Deconvolution of echoes scattered by a surface tends to give the response function to a Dirac pulse incident on the surface. In some cases, this response function is easily related to the geometry of the scatterer and could be used to characterize it. In practical, the situation of the Dirac pulse with infinite bandwidth is not realized even by a broad band transducer which acts as a band-pass filter. We propose here some simple arguments to extend the Fourier spectrum in order to improve the results of deconvolution. Experiments are performed with targets consisting either of small plane surfaces of various shapes or of randomly rough surfaces. Results are in good agreement with those expected using the Kichhoff-Helmholtz integral.