Talk:Doppler effect

Need more sources, cross check other wp

The formulas (example section 2) aren´t coherent with the other wikipedia´s and/or don´t completely specify the conditions in which the are true, sources should be citated.

Also there is this Rayleigh backwards orchestra effect that requires the source travelling a twice the speed of sound and the given equations do not hold in these conditions. —Preceding unsigned comment added by 200.127.24.77 (talk) 05:43, 16 October 2007 (UTC)

The equation does hold if v_s,r = -2v, it results in a sinewave with a negative frequency, which corresponds to playing the signal backwards. Ceinturion (talk) 22:23, 26 August 2008 (UTC)

Sign Conventions

Is there any particular reason that the sign conventions are switched between the General and Analysis sections? Ehinson56 21:37, 3 January 2007 (UTC)

Problem solved because somebody made the sign convention consistent today. Ceinturion (talk) 17:05, 7 October 2008 (UTC)

Uniformed--Efa2 (talk) 09:16, 24 October 2008 (UTC)

Speed / velocity

Perhaps I am being pedantic here but I have noted that there seems to be some inconsistence in the article as to referencing v as speed and velocity. As it is scalar, should this not really be referred to speed? I realize this is a minor concern. Agaudin 22:23, 7 November 2006 (UTC)

I don't think so. My physics textbook has a similiar treatment and uses the term "velocity". Since v is signed, it can't be treated as speed (magnitude of velocity). The direction isn't unspecified; it's assumed to be along a line joining the source and observer. Pfalstad 00:24, 13 November 2006 (UTC)

Relativistic treatment

Is the consensus still for placing the description of the relativistic treatment in its own article or should it be pulled back here? By the way, sorry for omitting the minor change flag on some of my recent updates. -- Alan Peakall 18:42 Dec 6, 2002 (UTC)

Doppler did not test his hypothesis (?)

According to Alec Eden: The Search for Christian Doppler. Springer Verlag 1992. Doppler didn't test his hypothesis, neither did he base it on observations. However, I am not quite comfortable with writing english, so I would not like to make alterations in the article totally on my own. Could anyone be ready to correct my grammar and spelliong?

Well, according to "Asimov's Biographical Encyclopedia of Science and Technology" (1972 edition, Pan), Doppler is supposed to have spent two days in Holland with a flatbed carriage being pulled back and forth along a railway track, with trumpeters on the carriage playing various notes, and observers with perfect pitch by the track jotting down he actual notes that they heard. It could be a myth, of course, but it sounds like a rather elaborate thing to make up. Unfortunately, that book doesn't provide any further trackable references. ErkDemon 22:06, 30 October 2006 (UTC)

At this time (February 1845) Doppler lived in Prague with his family. The source above states that it was Christoph Hendrik Diederik Buys Ballot that performed the experiment. --Ekko 11:13, 8 November 2006 (UTC)

Okey-doke. Asimov's "biog" encyclopedia is rather lacking in detail, so your (more specific) book sounds like the more reliable source. ErkDemon 11:38, 16 January 2007 (UTC)

Not sure one of the formulas is correct

A similar analysis for a moving observer and a stationary source yields the observed frequency...

am I wrong, or does this formula seem incorrect... it would seem if one's speed equals the speed of the wave through the medium, the perceived wavelength should be infinite, and frequency should be zero. This is not what the equation suggests.

It's okay, the quoted velocities are recession velocities. In the "moving-observer" formula, 1- (v0/v) can be rewritten to be more consistent with the format of the previous equation, as (v-v0) /v, which makes it more obvious that when v0=v (moving observer receding from a stationary source at the speed of sound), the predicted frequency does indeed drop to zero. Unfortunately textbook writers seem to quote the various Doppler equations and variants directly from previous books (probably to avoid awful typos), so the formats used can be rather inconsistent and seem to be based more on tradition than mathematical efficiency or consistency. Sometimes the usage of terms in the equations isn't compatible with the accompanying text, so sometimes even the "pros" can end up messing these things up. ErkDemon 22:30, 30 October 2006 (UTC)

Time Dependence?

I just learned about the doppler effect in my high school physics class, but it seems to me that if the source or observer are not colinear in their motion (they never pass through each other) then the percieved frequency would be related to the cosine of the angle between the motion and the line between the observer and the source. Specifically could the percieved frequency by something like: fa=(c-v*cos(A))fo/c where fa is the apparent frequency, c is the speed in a medium, A is the angle, and fo is the original frequency Also, couldnt you express the cos(A) between the direction of the motion and the line between the observer and the source as: x/(y^2+x^2)^1/2 since the cosine is adjacent (the "x" var) over the hypotenuse. Lastly, x, which is the distance along the line of motion, will be determined by time and velocity Soooo it seems that:

                         fa=[c-v*(v*t)/[y^2+(v*t)^2]^1/2]fo/c

for a stationary observer displaced by "y" from the net motion at time t (unfortunately i can't quite think of what t(0) would be)

Doppler effect / red shift

I notice that there is a comment about red shift not being a result of doppler effect. I am not sure that is true, and it does seem to be in some dispute, especially considering the wikipedia article lists it specifically as a doppler effect measurement. Even if it is true that there is a subtle difference in that implementation, that is information that belongs on the red shift page and/or discussion. I do not think it belongs in this article. If there are no objections, I will remove that paragraph.

Yes, remove it. I think the sentence is accurate but misleading. According to the redshift article, there are several sources of redshift, not just the doppler effect. Pfalstad 20:57, 30 June 2006 (UTC)

"A stationary microphone records moving police sirens at different pitches depending on their relative direction".

I found this a little confusing at first, as both cars have the same general direction. Would be clearer thus: "A stationary microphone records moving police sirens at different pitches depending on the direction of travel, relative to the microphone at any instant" MalFarrelle 11:07, 21 September 2006 (UTC)

More info...

Hi! Im doing a reasearch on the doppler effect in school... Does anyone know if there is some more info out there.. the only thing i seem to find is java applets demonstrating the doppler effect :( —The preceding unsigned comment was added by 85.225.22.158 (talk) 13:08, 21 March 2007 (UTC).

Combined formula

There's a really neat combination of the two formulas in the german WP, so I'm going to paste it here and see if anyone else thinks that it should be included:
${\frac {f'}{f}}={\frac {c\pm v_{\rm {D}}}{c\mp v_{\rm {S}}}}$
$v_{\rm {D}}$ is the velocity of the observer and $v_{\rm {S}}$ that of the source. The operators on top are used when they are moving towards and the ones below when they're moving away from each other. —Preceding unsigned comment added by Merctio (talk • contribs)

That's quite cool! :) I'd not seen the "minusplus" symbol before, only the "plusminus". Very useful to be able to use both together in this context! Mucho efficient. Elegant, too, it makes for a nice "reflection" image. Award a point to the German-language Wikians! :) ErkDemon 03:00, 11 June 2007 (UTC)

Relative speed / relative velocity

See my last comments on the talk page of relative velocity : some cleaning up needs to be done concerning "relative speed" and "relative velocity" - at the moment this is messy. Only for 1D cases is there no difference between vectorial relative velocity and relative speed. Harald88 12:58, 3 October 2007 (UTC)

Doppler Techniques for geodetic purposes

In my research on Satellite Geodesy, I have found that Doppler techniques have been used extensively as a method of satellite orbit determination. The basic concept being that satellites transmit on a stable frequency, so by measuring the frequency shift, one could derive velocity changes and other orbital parameters. One book that I have found that has a lot of information about this technique is:

Seeber, G. (2003). Satellite Geodesy (2nd ed.). Berlin, Germany: Walter de Gruyter

A limited preview of this book is available on Google Books (see page 181 if it does not take you there automatically) here: http://books.google.com/books?id=WgQVlzGR5GYC&pg=PA181&sig=MmdXwfksC4aR5phjLE2k5Iv7F64#PPA180,M1

I thought that this reference might provide some useful information on this topic as it relates to astronomy and geodesy. ChrisTracy (talk) 23:32, 9 December 2007 (UTC)

Vandalism

Would it make sense to ask for semi-proection of this page? It appears to be a popular target for vandalism. Retoo (talk) 14:55, 2 March 2008 (UTC)

Hypnotic illustration

Does anyone else find the illustration near the lead/toc difficult to look at, or even look indirectly at? It may be just that I am tired, but it seemed to spark quite a lot of lateral inhibition which can, of course, be pretty cool if thats what you're looking for. Possibly though considering we are reading text beside it, Image:Velocity0 70c.jpg might be nicer on the eyes and would be able to illustrate the same information? Any thoughts? aliasd·U·T 19:36, 9 May 2008 (UTC)

I find the existing image perfectly suitable for this article, especially as it could stand in for normally experienced forms of doppler effect. The image you suggest, with its pictured velocity of 70% light speed, isn't going to reverberate as clearly with most readers. I say leave the lead/toc image in place, and add the other one elsewhere in the article. Binksternet (talk) 20:24, 9 May 2008 (UTC)

Complicated sentence

The received frequency is higher than the emitted frequency when the siren approaches, is equal to the emitted frequency as it passes the observer and is lower than the emitted frequency as it recedes from the observer.

Am I illiterate or does that sentence make no sense. I don't want to edit it because I'm not knowledgeable enough in this field to edit the definition of what I'm trying to find about but could someone fix that sentence, or if it's not wrong and I'm being a fool just make it more straightforward. —Preceding unsigned comment added by 99.243.192.198 (talk) 03:00, 23 July 2008 (UTC)

I have changed it into "The received frequency is increased (compared to the emitted frequency) during the approach, it is identical at the instant of passing by, and it is decreased during the recession" Ceinturion (talk) 17:05, 7 October 2008 (UTC)

Monotonic decrease

I have reverted two edits that replaced "monotonic decrease" with "monotonic increase" of the observed frequency as the source moves along a given trajectory. If you think about it, the monotonic decrease is correct (monotonic increase would mean a higher frequency after the source has passed the observer, which is obviously false). Sure, as long as the source is approaching, the observed frequency is higher than the source frequency, but it is decreasing (unless the source is on a collision course with the observer). --Blennow (talk) 14:15, 7 November 2008 (UTC)

Advert-ish sentence

An extract from "Development": "An English translation of Doppler's 1842 treatise can be found in the book The Search for Christian Doppler by Alec Eden."

It sounds like someone's trying to sell a book with the words "Can be found in the".

This could be changed to "Alec Eden made a translation of Doppler's 1842 treatise called The Search for Christian Doppler".

English is not my first language so I feel that someone else should have the last call on this one..

~~Thymo~~ —Preceding unsigned comment added by 84.202.236.123 (talk) 16:18, 21 January 2009 (UTC)

I was the author of that line, and English is not my first language either. The reason for putting it that way was that this is the only English translation available, as far as I know. Feel free to change it to a more idiomatic English. And you don't have to buy the book (which may not be easy), borrow my copy when you're in Oslo! --Ekko (talk) 10:18, 24 January 2009 (UTC)

Error (or is it me)?

Should

$\Delta f=-{\frac {v_{s,r}}{c}}f_{0}$

be

$\Delta f=-{\frac {v_{s,r}}{c}}f$ ,

or did I confuse myself? — Aldaron • T/C 22:19, 6 February 2009 (UTC)

Radial velocity

The doppler effect in a medium depends on the RELATIVE velocity of the source and the medium AT THE TIME OF EMISSION, and also the RADIAL velocity of the observer and the wavefront normal AT THE TIME OF ABSORPTION.

The doppler effect for light depends on the RADIAL (not relative) velocity of the source AT THE TIME OF EMISSION, and the RADIAL velocity of the observer AT THE TIME OF ABSORPTION.

(This is demonstrated by the annuall variance of the doppler shift of the stars due to the earth's changing radial velocity.

(relative velocity = radial velocity + transverse velocity)

Due to propagation delays, the emitted frequency doesn't equal the absorbed frequency until some time AFTER the source has passed.

"Emitted frequency doesn't equal the absorbed frequency..."? Totally depends on relative motion (or lack of motion) of each party. Binksternet (talk) 01:02, 18 July 2009 (UTC)

Pictures

I found the two images on the Simple English Wikipedia in the article of the same name to be much easier to understand than for the instance the one on the top right of this article. The images I'm referring to are Doppler_effect_diagrammatic.svg[1] and Dopplerfrequenz.gif[2], both which are found on Wikimedia Commons. Doppler_effect_diagrammatic.png[3] may also be a good one. All three images can be found on Wikimedia Commons and are therefore, as far as I know (I'm new) allowed to be used on this article. I believe these images would make the effect clearer to people that are not very familiar with physics and thus may have a harder time understanding the text. Woodcutterty (talk) 15:10, 28 November 2009 (UTC)

• 
  Current
• 
  Alternative 1
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  Alternative 2
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  Alternative 3

I agree. Let's give it a try. Ceinturion (talk) 15:02, 29 November 2009 (UTC)

Change of wavelength caused by motion the source

It turns out that thumbnailing animated GIFs is not fully supported (Wikipedia:Extended image syntax#Type). Compare the two versions at the right. Users of Internet Explorer (IE8) may notice a background artifact in the thumbnail version. This artifact does not appear in Firefox. To avoid it I am going to use the non-thumbnail version in the article. The disadvantage is that a non-thumbnail image cannot be resized. Ceinturion (talk) 16:17, 29 November 2009 (UTC)

Radar Section (Re-Write) Suggestion

This doesn't seem right, esp. the proximity fuze bit. Doppler is widely used in weather radar and I believe aircraft radar and air traffic control radar as it allows much better discrimination between moving / non moving objects.

It sounds as if the editor hasn't read/doesn't understand the Doppler effect article.I can see what they mean, but it's hard to understand in this form. It is not necessarily or only used to "measure the velocity". Its main feature is it can detect moving objects while ignoring objects that are stationary ie Trees and parked vehicles. Too much emphasis on the "Distance" aspect.

New text in BOLD, Removed text crossed out

Radar
"The Doppler effect is used in some applicationstypes of 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 reflected wave increases, decreasing the frequency. In some situations, If the radar beam is fired at the moving car as it approaches, in which case each successive reflected wave travels a lesser distance, increasing the frequency. In either situation, calculations from the Doppler effect based on the frequency/wavelength change accurately determine the cars' velocity.

Moreover, the proximity fuze, developed during World War II, relies upon Doppler radar[fact] to explode at the correct time, height, distance, etc.[citation needed]

Other applications are weather radar, air traffic control radar, terrain following radars for low-flying military aircraft ie. F-111, B1-B, in fact any application where it is helpful to detect moving objects, not just a raw reflection irrespective of relative motion, eg. A doppler radar will ignore immobile/slow ground reflections (mountains, buildings, slow vehicles), ensuring that this 'ground clutter' does not get mistaken for fast moving passenger aircraft.[citation needed]"

Do laser speed 'traps' use doppler effect at all.? Or just make several distance measurements, and then calculate distance travelled between measurements vs time to get speed? Doppler should stop them measuring a road-side tree at 100 Kph for example.
--220.101.28.25 (talk) 23:06, 5 December 2009 (UTC)

Subsonic?!

The article currently reads

In classical physics (waves in a medium), where the source and the receiver velocities are not supersonic, the relationship between observed frequency f and emitted frequency f₀ is given by:

and goes on with the non-relativistic equation (emphasis mine above). Does that really mean the equation is not accurate at Mach 2? Why? Either that's a mistake, or the article should clarify the matter. I don't know which one it is, that's why I'm not fixing it myself. --Gutza ^{T T+} 23:25, 27 February 2010 (UTC)

Doppler effect, in general, happens for the wave at all speed (including the speed that near the speed of light). Classical treatment for Doppler Effect may take sound wave for example. Using sound wave for example, the classical treatment is only valid if the observer and source are both slower than the speed of sound relative to the medium. Speed of emitted wave relative to the medium is regardless of the state of motion of the source. Gutza, I think you are right that there is a mistake then. I will correct it. Thanks for pointing it out. Thljcl (talk) 20:46, 20 March 2010 (UTC)

Confusing digressions on increase and decrease

Hunter33, I reverted your edit, as the original was correct.[4] On the other hand, although correct, that section is confusing instead of lucid to many readers. Probably it would be better to remove the lines "The above formula assumes that the source is either directly approaching or receding from the observer. 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 increase in the observed frequency as it gets closer to the observer, through equality when it is closest to the observer, and a continued monotonic decrease as it recedes from the observer." Actually I think that applies to the digression "A common misconception" as well. Ceinturion (talk) 09:39, 10 May 2010 (UTC)

Clearer Formula

http://upload.wikimedia.org/math/4/9/9/49974b0549d56e645a5125c5ba60b6df.png Should not the flowing formula be better f=f'(v+-vr)/(v-+vs) (134.184.100.155 (talk) 03:48, 9 June 2010 (UTC))