Abstract: Depth of a top (24) and bottom (28) of an under water mud layer (26) are measured as a function of position from acoustical scattering measurement. The measurement involves transmitting sound from a transmitter (12) in a body of water (22) above the mud layer (26), using a higher and lower frequency range, above 100 kHz and below 20 kHz respectively. A higher frequency signal due to scattering of the sound in the higher frequency range from scatter positions along a selected horizontal direction is detected as a function of time from said transmitting, and a first depth, of a top surface (24) of the under water mud layer (26), is computed using this signal. A plurality of received lower frequency signals due to scattering of the sound in the lower frequency range is detected at different height in the body of water (22).