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What is the true difference between radar and sonar? My understanding is that radar uses a reflected EM wave, while sonar uses a compression (shock wave) of the material it's in. (It compresses water, and then looks to see if any of the shock wave is reflected back?)

If that is true, than any spacecraft with one of these devices would be better off using radar to track objects in space?

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  • $\begingroup$ If the spacecraft has only one device, it will have radar; so I don't understand your question. $\endgroup$
    – LDC3
    Oct 1, 2014 at 3:48
  • $\begingroup$ But if the spacecraft designers had a choice between a sonar device and a radar system, they should use radar. (Because sonar cannot work without something to travel in. Or for the same reason you can't hear sound in space.) Right? $\endgroup$
    – CoilKid
    Oct 1, 2014 at 3:53
  • $\begingroup$ Yes. Is that your question? $\endgroup$
    – LDC3
    Oct 1, 2014 at 3:55
  • $\begingroup$ Yup, but that is why I cannot use it right? That is the difference between radar and sonar? $\endgroup$
    – CoilKid
    Oct 1, 2014 at 3:56
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    $\begingroup$ Sonar might use an ordinary sound wave and not a shock wave, but otherwise yes, that is the difference. $\endgroup$
    – The Photon
    Oct 1, 2014 at 5:03

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Radar (radio detection and ranging) uses electromagnetic waves (typically of the radio or microwave region of the spectrum) to detect the presence of remote objects along with other properties including the object's range and angular location relative to the radar.

Sonar (sound navigation and ranging) is a similar technique to radar, but uses sound waves (rather than electromagnetic). As a consequence, sonar required a medium for sound waves to propagate in, typically water or air.

There is also Lidar (light detection and ranging) which, like radar, operates with electromagnetic waves but in the optical portion of the spectrum.

Of the three of these, radar and lidar are suitable for spacecraft as their electromagnetic signal do not require a medium to propagate in. Sonar, requiring some contiguous material for both the sonar system and any targets to be immersed in, would be unsuitable in the vacuum of space.

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