Ultrasonic Phase-Sensitive Rangefinder with Double Modulation Doppler-Free Method for Shallow Seafloor Survey

A Doppler free double modulation phase -sensitive method was proposed to obtain shallow sea-depth, relatively thin sub-bottom profiles and the velocity between the target and the measurement system. The values of the distance and the velocity obtained by this method in the air agreed well with the actual values. The field experiments to evaluate this method at the Matsushima bay were carried out by the use of the double modulation system on the basis of such a method. The shallow sea -depth obtained by this system agreed well