A method (100; 200) for digital signal processing (S(t)) of a pulse and scanning radar during an observation of a coastal zone in land/sea detection mode, the signal being sampled according to a two-dimensional temporal map, a distance dimension (d) and a recurrence dimension (rec), comprising: selecting a digital terrain model file (MNT) of the observed coastal zone; transforming (110; 210) the temporal map and/or the digital terrain model file to obtain a transformed temporal map and/or a transformed digital terrain model file the data of which are expressed in a common reference frame; constructing (120) a mask (MT; MF) from the transformed digital terrain model file; and applying (130) the mask to the samples (E(d, rec); E(d, Δf)) of the map associated with the transformed temporal map, in such a way as to obtain filtered samples (Ef(d, rec); Ef(d, Δf)).