In this talk, we will present the identifications of scattering inhomogeneities in a 3D shallow ocean waveguide with an elastic seabed or an icecap, which are motivated by applications in ocean acoustics. A type of direct imaging method (DIM) is proposed to identify the marine point sources and medium objects from the observation data, and the key component of the DIM is an imaging functional whose indicator property is quantitatively characterized. The DIM can generate reliable initial estimates of submerged inhomogeneities, which advanced inversion methods can then utilize to accurately determine their physical properties.