[Serviceman using Rawin weather device]

Photograph of an unidentified U.S. Army Air Forces serviceman using a Rawin weather device to measure wind velocity at different altitudes, circa 1940s.

Typed on verso: "Above is pictured a weather 'rawin' in operation. It is a weather device used by the weather men of the U.S. Army Air Forces for visual observation of a balloon, called a 'pibal' which is released to determine wind velocity at different altitudes. The 'rawin' principle is based on radio 'triangulation', a method of direction finding well understood by all amateur radio 'hams.' By timing the ascent of the balloon and computing the speed with which it drifts with the wind, 'rawin' is able to tell at any given moment the altitude it has reached. It gives to weather men a clear picture of what is happening above the earth's surface. (Official USAAF photo."

Stamped on verso: "Official Photograph. U.S. Army Air Corps."