  The structure function is a useful quantity to characterize wavefront
distortions. We derive expressions for the structure functions of the averaged
wavefront phase and slopes. The expressions are valid within the inertial range
of atmospheric turbulence, and are meant to serve as engineering formulae when
reconstructing profiles of the atmospheric turbulence, specifically in the
context of atmospheric profiling instruments (e.g. SLODAR and S-DIMM+) and
multi-conjugate adaptive optical systems.
