EISCAT (European Incoherent Scattter) studies the interaction between the Sun and the Earth as revealed by disturbances in the magnetosphere and the ionised parts of the atmosphere (these interactions also give rise to the spectacular aurora, or Northern Lights). The radars are operated in both Common and Special Programme modes, depending on the particular research objective, and Special Programme time is accounted and distributed between the Associates according to rules which are published from time to time.

One EISCAT transmitter site is located close to the city of Tromsø, in Norway, and additional receiver stations are located in Sodankylä, Finland, and Kiruna, Sweden. See an animation that shows the basic operation. The EISCAT Headquarters are also located in Kiruna. 1996 the EISCAT Scientific Association constructed a second incoherent scatter radar facility, the EISCAT Svalbard Radar, near Longyearbyen on the island of Spitsbergen, far to the North of the Norwegian mainland.

The Incoherent Scatter Radar technique requires sophisticated technology and EISCAT engineers are constantly involved in upgrading the systems.

In addition to the incoherent scatter radars, EISCAT also operates an Ionospheric Heater facility at Ramfjordmoen (including a Dynasonde) to support various active plasma physics experiments in the high latitude ionosphere. 

SOURCE ARTICLE

SOURCE: EISCAT Tromsø Site

EISCAT New Home Page

The Heating facility is situated next to the UHF and VHF incoherent scatter radars. See the list of publications that have come out of this facility since its construction in 1979.

The Heater is used for ionospheric modification experiments applying high-power transmissions of high-frequency electro-magnetic waves to study plasma parameters in the ionosphere. The name Heating stems from the fact that these high power electromagnetic waves, which are transmitted into the ionosphre with high-gain atennas, heat the electrons and thus modify the plasma state. To create plasma turbulence, the transmitted frequencies have to be close to the plasma resonances, which are 4 to 8 MHz. 

SOURCE ARTICLE

Abstract

It is well known that the electric field of a high power HF wave transmitted into the ionosphere will interact with the free electrons in the plasma by causing them to oscillate at the same frequency as the transmitted wave, and then to re-emit other electromagnetic waves, with frequencies near the original wave, but with the power in the new emission being much weaker than the original. This effect is known as stimulated electromagnetic emission, or SEE. On 11 and 12 November 2001, high power HF radio wave heating experiments were carried out in the ionosphere above the EISCAT observatory near Tromsø, Norway. Optical observations revealed artificial aurora in the form of rings, which lasted for several seconds before collapsing into blobs, while at the same time descending in altitude, and then disappearing. During this experiment SEE were recorded on a traditional spectrum analyzer system; this can tell us information about the relationship between the auroral rings and the local electron gyrofrequency, and thus help to determine why the rings occur. The geometry of the rings suggests a dependence of the emissions to the angle with respect to the geomagnetic field, or possibly to the spatial gradient in the HF radio wave pump beam. An angular dependence in the artificial excitation of enhanced ion-acoustic and Langmuir waves has also been seen in incoherent scatter radar (ISR) observations. In an attempt to determine if such a dependence exists in SEE, an interferometric SEE system is being developed and will be described. ISR observes Langmuir turbulence and SEE is a result of upper hybrid turbulence, either of which may accelerate electrons and produce optical emissions. The combination of angle-sensitive SEE and ISR observations, along with other available measurements, will thus help to determine if the optical emissions are due primarily to one type of turbulence or to a combination of both.

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Figure 1 shows a schematic overview of ARIES. The signals from the two arms of the Mills Cross antenna array are fed into two separate Butler matrices, one for each arm. Each output of the Butler matrix forms one fan shaped beam. Figures 2 and 3 show one example of a fan beam formed by the Butler Matrix for the North-South arm and one example of a fan beam formed by the Butler Matrix for the East-West arm of the Mills Cross antenna array, respectively.

You can also watch an animated version of figure 1 or an animated version of figure 2. 

The final narrow beams (so-called pencil beams because of their pencil-like shape) are formed digitally by means of cross correlation. Cross correlation detects the signal that is common to the signal of two perpendicular fan shaped beams, and this common signal is the signal coming from the direction where these two fan beams intersect.

Thus by intersecting each fan beam from the North-South arm with each fan beam from the East-West arm, we get many pencil shaped narrow beams over the whole field of view. Figure 4 shows an example pencil beam, together with the two fan beams that were used to create this particular pencil beam. You can also watch a movie showing several pencil beams. 

Two perpendicular arms of 32 antennas each theoretically provide the same spatial resolution as a 32 by 32 filled antenna array. As the sidelobe performance of such a system is worse than that of a filled array, tapering reduces this resolution slightly. Still, a resolution at least equal to that of a 16 by 16 element filled antenna array is achievable, with only a quarter of the antenna elements that would be required to build a full 16 by 16 element phased array. 

Data from various prototype stages has been collected starting from 2002, and the current system with fully digital beamforming went live in March 2007.

You may be interested in downloading a PDF version of a poster on ARIES (3.5MB), or have look at the very-low-resolution bitmap preview (140KB).

See the following links for more information about ARIES:

• ARIES entry in our Riometers Database
• ARIES related publications as contained in our Publication Database