An assembly for determining speed of a supercavitating underwater vehicle
during underwater travel includes a fin mounted on the vehicle aft of a
cavitator portion of the vehicle and adapted to be extended outwardly
beyond a hull of the vehicle and through a boundary of a gas-filled
cavity around the vehicle to form a disturbance in the cavity boundary,
which disturbance propagates along the boundary. An acoustic transmitter
is mounted on the vehicle and directs acoustic energy toward the boundary
and the disturbance. An acoustic receiver is mounted on the vehicle and
receives acoustic energy reflected off the disturbance. An autopilot is
mounted on the vehicle and clocks times of projection of the fin and
acoustic transmission receptions of reflected acoustic energy to
determine the speed of the vehicle through the water.