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Is it possible to define any camera without "flash" (sensible to any band of radio wave) as a passive radar?

If so, where could I find references to that? I've been looking all over the place and nothing has come up.

If anyone has any sources or comments, please let me know. Thanks!

Edit: The idea of camera is merely a device that captures light in any range (visible light, infrared, ultraviolet). This is close in meaning to a passive radar, which is sensible to the electromagnetic waves coming from a target.

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  • $\begingroup$ Welcome to Engineering! This looks like a resource-hunting question. Such questions are prone to becoming out-dated, and are therefore considered off-topic for this site. $\endgroup$
    – Wasabi
    Mar 8 '17 at 11:03
  • $\begingroup$ By definition, the first "R" in Radar refers to Radio, so you are asking if optical frequencies can be referred to as radio frequencies. Optical and radio are different - and currently, non overlapping - parts of the EM spectrum, so I would have to say, no. $\endgroup$ Mar 8 '17 at 11:18
  • $\begingroup$ Wait... cameras are only sensitive to a pretty narrow band of electromagnetic waves - visible light plus a little infrared. What is commonly understood as radio waves usually starts with UHF (microwaves and above). Could you clarify what exactly you mean? $\endgroup$
    – SF.
    Mar 8 '17 at 11:18
  • $\begingroup$ Cameras may be used to measure location, distance and speed of objects, but that is considerably different from radar principles of operation. $\endgroup$
    – SF.
    Mar 8 '17 at 11:19
  • $\begingroup$ The idea is to define a more general concept of sensors based purely on electromagnetic waves. @SF. My point would be if I have an infrared camera, would it be a passive radar? If so, why not a normal camera isn't defined as such? $\endgroup$ Mar 8 '17 at 11:24
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Not really.

Firstly the RA in RADAR stands for RAdio which covers significantly longer wavelengths than the visible light (an in some cases near infra-red) which cameras can detect.

While light and radio are both part of the electromagnetism spectrum they are different parts of it and not interchangeable. While they are all part of a spectrum in terms of physics, from an engineering perspective they might as well not be.

Equally there are laser based systems analogous to radar, usuallly called LIDAR

Also radar implies a device which is capable of deducing information about the range and possibly speed and direction of a target object, most cameras can't do this, or if they can it is through a separate system. In fact the auto-focus on most cameras is more akin to the optical rangefinders widely used for military purposes before the advent of radar.

A radar system consists not just of an emitter and receiver but also the processing equipment to deduce the required information while a camera is intended to capture and store a 2D image.

The closest thing to a 'radio camera' is a radio telescope. A key point here is that the differences in wavelength between radio and visible light means that a radio telescope is very different from any camera in terms of both scale and structure.

While radar and cameras could both be described as devices for detecting electromagnetic radiation that about as far as the similarity goes and is not a complete definition of either.

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  • $\begingroup$ Thanks @Chris. As Brian just commented on my question, i didnt think of that the second R for range .. But even though, Ill have to find different paths to explainon my paper about radar sensors. =) $\endgroup$ Mar 8 '17 at 12:39
  • $\begingroup$ But lightfield cameras are able to tell the distance. $\endgroup$
    – joojaa
    Mar 8 '17 at 21:01

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