Smaller is better for Arctic radar scattering facility

In converting from a set of cumbersome radar dishes to an agile arrangement of dipoles, the European Incoherent Scatter Scientific Association (EISCAT) is angling to study the atmosphere at the highest spatial and temporal resolutions to date.

Construction on EISCAT_3D, as the project is called, is to begin next year, pending funding from the six partners. Norway and Sweden each plan to pony up about a quarter of the €130 million ($170 million) tab, with Finland, the UK, China, and Japan covering the rest. If all goes as planned, observations could start in 2016, with the full EISCAT_3D up and running in 2019. Significantly, the project has the stamp of approval of the European roadmap for large scientific infrastructure.

The current EISCAT mainland transmitters send up UHF and VHF electromagnetic waves—around 931 MHz and 224 MHz, respectively—that scatter off electrons at altitudes from about 50 km to 2000 km. By analyzing the signals that return, scientists learn about the densities, temperatures, composition, and dynamics of the ionospheric plasma. The two huge transmitters are located outside of Tromsø, Norway, with receivers there and in Kiruna, Sweden, and Sodankylä, Finland. Vectors for ion motion can be obtained by combining observations from multiple sites.

With EISCAT_3D, the receivers and transmitters would be replaced by arrays of 10 000 crossed dipoles. Controlled electronically rather than mechanically, the arrays make possible different beam shapes, multiple beams, and rapid steering. “Instead of profiles along the line of sight,” explains Cesar La Hoz, project leader for Norway, “you will get volumetric data.” The software steering will also allow the facility to “run 24/7,” says EISCAT director Craig Heinselman. “The solid-state phased array technology can be on all the time. You are not killing the energy budget. And when the system sees something, it will be able to react. Or you can set up campaigns with optical imagers and other instruments.”

Temporal resolution of EISCAT_3D will be improved over EISCAT’s, from a few seconds to a fraction of a second, and spatial resolution will go from a few kilometers to about 100 meters. Scientists will be able to measure smaller, nonhomogeneous structures and rapid-firing, time-varying processes, many of them related to the aurora, says La Hoz. “We know the aurora is produced by accelerated electrons” from the solar wind interacting with the ionosphere, he says. “But we don’t know the acceleration mechanisms. This is fundamental. The universe is full of plasma.”

Heinselman ticks off “noctilucent clouds, polar mesospheric summer echoes, wind systems at stratospheric altitudes—which are implicated in ozone holes over the Antarctic,” as phenomena that EISCAT_3D could shed light on. “One big open question,” he adds, “is how much energy and momentum are being dumped into the atmosphere by the solar wind? And where and when are they being deposited?” The upgraded radar facility will also be used to keep tabs on space debris, detect small meteors, and help predict space weather.

In a separate EISCAT development, China is planning to add a 50-meter dish to the collaboration on the Arctic archipelago of Svalbard, which is already home to two EISCAT antennas—one 32 meters and the other 42 meters—that both receive and transmit radar signals. In addition to studying the atmosphere, the new dish will be used to conduct very long baseline interferometry, map the Moon, and track space debris.