# Do adaptive optics work the other way around?

Could the current technology used in adaptive optics to see far into the sky, be used to improve satellite or even aerial photographs?

Well yes, degradation due to blurring and scintillation of atmospheric turbulence goes both ways, and the most apparent benefits could be not for optical imaging systems, but for data communications and reducing signal degradation. See e.g. Improved optical communications performance combining adaptive optics and pulse position modulation or Effectiveness of adaptive optics system in satellite-to-ground coherent optical communication. Optical imaging from orbit can benefit also from other, less invasive image enhancement techniques (see below), but AO could be one of them. If we used them to image some other worlds than the Earth;

There are a few problems with using adaptive optics in orbit, though. First is that AO use powerful lasers and those drain a lot of power. To my knowledge far more of it than laser communications systems, even from such a distance as the Moon, like e.g. LADEE's LLCD (Lunar Laser Communications Demonstration). But perhaps more importantly, that I can't imagine pointing such powerful lasers from orbit to ground without protest from targeted nations. As I hear, Air Force doesn't exactly approve the use of ground based AO either:

Air Force Space Command regulates their use to protect passing satellites. All uses of the lasers must be approved days ahead of time by the Laser Clearing House at Vandenberg Air Force base to prevent the beam from crossing paths with an approaching spacecraft. The lasers cannot damage a craft’s hull, but they could potentially burn out sensitive optical equipment.

Now, for the other way around, you can imagine FAA and FCC, possibly DOE, having something to say about their use. Not to mention what all problems would ensue, if AO rated lasers were used to improve optical imaging of territories of other nations. Imaging other worlds with thick atmospheres though (but with refractive index below critical angle, which rules out, say, Venus), sure. Power budget permitting.

Adaptative Optics systems correct the wavefront error by deforming the mirror, and they do so several times per second,ie at a specific frequency $f$. This frequency depends on the speed $v$ of the turbulence in the atmosphere in relation to the observer, and the characteristic size of the turbulence $r_{0}$ (actually it is the coherence length).

A rule of thumb is $f>\frac{v}{r_{0}}$

For ground system, $v$ is roughly the wind velocity in altitude. If you want to put an adaptative optics sytem in a satellite, $v$ will be on the order of the orbital velocity, ie ~8km/s. You will have to increase f a lot to compensate for that, meaning your mirror actuators and your wavefront sensor will have to work a lot faster, which is very challenging.

The other aspect of the problem is that AO is not needed for satellite imaging: the blur due to turbulence is in genral negligible compared to the blur due to diffraction, because satellite have much smaller mirrors than ground telescopes, and their distance to the turbulent layers in the atmosphere is much larger.

Edit: a good read on adaptative optics:The Effects of Atmospheric Turbulence on Astronomical Observations A. Quirrenbac

• +1 This is a very good point! By the way, I've just noticed that you're the one who wrote this answer to the question "Atmospheric influences on earth to satellite visibility and vice versa (e.g. atmospheric seeing)" as well. You may want to refer to that explicitly in this answer as well. – uhoh Mar 9 '18 at 15:27