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In Radar concept the SAR-Synthetic Aperture radar performs as side-looking to collect information, why it is not downlooking? There are down-looking radar also. So what are the differences between them

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    $\begingroup$ Great question! See also answers and links at How can ICEYE-X1 capture 2D high resolution SAR images in “tens of seconds”? I don't believe that downward looking radar (nadir viewing) radar can generate 2D images, but I would be happy to read about an example, thanks! $\endgroup$
    – uhoh
    Jan 21, 2020 at 1:10
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    $\begingroup$ I assume you are asking about radar used in Earth Science and not military radar systems? $\endgroup$
    – uhoh
    Jan 21, 2020 at 1:16
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    $\begingroup$ Yes.I am looking for answers in the field of earth science $\endgroup$
    – Gokul Anand
    Jan 22, 2020 at 0:16

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A radar measures the time of arrival of the backscattered signal to infer the distance between the target and the platform (satellite, aircraft, whatever). If two targets are at the same distance from the platform, one on the left and one on the right because the platform is looking down, then their signals will arrive at the same time, making them impossible to distinguish. Looking sideways removes this ambiguity. Look at this figure from the Center for Space Research of the University of Texas (there is also a text explanation in the link).

down looking versus side looking

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  • $\begingroup$ I only know the X/S band navigation/weather radars on ships. They have a rotating antenna and the resolution depends on the "narrowness" of the beam and some software magic. The orientation there would not matter since they have a direction from antenna's orientation, but they are usually interested in "where is the way and is somebody else there" ... $\endgroup$
    – user18607
    Jan 21, 2020 at 9:50
  • $\begingroup$ @Jean-Marie Prival en.wikipedia.org/wiki/Side_looking_airborne_radar $\endgroup$
    – user1066
    Jan 21, 2020 at 9:55
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Both down-looking and side looking radar look down.

Down-looking radar illuminates terrain forward and below the aircraft to detect targets on or near the ground. Stationary targets would be lost among the ground clutter, but moving targets on or near the ground can be separated by their doppler shift. Software eliminates the background clutter and leaves only small objects with a doppler shift displayed on the screen. These objects will be vehicles or low flying aircraft, which is what the fighter pilot is looking for.

Side-looking radar scans a wide swathe of land below and to one side of the aircraft, usually for mapping purposes, rather like side-scan sonar maps the ocean floor.

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    $\begingroup$ A check of Wikipedia's Side looking airborne radar and especially Range resolution (across track) explains why side-looking is so important for generation of images. Satellites can not effectively image using radar looking straight down; there is no mechanism for lateral resolution (cross-track). I'm guessing that the OP is asking about applications to Earth science rather than military radars. $\endgroup$
    – uhoh
    Jan 21, 2020 at 1:15
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    $\begingroup$ I suggest you replace "aircraft" by the more generic "platform", as it can of course also be carried on a satellite (or even on a balloon) (I would edit it myself, but I want to make sure you agree with the edit). $\endgroup$
    – gerrit ♦
    Jan 21, 2020 at 9:04
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    $\begingroup$ Could you elaborate using sar satellite imageries for supporting your statement ? $\endgroup$
    – Gokul Anand
    Jan 22, 2020 at 4:54

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