Image Processing Reference
In-Depth Information
16
Chapter 2
2.4 Angle of Arrival Fluctuations
A beam of light passing at an angle though the atmosphere arrives at the earth's sur-
face displaced from its original path. In addition, the beam continues to move or os-
cillate about some point because of the effects of turbulence or mixing in the atmo-
sphere. This creates fluctuations in the index of refraction which both evolve and
move across the beam over time. As a result of these turbulence fluctuations, the
beam wanders over the surface about a central point.
In the case in which a beam overfills the receiver, the effect of beam wander in-
troduces small changes in the angle of the wavefront to the aperture or its optical
axis as shown in Fig. 2.5.
A wavefront passing through the atmosphere can be thought of as a large num-
ber of narrow beams of light that were in phase before entering the atmosphere. The
Figure 2.5
A tilted wavefront results in the displacement of the focus point in the focal
plane. Over time, the long-exposure profile is generated.
