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The Doppler effect or Doppler shift (or simply Doppler, when in context) is the change in
frequency Frequency is the number of occurrences of a repeating event per unit of time A unit of time is any particular time Time is the indefinite continued sequence, progress of existence and event (philosophy), events that occur in an apparent ...

frequency
of a
wave In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. " ...

wave
in relation to an
observer An observer is one who engages in observation or in watching an experiment. Observer may also refer to: Computer science and information theory * In information theory Information theory is the scientific study of the quantification, storage ...
who is moving relative to the wave source. It is named after the
Austria Austria (, ; german: Österreich ), officially the Republic of Austria (german: Republik Österreich, links=no, ), is a landlocked A landlocked country is a country that does not have territory connected to an ocean or whose coastli ...

Austria
n physicist
Christian Doppler Christian Andreas Doppler (; 29 November 1803 – 17 March 1853) was an Austrian mathematician and physicist. He is celebrated for his principle – known as the Doppler effect – that the observed frequency of a wave depends on the relative sp ...

Christian Doppler
, who described the phenomenon in 1842. A common example of Doppler shift is the change of
pitch Pitch may refer to: Acoustic frequency * Pitch (music), the perceived frequency of sound including "definite pitch" and "indefinite pitch" ** Absolute pitch or "perfect pitch" ** Pitch class, a set of all pitches that are a whole number of octaves ...
heard when a
vehicle A vehicle (from la, vehiculum) is a machine that transports people or cargo. Vehicles include wagons, bicycles, motor vehicles (motorcycles, cars, trucks, buses), railed vehicles (trains, trams), watercraft (ships, boats), amphibious vehicles ...

vehicle
sounding a horn approaches and recedes from an observer. Compared to the emitted frequency, the received frequency is higher during the approach, identical at the instant of passing by, and lower during the recession. The reason for the Doppler effect is that when the source of the waves is moving towards the observer, each successive wave
crest Crest or CREST may refer to: Buildings *The Crest (Huntington, New York) The Crest is a historic house on Eatons Neck in Suffolk County, New York. Although on the land mass of Eatons Neck, the house today is within the jurisdiction of the Incor ...
is emitted from a position closer to the observer than the crest of the previous wave. Therefore, each wave takes slightly less time to reach the observer than the previous wave. Hence, the time between the arrivals of successive wave crests at the observer is reduced, causing an increase in the frequency. While they are traveling, the distance between successive wave fronts is reduced, so the waves "bunch together". Conversely, if the source of waves is moving away from the observer, each wave is emitted from a position farther from the observer than the previous wave, so the arrival time between successive waves is increased, reducing the frequency. The distance between successive wave fronts is then increased, so the waves "spread out". For waves that propagate in a medium, such as
sound In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Spacetime, space and time, and the related entities of energy and force. ...

sound
waves, the velocity of the observer and of the source are relative to the medium in which the waves are transmitted. The total Doppler effect may therefore result from motion of the source, motion of the observer, or motion of the medium. Each of these effects is analyzed separately. For waves which do not require a medium, such as
electromagnetic waves In physics Physics (from grc, φυσική (ἐπιστήμη), physikḗ (epistḗmē), knowledge of nature, from ''phýsis'' 'nature'), , is the natural science that studies matter, its Motion (physics), motion and behavior through ...

electromagnetic waves
or
gravitational waves Gravitational waves are disturbances in the curvature of spacetime In physics Physics is the natural science that studies matter, its Elementary particle, fundamental constituents, its Motion (physics), motion and behavior through Space ...
, only the relative difference in velocity between the observer and the source needs to be considered. When this relative velocity is not negligible compared to the
speed of light The speed of light in vacuum A vacuum is a space devoid of matter. The word is derived from the Latin adjective ''vacuus'' for "vacant" or "Void (astronomy), void". An approximation to such vacuum is a region with a gaseous pressure m ...
, a more complicated
relativistic Doppler effect Figure 1. A source of light waves moving to the right, relative to observers, with velocity 0.7c. The frequency is higher for observers on the right, and lower for observers on the left. The relativistic Doppler effect is the change in frequency ...
arises.


History

Doppler first proposed this effect in 1842 in his treatise "''
Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels 110px, binary stars A binary star is a star system consisting of two star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star ...
and some other stars of the heavens).Alec Eden ''The search for Christian Doppler'', Springer-Verlag, Wien 1992. Contains a facsimile edition with an
English English usually refers to: * English language English is a West Germanic languages, West Germanic language first spoken in History of Anglo-Saxon England, early medieval England, which has eventually become the World language, leading lan ...

English
translation.
The hypothesis was tested for sound waves by Buys Ballot in 1845. He confirmed that the sound's
pitch Pitch may refer to: Acoustic frequency * Pitch (music), the perceived frequency of sound including "definite pitch" and "indefinite pitch" ** Absolute pitch or "perfect pitch" ** Pitch class, a set of all pitches that are a whole number of octaves ...
was higher than the emitted frequency when the sound source approached him, and lower than the emitted frequency when the sound source receded from him.
Hippolyte Fizeau Armand Hippolyte Louis Fizeau FRS FRSE MIF (23 September 181918 September 1896) was a French physicist A physicist is a scientist A scientist is a person who conducts Scientific method, scientific research to advance knowledge in an Branch ...

Hippolyte Fizeau
discovered independently the same phenomenon on
electromagnetic wave In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular s ...

electromagnetic wave
s in 1848 (in France, the effect is sometimes called "effet Doppler-Fizeau" but that name was not adopted by the rest of the world as Fizeau's discovery was six years after Doppler's proposal).Fizeau: "Acoustique et optique". ''Lecture, Société Philomathique de Paris'', 29 December 1848. According to Becker(pg. 109), this was never published, but recounted by M. Moigno(1850): "Répertoire d'optique moderne" (in French), vol 3. pp 1165–1203 and later in full by Fizeau, "Des effets du mouvement sur le ton des vibrations sonores et sur la longeur d'onde des rayons de lumière"; aris, 1870 ''Annales de Chimie et de Physique'', 19, 211–221. In Britain,
John Scott Russell John Scott Russell FRSE FRS FRSA (9 May 1808, Parkhead, Glasgow Glasgow, (, also , ; sco, Glesca or ; gd, Glaschu ) with an estimated city A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geogr ...
made an experimental study of the Doppler effect (1848).


General

In classical physics, where the speeds of source and the receiver relative to the medium are lower than the velocity of waves in the medium, the relationship between observed frequency f and emitted frequency f_\text is given by: f = \left( \frac \right) f_0 where *c is the propagation speed of waves in the medium; *v_\text is the speed of the receiver relative to the medium, added to c if the receiver is moving towards the source, subtracted if the receiver is moving away from the source; *v_\text is the speed of the source relative to the medium, added to c if the source is moving away from the receiver, subtracted if the source is moving towards the receiver. Note this relationship predicts that the frequency will decrease if either source or receiver is moving away from the other. Equivalently, under the assumption that the source is either directly approaching or receding from the observer: \frac = \frac = \frac where *v_ is the wave's velocity relative to the receiver; *v_ is the wave's velocity relative to the source; *\lambda is the wavelength. If the source approaches the observer at an angle (but still with a constant velocity), the observed frequency that is first heard is higher than the object's emitted frequency. Thereafter, there is a
monotonic Figure 3. A function that is ''not'' monotonic In mathematics Mathematics (from Ancient Greek, Greek: ) includes the study of such topics as quantity (number theory), mathematical structure, structure (algebra), space (geometry), and calc ...
decrease in the observed frequency as it gets closer to the observer, through equality when it is coming from a direction perpendicular to the relative motion (and was emitted at the point of closest approach; but when the wave is received, the source and observer will no longer be at their closest), and a continued monotonic decrease as it recedes from the observer. When the observer is very close to the path of the object, the transition from high to low frequency is very abrupt. When the observer is far from the path of the object, the transition from high to low frequency is gradual. If the speeds v_\text and v_\text \, are small compared to the speed of the wave, the relationship between observed frequency f and emitted frequency f_\text is approximately where *\Delta f = f - f_0 *\Delta v = -(v_\text - v_\text) is the opposite of the velocity of the receiver relative to the source: it is positive when the source and the receiver are moving towards each other. File:Dopplereffectstationary.gif, Stationary sound source produces sound waves at a constant frequency , and the wave-fronts propagate symmetrically away from the source at a constant speed c. The distance between wave-fronts is the wavelength. All observers will hear the same frequency, which will be equal to the actual frequency of the source where . File:Dopplereffectsourcemovingrightatmach0.7.gif, The same sound source is
radiating File:Radioactive.svg, upThe international symbol for types and levels of ionizing radiation (radioactivity) that are unsafe for Radiation shield, unshielded humans. Radiation, in general, exists throughout nature, such as in light and sound. ...
sound waves at a constant frequency in the same medium. However, now the sound source is moving with a speed . Since the source is moving, the centre of each new
wavefront In physics, the wavefront of a time-varying field is the set () of all where the wave has the same of the sinusoid. The term is generally meaningful only for fields that, at each point, vary in time with a single temporal frequency (otherwise ...

wavefront
is now slightly displaced to the right. As a result, the wave-fronts begin to bunch up on the right side (in front of) and spread further apart on the left side (behind) of the source. An observer in front of the source will hear a higher frequency and an observer behind the source will hear a lower frequency . File:Dopplereffectsourcemovingrightatmach1.0.gif, Now the source is moving at the speed of sound in the medium (). The wave fronts in front of the source are now all bunched up at the same point. As a result, an observer in front of the source will detect nothing until the source arrives and an observer behind the source will hear a lower frequency . File:Dopplereffectsourcemovingrightatmach1.4.gif, The sound source has now surpassed the speed of sound in the medium, and is traveling at 1.4 ''c''. Since the source is moving faster than the sound waves it creates, it actually leads the advancing wavefront. The sound source will pass by a stationary observer before the observer hears the sound. As a result, an observer in front of the source will detect nothing and an observer behind the source will hear a lower frequency .


Consequences

With an observer stationary relative to the medium, if a moving source is emitting waves with an actual frequency f_0 (in this case, the wavelength is changed, the transmission velocity of the wave keeps constant; note that the ''transmission velocity'' of the wave does not depend on the ''velocity of the source''), then the observer detects waves with a frequency f given by f = \left ( \frac \right ) f_0 A similar analysis for a moving ''observer'' and a stationary source (in this case, the wavelength keeps constant, but due to the motion, the rate at which the observer receives waves and hence the ''transmission velocity'' of the wave ith respect to the observeris changed) yields the observed frequency: f = \left ( \frac \right ) f_0 Assuming a stationary observer and a source moving at the speed of sound, the Doppler equation predicts a perceived momentary infinite frequency by an observer in front of a source traveling at the speed of sound. All the peaks are at the same place, so the wavelength is zero and the frequency is infinite. This overlay of all the waves produces a
shock wave of an attached shock on a sharp-nosed supersonic F/A-18F Super Hornet in transonic flight Flight or flying is the process by which an object (physics), object motion (physics), moves through a space without contacting any planetary surfac ...
which for sound waves is known as a
sonic boom A sonic boom is a sound associated with shock wave of an attached shock on a sharp-nosed supersonic F/A-18F Super Hornet in transonic flight Flight or flying is the process by which an object (physics), object motion (physics), m ...

sonic boom
. When the source moves faster than the wave speed the source outruns the wave. The equation gives
negative frequency The concept of signed frequency (negative and positive frequency) can indicate both the rate and sense of rotation A rotation is a circular movement of an object around a center (or point) of rotation. The plane (geometry), geometric plane al ...

negative frequency
values, which have no physical sense in this context (no sound at all will be heard by the observer until the source passes past them).
Lord Rayleigh John William Strutt, 3rd Baron Rayleigh, (; 12 November 1842 – 30 June 1919) was a British scientist who made extensive contributions to both theoretical A theory is a rational type of abstract thinking about a phenomenon A phenome ...
predicted the following effect in his classic book on sound: if the observer were moving from the (stationary) source at twice the speed of sound, a musical piece ''previously'' emitted by that source would be heard in correct tempo and pitch, but as if played ''backwards''.


Applications


Acoustic Doppler current profiler

An
acoustic Doppler current profiler An acoustic Doppler current profiler (ADCP) is a similar to a , used to measure over a depth range using the of scattered back from particles within the water column. The term ADCP is a generic term for all acoustic current profilers, althoug ...
(ADCP) is a hydroacoustic
current meter Currents or The Current may refer to: Science and technology * Current (fluid) A current in a fluid In physics, a fluid is a substance that continually Deformation (mechanics), deforms (flows) under an applied shear stress, or external force. ...
similar to a
sonar Sonar (sound navigation and ranging) is a technique that uses sound propagation (usually underwater, as in submarine navigation) to navigation, navigate, measure distances (ranging), communicate with or detect objects on or under the surface o ...

sonar
, used to measure
water current A current in a fluid In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other w ...
velocities The velocity of an object is the Time derivative, rate of change of its Position (vector), position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of an object's speed and direction o ...

velocities
over a depth range using the Doppler effect of
sound waves In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular ...
scattered back from particles within the water column. The term ADCP is a generic term for all acoustic current profilers, although the abbreviation originates from an instrument series introduced by RD Instruments in the 1980s. The working frequencies range of ADCPs range from 38 
kHz The hertz (symbol: Hz) is the unit Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action, a discrete piece of action (or beat) in a theatric ...
to several
Megahertz The hertz (symbol: Hz) is the unit Unit may refer to: Arts and entertainment * UNIT Unit may refer to: Arts and entertainment * UNIT, a fictional military organization in the science fiction television series ''Doctor Who'' * Unit of action ...
. The device used in the air for wind speed profiling using sound is known as and works with the same underlying principles.


Robotics

Dynamic real-time path planning in robotics to aid the movement of robots in a sophisticated environment with moving obstacles often take help of Doppler effect. Such applications are specially used for competitive robotics where the environment is constantly changing, such as robosoccer.


Sirens

A siren on a passing
emergency vehicle An emergency vehicle is a vehicle that is used by emergency services There are three primary emergency services that can be summoned directly by the public: * Police — law enforcement, criminal investigation, and maintenance of public order ...
will start out higher than its stationary pitch, slide down as it passes, and continue lower than its stationary pitch as it recedes from the observer. Astronomer John Dobson explained the effect thus: In other words, if the siren approached the observer directly, the pitch would remain constant, at a higher than stationary pitch, until the vehicle hit him, and then immediately jump to a new lower pitch. Because the vehicle passes by the observer, the radial velocity does not remain constant, but instead varies as a function of the angle between his line of sight and the siren's velocity: v_\text = v_\text \cos(\theta) where \theta is the angle between the object's forward velocity and the line of sight from the object to the observer.


Astronomy

The Doppler effect for electromagnetic waves such as light is of widespread use in
astronomy Astronomy (from el, ἀστρονομία, literally meaning the science that studies the laws of the stars) is a natural science that studies astronomical object, celestial objects and celestial event, phenomena. It uses mathematics, phys ...
to measure the speed at which
star A star is an astronomical object consisting of a luminous spheroid of plasma Plasma or plasm may refer to: Science * Plasma (physics), one of the four fundamental states of matter * Plasma (mineral) or heliotrope, a mineral aggregate * Quark ...

star
s and
galaxies A galaxy is a gravitationally bound system of star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to ...

galaxies
are approaching or receding from us, resulting in so called
blueshift A blueshift is any decrease in wavelength (increase in energy), with a corresponding increase in frequency, of an electromagnetic wave Electromagnetism is a branch of physics involving the study of the electromagnetic force, a type of ph ...

blueshift
or
redshift In physics Physics is the that studies , its , its and behavior through , and the related entities of and . "Physical science is that department of knowledge which relates to the order of nature, or, in other words, to the regular ...

redshift
, respectively. This may be used to detect if an apparently single star is, in reality, a close
binary Binary may refer to: Science and technology Mathematics * Binary number In mathematics and digital electronics, a binary number is a number expressed in the base-2 numeral system or binary numeral system, which uses only two symbols: ty ...

binary
, to measure the rotational speed of stars and galaxies, or to detect exoplanets. This effect typically happens on a very small scale; there would not be a noticeable difference in visible light to the unaided eye. The use of the Doppler effect in astronomy depends on knowledge of precise frequencies of discrete lines in the spectra of stars. Among the
nearby stars There are currently 63 stars contained in the 53 stellar systems within of the Solar System. 50 of those stars are red dwarfs; the remaining 13 stars are more massive with the largest of them being Sirius, "the brightest star in the night sky". ...
, the largest
radial velocities The radial velocity of an object with respect to a given point is the rate of change of the distance between the object and the point. That is, the radial velocity is the component of the object's velocity that points in the direction of the radi ...
with respect to the
Sun The Sun is the star A star is an astronomical object consisting of a luminous spheroid of plasma (physics), plasma held together by its own gravity. The List of nearest stars and brown dwarfs, nearest star to Earth is the Sun. Many othe ...

Sun
are +308 km/s ( BD-15°4041, also known as LHS 52, 81.7 light-years away) and −260 km/s ( Woolley 9722, also known as Wolf 1106 and LHS 64, 78.2 light-years away). Positive radial velocity means the star is receding from the Sun, negative that it is approaching. Redshift is also used to measure the
expansion of space The expansion of the universe is the increase in proper length, distance between any two given Gravitational binding energy, gravitationally unbound parts of the observable universe with time. It is an intrinsic and extrinsic properties (philosoph ...
, but this is not truly a Doppler effect. Rather, redshifting due to the expansion of space is known as
cosmological redshift Hubble's law, also known as the Hubble–Lemaître law, is the observation in physical cosmology Physical cosmology is a branch of cosmology concerned with the study of cosmological models. A cosmological model, or simply cosmology, provides ...
, which can be derived purely from the Robertson-Walker metric under the formalism of
general relativity General relativity, also known as the general theory of relativity, is the geometric Geometry (from the grc, γεωμετρία; '' geo-'' "earth", '' -metron'' "measurement") is, with arithmetic, one of the oldest branches of mathema ...
. Having said this, it also happens that there ''are'' detectable Doppler effects on cosmological scales, which, if incorrectly interpreted as cosmological in origin, lead to the observation of redshift-space distortions.


Radar

The Doppler effect is used in some types of
radar Radar (radio detection and ranging) is a detection system that uses radio waves to determine the distance (''ranging''), angle, or velocity of objects. It can be used to detect aircraft, Marine radar, ships, spacecraft, guided missiles, motor ...

radar
, to measure the velocity of detected objects. A radar beam is fired at a moving target — e.g. a motor car, as police use radar to detect speeding motorists — as it approaches or recedes from the radar source. Each successive radar wave has to travel farther to reach the car, before being reflected and re-detected near the source. As each wave has to move farther, the gap between each wave increases, increasing the wavelength. In some situations, the radar beam is fired at the moving car as it approaches, in which case each successive wave travels a lesser distance, decreasing the wavelength. In either situation, calculations from the Doppler effect accurately determine the car's velocity. Moreover, the
proximity fuze A proximity fuze (or fuse) is a fuze In military munition Ammunition (informally ammo) is the material fired, scattered, dropped or detonated from any weapon A weapon, arm or armament is any implement or device that can be used wi ...
, developed during World War II, relies upon Doppler radar to detonate explosives at the correct time, height, distance, etc. Because the doppler shift affects the wave incident upon the target as well as the wave reflected back to the radar, the change in frequency observed by a radar due to a target moving at
relative velocity The relative velocity \vec_ (also \vec_ or \vec_) is the velocity of an object or observer B in the rest frame of another object or observer A. Classical mechanics In one dimension (non-relativistic) We begin with relative motion in the classic ...

relative velocity
\Delta v is twice that from the same target emitting a wave: \Delta f=\fracf_0.


Medical

An
echocardiogram An echocardiography, echocardiogram, cardiac echo or simply an echo, is an Medical ultrasound, ultrasound of the heart. It is a type of medical imaging of the heart, using standard ultrasound or Doppler echocardiography, Doppler ultrasound. Echoc ...

echocardiogram
can, within certain limits, produce an 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 Ultrasound is s with higher than the upper audible limit of human . Ultrasound is not different from "normal" (audible) sound in its physical properties, except that humans cannot hear it. This limit varies from person to person and is appro ...

ultrasound
beam should be as parallel to the blood flow as possible. Velocity measurements allow assessment of cardiac valve areas and function, abnormal communications between the left and right side of the heart, leaking of blood through the valves (valvular regurgitation), and calculation of the
cardiac output Cardiac output (CO), also known as heart output denoted by the symbols Q, or \dot Q_ , is a term used in cardiac physiologyCardiac physiology or heart function is the study of healthy, unimpaired function of the heart: involving blood flow; Ca ...
.
Contrast-enhanced ultrasound Unspecific cortical lesion on CT is confirmed cystic and benign with contrast-enhanced renal ultrasonography using image fusion. Contrast-enhanced ultrasound (CEUS) is the application of ultrasound Ultrasound is sound waves with frequency, f ...
using gas-filled microbubble contrast media can be used to improve velocity or other flow-related medical measurements. Although "Doppler" has become synonymous with "velocity measurement" in medical imaging, in many cases it is not the frequency shift (Doppler shift) of the received signal that is measured, but the phase shift (''when'' the received signal arrives). Velocity measurements of blood flow are also used in other fields of
medical ultrasonography Medical ultrasound includes diagnostic Diagnosis is the identification of the nature and cause of a certain phenomenon. Diagnosis is used in many different academic discipline, disciplines, with variations in the use of logic, analytics, and ...
, such as
obstetric ultrasonography ultrasonography, or prenatal ultrasound, is the use of in , in which sound waves are used to create real-time visual images of the developing or in the (womb). The procedure is a standard part of care in many countries, as it can provide a v ...
and
neurology Neurology (from el, , "string, nerve" and the suffix , "study of") is a branch of dealing with . Neurology deals with the diagnosis and treatment of all categories of conditions and disease involving the and s (and their subdivisions, the ...
. Velocity measurement of blood flow in arteries and veins based on Doppler effect is an effective tool for diagnosis of vascular problems like
stenosis A stenosis (from Ancient Greek στενός, "narrow") is an abnormal narrowing in a blood vessel or other tubular Organ (anatomy), organ or structure such as foramina and canals. It is also sometimes called a stricture (as in urethral stricture) ...
.


Flow measurement

Instruments such as the laser Doppler velocimeter (LDV), and acoustic Doppler velocimeter (ADV) have been developed to measure
velocities The velocity of an object is the Time derivative, rate of change of its Position (vector), position with respect to a frame of reference, and is a function of time. Velocity is equivalent to a specification of an object's speed and direction o ...

velocities
in a fluid flow. The LDV emits a light beam and the ADV emits an ultrasonic acoustic burst, and measure the Doppler shift in wavelengths of reflections from particles moving with the flow. The actual flow is computed as a function of the water velocity and phase. This technique allows non-intrusive flow measurements, at high precision and high frequency.


Velocity profile measurement

Developed originally for velocity measurements in medical applications (blood flow), Ultrasonic Doppler Velocimetry (UDV) can measure in real time complete velocity profile in almost any liquids containing particles in suspension such as dust, gas bubbles, emulsions. Flows can be pulsating, oscillating, laminar or turbulent, stationary or transient. This technique is fully non-invasive.


Satellites


Satellite navigation

The Doppler shift can be exploited for
satellite navigation A satellite navigation or satnav system is a system that uses satellite In the context of spaceflight Spaceflight (or space flight) is an application of astronautics to fly spacecraft into or through outer space, either human spacefl ...
such as in
Transit Transit may refer to: Arts and entertainment Film * Transit (1979 film), ''Transit'' (1979 film), a 1979 Israeli film * Transit (2005 film), ''Transit'' (2005 film), a film produced by MTV and Staying-Alive about four people in countries in the wo ...
and
DORIS Doris may refer to: People Given name * Doris (mythology) of Greek mythology, daughter of Oceanus and Tethys * Doris, fictional character in the Canadian television series '' Caillou'' * Doris (singer) (born 1947), Swedish rock and pop singer * ...
.


Satellite communication

Doppler also needs to be compensated in
satellite communication A communications satellite is an artificial satellite that relays and amplifies radio Radio is the technology of signaling and telecommunication, communicating using radio waves. Radio waves are electromagnetic waves of frequency between 30 ...
. Fast moving satellites can have a Doppler shift of dozens of kilohertz relative to a ground station. The speed, thus magnitude of Doppler effect, changes due to earth curvature. Dynamic Doppler compensation, where the frequency of a signal is changed progressively during transmission, is used so the satellite receives a constant frequency signal. After realizing that the Doppler shift had not been considered before launch of the
Huygens probe ''Huygens'' ( ) was an atmospheric entry robotic space probe A space probe or a spaceprobe is a robotic spacecraft that doesn't Earth orbit, orbit the Earth (planet), Earth, but instead explores farther into outer space. A space probe may ...
of the 2005
Cassini–Huygens The ''Cassini–Huygens'' space-research mission ( ), commonly called ''Cassini'', involved a collaboration among NASA The National Aeronautics and Space Administration (NASA; ) is an independent agencies of the United States government, ...
mission, the probe trajectory was altered to approach
Titan Titan most often refers to: * Titan (moon), the largest moon of Saturn * Titans, a race of deities in Greek mythology Titan or Titans may also refer to: Arts and entertainment Fictional entities Fictional locations * Titan in fiction, fictional ...
in such a way that its transmissions traveled perpendicular to its direction of motion relative to Cassini, greatly reducing the Doppler shift. (offline as of 2006-10-14, se
Internet Archive version
Doppler shift of the direct path can be estimated by the following formula: f_ = \frac\cos\phi \cos\theta where v_\text is the velocity of the mobile station, \lambda_ is the wavelength of the carrier, \phi is the elevation angle of the satellite and \theta is the driving direction with respect to the satellite. The additional Doppler shift due to the satellite moving can be described as: f_ = \frac where v_ is the relative speed of the satellite.


Audio

The
Leslie speaker The Leslie speaker is a combined amplifier An amplifier, electronic amplifier or (informally) amp is an electronic device that can increase the power (physics), power of a Signal (information theory), signal (a time-varying voltage or Elect ...

Leslie speaker
, most commonly associated with and predominantly used with the famous
Hammond organ The Hammond organ is an electric organ invented by Laurens Hammond and John M. Hanert and first manufactured in 1935. Multiple models have been produced, most of which use sliding #Drawbars, drawbars to vary sounds. Until 1975, Hammond organs ...
, takes advantage of the Doppler effect by using an electric motor to rotate an acoustic horn around a loudspeaker, sending its sound in a circle. This results at the listener's ear in rapidly fluctuating frequencies of a keyboard note.


Vibration measurement

A
laser Doppler vibrometer A laser Doppler vibrometer (LDV) is a scientific instrument that is used to make non-contact vibration measurements of a surface. The laser beam from the LDV is directed at the surface of interest, and the vibration amplitude and frequency are extra ...
(LDV) is a non-contact instrument for measuring vibration. The laser beam from the LDV is directed at the surface of interest, and the vibration amplitude and frequency are extracted from the Doppler shift of the laser beam frequency due to the motion of the surface.


Developmental biology

During the
segmentation Segment or segmentation may refer to: Biology *Segmentation (biology), the division of body plans into a series of repetitive segments **Segmentation in the human nervous system *Internodal segment, the portion of a nerve fiber between two Nodes of ...
of
vertebrate Vertebrates () comprise all species of animal Animals (also called Metazoa) are multicellular A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an indiv ...
embryo An embryo is the early stage of development of a multicellular organism A multicellular organism is an organism In biology, an organism () is any organic, life, living system that functions as an individual entity. All organisms ar ...

embryo
s, waves of
gene expression Gene expression is the process by which information from a gene is used in the synthesis of a functional gene product that enables it to produce end products, protein or non-coding RNA, and ultimately affect a phenotype, as the final effect. The ...

gene expression
sweep across the presomitic
mesoderm The mesoderm is the middle layer of the three germ layer A germ layer is a primary layer of cell (biology), cells that forms during embryonic development. The three germ layers in vertebrates are particularly pronounced; however, all eumetazoa ...

mesoderm
, the tissue from which the precursors of the
vertebra In the vertebrate spinal column The vertebral column, also known as the backbone or spine, is part of the axial skeleton. The vertebral column is the defining characteristic of a vertebrate in which the notochord (a flexible rod of uniform c ...
e (
somite The somites (outdated term: primitive segments) are a set of bilaterally paired blocks of paraxial mesoderm that form in the embryogenesis, embryonic stage of somitogenesis, along the head-to-tail axis in segmentation (biology), segmented animals. ...

somite
s) are formed. A new somite is formed upon arrival of a wave at the
anterior Standard anatomical terms of location deal unambiguously with the anatomy Anatomy (Greek ''anatomē'', 'dissection') is the branch of biology concerned with the study of the structure of organism In biology, an organism (from Ancient ...
end of the presomitic mesoderm. In
zebrafish The zebrafish (''Danio rerio'') is a freshwater fish are common freshwater fish throughout temperate Eurasia. Freshwater fish are those that spend some or all of their lives in fresh water, such as river A river is a natural flowing wate ...

zebrafish
, it has been shown that the shortening of the presomitic mesoderm during segmentation leads to a Doppler-like effect as the anterior end of the tissue moves into the waves. This effect contributes to the period of segmentation.


Inverse Doppler effect

Since 1968 scientists such as
Victor Veselago Victor Georgievich Veselago (13 June 1929, Ukraine – 15 September 2018)negative refraction Negative refraction is the electromagnetic phenomenon where light Light or visible light is electromagnetic radiation within the portion of the electromagnetic spectrum that can be visual perception, perceived by the human eye. Visible light i ...
, which should lead to a Doppler shift that works in a direction opposite that of a conventional Doppler shift. First experiment that detected this effect was conducted by Nigel Seddon and Trevor Bearpark in
Bristol Bristol () is a city A city is a large human settlement.Goodall, B. (1987) ''The Penguin Dictionary of Human Geography''. London: Penguin.Kuper, A. and Kuper, J., eds (1996) ''The Social Science Encyclopedia''. 2nd edition. London: Routle ...

Bristol
,
United Kingdom The United Kingdom of Great Britain and Northern Ireland, commonly known as the United Kingdom (UK) or Britain,Usage is mixed. The Guardian' and Telegraph' use Britain as a synonym for the United Kingdom. Some prefer to use Britain as shorth ...

United Kingdom
in 2003. Later inverse Doppler effect was observed in some inhomogeneous materials and predicted inside Vavilov–Cherenkov cone.


See also

* Differential Doppler effect *
Doppler cooling Doppler cooling is a mechanism that can be used to trap and slow the Motion (physics), motion of atoms to cold, cool a substance. The term is sometimes used synonymously with laser cooling, though laser cooling includes other techniques. History ...
* Dopplergraph * Fading * Fizeau experiment * Photoacoustic Doppler effect * Rayleigh fading * Redshift * Laser Doppler imaging * Relativistic Doppler effect


Primary sources


References


Further reading

* Doppler, C. (1842). ''Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels, Über das farbige Licht der Doppelsterne und einiger anderer Gestirne des Himmels (About the coloured light of the binary stars and some other stars of the heavens)''. Publisher: Abhandlungen der Königl. Böhm. Gesellschaft der Wissenschaften (V. Folge, Bd. 2, S. 465–482) [Proceedings of the Royal Bohemian Society of Sciences (Part V, Vol 2)]; Prague: 1842 (Reissued 1903). Some sources mention 1843 as year of publication because in that year the article was published in the Proceedings of the Bohemian Society of Sciences. Doppler himself referred to the publication as "Prag 1842 bei Borrosch und André", because in 1842 he had a preliminary edition printed that he distributed independently. * "Doppler and the Doppler effect", E. N. da C. Andrade, ''Endeavour'' Vol. XVIII No. 69, January 1959 (published by ICI London). Historical account of Doppler's original paper and subsequent developments. * David Nolte (2020). ''The fall and rise of the Doppler effect.'' Physics Today, v. 73, pgs. 31 - 35
DOI: 10.1063/PT.3.4429
*


External links

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ScienceWorld {{DEFAULTSORT:Doppler Effect Doppler effects, Wave mechanics Radio frequency propagation Radar signal processing Sound Acoustics