COMBINED DISPLACEMENT
If there are several anisoplanatic effects present, with each not
decreasing the Strehl ratio much, it is a common practice to
multiply the Strehl ratios for the individual effects to get a
combined Strehl ratio. The validity of this assumption is now
examined. The total displacement that is due to a translation, an
angular offset, a time delay, and a chromatic offset is
dt(z) = d + θz + v(z)τ + dc(z), |
|
|
(46) |
where chromatic displacement is given in Eq. (50).
The two terms necessary for calculating the Strehl ratio are
E |
= |
, |
(47) |
σ 2 |
= |
d 5/3, |
(48) |
where
dm = 2.91 k02 dz Cn2(z) dt(z) . |
|
|
(49) |
...
...
Tyler et al.[#!18!#] took advantage of the vector nature of
the displacement almost to eliminate the effect of chromatic
anisoplanatism on an adaptive-optics system by choosing an optimal
offset angle of a beacon from the propagation direction.