Remote sensing — Geography, 11–13
How satellites and aircraft collect information about places without someone standing there.
What remote sensing is
Remote sensing means finding out about Earth from a distance. A satellite or aircraft records reflected light, heat or radar signals, and computers turn those measurements into an image or map. Different surfaces give different signals, so a forest, a road and a lake can be told apart without visiting each one.
Why use it?
Some places are too large, dangerous or remote to survey on foot, and they may change quickly. Remote sensing lets geographers compare the same area again and again, such as a forest before and after a fire. It came from the need to make reliable maps and decisions over wide areas with fewer field visits.
Reading a satellite image
Imagine an image where a lake looks dark, a road looks bright and a forest looks textured green. First, check the image date and scale. Next, compare those patterns with a known map and mark each feature. Finally, measure a new cleared patch: if its length is 3 cm and the scale says 1 cm represents 500 m, it is 1,500 m long.
The picture is not the truth
It is tempting to treat a satellite image like a normal photograph, where every colour has one obvious meaning. But colours can be changed to show heat, vegetation or height, and clouds can hide the ground. Check the key, date and sensor before deciding what you see; a red patch may be healthy plants in one image and bare ground in another.
Where it is used
Remote sensing helps track deforestation, map floods, check crops and plan roads. During a flood, an image can show which fields and bridges are underwater even when roads are blocked. Scientists also use repeated satellite images to measure how a coastline, glacier or city changes over years.
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