Ptolemy's Ptools

Cloud Altitude and Wind Speed

Materials Needed:

	2 Vertical Viewers
	Quadrant
	Tapemeasure
	Clipboard, paper & pencil

The Plan:

Prepare Ahead: Weather Conditions: You will need low flying, puffy clouds, with somewhat flat bottoms. A breezy day is best, so that the clouds aren't moving too slowly. Choosing a Site: Set the project up in an open, flat area. You will need to set your observation stations up at least 60 meters (180 feet) apart while remaining within sight and hearing of each other. Both stations need to have an unobstructed view of the sky in the direction that the clouds are coming from.

Go for it! : Preparing the Site: Set station #1 up at the opposite end of the observing field from the direction the clouds are coming from. Station #1 will have a vertical viewer and a quadrant angle viewer. Set station #2 up on a line between station #1 and the direction the clouds are coming from, at least 60 meters (180 feet) from station #1. Station #2 will have a vertical viewer only. Measure the distance between stations carefully and write it down. (Make it an easy to work with number.) Mark the two spots and place a vertical viewer on each when you are ready to start the observations. The quadrant viewer will be situated on a line between the vertical viewers, about 6 feet from station #1. Collecting the Data: With one person stationed at each of the vertical viewers and the quadrant viewer, wait for a cloud's leading bottom edge to come into view through the vertical viewer at station #2. If possible have another person ready to be the time keeper and data recorder. START the timer and signal the quadrant viewer to record the angle read when sighting the leading bottom edge of the cloud. When the clouds leading edge appears in the vertical viewer at station #1 STOP the timer. Record start and stop times and the angle read. Do this with several clouds to get an average. Processing the Data: Look up the Tangent Ratiofor the angle measured and MULTIPLY this by the distance between stations. The result will be the clouds' heights above the ground, or the altitude, in the same units as that used for the distance between stations. For the clouds' speed (and wind speed) in Kilometers per Hour (KPH), DIVIDE 1000 by the number of meters between stations; or for Miles Per Hour (MPH), divide 5280 by the number of feet between stations. MULTIPLY the time recorded above by this result and you have the speed (in whatever units you took the original time reading in). If you made the observation in minutes, MULTIPLY by 60 to get MPH or KPH. Repeat for each cloud you took readings on and determine an average altitude and speed.

An EXAMPLE:

Data collected: Distance - 30 meters Angle measured - 35° Time elapsed - 3 minutes

1) 35° = tangent ratio of .7002 60m x .7002 = 42m altitude 2) 60m/1000 = .06km .06km x 3 min = .18km per min .18kpm x 60min = 19.8km per hour

How it works: Using the Properties of Triangles

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(last updated 8/31/98)