It's based on the radio altimeter, which measures altitude directly beneath an aircraft based on how long it takes a beam of radio wave to travel to ground, reflect, and return back to the aircraft. The radio altimeter indication also appears in the cockpit Heads Up Display, and the pilot can also preset an altitude so that an aural and visual warning is triggered if he/she flies below the set altitude.pardon my ignorance in asking this stupid question.
how can the planes fly so low, seemingly only 10m or so above water surface?
is such low level flight controlled automatically by the avionics, or manually by the pilots ?
thanks in advance for the explanation.