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Name: Cayan
Status: educator
Grade: 6-8
Location: MN
Country: N/A
Date: 2/21/2005
Question:
What would be the best way to measure the speed of clouds through photography?

Replies:
Cayan -

I would not use photography, but mathematics. I would make a gadget that would point a stick at a cloud (preferably directly overhead)... perhaps clamp it to a ladder. Then monitor the time before I would site another stick at the clouds new position. By having the two sticks cross I could measure the angle.

I would then contact one of the weather web sites that reports cloud heights. Perhaps calling a local airport and asking... or some of the airports have automated telephone systems that report cloud height.

With a little help, the students could plug numbers into a calculator and calculate the distance moved using trig or similar triangles. Divide that distance by the time and you have the speed.

Sounds like a fun project.

Larry Krengel

Cayan,

One method that has been used in the past is to time a feature of a cloud as it passes from one side of a mirror to the other. Then divide the width of the mirror by the time it takes for the cloud feature to pass.

That could also be done by taking photographs at two widely separated locations (with the camera pointed straight up) and at fixed intervals of time. The photographs and time of them (which can be superimposed on the photo with many digital cameras) can be compared later to determine the speed in the same way as calculated from the mirror technique. Remember to synchronize the times on the cameras before taking the photos or determine the difference in time of the two cameras and adjust accordingly.

David R. Cook
Atmospheric Physics and Chemistry Section
Environmental Research Division
Argonne National Laboratory

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