A method and apparatus for the sounding of waters, particularly suitable for depth (and the like) sounding of Arctic waters, comprises shooting an energetic projectile at the water or ice surface from, say, a helicopter which has suspended close to the waters surface a suitably housed microphone for receiving the echo energizing from the waters. By measuring elapsed time between firing of the projectile and reception of the echo, and knowing all distances except the depth of the reflecting boundary (be it the bottom or a submarine), the unknown depth is easily determined.