Public Lab Research note


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Action sequence photography to study turbulence

by Ecta64 |

This method was devised to try and generate a visual indication of turbulence through interval photography of a tethered aerodynamic lifting anemometer (TALA design) kite in-flight. The images were taken over a 20 second time period with one photo being taken every 5 seconds. The camera was mounted on a tripod and fixed in terms of position throughout all of the images (you can use handheld images as long as you register them first using a program such as Hugin, http://hugin.sourceforge.net/ , but it is much easier to just use a tripod). By fixing the camera and photographing the moving kite in-flight it is possible to combine the images in a manner similar to a multiple exposure or action sequence photograph. The motions of the kite over time are immediately visible in a single image. These motions can indicate turbulence and changing direction of the wind over time. I recommend shooting wide-angle and at high resolution. It is highly advised to have a camera with an interval shooting option. In terms of post-processing

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there are number of available programs though in my case I used gimp for the general processing. A sighting compass is another important piece of kit in that it can be used to get readings of various landmarks as well as the kite itself to give a better overall spatial awareness.

This process could be further enhanced through the use of stereo photography and possibly using a portion of the kite as a marker that could then be used to mark data points to try and quantify the kite's movement through the sky over a particular period of time.

In the literature that is available on the TALA kite design, the monitoring of kite behavior in the air is listed as being quite accurate compared to other kites in one report while another does discuss the possibility of certain kite movements being the product of "bluff body" dynamics that were not fully defined.

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In the actual manual for the kite design that was used it was stated that readings of the kite movement in terms of vector and vertical inclination could be used with no mention of any aerodynamic interference from the kite design that would necessitate any kind of care in taking such readings.

There are a variety of ways to create action sequence imagery. One tutorial on how to do it through Photoshop can be found here: http://abduzeedo.com/reader-tutorial-how-create-awesome-action-picture-gimp , a number of videos on YouTube are available as well for both Photoshop and Gimp.



diy-kite

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