Abstract
We present control policies for use with a modified autonomous underwater glider that are intended to enable remote launch/recovery and long-range unattended survey of the Arctic's marginal ice zone (MIZ). This region of the Arctic is poorly characterized but critical to the dynamics of ice advance and retreat. Due to the high cost of operating support vessels in the Arctic, the proposed glider architecture minimizes external infrastructure requirements for navigation and mission updates to brief and infrequent satellite updates on the order of once per day. This is possible through intelligent power management in combination with hybrid propulsion, adaptive velocity control, and dynamic depth band selection based on real-time environmental state estimation. We examine the energy savings, range improvements, decreased communication requirements, and temporal consistency that can be attained with the proposed glider architecture and control policies based on preliminary field data, and we discuss a future MIZ survey mission concept in the Arctic. Although the sensing and control policies presented here focus on under ice missions with an unattended underwater glider, they are hardware independent and are transferable to other robotic vehicle classes, including in aerial and space domains.
Highlights
The Arctic is the most rapidly warming region on Earth and over the past several decades these rising temperatures have had a substantial impact on the region’s seasonal sea-ice cover and volume (Serreze and Barry, 2011; Stammerjohn et al, 2012)
The methods and policies proposed here are extensible to many classes of autonomous underwater vehicles and mission scenarios, we focus on unattended subsea observation of the marginal ice zone (MIZ) during seasonal advance and retreat because its associated dynamics are difficult to observe with conventional technologies
Our focus on active management of onboard resources centers principally on energy efficiency for improving the overall performance of Polar Sentinel (Figure 2), a hybrid glider with 10 W folding thruster [Slocum G3 electric, Teledyne Webb Research], equipped with a 600 kHz phased array Doppler velocity log (DVL) [Pathfinder, Teledyne RDI], 700 kHz Mechanically Scanning Imaging Sonar (MSIS) [Micron, Tritech] housed within a modified nosecone, a payload Conductivity, Temperature, and Depth (CTD) sensor [GPCTD, Sea-Bird Scientific], and an environmental state estimator and continuous replanner operating on an embedded single board computer [Pi-Zero, Raspberry Pi], referred to as the Backseat Driver (BSD) computer
Summary
The Arctic is the most rapidly warming region on Earth and over the past several decades these rising temperatures have had a substantial impact on the region’s seasonal sea-ice cover and volume (Serreze and Barry, 2011; Stammerjohn et al, 2012). Diminished sea-ice volume results in diminished latent heat thermal buffering capacity, which will further accelerate warming of the Earth’s oceans (Jackson et al, 2012; Jeffries et al, 2013; Horvat and Tziperman, 2015). It is critical to accurately understand Arctic sea ice inventory. In addition to rising temperatures, positive feedback mechanisms of albedo (Curry et al, 1995) and momentum transfer (Zippel and Thomson, 2016) are causing the decline of Arctic sea-ice to accelerate. Sea-ice, and the snow settling on top of sea-ice, has a characteristic albedo that is among the highest of all natural materials found
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