Riccati equations for scattering matrices on level surfaces

Layer stripping based on the Riccati equation for the scattering matrix is a natural approach to the solution of the inverse scattering problem for the Helmholtz equation. But it has so far failed to work in two and three dimensions. This paper examines a cause of failure and establishes a Riccati equation for the scattering matrix on the level surfaces of the index of refraction. The new Riccati equation overcomes a common drawback shared by the traditional Riccati equations - the waves are unnaturally forced to propagate with a Green's function of an artificially fixed background wave number, and this man-made mismatch will mix and deform the propagating and evanescent modes, which skews the regularization of the backward solve of the Riccati equations for layer stripping.