What relevance does the ground have anyway - we don't deploy our canopies on the ground. The next four slides (thanks to Winsor Naugler) illustrate how the concept of groundspeed can lead to completely erroneous conclusions under some circumstances. What we will do is imagine our jumpers equipped with strobe lights, photographed from the ground to indicate the path they take relative to the ground, and also carrying a smoke canister. Since the smoke blows with the wind, the smoke trail indicates the path relative to the airmass. Another way of looking at this is that the smoke trail indicates the center of the jumper's column of air. When there is no wind, these trails coincide. For convenience we ignore any forward drive of the canopy.