From deconvolution of the echo scattered by a surface, it is theoretically possible to obtain the impulse response of this scatterer. In some cases, this response can be closely related to the geometry of the scatterer and can be used for its characterization. In practice, even in the field of ultrasonic spectroscopy, the transducers always exhibit a finite bandwidth. We suggest a method for extending the Fourier spectrum which leads to better results after deconvolution. The experiments are performed with targets consisting either of small plane surfaces with various shapes, or of large randomly rough surfaces. The results are in good agreement with those expected using the Kirchhoff‐Helmholtz approximation.