Doppler EffectBasics:The Doppler effect owes its name to the Austrian physicist Christian Doppler, who proposed it in 1842, "it is the change in frequency of a wave to an observer moving relative to its source. It is mainly heard when a vehicle equipped with a siren approaches the observer. The received frequency is higher during approach compared to the transmitted frequency, the same when passing the observer, and decreases as one moves away. As the source of the waves moves toward the observer, each successive wave crest is emitted closer to the observer than the previous wave. For this reason, each wave takes slightly less time to reach the observer than the previous one. The time between the arrival of successive wave crests at the observer is therefore reduced. This eventually causes an increase in frequency. As the waves move, the distance between successive wave fronts is reduced so that the waves move closer together (group). Similarly, if the wave source moves away from the observer, each wave is emitted from a position further from the observer than the wave preceding it, so that the arrival time between successive waves is increased. This eventually causes a decrease in frequency. The distance between successive wave fronts is increased, so that the waves move further apart (spread out). Applications: Medical imaging and blood flow measurement, Flow measurement, Velocity profile measurement, Satellite communication, Underwater acoustics, Audio, Vibration measurement, Astronomy, Temperature measurement. , Doppler radar and sirens.Radar: Radar is the abbreviation of “radio detection and ranging”. A transmitter sends pulses of high frequency radio waves, then an echo from the radar appears on a monitor and appears...... middle of paper...... common in winter. Radar also has more difficulty detecting in rain due to the constant change in the refractive index of the air. Another problem for the radar also occurs when a temperature inversion exists, which causes the radar screen to fill with noise and splodges. So weather radar can detect valuable observations of the atmosphere, but sometimes the image is foggy.Bibliography/References:http://en.wikipedia.org/wiki/Weather_radar http://hyperphysics.phy-astr. gsu.edu/hbase/sound/radar.html http://www.straightdope.com/columns/read/2227/how-do-radar-guns-work http://www.infoplease.com/cig/weather/ radar-scanning- skies.html#ixzz2yXGyzwHO http://www.weatherquestions.com/What_is_a_temperature_inversion.htm http://www.everythingweather.com/weather-radar/principles.shtml Weather radar: principles and advanced applications - Peter Meischner Springer, 2004