Divergence measurements from an aircraft

A comparison between the changes in wind calculated from Doppler data and from an inertial system shows that variations in Doppler winds of over five knots may be caused by small changes of heading and air speed. The accuracy of average winds over a ten minute period is thought to be better than five or six kt. A 500 mb wind field has been measured across a 50 nm square centred on the Scilly Isles and a value for the divergence out of the square has been calculated from the wind measurements. The accuracy of this measurement is estimated to be ± 3 × 10−5 sec−1.