"Tim.Ward" wrote:

It does work, but they use a little different technique.
The Doppler is only measured on particles at the focal length of the
optics.
The assumption is that the airmass (at least locally) is all the same,
and that the Doppler measurement is taken far enough away so the
effects of the airplane on the airmass are negligible.
So you send out two beams -- say, one forward at 45 degrees, one aft at
45 degrees.
It turns out that if you sum the signals from the two beams, you get
the vertical component of velocity, and if you difference the two
signals, you get the horizontal component.
Since we're measuring frequency, we can get sum and difference
frequencies from a mixer, though I have no doubt it runs through a DSP
somewhere.

So you only need one sensor head (though it puts out multiple beams).

By sending out two more beams, to each side, you can also pick up
sideslip information.
The clever thing is that they're using components developed for the
communications field, which helps to keep costs down.

Tim Ward

With these two beams at 45 degrees, you don't get truly the vertical and
horizontal components, rather the components along the two bissectors
of both beams, you would think this is nearly the same thing as the direction
of the components are just changed by the pitch attitude of the glider,
which is a very small angle usually, but this is sufficient for changing
lift into sink or vice-versa.