A LiDAR measures wind speed along its detection beam at different locations. Each measurement at one location lasts about one second. The desired horizontal wind speed has to be calculated from this data under the assumption, that the wind speed is the same at every beam position. There are two ways to arrive at a 10-minute average horizontal wind speed:
First calculate the horizontal wind speed for every measurement and then average over 10 Minutes, or
First average the measurements of each beam position and after that calculate the horizontal wind speed.
Approach 1) averages the scalar horizontal wind speed and is therefore called scalar averaging, whereas approach 2) results in averaging the full wind vector, which gives it its name: vector averaging.