The North West Shelf of Australia is a difficult data area . The seafloor and near surface comprises a Tertiary carbonate wedge which thickens away from the coast. Strong multiple sequences are generated between the sea surface, the seafloor and other strong reflectors in the near surface. The absorption of the primary energy by the carbonate wedge and the low reflectivities in the zone of interest results in the masking of these reflectors by the multiple train. Back scattered energy is not a severe problem because the seafloor is generally smooth and flat .