Weather forecasting is one of those sciences that never seems to be quite as good as we want it to be. But what if it had more data? That's the idea behind Spire, a tech startup which wants to use a huge fleet of tiny, cheap satellites to tell you when it's going to rain.
The company wants to deploy a fleet of 100 CubeSats -- small, cheap, ubiquitous mini-satellites into a low-earth Orbit with GPS receivers onboard. Once in position, the CubeSats will receive signals from the existing constellation of GPS satellites. As the signal travels from the GPS satellites (which are in a much more distant orbit), it passes through the Earth's atmosphere.
When the Spire CubeSat measures the incoming GPS signal, therefore, it can also pick up a bunch of information about the atmosphere it's passed through, a technique known as GPS Radio Occultation. The CubeSat will then pass the data down to a ground station, where it will be combined with reports from the 99 other CubeSats, allowing forecasters a detailed, worldwide sampling of the atmosphere.