The "C" data set contains buoy locations interpolated by the International Arctic Buoy Programme (IABP) to six-hour intervals from a maximum of 14 daily locations tracked by satellite. Using the 12:00 GMT positions, Fowler calculated the distance the buoys traveled in a 24-hour period. The number of buoys and their locations varies from year to year, but the maximum number is about 30 buoys. Usually these buoys are widely spaced; very few are placed in the Eastern Arctic. The following image shows ice motion from buoys on 20 April 2000:
Daily-averaged ice motion vectors from buoys
It is difficult to assign an error value to a buoy velocity. The position accuracy of the buoys is about 0.5 km. The locations are interpolated to the 6-hour interval times. The accuracy is then dependent upon the initial position error and the interpolation error. It could be assumed that the overall error would be less than 1 cm/sec for the average velocity over 24-hours.