Aerospace and Electronic Systems Magazine December 2017 - 38

Feature Article:

DOI. No. 10.1109/MAES.2017.170025

High-Latitude Application of Three-Dimensional Overthe-Horizon Radar
Ryan J. Riddolls, Defence Research and Development Canada, Ottawa, Ontario,
Canada

INTRODUCTION

In 1972, a collaboration between the U.S. Air Force and the
Canadian Defence Research Board led to the installation of the
The Earth's geomagnetic poles represent the axis of a dipole field
Polar Cap III OTHR in Hall Beach, Northwest Territories, Canada,
of best fit to the Earth's true magnetic field. Canada currently hosts
and a second receive site in Cambridge Bay [3]. As suggested by
the Geomagnetic North Pole on Ellesmere Island, near 80 N 75 W.
the project name, the aim was to determine OTHR performance at
In the vicinity of the geomagnetic pole, the magnetic field lines of
the location of the Earth's polar cap. There was a hypothesis that
the Earth extend many Earth radii into space and interact with the
auroral clutter would be absent in the polar cap, because there was
solar wind, leading to particle precipitation and horizontal ionono visible indication of disturbed plasma. This radar would go on
spheric plasma drifts. Particle precipitation produces the visible
to provide, however, some of the earliest observations of largeAurora Borealis in the area shown as green in Figure 1, which we
scale horizontal plasma drifts within the polar cap. These drifts
denote the auroral oval. North of the auroral oval is the region of
transport plasma irregularities from the auroral oval into the polar
the polar cap, where the solar wind drives horizontal plasma drifts,
cap without any visible wavelength indications, leading to radar
shown by the red contours in Figure 1. Previous over-theclutter throughout the polar cap. Nowadays, this radar
horizon radar (OTHR) experiments have looked at
clutter is used to image the plasma drift, via the
operation in both the auroral oval and the polar
Super Dual Auroral Radar Network (Supercap.
DARN) [4]. The SuperDARN radars obIn 1971, the Rome Air Development
tain vector velocity measurements of the
Center installed the northward-pointdrifts by collecting radar echoes from
ing Polar Fox II OTHR in Caribou,
the plasma irregularities at two look
Maine, along with transponders in
angles.
Narsarsuaq and Thule, Greenland,
The frequent presence of backand Keflavik, Iceland [1]. The aim
scatter clutter within both the auwas to determine OTHR perforroral oval and polar cap and the
mance at the location of the auroabsence of viable mitigations, led
ral oval. It was expected that there
to decisions during the U.S. Air
would be radar backscatter clutter
Force over-the-horizon backscatfrom plasma irregularities in the
ter (OTH-B) radar acquisition proauroral oval. The clutter levels and
gram to restrict the OTHR field of
occurrence patterns were meaview to the east, south, and west.
sured during the experiments and
For north-looking surveillance, a
were later compiled into an aurotrip wire line of microwave radars,
ral clutter model [2]. It was well
called the North Warning System
Figure 1.
recognized that without any miti(NWS), was deployed along the
Location of Geomagnetic North Pole, auroral oval, and polar
gation measures, the clutter would
cap plasma drift.
70th parallel in Canada in 1985.
impact the detection of targets.
After the end of the Cold War in
1991, the OTH-B program was suspended, and the operation of
the NWS was turned over to the Canadian Armed Forces.
Author's current address: Defence Research and DevelopIn 2006, Canada started to revisit the high-latitude OTHR surment Canada, 3701 Carling Avenue, Ottawa, Ontario K1A 0Z4
veillance problem in light of technical advances in OTHR techCanada, E-mail: (ryan.riddolls@drdc-rddc.gc.ca).
nology [5]. Specifically, it was the realization that next-generation
Manuscript received January 26, 2017, revised June 23, 2017,
OTHR techniques being proposed for midlatitude systems, such as
and ready for publication August 31, 2017.
planar antenna arrays and multiple-input multiple-output methods
Review handled by D. O'Hagan.
[6], [7], could be applied to attack the unique problems of high-lat0885/8985/17/$26.00 © 2017 Crown
36

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DECEMBER 2017

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