But a geostationary orbit is much farther out, beyond the range of smaller anti-satellite launched from the surface, In a geostationary orbit a satellite can cover a much larger area. In the case of Gaofen this is a circular patch of the planet 7,000 kilometers wide off the coast of China. Satellites like Gaofen use an optical sensor which can detect objects at sea as small as 50 meters from a geostationary orbit. An American aircraft carrier is over 300 meters long and when its moving the Gaofen can not only spot, identify and track it but does so in real time.
This not only lets China know where the American carrier task forces are but provides targeting information for their new ballistic missile (DF-21D) that has a guidance system enabling it to hit moving warships at sea. DF-21 is a 15 ton, two stage, solid fuel missile that is 10.7 meters (35 feet) long and 140cm (4.6 feet) in diameter. The DF-21D (the carrier killer version) missile gets precise location information from the Gaofen satellites and when it gets to the area within fifty kilometers of where the carrier the DF-21 warhead terminal guidance system can lock onto and hit the moving carrier.
Full article: Space: The High Eyes Of The Chinese Carrier Killer (StrategyPage)