[burfog]

You'll need the air speed and direction.

Normally, speed is from a tube aimed into the air. Normally, direction is from a little fin that can spin.

There are lots of alternatives:

Direction can be via multiple tubes aimed into the air, each with slightly different direction.

Speed can be from a hot wire. Weather stations sometimes use this.

You can get both via lidar. You just need to make it sensitive enough to pick up a response from minute particles of dust or ice.

I think I just invented a new way: do a short-duration high-power pulse of an electron source or an EUV laser, causing the air to fluoresce at enough distance from the aircraft to be clear of the boundary layer. Track the motion of the fluorescing air with multiple cameras.

[mnw21cam]

Yay, yet another way to accidentally fry people on the ground if you accidentally switch on the wrong system. Radar already provides a way to do that.