The Value and Importance of Ionospheric Research
Background
In 1864, a Scottish mathematician named James Clerk Maxwell published a remarkable paper
describing the means by which a wave consisting of electric and magnetic fields could
propagate (or travel) from one place to another. Maxwell's theory of electromagnetic (EM)
radiation was eventually proven correct by the German physicist, Heinrich Hertz in the
late 1880's in a series of careful laboratory experiments.
It was not until the last decade of the 19th century that an Italian scientist named
Guglielmo Marconi converted these theories and laboratory experiments into the first
practical wireless telegraph system for which he was granted a British patent. In 1899,
Marconi demonstrated his wireless communication technique across the English Channel.
In a landmark experiment on December 12, 1901, Marconi, who is often called the "Father
of Wireless," demonstrated transatlantic communication by receiving a signal in St. John's
Newfoundland that had been sent from Cornwall, England. Because of his pioneering work
in the use of electromagnetic radiation for radio communications, Marconi was awarded
the Nobel Prize in physics in 1909.
Figure 1. Areas in the light blue region are within the radio
"Line of Sight" (LOS). The receiving antenna is in the shadow region (SR) and
cannot receive a signal directly from the transmitter.
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Marconi's famous experiment showed the way toward world wide communication, but it
also raised a serious scientific dilemma. Up to this point, it had been assumed that
electromagnetic radiation traveled in straight lines in a manner similar to light
waves. If this were true, the maximum possible communication distance would be determined
by the geometry of the path as shown in Figure 1 to the left. The radio signal would be
heard up to the point where some intervening object blocked it. If there were no objects
in the path, the maximum distance would be determined by the tranmitter and receiver
antenna heights and by the bulge (or curvature) of the earth. Drawing from light as an
analogy, this distance is often called the "Line-of-Sight" (LOS) distance. In Marconi's
transatlantic demonstration, something different was happening to cause the radio waves
to apparently bend around the Earth's curvature so that the communication signals from
England could be heard over such an unprecedented distance.
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Figure 2. A conductive region at high altitude would "reflect"
radio signals that reached it and return them to Earth.
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In 1902, Oliver Heaviside and Arthur Kennelly each independently proposed that a
conducting layer existed in the upper atmosphere that would allow a transmitted EM
signal to be reflected back toward the Earth. Up to this time, there was no direct
evidence of such a region and little was known about the physical or electrical properties
of the Earth's upper atmosphere. If such a conductive layer existed, it would permit a
dramatic extension of the "Line-of-Sight" limitation to radio communication as shown in
Figure 2 to the left. During the mid-1920's, the invention of the ionosonde (an
instrument that is an important part of the HAARP diagnostic
suite) allowed direct observation of the ionosphere and permitted the first scientific
study of its characteristics and variability and its effect on radio waves.
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The excitement of Marconi's transatlantic demonstration inspired numerous private and
commercial experiments to determine the ultimate capabilities of this newly discovered
resource, the ionosphere. Among the most important early experiments were those conducted
by radio amateurs who showed the value of the so-called high frequencies above 2 MHz for
long distance propagation using the ionosphere.
The Importance of Ionospheric Research
Although our society has learned to use the properties of the ionosphere in many beneficial
ways over the last century, there is still a great deal to learn about its physics, its
chemical makeup and its dynamic response to solar influence. The upper portions of the
ionosphere can be studied to some extent with satellites but the lower levels are below
orbital altitudes while still too high to be studied using instruments carried by balloons
or high flying aircraft. Much of the current theory is inferred by observing the ionosphere's
effect on communication systems. In addition, some very useful information has been obtained
using rockets (for example, from the Poker Flat
Research Range near Fairbanks, AK). Active ionospheric research facilities, like HAARP,
have provided detailed information that could not be obtained in any other way, about the
dynamics and responses of the plasma making up the ionosphere. Incoherent Scatter Radars
(ISRs), such as the one that will be built at the HAARP observatory, can study from the
ground, small scale structures in the ionosphere to nearly the degree that an instrument
in the layer could provide.
The ionosphere affects our modern society in many ways. International broadcasters such as
the Voice of America (VOA) and the British Broadcasting Corporation (BBC) still use the
ionosphere to reflect radio signals back toward the Earth so that their entertainment
and information programs can be heard around the world. The ionosphere provides long range
capabilities for commercial ship-to-shore communications, for trans-oceanic aircraft links,
and for military communication and surveillance systems. The sun has a dominant effect on
the ionosphere and solar events such as flares or coronal mass ejections can lead to worldwide
communication "blackouts" on the short wave bands. We have created an
Example Page with data from a communications blackout that occurred
on August 3, 1997 showing how the instruments at the HAARP observatory can be used to study
the underlying physics of these telecommunication disruptions.
Signals transmitted to and from satellites for communication and navigation purposes must pass
through the ionosphere. Ionospheric irregularities, most common at equatorial latitudes
(although they can occur anywhere), can have a major impact on system performance and
reliability, and commercial satellite designers need to account for their effects.
In the Auroral latitudes, the ionosphere carries a current that may reach magnitudes up to or
beyond a million amperes. This current, which is called the auroral electrojet, can change
in dramatic ways under solar influence, and, when it does, currents can be induced in long
terrestrial conductors like power lines and pipe lines. While such effects found in nature
cannot be reproduced by active ionospheric research, the sensitive instruments at observatories
like HAARP can follow the progress of natural magnetic storms and provide insight into the
physical mechanisms at work in the ionosphere.
To varying degrees, the ionosphere is a plasma, the most common form of matter in the universe,
often called the fourth state of matter. Plasmas do not exist naturally on the Earth's surface,
and they are difficult to contain for laboratory study. Many current active ionospheric
research programs are efforts to improve our understanding of this type of matter by studying
the ionosphere, the closest naturally occurring plasma.
Recently, it has become possible to produce computer simulations of ionospheric processes. The
development of computer visualizations have allowed us to see and appreciate the enormous
variability and turbulence that occurs in the ionosphere during a major solar geomagnetic
storm and the resultant effects that can impact radio communication and navigation systems.
Active ionospheric research facilities like HAARP attempt to produce small temporary changes
in a limited region directly over the facility which, in no way, compare to the worldwide
events frequently caused by the sun. But the extraordinary suite of sensitive observational
instruments installed at observatories like HAARP permit a detailed and comprehensive
correlation with the induced effects, resulting in new insights into the ways the ionosphere
responds to a much wider variety of natural conditions.
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