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The Air Up There : CIRES Kites

Imagine the sun is out and steady winds are blowing from the west. "This is a great day to fly a kite," you might think. That is just what researchers at the Cooperative Institute for Research in the Environmental Sciences (CIRES) would be doing. As fun as kite flying may be, Research Associates Ben Balsley, Michael Jensen and Rod Frehlich have turned this pastime into a powerful instrument for measuring atmospheric conditions.

While kites have been employed for thousands of years for entertainment, their use for atmospheric research has come in the last two centuries. Around the turn of the twentieth century, near-daily kite flights were gathering measurements to build the first systematic study of the lower atmosphere. By collecting enough atmospheric data, CIRES hopes to be able to refine global weather pattern models and prediction techniques.

Today the work at CIRES is complementing other collection techniques such as balloons, satellites and aircraft. As early as 1749, Professor Alexander Wilson and student Thomas Melville, of the University of Edinburgh, Scotland, were using kites for lower atmosphere temperature measurements. Using simple equipment, thermometers attached to paper kites, they were able to get a rough estimate for the temperature profile of heights up to one thousand feet.

In 1752, Benjamin Franklin conducted his famous atmospheric electricity experiment. Franklin's materials were also quite simple, just a paper kite. Nearly a century later, in 1837, Admiral Black used kite born thermometers to help survey his Arctic expedition. By towing the kites by ship, heights of 1200 feet were reached, an amazing height for the time.

At this height, Black recorded an unexpected 8 degree Fahrenheit decrease in temperature relative to sea level. Similar ship and land based experiments were carried out throughout the world up until the early 1930's. The highlight being the single kite altitude record of 12,507 feet, by Blue Hill Observatory, outside of Boston, which still holds today.

The use of kites for atmospheric measurements declined in the 1930's due to the advent of aircraft and inexpensive balloons. In the late 1980's, the researchers at CIRES rescued the kite technology when faced with a special problem. The CIRES researchers were studying the fair weather global electric field over Christmas Island, in the south Pacific Ocean.

In order to quantify the global electric field's influence on lighting conditions accurate data was necessary. To obtain the best measurements, a series of electrometers needed to be placed at height intervals over the lower atmosphere. Tethered balloons could only be used for the first kilometer at best, necessitating aircraft.

However, aircraft were not able to collect the sensitive data needed. In addition, un-tethered balloons, with their difficulty in recovering, could not be used due to the cost of the equipment. What the CIRES team needed was a stable stationary anchor point, several kilometers up. To fulfill this need, CIRES developed the WindTRAM system.

The WindTRAM is a basic system consisting of two parts; a large parafoil kite and a tram to go up and down the kite string. The tram is connected to the kevlar string, and by using its large airfoil wings it can traverse the length of the string. Any desired instrumentation payloads are then carried by the WindTRAM. Having the flexibility to stop at any height, measurements can be taken at varying altitudes.

This feature is very useful when a profile over different altitudes is needed. Past kite based instrumentation had one major drawback being that the kite launching procedure is time consuming. Ground wind conditions must be strong and stable so the parafoil shape can catch the wind. The WindTRAM is a preferable system because instrument payloads can be brought back to the ground for adjustment without having to lower the kite.

To give the WindTRAM the ability to stop at different heights and fly up and down the tether, wing position is controlled by remote control. To aid downward flight, an inverted airfoil wing is used to provide lift. The WindTRAM is designed to act as a crane, but also carries several of its own instruments.

These include a tachometer (to measure speed along the line), an anemometer (to measure relative wind speed), a tilt sensor (to measure the tether angle), a potentiometer (to measure wing angle relative to the tether), and a pressure sensor (to measure altitude). For additional sensors, payloads are carried, but their weights are restricted to 3 to10 kilograms.

Additional lift can be achieved by adding wing extensions, thus increasing wing area. However, large payloads are less desirable as payload capabilities are strongly dependent on local wind conditions. Some of the current instruments designed by CIRES to be lifted by the WindTRAM include, an ozone sensor to detect ozone gas levels and a thermocouple probe to measure micro changes in temperature.

Payloads from other organizations may be used so long as the meet the weight and size requirements. The Cooperative Institute for Research in the Environmental Sciences has shown great promise with the WindTRAM kite born instrument system. Examples of data collected prove that the WindTRAM will have a bright future in measuring the world's atmospheric conditions for years to come.

Using the WindTRAM measurements have been recorded over periods of days, time spans previously unattainable. The only current limitation for time aloft is the lifetime of the onboard battery packs. Alternative power sources such as wind or solar power that will extend time aloft indefinitely are currently being developed. Once these obstacles are overcome the only thing that can hold the CIRES researchers back is the need for good wind conditions.

So as long as the wind is blowing, the WindTRAM will continue to yield unprecedented results.

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