Rough-surface retroreflection by focusing and shadowing below a randomly undulating interface

Lens retroreflection is retroreflection by a surface that contains optically smooth, convex sections of interface and below-interface scatterers. It has been verified quantitatively only for sections of the rough interface that are spherical. In this paper Monte Carlo ray tracing is used to verify quantitatively lens retroreflection for an interface that is totally randomly undulating. This random-interface lens-retroreflection mechanism gives retroreflections that not only have magnitudes that can be observed in existing measurements but that also have phase curves that cover the variety of shapes observed. Furthermore, this mechanism gives these magnitudes and phase curves for both kinds of below-interface scatterers, that is, those that do and those that do not cast distinct shadows upon one another.