The purely singular 1-D acoustic reflection problem
  This paper analyzes the nonlinear correspondence between the reflectivity profile (model) and the plane wave impulse response at the boundary (data) for a three-dimensional half space consisting of a sequence of homogeneous horizontal layers. This correspondence is of importance in geophysical imaging, where it has been studied for more than half a century from a variety of perspectives. The main contribution of the present paper is to derive something new in the context of a time-limited deterministic approach: (i) an exact finite (non-asymptotic) formula for the data in terms of the model, (ii) a corresponding exact inverse algorithm, and (iii) a precise characterization of the inherent nonlinearity. Regarding (iii), for generic models the correspondence is characterized as a pair of maps, one of which is locally linear, and the other of which is locally polynomial. Both are determined by a local combinatorial invariant, an integer matrix. Concerning (ii), the basic inverse algorithm is modified to allow for erroneous amplitude data, taking advantage of the overdeterminacy of the inverse problem to recover the exact model even in cases where the data is badly distorted. The results are illustrated with numerical examples. 
Peter C. Gibson
math-ph math.AP math.MP