Viewed from above

摘要

We've long had eyes in the sky. But now a handful of start-ups are using these satellites to monitor everything from flood damage to crop yield with greater frequency and detail than ever before. Efforts to keep tabs on Earth from above began with NASA's Landsat programme, which started in 1973. It currently has two satellites in orbit imaging the whole of Earth's surface every 16 days. The resolution is high enough to capture major roads, but not individual houses.