DECONVOLUTION BY THE CONJUGATE GRADIENT METHOD.

Since it is difficult in practice to generate and propagate an impulse, often a system is excited by a narrow time-domain pulse. The output is recorded, and then a numerical deconvolution is used to extract the impulse response of the object. Classically, the fast Fourier transform technique has been applied with much success to this deconvolution problem. However, when the signal-to-noise ratio becomes small, one sometimes encounters instability with the FFT approach. Here, the method of conjugate gradient is applied to the deconvolution problem entirely in the time domain. The method converges for any initial guess in a finite number of steps. Also, the time samples need not be uniform as with the FFT. Computed impulse responses utilizing this technique are presented for measured incident and scattered fields from a sphere and a cylinder.