Internal waves in the ocean lead to small-scale fluctuations in the speed of sound. These fluctuations lead to measurable features in the sound field received at long distances (thousands of kilometers). I will discuss direct problem modeling, and the identification of some features that can be used in an inversion, as well as some that cannot.

The division of useful features from those that we don't know how to use is based on a new view of the nature of long-range propagation through the rather unique ocean environment.