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| 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 Earth’s surface. We thus talk about ‘ground resolution’. For example, each sensitive element of the SPOT satellite’s
high-resolution sensor’s CCD is only 13 µm (0.013 mm)
across but ‘sees’ an approximately 10x10m area on the
Earth’s surface through the observation system’s telescope.
The sensor’s resolution is thus said to be 10m. Since this
satellite’s CCD sensor consists of 6000 sensitive elements
placed along a bar, the satellite sweeps a 6000 x 10m (= 60 km)-wide
strip on the Earth’s surface as it orbits around the planet. |
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The resolutions of the commonest Earth-observing satellites are given in this table:
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To show the importance of resolution for picture quality, here is a detail of an image taken by the US Landsat satellite’s Thematic Mapper sensor compared with the same area seen by the French SPOT satellite’s HRV sensor working in the panchromatic mode. Part of the image has been enlarged. The area covered is Brussels National Airport (Zaventem). |
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Landsat Thematic Mapper - pixels: 30 m
© ESA, distributed by Eurimage |
SPOT Pan - pixels: 10 m |
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