Image Processing Reference
In-Depth Information
18
Chapter 2
Figure 2.7
Image jitter induced by the atmosphere as a function of r
0
. The curves cor-
respond to increasing aperture size ranging from 0.1 m to 100 m apertures.
little change in the overall shape of the wavefront. Thus, the change in the angle of
arrival of the wavefront can be described as an angular change in two axes, tip and
tilt. As different turbulence cells pass in front of the wavefront, the angle changes.
Wavefronts passing through the atmosphere shows changing angle of arrival or
jitter at the receiver. The average jitter is described by (Hardy 1998)
)
12
/
(
2
−
1 3
/
−
53
/
α
=
0 182
.
λ
Dr
,
(2.4)
0
where
D
is the aperture diameter and
r
0
is the scale length of the atmosphere. The
jitter as a function of the atmospheric scale is plotted in Fig. 2.7.
2.5 Higher-Order Modes
Any effect that degrades the performance of an optical system is referred to as an
aberration (Smith 2000). The most commonly encountered optical aberration is
defocus; it is often used as a reference. Defocus is the out-of-focus or blurred image
