RECONSTRUCTION OF ACOUSTIC PARAMETERS OF A STRATIFIED SEABED FROM THE REFLECTION COEFFICIENT

The seabed is modeled as a fluid inhomogeneous layer above a homogeneous fluid half-space. Acoustic parameters (P-wave velocity c, density-rho) depend on depth z only. In case of a plane insonification at given incidence-theta, introducing an apparent depth s function of the density leads to a refractive index N(theta)(s) whose knowledge at two incidences yields seabed profiles c(z) and rho(z). Calculation of N(theta) from the reflection coefficient (non linear inverse problem) is carried out by two methods. The first one is a distorted-Born iterative method and implies solving a succession of linear inverse problems. The second, developed earlier for probing electrical permittivity with median contrasts, directly provides an approximate profile N(theta).