Climate Research in the Polar Regions
Melting glaciers and ice sheets in the polar regions (Antarctica & Greenland) are increasingly contributing to global sea level rise. Climate models don’t yet adequately capture the true dynamics of these hard-to-measure geophysical wonders. One important technique is airborne radar sounding, which allows the imaging of large swaths of terrain underlying icesheets and glaciers; the shape of this underlying terrain, otherwise invisible to researchers, is a primary factor that governs how these bodies of ice respond to a warming climate and whether (and how fast) they move towards the ocean and disintegrate, contributing to sea level rise.
Radar measurements of glaciers that are rough, heavily crevassed, or contain large amounts of debris and water poses a particular challenge in radio glaciology. Water pockets scatter radar signals, which makes the underlying topography difficult to determine. Using multiple unmanned aerial systems (UASs) in a precisely controlled swarm can overcome these challenges, along with the use of tailored antenna beam orientations combined with synthetic and physical aperture processing methods.
UASs’ environmental footprints are much smaller than manned aircraft (and are generally more cost effective). In addition, they can stay in the air much longer than human pilots and can follow ground tracks with much higher precision, which is extremely important for glacier radar sounding and for developing synthetic aperture radar (SAR) models. These combined advantages are driving many within the earth science community to consider UASs as a preferred option over manned aircraft.
Vulcan Inc's philanthropic team with funding from the Paul G. Allen Family Foundation is supporting the University of Kansas's development of advanced radar systems for UAS platforms. The next generation of ice sheet models require fine-resolution data near the terminus of key glaciers; UAS swarms provide the best approach because of their ability to form large two-dimensional SARs.
A UAS platform called G1X was successfully tested during the 2013-14 Antarctic field season where performance of the radar and UAS technology was assessed.
The Yak-54 UAS on a test flight over the ice.
With their lack of depth perception and active distance measurements, swarming birds rely mainly on their visual perception of other birds to estimate proximity and adjust their flight path. This dynamic provides inspiration for the swarm algorithms under development by KU. The algorithms are tailored for leaderless and self-organizing large fixed-wing UASs with high inertia and high speed. In KU’s control algorithms, classical and proximity-based guidance logics are utilized.
Through the Foundation's support, two new radar-equipped G1X UASs are under development. These UASs will go through a series of flight test validations, incorporating lessons learned from the 2013-14 Antarctic mission. G1Xs are mid-wing, semi-autonomous, and high aspect ratio UASs that have been modified by the KU team for Earth and Science missions in polar region. The G1X UAS weighs 86 lbs with a 18.7-foot wingspan.
AT LEFT: Two compact UAS sounding radars (~2.5 kg) have been designed to operate at both 14 MHz and 35 MHz with approximately 80 W peak power, using only 20 W of average DC power and a 1.0 and 0.2 μsec pulse duration for the 14 and 35 MHz bands. Separate 14 and 35 MHz antennas were integrated into the aircraft structure. The radar systems were also modified to provide additional in-flight antenna characterization to validate antenna performance in the more representative free-space survey environment.
Three new UASs were instrumented to support research on the control of multi-agent fixed-wing UASs. Forty three UAS validation and verification flight tests were successfully conducted through February 2015. The 40% scale Yak-54 UAS (above) weighs 60 pounds with a 9.3-foot wingspan. One of the three, the Bird of Time UAS (below), is a glider that weighs less than 7 pounds with a wingspan of 9 feet.
The Bird of Time UAS glider.
The KU team came up with a novel approach to safely assess the bio-inspired proximity swarm and associated control algorithms. In this validation, an actual UAS flew autonomously with two virtual UASs. The validation successfully measured the sensitivity of a swarm of small UASs to external disturbances. Actual and virtual UASs held the formation in the presence of windshear, demonstrating the importance of flight control system robustness to external disturbances. The research team was thrilled to see their mathematical modeling and simulations successfully validated.
(Above) An actual UAS flew autonomously with two virtual UAS