# Practical uses of the Doppler Effect

The change in the frequency or wavelenght when a source or an observer is moving away or towards each other and the medium in which they are is called Doppler effect. It was named after Christian Doppler. He was an Austrian mathematician and physicist. He published Doppler effect in 1842 at the age of 39. The Doppler effect has many uses in science and a variety of practical applications as well.

Practical Uses:

Used for Measuring automobile speeds:

Measurements of shifts of radio waves from orbiting satellites, for example, are used in maritime navigation, and the effect is also employed in the radar surveillance of automobile speeds.

As it is described earlier that this effect is used in radars. It is also used in aeronautical department for measuring the speed of the flying object.

Use in astronomy:

As we all should know that astronomy is the knowledge of celestial objects (such as stars, planets etc. ) and phenomena that originates outside the earth’s atmosphere. As telescopes have a limit. At certain distance there is an aberration in the image. So Doppler Effect has been used to measure the speed at which stars and galaxies are approaching toward or receding from us, that is, the radial velocity. This is used to detect if a single star is, in fact, a close binary and even to measure the speed of rotation of stars and galaxies.

The use of the Doppler effect for light in astronomy depends on the fact that the spectra of stars are not continuous. They show absorption lines at well defined frequencies that are correlated with the energies required to excite electrons in various elements from one level to another. The Doppler effect is recognizable in the fact that the absorption lines are not always at the frequencies that are obtained from the spectrum of a stationary light source. Since blue light has a higher frequency than red light, the spectral lines from an approaching astronomical light source show a blueshift and those of receding sources show a redshift.

Use in medical field:

There are many uses of doppler effect in medical field. One is as follows:

As described earlier that basic objective we achieve from doppler effect is to measure the velocity. This phenomena is used in measuring the velocity and flow of direction of blood in the medical field. An echocardiogram can, within certain limits, produce accurate assessment of the direction of blood flow and the velocity of blood and cardiac tissue at any arbitrary point using the Doppler effect. One of the limitations is that the ultrasound beam should be as parallel to the blood flow as possible.

Velocity measurements allow assessment of cardiac valve areas and function, any abnormal communications between the left and right side of the heart, any leaking of blood through the valves (valvular regurgitation), and calculation of the cardiac output. Contrast-enhanced ultrasound using gas-filled microbubble contrast media can be used to improve velocity or other flow-related medical measurements.

Use in military:

It is also used in military to measure the speed of submarines by the help of sonars. Stable frequencies generated by the sonobuoy will undergo doppler effect when they strike the submarine or any moving object. Then it will be recorded and it is worked out and the velocity in which that moving object is approaching or receeding from the observer is recorded.

Sonic boom:

Some people today have had the experience of hearing a jet fly high overhead, producing a shock wave known as a sonic boom. A sonic boom, needless to say, is certainly not something of which Doppler would have had any knowledge, nor is it an illustration of the Doppler effect, per se. But it is an example of sound compression, and, therefore, it deserves attention here. The speed of sound, unlike the speed of light, is dependant on the medium through which it travels. Hence, there is no such thing as a fixed “speed of sound”; rather, there is only a speed at which sound waves are transmitted through a given type of material. Its speed through a gas, such as air, is proportional to the square root of the pressure divided by the density.

This, in turn, means that the higher the altitude, the slower the speed of sound: for the altitudes at which jets fly, it is about 660 MPH (1,622 km/h). As a jet moves through the air, it too produces sound waves which compress toward the front, and widen toward the rear. Since sound waves themselves are really just fluctuations in pressure, this means that the faster a jet goes, the greater the pressure of the sound waves bunched up in front of it. Jet pilots speak of “breaking the sound barrier,” which is more than just a figure of speech. As the craft approaches the speed of sound, the pilot becomes aware of a wall of high pressure to the front of the plane, and as a result of this high-pressure wall, the jet experiences enormous turbulence.

The speed of sound is referred to as Mach 1, and at a speed of between Mach 1.2 and Mach 1.4, even stranger things begin to happen. Now the jet is moving faster than the sound waves emanating from it, and, therefore, an observer on the ground sees the jet move by well before hearing the sound. Of course, this would happen to some extent anyway, since light travels so much faster than sound; but the difference between the arrival time of the light waves and the sound waves is even more noticeable in this situation.

Meanwhile, up in the air, every protruding surface of the aircraft experiences intense pressure: in particular, sound waves tend to become highly compressed along the aircraft’s nose and tail. Eventually these compressed sound waves build up, resulting in a shock wave. Down on the ground, the shock wave manifests as a “sonic boom”or rather, two sonic boomsone from the nose of the craft, and one from the tail. People in the aircraft do not hear the boom, but the shock waves produced by the compressed sound can cause sudden changes in pressure, density, and temperature that can pose dangers to the operation of the airplane. To overcome this problem, designers of supersonic aircraft have developed planes with wings that are swept back, so they fit within the cone of pressure.

These were some of the uses of Doppler Effect which I tried to explain. But there are number of uses of Doppler Effect.

References:
http://www.wikipedia.org