The launch of the European satellite is now scheduled for Wednesday evening at 23.20 (Dutch time). The satellite goes, once at 320 kilometers altitude, to map the wind on earth.
Measuring the wind is still done by weather stations on the ground, such as at the KNMI in De Bilt. Occasionally weather balloons go into the air. Aircraft indicate after landing which winds they encountered along the way. The problem is that they are all snapshots. We only know how the wind at a certain moment blows at a certain place. There is no overall picture.
The mission will take at least three years, and possibly another two years longer.