You're making a good distinction here. The research on using GPS occultation for sensing water vapor that I'm most familiar with uses two satellites, and does not use ground stations.
I am biased here, because I know the people who are developing this technology, so I'd be welcome to further information on this point! E.g., I took a look at the thesis abstract pointed to by @kubiii, but it wasn't specific enough to tell what their exact sensing method was.
The main advantages of GPS occultation for H2O sensing are that it's relatively bias-free (compared to microwave radiometers), that it can see through clouds, and that it has better usable vertical resolution.
I am biased here, because I know the people who are developing this technology, so I'd be welcome to further information on this point! E.g., I took a look at the thesis abstract pointed to by @kubiii, but it wasn't specific enough to tell what their exact sensing method was.
There are some generally good-quality summaries of GPS radio occultation here: http://geooptics.com/?page_id=148
The main advantages of GPS occultation for H2O sensing are that it's relatively bias-free (compared to microwave radiometers), that it can see through clouds, and that it has better usable vertical resolution.