Image Processing Reference
In-Depth Information
22
Chapter 2
Figure 2.11
Wavefront from Fig. 2.9 with the global tilt subtracted.
The evaluation of most wavefronts is simplified when the first three Zernike
modes (piston, tip and tilt) have been removed.
2.7 Effect of the Atmosphere on Intensity at a Receiver
Wavefronts arriving at the aperture of a receiver have some angle to the optical axis
that is normal to the aperture. These angle-of-arrival fluctuations in the wavefront
are a dynamic variation of the incident angle. In the final focal plane of the receiver,
the image appears to move around in the image plane. The resulting image recorded
over a long exposure is blurred, reducing the resolution of the optical system. This
blurring is seen quite often in astronomical imaging, where stars provide an ideal
wavefront point source, yet the recorded image is far from ideal.
The effect of beam wander and image jitter on the intensity (
I
) of the beam on a
receiver is given by Eq. 2.5, (Hardy 1998; Tyson 2000)
)
(
2
IT
exp
−
σ
0
p
I
=
,
(2.5)
2
D
+
12 7
.
σ
α
λ
