Method for estimating the equivalent radar cross section on the basis of a first near-field diffraction model of said object and a second near-field diffraction model of said object, the first and second models being able to be respectively represented by a first matrix (A b) and a second matrix (A' b) of complex diffracted wave and incident wave amplitude ratios, for a plurality (4 N 2) of pairs of respective directions and polarisations of the incident wave and observation of the diffracted wave, in which: - a modal decomposition of said first and second matrices is carried out and the most significant modal vectors (V,V') of the first and second matrices thus decomposed are selected in order to obtain a first base and a second base of modal vectors; - a correspondence is established between modal vectors of the first base and modal vectors of the second base; - an operator for passing from the second modal vectors (λ' s) associated with the modal vectors of the second base to the first modal values (λ s) associated with the modal vectors corresponding to the first base is determined; - a plurality ( N μ) of measurements of complex diffracted wave and incident wave amplitude ratios in near field are made for a plurality of pairs of directions and at least one pair of respective polarisations of the incident wave and observation of the diffracted wave; - the vector (a'), formed by the ratios thus measured, is projected onto said modal vectors of the second base, in order to obtain second modal components (λ' μ) on this base; - first modal components (λ μ) on the first modal base are obtained by applying said operator to the second modal components; - from the first modal components and the modal vectors of the first base a reconstructed vector (ã) is generated, the components of which represent the complex incident wave and diffracted wave amplitude ratios for said plurality of pairs of directions and polarisations; - the equivalent radar cross section is determined from at least one component of the reconstructed vector. - a modal decomposition of said first and second matrices is carried out and the most significant modal vectors (V,V') of the first and second matrices thus decomposed are selected in order to obtain a first base and a second base of modal vectors; - a correspondence is established between modal vectors of the first base and modal vectors of the second base; - an operator for passing from the second modal vectors (λ' s) associated with the modal vectors of the second base to the first modal values (λ s) associated with the modal vectors corresponding to the first base is determined; - a plurality ( N μ) of measurements of complex diffracted wave and incident wave amplitude ratios in near field are made for a plurality of pairs of directions and at least one pair of respective polarisations of the incident wave and observation of the diffracted wave; - the vector (a'), formed by the ratios thus measured, is projected onto said modal vectors of the second base, in order to obtain second modal components (λ' μ) on this base; - first modal components (λ μ) on the first modal base are obtained by applying said operator to the second modal components; - from the first modal components and the modal vectors of the first base a reconstructed vector (ã) is generated, the components of which represent the complex incident wave and diffracted wave amplitude ratios for said plurality of pairs of directions and polarisations; - the equivalent radar cross section is determined from at least one component of the reconstructed vector.