Earth observation is the use of satellites to watch the Earth, and of software to turn their pictures into answers. The weather map on the evening news, with a cyclone moving towards the coast, is a satellite picture. These satellites are different from the ones that carry internet and phone signals.
Earth observation satellites carry three main kinds of sensor. Optical cameras take pictures like an ordinary camera, but need daylight and a clear sky. Radar sends out radio waves and reads their echo, so it sees through cloud and works at night. Hyperspectral sensors see hundreds of narrow bands of colour, so each material shows its own signature. See Earth observation satellites, synthetic aperture radar and hyperspectral imaging.
Most of these satellites fly in low Earth orbit, a few hundred kilometres up. See LEO and GEO satellites. A satellite at this height goes round the Earth in about 90 minutes. To see the same place often, companies fly many together, called a constellation.
The satellites produce more images than people can look at. So the value moves from the picture to the answer: which fields are stressed, what has changed since yesterday, which ships have switched off their transponders. Satellite imagery analytics does this work, with geospatial AI. The buyers are governments and armed forces, farming and insurance companies, mining companies and those who watch shipping.
Imagine a cyclone that crosses the coast of Odisha. The state disaster agency wants to know, within a day, which fields and villages are under water. Radar satellites see through the storm cloud and photograph the coast. The pictures come down to the ground, and software compares them with older pictures and marks the flooded area. The agency gets a map and sends relief to those places first.
Thousands of satellites and many pieces of debris now circle the Earth. A collision can destroy a satellite. So operators use space situational awareness to track every object and to know when to move out of the way.
In 2020, India opened its space sector to private companies, and a small group of start-ups in Bengaluru now builds imaging satellites and the software to read their images.