The number of pixels per millimetre defines a digital image's resolution.
In remote sensing, the images resolutions are expressed by the
size of the area covered by a pixel. Each pixel in an image corresponds
to a patch on the Earths surface. We thus talk about ground
For example, each sensitive element of the SPOT satellites
high-resolution sensors CCD is only 13 µm (0.013 mm)
across but sees an approximately 10x10m area on the
Earths surface through the observation systems telescope.
The sensors resolution is thus said to be 10m. Since this
satellites CCD sensor consists of 6000 sensitive elements
placed along a bar, the satellite sweeps a 6000 x 10m (= 60 km)-wide
strip on the Earths surface as it orbits around the planet.