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Thread: Echo of a wave length

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    Echo of a wave length

    In the electromagnetic wave lengths say from x-rays to the 21 cm hydrogen line, the wave has a wave length. When it hits a receiver, eye, camera sensor whatever, it is turned into an electrical signal that can be interpreted by that device. Now we get to my question, is there an echo of that wavelength in the final signal? Why I can hear you ask. If there is an echo then a generic receiver could be built that covered all wave lengths at the same time.
    I know the answer "no echo" but has anyone looked?

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    What do you mean by "echo"?

    I also have no idea what you have in mind by "generic receiver".

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    'Echo' is there something in the new wavelength, the one that has been altered by the sensor to make it visible to us, that what type of EM and it's wavelength before it was decoded by the sensor?
    'Generic receiver' a receiver that would translate all the wavelengths that fell on it.

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    There are what is known as energy resolved photon counting detectors - they capture the number and energies of incoming photons. The energy is related to the wavelength. But you can't have one system that works at all wavelengths because the physics of detection is so different as you change wavelength domain. For example CCDs used to detect visible/NIR photons are very bad at detecting UV, IR and radio photons. Antenna are great for radio, not for anything else. Scintillators are good for high energy particles but not low.

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    Should I post this in "against the mainstream"?

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    Quote Originally Posted by speach View Post
    In the electromagnetic wave lengths say from x-rays to the 21 cm hydrogen line, the wave has a wave length. When it hits a receiver, eye, camera sensor whatever, it is turned into an electrical signal that can be interpreted by that device. Now we get to my question, is there an echo of that wavelength in the final signal? Why I can hear you ask. If there is an echo then a generic receiver could be built that covered all wave lengths at the same time.
    I know the answer "no echo" but has anyone looked?
    Antennas directly convert the electromagnetic wave into an electrical current. There are limitations due to the size of the antenna and frequency range the attached circuitry can handle, but within those limits a signal could be recorded and demodulated later, or a computer can do the demodulation in software (https://en.wikipedia.org/wiki/Software-defined_radio). Antennas can be used to directly sample or reproduce electromagnetic waves, within the limits imposed by geometry and the electronics.

    Most sensors produce a signal with at best an indirect and imprecise relationship to the wavelength. An RGB camera essentially lumps received light into 3 wavelength ranges. There are infinitely many spectral distributions that will yield the same output. There is no way for you to do spectral analysis with your unassisted eyes or with a photo taken with an unmodified camera, the information about the original wavelength distribution is gone.

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    I'm going to say a little bit about detecting electromagnetic radiation
    that I hope might help speach.

    The radio part of the spectrum is distinguished by use of antennas
    to transform the radiation into an electric current, and by the very
    low energy of each photon, requiring enormous numbers of photons
    acting in unison in order for them to be detected at all. The shortest
    wavelengths detectable by antenna are roughly a millimeter long.
    Shorter wavelengths have more energy per photon, and so can be
    detected as individual photons with an appropriate detector such
    as a CCD or a photomultiplier tube. Photons with enough energy
    are able to make changes in photosensitive chemicals. That is
    how eyes and photographic film work. Photons with more energy
    yet, in the ultraviolet and beyond, are able to remove electrons from
    molecules, ionizing and sometimes breaking them. That causes
    sunburn, degrades plastics and other organic materials, and fades
    certain dyes and pigments.

    -- Jeff, in Minneapolis
    Last edited by Jeff Root; 2018-Jan-05 at 12:09 AM.
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    "I find astronomy very interesting, but I wouldn't if I thought we
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    point of rockets is to explore them!" -- Kai Yeves

  8. #8
    If a wavelength of light is reflected back like an echo is a reflection of sound, if it is in phase it would not look any different, if out out of phase it would be interference. Out of phase is when parts of a wave like crest and the trough do not match each other, and in phase the two waves would match perfectly.
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    Quote Originally Posted by astrotimer View Post
    If a wavelength of light is reflected back like an echo is a reflection of sound, if it is in phase it would not look any different, if out out of phase it would be interference. Out of phase is when parts of a wave like crest and the trough do not match each other, and in phase the two waves would match perfectly.
    No you don't understand my use of the word echo. What I mean is there a small part of the transcribed image of that Wavelength, that has embedded in the image to describe what was the original wavelength?

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    Quote Originally Posted by speach View Post
    No you don't understand my use of the word echo. What I mean is there a small part of the transcribed image of that Wavelength, that has embedded in the image to describe what was the original wavelength?
    Well, if a system is used to detect radio waves or x-rays then the wavelength of the received signal will be known. Look at an (analog) radio: it will be tuned in terms of the wavelength. And an x-ray image will show might be colour coded to show different wavelengths.

    But I don't really know what you mean by "echo" or why you think it would enable a generic receiver. Jeff has said most of what I was going to say regarding different types of sensors. Consider the human eye, for example. Radio waves will have no effect (too little energy), visible light will produce nerve impulses (which encode information about the wavelength) and x-rays will pass straight through (possibly causing damage because of their high energy).

    The fact that the bran receives information abut the wavelength (colour) of the light doesn't mean that eyes are a generic receiver.

  11. #11
    The closest thing I can think of is what some in the tv trade referred as ghosting, sometimes when there a two channels with a similar frequency broadcast in the same area their signals can interfere and on one or both you get a weaker image on the screen. This happened in my are because PBS broadcast two channels in the area and they were the strongest signals and you got this effect.

    Another you could be meaning is if you have a source and the light reflects off another object in the background and it is moving and shifts the light. The original source will still be sending out its waves and when the shifted light from the reflection catches up it will interfere with it. You can figure out what the base signal doing something called Fourier transforms.
    ...I'm still free, you can't take the sky from me.
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  12. #12
    Or a third case where the reflected light goes off into another direction and that is called scattering and probably no way of knowing what the original wavelength was.
    ...I'm still free, you can't take the sky from me.
    You cannot run away from the truth, the world is not big enough. DI Jack Frost
    Don't Panic THGTTG
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    http://davidsuniverse.wordpress.com/

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    Part of the problem is that you are asking about "the original wavelength". There is no one to one correspondence between wavelength and color. The eye produces intensity measurements from three overlapping bands, giving it a rough measurement of a distribution of wavelengths. Distributions that produce different patterns of activation of those sensors are perceived as different colors, but there are infinitely many distributions that will give the same response as monochromatic light of a given wavelength, and distributions that produce colors that can not be reproduced with any single wavelength.

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    I'm very well aware of all that

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    Quote Originally Posted by cjameshuff View Post
    Part of the problem is that you are asking about "the original wavelength". There is no one to one correspondence between wavelength and color. The eye produces intensity measurements from three overlapping bands, giving it a rough measurement of a distribution of wavelengths. Distributions that produce different patterns of activation of those sensors are perceived as different colors, but there are infinitely many distributions that will give the same response as monochromatic light of a given wavelength, and distributions that produce colors that can not be reproduced with any single wavelength.
    Who mentioned colour?

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    Quote Originally Posted by speach View Post
    Who mentioned colour?
    You did. You can not claim you did not have color in mind when talking about wavelengths and vision.

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    Could you describe a "generic receiver" for us? What form would
    the output have? How would you interpret that output? Describe
    in as much detail as possible an example of how such a receiver
    would work and how it would be used.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

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    Quote Originally Posted by cjameshuff View Post
    You did. You can not claim you did not have color in mind when talking about wavelengths and vision.
    No you have got the concept of the question wrong, nothing to do with colour. The simple question was THIS after a wavelength is converted into a form that we can see or hear, in that converted form is there an echo of the form that the original wavelength took. simple yes or no. If the answer is yes (which I very much dought), can we see this and know what the wave length was.

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    Quote Originally Posted by speach View Post
    No you have got the concept of the question wrong, nothing to do with colour. The simple question was THIS after a wavelength is converted into a form that we can see or hear, in that converted form is there an echo of the form that the original wavelength took. simple yes or no. If the answer is yes (which I very much dought), can we see this and know what the wave length was.
    We certainly have information about the original wavelength (in many cases) because we detected it. But that is "meta" information - it is something we know rather about the signal, rather than being contained in the converted signal. But the range or variation of wavelengths detected will probably still be encoded in the resulting signal. Does that count?

    I still don't understand what you mean by "echo" or why you think it is relevant to creating a detector.

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    Quote Originally Posted by speach View Post
    No you have got the concept of the question wrong, nothing to do with colour. The simple question was THIS after a wavelength is converted into a form that we can see or hear, in that converted form is there an echo of the form that the original wavelength took. simple yes or no. If the answer is yes (which I very much dought), can we see this and know what the wave length was.
    Um, it is not a simple yes or no answer. For example I could easily build a system that did include some information about wavelength. I could build an RGB image where the LSB of each colour vector was used to encode any arbitrary data I wanted, including wavelength data. Or I could convert the data to a hypercube which does contain that data. Or I could build a dispersive system that uses the spatial component of the image to capture wavelength information (something like a chromotomographic hyperspectral system). Or I could use a scanning sparse aperture to do the same.

    There are lots of ways to convert a signal and process it before presenting it to a person. If you want a simple yes/no answer you need to specify the system and what it is doing more accurately.

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    Quote Originally Posted by speach View Post
    Should I post this in "against the mainstream"?
    Well, maybe ...

    Quote Originally Posted by speach View Post
    In the electromagnetic wave lengths say from x-rays to the 21 cm hydrogen line, the wave has a wave length. When it hits a receiver, eye, camera sensor whatever, it is turned into an electrical signal that can be interpreted by that device. Now we get to my question, is there an echo of that wavelength in the final signal? Why I can hear you ask. If there is an echo then a generic receiver could be built that covered all wave lengths at the same time.
    I know the answer "no echo" but has anyone looked?
    I'm not sure what you mean by "final signal" either. Could you take a specific example, maybe at a single particular wavelength, and describe what the final signal is in that example?

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    Quote Originally Posted by Strange View Post
    We certainly have information about the original wavelength (in many cases) because we detected it. But that is "meta" information - it is something we know rather about the signal, rather than being contained in the converted signal. But the range or variation of wavelengths detected will probably still be encoded in the resulting signal. Does that count?

    I still don't understand what you mean by "echo" or why you think it is relevant to creating a detector.
    Yes Yes Yes That is all I'm trying to establish. When a EM wave, of say 102nm, is converted to a 'visible to us form', does that 'visible form' contain anything that relates to the original 102nm. Of course the question now is how do we read the code, echo but as they say in the classics 'that's another story'!
    For my echo read your encode

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    Quote Originally Posted by speach View Post
    No you have got the concept of the question wrong, nothing to do with colour. The simple question was THIS after a wavelength is converted into a form that we can see or hear, in that converted form is there an echo of the form that the original wavelength took. simple yes or no. If the answer is yes (which I very much dought), can we see this and know what the wave length was.
    Define "form that the original wavelength took". A wavelength is a length. Define "generic receiver" while you're at it.


    Quote Originally Posted by speach View Post
    Yes Yes Yes That is all I'm trying to establish. When a EM wave, of say 102nm, is converted to a 'visible to us form', does that 'visible form' contain anything that relates to the original 102nm. Of course the question now is how do we read the code, echo but as they say in the classics 'that's another story'!
    For my echo read your encode
    Converted how? In what way is it being made visible to us? You need to be a lot more specific.

    A multispectral camera image will have a color (sorry, but that's how vision works) that depends on energy content in different wavelength bands. Depending on the mapping, contribution by 102 nm photons might make the image redder, greener or bluer. There's no way to tell that the cause is photons of exactly 102 nm wavelength, but you could constrain it to an arbitrarily narrow range by careful selection of filters. That won't help for wavelengths in other ranges though.

    A spectrograph will give you a measurement of the frequency content across wavelength bands. If its resolution is sufficient, you can detect features like spectral lines. Reading a spectrograph is pretty straightforward, you'll have to be more specific about your question. But a spectrograph is just a depiction of a spectrum, it doesn't innately identify anything about the form of the original signal, not even that it was electromagnetic...it might be visible range light or radio range EM, it might be acoustic or gravitational radiation. They all have wavelengths, they can all have identical wavelengths.

    And of course, all instruments have a limited range, and limited precision. You could conceivably build an imaging spectrograph with extremely wide range, but there's still going to be wavelengths outside its range, and features that it can't discern due to its precision limitations. And of course, something designed to measure star spectra is not going to be useful for spectral analysis of earthquakes, at most the latter is going to disrupt its ability to measure the former.

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    Quote Originally Posted by speach View Post
    When a EM wave, of say 102nm, is converted to a 'visible to us form', does that 'visible form' contain anything that relates to the original 102nm.
    The answer you are looking for is: No.

    To explain a little more, the situation is analogous to, if an English person is listening to someone talking on the phone, and so is a French person, they are gaining understanding of what the other person is saying. But the English person would not necessarily understand the French one, or vice versa. Still, there is no "echo" of what language is being spoken, there is only the ability to understand that language, and the "echo" of what is being said. Indeed wavelength is simpler than language, so we needn't worry about nuances in the analogy!

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    Quote Originally Posted by Ken G View Post
    The answer you are looking for is: No.

    To explain a little more, the situation is analogous to, if an English person is listening to someone talking on the phone, and so is a French person, they are gaining understanding of what the other person is saying. But the English person would not necessarily understand the French one, or vice versa. Still, there is no "echo" of what language is being spoken, there is only the ability to understand that language, and the "echo" of what is being said. Indeed wavelength is simpler than language, so we needn't worry about nuances in the analogy!
    That is an interesting analogy. Sometimes when I hear a sentence I can only remember the meaning, not which language it was spoken in!

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    Quote Originally Posted by speach View Post
    When a EM wave, of say 102nm, is converted to a 'visible to us form',
    does that 'visible form' contain anything that relates to the original 102nm.
    Quote Originally Posted by Ken G View Post
    The answer you are looking for is: No.
    I think the answer he is looking for is "Usually, to a limited extent."
    But usually to such a limited extent that it approximates your
    answer of "No", for the reasons Strange tried to explain in
    post #19. I have tried to explain it in my own words, but have
    given up each time because it would require many hours to say
    everything that would need to be said. I can't do any better than
    Strange did.

    I think the answer to speach's question is a fairly detailed explanation
    of how all sensors work AND how all information display media work.

    That is, for example, how radio recievers work, how eyes work, how
    CCDs work, how photographic film works, how fluorescent tubes
    work, how photomultiplier tubes work, how oscilliscopes work, how
    spectroscopes work, how TV screens and computer monitor screens
    work, how audio speakers work, how chart recorders work, and on
    and on. Then he can see how the outputs from each of these things
    relate to the inputs. Usually there are *some* clues in the outputs
    what sort of wavelengths were in the inputs. But as Strange said,
    that is mostly in the metadata, not something directly observed.

    -- Jeff, in Minneapolis
    http://www.FreeMars.org/jeff/

    "I find astronomy very interesting, but I wouldn't if I thought we
    were just going to sit here and look." -- "Van Rijn"

    "The other planets? Well, they just happen to be there, but the
    point of rockets is to explore them!" -- Kai Yeves

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    Quote Originally Posted by speach View Post
    Yes Yes Yes That is all I'm trying to establish. When a EM wave, of say 102nm, is converted to a 'visible to us form', does that 'visible form' contain anything that relates to the original 102nm. Of course the question now is how do we read the code, echo but as they say in the classics 'that's another story'!
    For my echo read your encode
    I think I understand your question, but perhaps not. Your 102nm choice is puzzling since the eye would not convert this to a visible form since it is beyond the visible light range. UV sensors can detect this and this will produce information that can be converted, which is similar to how the retinex (eye-brain functions) works, but I suspect that's not your intent.

    Like a color camera sensor, the eye has three different types of sensors (i.e. cones) that allow the brain to assign a net color result for the signal. If you send a monochromatic packet of photons, say at 500nm (green), all three cones in the retina will respond to this signal, not just the "green" cone. But the brain looks at the intensity level of all three signals to derive a "green" result. But, to your question, I think, there are multiple ways to produce the same signal to the brain but using a different set of photons and at different intensities that generate the same exact signal going to the brain, so "green" is the result. Are we green? [I recently saw 5th Element again. ] "Metamers" is the name for this effect and the lighting industry often make use of this. There is no way to know exactly what the original wavelengths were without using a spectrometer or something similar.

    A crude analogy, perhaps, would be like reading a rain gauge then trying to determine the size of the original drops.
    Last edited by George; 2018-Jan-09 at 05:22 PM.
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    Quote Originally Posted by Jeff Root View Post
    I think the answer he is looking for is "Usually, to a limited extent."
    But usually to such a limited extent that it approximates your
    answer of "No", for the reasons Strange tried to explain in
    post #19. I have tried to explain it in my own words, but have
    given up each time because it would require many hours to say
    everything that would need to be said. I can't do any better than
    Strange did.

    I think the answer to speach's question is a fairly detailed explanation
    of how all sensors work AND how all information display media work.

    That is, for example, how radio recievers work, how eyes work, how
    CCDs work, how photographic film works, how fluorescent tubes
    work, how photomultiplier tubes work, how oscilliscopes work, how
    spectroscopes work, how TV screens and computer monitor screens
    work, how audio speakers work, how chart recorders work, and on
    and on. Then he can see how the outputs from each of these things
    relate to the inputs. Usually there are *some* clues in the outputs
    what sort of wavelengths were in the inputs. But as Strange said,
    that is mostly in the metadata, not something directly observed.

    -- Jeff, in Minneapolis
    No you have not got the concept of the question, it has nothing to do with the wavelength that the receiver collects. I am fully aware that every type of wavelength needs a receiver that is 'tuned' to that peculiar band of wave lengths. The question was (I'm getting very fed up with the narrow minded answers Strange is the only person that seems to have grasped the question. Now the question was, after the said wavelength as been received and translated into a form we can interpret is there an Echo still in that converted image that refers to the original length?

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    Quote Originally Posted by speach View Post
    Strange is the only person that seems to have grasped the question.
    So it would be nice to get some feedback on the comments I made and the questions I asked. Others have asked questions to try and clarify what you are thinking of, but you have largely ignored them, leaving people to guess what you mean. I can see that could be frustrating but it is up to you to provide the clarity.

    I am fully aware that every type of wavelength needs a receiver that is 'tuned' to that peculiar band of wave lengths.
    It is not a matter of tuning (except within relatively narrow ranges, such as RF). It is the fact that different frequency ranges may require completely different technologies to detect a signal. You can't "tune" an RF antenna to receive visible light.

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    Quote Originally Posted by speach View Post
    <snip>
    (I'm getting very fed up with the narrow minded answers
    I suggest you lose the attitude. No one is obligated to answer your questions at all and they are doing you a favor by doing so. If they didn't understand the question, maybe you need to do better explaining it.
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