It has not been feasible to quantify this risk, however, as systematic data are lacking on the actual amount of rays and the charged particles and neutrons they create in Earth's atmosphere that are encountered during typical flights. Researchers have now begun collecting that information, thanks to a newly developed instrument, the Low Linear-Energy-Transfer Radiation Spectrometer (LoLRS).

The need to know the precise level of cosmic and solar radiation along air routes has become more acute, as recent generations of commercial aircraft use "fly-by-wire" control systems, managed by on-board computers, which are subject to damage by high radiation levels. Future aircraft will employ even more sensitive technologies, and will therefore be more susceptible to damage.

"This substantially increases the need to improve the definition of the atmospheric radiation field as a function of location and time, and to reduce the significant uncertainties associated with present day predictions," says Epaminondas G. Stassinopoulos of NASA's Goddard Space Flight Center, lead researcher of the project. Their report is one of the first papers published in the American Geophysical Union's new journal, Space Weather.

With the cooperation of Evergreen International Airlines, which flies long distance cargo routes, LoLRS instruments have been flown aboard Boeing 747s across the Atlantic and Pacific Oceans, across the United States, the length of Africa, and, more recently, in the Arctic.

Repetitive flights over the same routes have enabled the scientists to begin studying the long term effects of solar and environmental influences at aviation altitudes.

During each flight, every change in the plane's altitude and direction is recorded, because such factors as weather and traffic affect the exact route and altitude of a flight, regardless of the original flight plan. It is essential for the researchers to know the precise location, altitude, and time of each radiation measurement.

Ultimately, Stassinopoulos and his colleagues hope to produce global maps that reflect the dynamic nature of the atmospheric radiation field. This will require the collection of a large quantity of data, and the researchers are therefore developing techniques for analyzing the collected information. The research will involve both aircraft and high altitude balloons that circle the polar regions for long periods.

The preliminary tests have confirmed that doses of radiation from cosmic rays and the particles they create are more intense at higher altitudes and at higher latitudes; that is, they are strongest in the Arctic and Antarctic regions.

This is particularly true during solar storms, during which large quantities of charged particles reach Earth's atmosphere. The scientists hope that the new study will go far beyond previous research in this field and facilitate the construction of models that would be of real use for planners of aircraft routes.

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