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B How is noise removed in radio telescopes?

  1. May 22, 2018 #26


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    Sure we are. Noise is the random variation in the signal away from a theoretical 'ideal' value. If I take an image of a star and count the number of electrons generated in the sensor's pixels by that star's light, I'll get some value, X. I then take another identical image and count the electrons again. This time X is a bit more or less than before. I then take another identical image and do the same thing, again getting a slightly different value for X. Let's say I continue to take images and I also average the values after each image to get the mean electron count, Y. As the number of images taken increases towards infinity, Y approaches some particular value, which I'll call the signal's theoretical perfect value. This theoretical perfect value is the value I'd get for each X in a world without any sources of noise. But noise causes X to vary around Y's value in each image.

    Is that any clearer?
  2. Jun 5, 2018 #27


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    "MAXENT" or "MEM" (maximum entropy method) processing has been used for decades in astronomy. As I recall, it was key to producing high-quality Hubble images before the optical defect in Hubble was fixed. Typically, it produces resolution improvements by 2x or so.

    Having said that, I do not know when, or for what kinds of imagery, it is commonly used now. Because the processing is nonlinear, I suspect people usually do not distribute MAXENT-processed data for further scientific analysis; they would expect that the user-scientists will apply whatever method is optimal for the research of interest (which may not be MAXENT).
  3. Jun 12, 2018 #28


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    The thread has gone a bit off topic I think because the title is to do with Radio Telescopes. Nontheless, very similar basic processes are involved. If you know something about the nature of the signal you are looking for then life is much easier than if you are just 'listening'. In general, a Wanted Signal has some structure and it will have some degree of self corellation and that can be spotted against truly random noise, which has zero self corellation. radio astronomers have one big advantage over optical astronomers in that the signals they are receiving can be analysed in terms of amplitude and phase whereas received light can only be observed in terms of its amplitude. (Numbers of Photons per second)
  4. Jun 12, 2018 #29


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    Yes, indeed! The same is true in acoustics, and for the same reason. The closest we can come in optics is probably holography, because that provides at least some phase information. But optical frequencies are simply to high to sample the waveform in real time and construct the phase information.
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