Does a radar altimeter see the surface of water?

[FlaZoomie]

Does a radar altimeter see the surface of water or the ground under the water?

 

[Andy Neill]

It indicates distance to the surface of the water.

 

[SPilot]

How do you turn it on? In the plane I fly the radar altimeter is there, but it doesn't show anything.

 

[MauleSkinner]

It doesn't "see" it, it "hears" it

If your RA is transmitting straight down to the surface of the water, it will return height above the water.

On the other hand, if you're in a turn and the RA is transmitting at a large enough angle, the signal will bounce off the water in another direction, not return to the receiver, and your RA will indicate its version of infinity...generally just "more than 2500 ft".

Fly safe!

David