GPS measures position of a receiver in regards to a satelite, can't measure wind speeds..
As far as winds measured in land...I don't sail in land..I sail on the water...
2 to 10 miles off the coast.
I never cared much for land observations and meteorological tables..I look at my st60, set it in True..that is what I see....TRUE..not APPARENT....
Thecnically it is stronger at sea because there are no objects and terrain deviations to make changes or cause drag..but generally wind also cools down at sea, and gusts have a different behaviour tha in land where montains etc, can cause deviations to airflows and velocities...normally they place these wnd measuring stations way up high, where winds are also consitently higher..as you know