Here is a thought:

Was in the back yard making thousands of soap bubbles (Mr. Bubbles)
for the baby. Slight breeze. Clearly could tell the entire airflow
pattern in the back yard....even a little ridge lift over the glider
trailer!

Wonder if you could add a soap bubble machine to a sailplane? Turn it
on when you first hit a thermal and a trail of bubbles is created.
After one circle, just fly toward the highest bubbles and that is
where the thermal's core is.

I could see the bubbles about 200 feet away, but might could add a
color die to enhance visibility further.

Any thoughts on this?