Temporal backward planar projection of acoustic transients

Backward projection schemes use data in front of a transmitter to reconstruct a field at closer points. Existing techniques have concentrated propagating radial and temporal information along constant planar cross sections in front of a planar source. This approach requires a careful consideration of evanescent waves, as the transfer function used to backproject in space causes evanescent wave solutions to increase exponentially with the projected distance. Erroneous signals may result from exponentially increasing noise, experimental error or roundoff error. A method is presented that is designed to work with imaging methods that record three-dimensional spatial data at constant times. Several widely used optical methods are of this type. Our algorithm projects the field backward in time via linear wave theory. The approach is similar to previously reported methods but is designed to work with time-constant data and avoids problems associated with evanescent waves.