L//2 -APPROXIMATION OF IMPULSE RESPONSE FROM TIME LIMITED INPUT AND OUTPUT: THEORY AND EXPERIMENT.

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