During the 1970s, a few theoretical physicists arrived on the seismic scene, young and naive enough to believe that the apparatus of quantum scattering theory could be applied to the inverse seismic problem. Among them was Art Weglein, who started at Cities Service in 1978 with a Ph.D. in physics from CUNY.

Art and I, among others, were fascinated with the inverse scattering series, and hopeful that it contained the key to the information hidden in seismic data. Apart from some success with the fi rst term in the series (the so-called Born approximation), early results were...