Doppler EffectBasics:The Doppler Effect is named after the Austrian physicist Christian Doppler, who proposed it in 1842, "is the change in frequency of a wave for an observer in movement relative to its source." It is mainly heard when a vehicle with a siren approaches the observer. The received frequency is higher during the approach than the emitted frequency, the same at the moment in which the observer passes, and lowers as one moves further away. As the source of the waves moves towards the observer, each subsequent 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. Therefore the time between successive wave crests reaching the observer is shortened. This ends up causing an increase in frequency. As the waves travel, the distance between successive wave fronts is reduced so that the waves move closer together (group). Similarly, if the source of the waves moves away from the observer, each wave is emitted from a location further from the observer than the previous wave, so the arrival time between subsequent waves increases. This ends up causing a decrease in frequency. The distance between successive wave fronts increases, so the waves move 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 Sounders. Radar: Radar is short for “radio detection and ranging.” A transmitter sends out pulses of high-frequency radio waves, then an echo from the radar is displayed on a monitor and shown... middle of paper... common in winter. A radar also has a harder time detecting in the rain due to the constantly changing refractive index of the air. Another problem for radar also occurs when there is a temperature inversion that causes the radar screen to fill with clutter and spray. So weather radar can pick up valuable observations of the atmosphere, but sometimes the picture is hazy. 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