Spurious effects reduction by the reconstruction of acoustic images from bispectrum
A method to improve the quality of acoustic images obtained by systems based on beamforming is described. The specific goal is to eliminate two additive spurious terms present in the beam signals. The first effect is due to side lobes and the second one is due to the nonlinear effects introduced by the modulus extractor present at the output of the beamformer. The relative importance of these two terms is assessed, showing that the term due to modulus extraction has a strong negative incidence on the final image quality. The Gaussian distribution of these spurious terms is discussed and verified in the case of punctiform scenes. Owing to the Gaussianity of the spurious terms, a method to eliminate them from the beam signals, based on higher order spectra analysis, is proposed, resulting in an evident image quality and reliability improvement.