It is helpful after an industrial accident (railcar with toxic gas) or when providing information for incoming aircraft, particularly helicopters, to know the wind direction and velocity. The usual advice is to watch for smoke, or to have smoke generating grenades on hand. Grenades (available at survival stores) unfortunately generate heat and may ignite gases. A windsock may be helpful. But one may not always be available.
A helicopter pilot likes to know the direction of the wind on the ground. Sometimes he can determine this easily, sometimes not. Helicopters land INTO the wind and take off INTO the wind.
As part of survival equipment a package of inexpensive ten-cent rubber balloons of various colors can be of value.
When the aircraft approaches, sequentially release the brightly colored balloons into the air and the pilot will see which way they blow. Make sure they are released when he is far enough away so the rotor wash doesn't get them. If you have two-way radio communications tell the pilot what you are going to do.
By judging how far/fast the balloons travel over the ground you can get a rough idea of wind velocity.
44 feet per second is thirty miles per hour.
22 feet per second is fifteen miles per hour.
11 feet per second is seven-point five miles per hour.
5 feet per second is three-four miles per hour.
This is also helpful when determining the downwind area from a chemical spill and how fast the wind if blowing. This is not always that easy. The traditional method of "wetting your finger and holding it in the air" does not work very well.
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