The invention concerns a method for focusing acoustic waves useful for obtaining an image of a field to be observed in a dissipative heterogeneous medium (2, 3) around which acoustic transducers (T1-Tn, T'1-T'm) forming an imaging network and a target network. The method consists in following a training step during which pulse responses from the medium are measured between each transducer (Ti) of the imaging network (5) and several transducers (Tj) of the target network (6); deducing therefrom reference signals to be emitted by the transducers of the imaging network to produce a focused acoustic pulse in each transducer of the target network, then cumulatively, in determining reference signals to be emitted to focus an acoustic pulse on predetermined points in the medium. Said reference signals are stored and used subsequently to generate an acoustic image of the medium.