Date: Winter 2013-14
I am trying to find out the name of an instrument on a rotatable pole with a rake like head which we used at air bases (RAF Kinloss, Scotland) to measure the speed of clouds overhead by timing how many points on the rake passed in so many seconds. (In the 1960's)
Measuring the speed of the movement is not easy. Indeed, it borders on the impossible. The website: http://en.wikipedia.org/wiki/Cloud gives you some reasons, but it is not a total list of cloud forms. A cloud doesn?t have a rigid form, so at one location it can move in 3 dimensions. Clouds come and go, depending on temperature and relative humidity or the dew point. These variables depend upon the speed of the atmosphere and its temperature. It is relative easy to measure large clouds, e.g. hurricanes, tornados, etc. because those clouds reflect cloud forms. But instruments that measure less water become not so useful for thin clouds.