Constructing a new polar radar network A next-generation phased array technology radar promises a breakthrough in the way environmental scientists monitor changes in the Earth's atmosphere. Digital Economy © Thinkstock Measuring and understanding man-made changes to Earth is a key focus for environmental scientists. Most of these changes cannot be seen with the naked eye or on our planet's surface. They need to be studied in the Earth's upper atmosphere and the surrounding interplanetary space known as geospace. This region has been studied for more than 30 years using incoherent scatter radars, remotely sensing geospace. The European Incoherent Scatter Scientific Association (EISCAT) operates radar sites in Scandinavia and the Norwegian archipelagos. However, radar technology has advanced significantly since their construction. EISCAT and partners initiated the EU-funded EISCAT_3D_2 (A European three-dimensional imaging radar for atmospheric and geospace research (Preparatory Phase)) project to prepare the way for an improved model of the previous radar system. The so-called EISCAT_3D will work at a new frequency and exploit phased array technology to provide observations well beyond what is currently available to the scientific community. The new radar system will address the needs of modern society to understand the geospace environment as a system and to forecast effects caused by space weather variations. EISCAT_3D is an improvement on traditional incoherent scatter radars that are not able to operate continuously as measuring geophysical instruments. It will consist of multiple large fields of antennas, known as phased arrays, some of which will be equipped to transmit as well as receive signals. EISCAT scientists have already designed at least five radar sites, one of which will be the central site and include a transmitter. The radar sites will be spread across the northern regions of Finland, Norway and Sweden, and located within the auroral oval. These locations offer unique research opportunities as the couplings of the solar wind to the magnetosphere, ionosphere and atmosphere are strongest there. EISCAT_3D_2 represented the preparatory phase that was scheduled to run until 2014. The project team worked on resolving issues blocking the path to beginning construction of the new radar. Among others, the site selection and frequency allocation were finalised taking into account scientific and environmental constraints. The optimal antenna array layout and receiver configuration was recommended based on simulation work. The assembly of prototypes of key antenna elements allowed scientists to determine their reliability and cost effectiveness. Furthermore, industrial partners were identified for the construction of relevant components. In addition to acquiring hardware components, dedicated signal processing techniques have been developed. However, handling the large amounts of data expected to be collected (several trillion bytes per second) will require close collaboration with regional and global e-infrastructures for the environment. EISCAT, through its participation in numerous consortia, will facilitate the sharing of data with other geospace observatories and environmental research entities. In the next construction phase, all computing, storage and networking facilities will be put in place, and the radar system will go through strict testing. The culmination of all work in EISCAT_3D_2 and the construction phase will ultimately result in the project entering its operational phase. The new EISCAT_3D will make significant contributions to identifying and monitoring solar-terrestrial interdependencies. Keywords Phased array, upper atmosphere, geospace, incoherent scatter radars, EISCAT
