GNSS (GPS and the like) can be used to measure water level, using reflectometry. The direct signal from the satellite also arrives late at the receiver due to reflection off the sea, and signal-to-noise levels change with the angle as the satellite passes overhead. 🌊

SWsdpwilliams.bsky.socialSep 27, 2024 2:23pm

The storm surge at Cedar Key, Florida from Hurricane Helene measured by a tide gauge and from GNSS-Interferometric Reflectometry

It's not as regular a signal as a tide gauge (hence the spline fit in that plot), but it has certain advantages. The receiver can be raised up safely on land, so long as it has a good view of the water.