NSSL | Education | Ideas

Ideas for Teaching

• Stereo photography
• Why radar can't (usually) see tornadoes
• Graphing information
• Vectors for wind speed
• Calculating %
• Simple math
• Not so simple math
• Wildflowers & rainfall

Vectors Help You Calculate Wind Speed

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Wind Speed and Direction

How do you determine the ambient wind speed and direction while the car is moving? The anemometer on the roof will measure the wind that results from both the vehicle speed and direction as well as the wind speed and direction. First, how does the computer know the car's speed and direction?

To obtain vehicle speed and direction in the computer, we outfitted the mobile mesonet vehicles with both a flux gate compass and a GPS, or Global Positioning System, sensor. The compass shows the direction the car is pointing when standing still and information from the GPS unit allows us to determine speed and direction when the car is moving. Although we could include that portion of the calculation, let's skip ahead to the next step.

We have a) a measurement from the anemometer, and b) the car's speed and direction.

If the car is not moving the direction the car is pointing is determined using the compass. This simplifies the problem a great deal.

What if the car is moving? Now we have a true vector problem. The GPS unit sends information that allows us to calculate the vehicle's speed and direction. The anemometer measures the wind as the moving car sees it but scientists want the wind speed and direction as if the car were standing still.

Thus, a vector problem.

Note: this could also be a computer program.... You could have tables of data and have students build a computer program to do the logic and math. Remember, efficiency counts - the data is plotted on the laptop screen in real time for the scientists to see.

See page 3 to try a calculation from real data from the field...

Last updated: March 25, 2002
Created by: DSZ