The more targets there are to scatter the pulse, the stronger the return will be. This means that many large raindrops will produce a stronger return than a few small raindrops. The quantity that a radar measures is the returned power which, with knowledge of other radar characteristics, is converted to a quantity called the reflectivity factor, or more simply, the "reflectivity".

Doppler radar

Doppler radars can measure the component of the velocity of targets toward or away from the radar. This component iscalled the "radial velocity". For example, at time T1 a pulse is sent towards a target and it returns a target distance "D".
At time T2, another pulse is sent towards the same target and returns a target distance "D+A". The distance to target has changed from times T1 to T2, resulting in a phase shift between the two return signals, which Doppler radars are capable of measuring. With this and other known quantities the velocity the target has moved toward or away from the radar can be computed.

Some Radar Images from Hurricane Lili are shown below:

NWS New Orleans/Baton Rouge, LA

To learn more about radar functioning and applications move to the WW2010 web page