Holographic images are obtained by computing the reflected energy profile existing directly at the flaw depth. This will be a footprint of the flaw. The computation is done by propagating the received C-Scan data back to the flaw depth. This procedure utilizes simple spatial Fourier transforms and can be done rapidly.
Both tone burst and impulse data may be successfully imaged. In either case, the Fourier amplitude coefficients of the raw data are collected at the frequency(ies) of interest. The coefficients are back-propagated to the desired depth and converted to magnitude [(a^2 +b^2)^0.5]. Plotting magnitude as a function of lateral position produces the final image.