Another technique utilized is airborne Light Detection and Ranging (LiDAR).  This technique uses either a plane or helicopter with positioning very accurately tracked using GPS.  A laser system is positioned on the base of the aircraft and light pulses are emitted and returned on a very high density.  By knowing very accurately the position of the aircaft and the distance between to the ground for each light return, a very high resolution elevation dataset can be collected.  Positional accuracy of the data is typically quoted as 0.3 m vertical and 0.5 m horizontal (based on a collection density of ~ 1 point per metre) but can be improved with higher density collection.