Johnson, Steven A.

Data and simulated data from circumscribing and linear sampled arrays has been used to form high resolution reflection images by two techniques. The first technique (synthetic focusing) uses the mathematical equivalent of a lense to focus the image at each point by adding either linear (uncompressed) or nonlinear (compressed) transforms of the data. Logarithmic and square root compression is studied. The lense effect is obtained by backprojecting convolved or other linear transformed versions of the data along equal time propagation surfaces in the image with appropriate corrections for refraction and frequency dependent attenuation. The choice of apodizing function and different wave forms can greatly improve image resolution. The second technique (reflection ART) is not based on a focusing model but rather on direct inversion of a matrix (linear transform) model of the object-acoustic field interaction and data acquisition process by a Kacmarz iterative inversion method. The two methods are compared.