1. A method for estimating the radar cross-section of a given object from a diffraction model of said object, said model being able to be represented by a matrix (A b ) of ratios of diffracted wave and incident wave complex amplitude, for a first plurality (4N 2 ) of pairs of respective incident wave and diffracted wave observation directions and polarizations, characterized in that: a modal decomposition ( 120 ) of said matrix is carried out and the most significant modal vectors of said thereby diagonalized matrix are then selected ( 130 ); a second plurality (N μ ) ( 140 ) of measurements of ratios of diffracted wave and incident wave complex amplitudes is carried out for a plurality of pairs of directions and at least one pair of respective incident wave and diffracted wave observation polarizations; the vector (a μ ) formed by the thereby measured ratios is projected ( 160 ) on said most significant modal vectors; from the thereby projected vector and from the most significant modal vectors, a reconstructed vector (ã) is generated ( 170 ), the components of which are representative of the ratios of incident and diffracted wave complex amplitudes for said first plurality of pairs of directions and of polarizations; and the radar cross-section is determined ( 180 ) from at least one component of the reconstructed vector.