If you were looking for, say, a 1m per pixel quality, what focal length/sensor size would you need? Would there be any off the shelf/commercial solutions?

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    $\begingroup$ If you are looking for 1m per pixel quality, you should also ask for the necessary exposure time to support this quality level. The image should move on the sensor not more than half a pixel width during exposure time. $\endgroup$
    – Uwe
    Commented Apr 25, 2017 at 19:28

1 Answer 1


The Planet Labs Flock 3p constellation is in LEO at 500 km and doing an effective job of imaging all the land area of the Earth daily, albeit at around 5 meter resolution.

The best angular resolution achievable for a given telescope diameter is determined by the diffraction limit. For visible light at 500 km distance this works out to a minimum aperture diameter of about 40 cm to achieve 1 meter ground resolution. That's assuming a perfect optical system, so you might need a somewhat larger lens or mirror in reality.

Atmospheric seeing conditions, solar illumination angle, attitude stability are a few more of the many considerations that go into the overall system design.

  • $\begingroup$ 40 cm for what aperture diameter? $\endgroup$
    – Tristan
    Commented Apr 25, 2017 at 21:27
  • $\begingroup$ @Tristan 40cm is the aperture diameter to achieve 1 meter ground resolution. I'll edit to clarify. $\endgroup$ Commented Apr 25, 2017 at 21:45
  • $\begingroup$ That makes sense. Much appreciated! $\endgroup$
    – Tristan
    Commented Apr 25, 2017 at 21:46

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