What science will EISCAT_3D enable?
The EISCAT_3D radar system will provide a thirty-year update to EISCAT’s existing mainland facilities, exploiting the capabilities of state-of-the-art electronics, networking, storage and computing. In doing so, it will outstrip the capabilities of any such radar operating in the world and become the centrepiece of the international network of instruments monitoring the Earth’s upper atmosphere and space environment in the first half of the twenty-first century.
EISCAT_3D combines five key attributes which have never before been available together in a single radar:
Volumetric imaging and tracking
The use of advanced beam-forming technology allows the beam direction to be switched in milliseconds, rather than the minutes which it can take to re-position dish-based radars. This allows very wide spatial coverage to be obtained, by interleaving multiple beam directions to carry out quasi-simultaneous volumetric imaging. It also allows objects such as satellites and space debris to be tracked across the sky, which cannot be done by the current EISCAT radars. At the passive sites, the design allows for five simultaneous beams at full bandwidth, rising to over twenty beams if the bandwidth is limited to the ion line, allowing the whole range of the transmitted beam to be imaged from each passive site, using holographic radar techniques.
Interferometric imaging
EISCAT_3D has a modular configuration, which allows an active array to be split into smaller elements to be used for aperture synthesis imaging. The result will be an entirely new data product, consisting of range-dependent images of small sub-beamwidth scale structures, with sizes down to 20 m. All of the EISCAT_3D data will be tested continuously for the presence of such structures, so that when they appear the data can be diverted to specialised processing to determine their shape and location.
Multistatic configuration
EISCAT_3D will be the first phased array incoherent scatter radar to use a multistatic configuration. The EISCAT_3D Design Study envisaged five radar sites, consisting of two pairs located around 120km and 250km from the active site respectively, on baselines running East and South from the active core. This provides an optimal geometry for calculation of vector velocities in the middle and upper atmosphere.
Greatly improved sensitivity
The gain of the EISCAT_3D antennas and the large size of the active site arrays will deliver an enormous increase in the figure-of-merit relative to any of EISCAT’s existing radars. An active site of 5,000 elements would already exceed the performance of the current EISCAT VHF system, while an active site comprising 16,000 elements, as suggested in the EISCAT_3D Design Study, will exceed the sensitivity of the present VHF radar by an order of magnitude.
Transmitter flexibility
Each transmitter unit will have its own signal generator, allowing the generation and transmission of arbitrary waveforms, limited only by the available transmission bandwidth and spectrum mask as allocated by the respective frequency management authorities. This unique innovation allows the implementation of all currently used and envisaged modulation schemes and antenna codings (such as polyphase alternating codes, array tapering, orbital angular momentum beams) and also provides the possibility to adopt any kind of future code. In addition, it will allow advanced clutter mitigation strategies such as adaptive null steering and null shaping.
EISCAT_3D is designed for year-round continuous operation, with the passive sites operating unattended. Automated systems will be used to control and monitor the radar operations and undertake the data handling, exploiting the new capabilities in high-speed networking, high performance computing and large volume data storage now available in the Nordic region. Intelligent scheduling algorithms will allow multiple experimental modes to be run in parallel, with experiments being interchanged automatically to exploit better the changing geophysical conditions, while the data handling system is designed to preserve the lowest level data for as long as practical, retaining all available information so that it can be re-processed in the optimum way to extract the most scientific value from each observation. No radar presently operating has such advanced capabilities for flexible and autonomous operation.
Because phased array radars are inherently modular, the system can, in principle, be scaled to whatever size is needed to deliver the scientific goals, either by increasing the size (and hence the sensitivity) of each site, or adding more sites to increase the spatial coverage of the system. Our ultimate aspiration is to implement a system with multiple active sites, capable of volumetrically imaging the whole region of ionosphere above Northern Scandinavia, and even extending into other neighbouring territories. This would obviously involve a much larger facility than the one aimed for here and hence its implementation will require additional technical work to ensure that the EISCAT_3D design remains sufficiently flexible for the system to be extended.