How can a weather radar detect windshear and microbursts ?

[flame_bringer]

Iv always wondered how can an aircraft do that , and input the signal to the EGPWS to get it to alert for windshear , i checked my school notes but nothing is mentioned about it in my notes alas .
i checked through google and i found something that mentions that a weather radar can do that using the doppler effect , but not much information on the thing and i didnt get a satisfactory answer for my question.
So i'd like to get a fully explained technical answer to satisify my question .
Thanks in advance

[ahmed88]

Doppler radar is radar (http://en.wikipedia.org/wiki/Radar) that makes use of the doppler effect (http://en.wikipedia.org/wiki/Doppler_effect) to produce data about objects at a distance. It does this by beaming a microwave (http://en.wikipedia.org/wiki/Microwave) signal towards a desired target and listening for its reflection, then analyzing how the original signal has been altered by the object(s) that reflected it. Variations in the frequency of the signal give direct and highly accurate measurements of a target's velocity relative to the radar source and the direction of the microwave beam.

source: wikipedia.org

[muduckace]

Seeing you mentioned EGPWS I would like to make sure you understand the difference between predictive windshear and reactive windshear.

Predictive as technically stated above is a function of weather radar, it is usually just a program option on newer model xmitter/recievers that is forward looking and reports between certain altitudes (I think 2500 down to 100ft in most cases. It senses the density of rain shifting that is conducive with windshear down drafts and updrafts, and warns of windshear ahead so you have a better chance of powering out of the windshear prior to it's effect on the aircraft. PWS displays on a nd as well to give visual reference to a danger zone.

Reactive is a function of EGPWS that is tied into other aircraft sensors to let you know what you have probably allready figured out, that you are knee deep in it. It's main advantage is the speed at which it may be tied into the FCC's or autoflight function during a coupled approach to usually level wings, TOGA 10 deg ANU in most cases.

Here is a link from NASA that does not really say much more than I did, but it is a reference if you are looking for one.

NASA - Making the Skies Safe from Windshear (http://www.nasa.gov/centers/langley/news/factsheets/Windshear.html)

[flame_bringer]

So predictive winshear is just an optional feature on the weather radar that sends out beams intended to detect wind updrafts and downdrafts to predict windshear and it uses the doppler effect to detect this phenomena which is directly related to the change in frequency of the recieved signals of the beam pretty much like doppler navigation but the beam is sent out horizzontally.
I understand now thanks everyone!:)

[muduckace]

Yeah, spot on.

Here is a good clip of one of the largest windshear disasters, shows aircraft profile and what is gong on in the cockpit.

YouTube - Delta 191 "Crash on Landing" (Updated) (http://www.youtube.com/watch?v=wA6DbzRr09U&feature=related)

[Hand Shandy]

You`ve got it. The return pulse will have a varying frequency due to the doppler shift, if you can imagine the turbulence within these weather systems, that spread of frequencies would be proportional to the severity of the storm . Normal heavy rain would have a pretty flat frequency return but w/s would be all over the place.

[flame_bringer]

Thanks everyone
I appreciate all your helps
Regards