There was a good story from NCAR/UCAR on using GPS signals to improve hurricane models. There are six COSMIC satellites orbiting now and 12 more to be launched in the next four years.
It is based on GPS radio signals refracting through the atmosphere. The satellites are receivers of the GPS satellite radio signals elsewhere in orbit. The signal refraction determines the state of the atmosphere along the path. This is useful in the open ocean where many hurricanes and other tropical cyclone systems roam. It is very difficult to get direct measurements over the open ocean far from land. The GPS signal refraction gives a good estimate of atmospheric conditions and improves models and future forecasts.