The fundamental problem of optical wave propagation is the determination of
the field at an observation point, given a disturbance specified over some
finite aperture. In both vacuum and inhomogeneous media, the solution of this
problem is given approximately by the superposition integral, which is a
mathematical expression of the extended Huygens-Fresnel principle. In doing so,
it is important to find the atmospheric impulse response (Green's function).
Within a limited but useful region of validity, a satisfactory optical
propagation theory for the earth's clear turbulent atmosphere could be
developed by using Rytov's method to approximate the Helmholtz equation. In
particular, we deal with two optical problems which are the time reversal and
apodization problems. The background and consequences of these results for
optical communication through the atmosphere are briefly discussed
