Geostationary imaging versus low Earth orbit remote sensing

Almost all Earth observation satellites, including India's Cartosat and RISAT series, fly in low Earth orbit, typically a few hundred kilometres up in a sun-synchronous polar orbit. They see a narrow strip at very fine resolution, but they only pass over a given place once every few days. A geostationary satellite sits about 36,000 km above the equator and circles the Earth in exactly one sidereal day, so from the ground it appears to hang motionless over the same longitude. That buys persistence at the cost of resolution: from that distance the ground sample is 42 metres rather than sub-metre, but the same scene can be revisited every few minutes instead of every few days. For a cyclone tracking eastward, a flood crest moving down a river, or a forest fire spreading through an afternoon, the ability to look again in five minutes is worth far more than extra detail in an image taken three days later.