Under-ice Operations Research Articles

Evaluating the impact of intermediate and deep sound speed uncertainty in the Irminger Sea on acoustic situational awareness

High-resolution observations from moorings and transect data can provide new insights into ocean structures, their variability, and the downstream effects on acoustic operations. Previously, we established a framework to maintain optimal communication and navigation for small-scale, under-ice operations that focused on spatio-temporal variability in the upper water column and around an autonomous underwater vehicle. However, mid- and deep-water sound speed fidelity are crucial for larger operations that exploit convergence zone ranging. The Irminger Sea is a useful case study for understanding how sound speed uncertainty, whether from partial data or models, obscures the informational content from acoustics. Generally, the density gradient dominates the sound speed at depth. In the Irminger Sea, hydrographic variability comes from the advection of different water masses through the region at all depths and also from water mass modification by local air-sea interaction. Instead of a uniform gradient as a result of hydrostatic loading, a shifted gradient in the mid-water column and a negative gradient near the bottom are often observed in mooring and transect data. This talk presents initial results for understanding the impacts of the environment through the lens of impact on acoustic propagation. [Work supported by the Office of Naval Research]

Fast indicators for robust acoustic communication and navigation in a double-ducted polar environment

A floating ice-buoy system equipped with GPS and acoustic modems provided communication and navigation to a Bluefin 21 Autonomous Underwater Vehicle (AUV) for under-ice operations in the Beaufort Sea, in March 2020. Acoustic modems were placed above and below the “Beaufort Lens,” at 30 and 90 m, where a data- and model-based autonomy selected which depth to use for transmitting messages to the AUV. Similarly, the AUV ran a depth adaptive path planning behavior to maintain acoustic communications with the ice buoy modems. The untethered mission showed a non-diverging navigation solution with the average error roughly 0.1% of the total 11 km traveled. This talk will summarize key metrics introduced for automated, on-the-fly processing of acoustic packets to navigate within a reliable acoustic channel and minimize navigation error. [Supported by Office of Naval Research.]

Real-Time Flight Simulation of Hydrobatic AUVs Over the Full 0$^{\circ}$–360$^{\circ}$ Envelope

Hydrobatic AUVsare very agile, and can perform challenging maneuvers that encompass the full 0 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ}$</tex-math></inline-formula> –360 <inline-formula xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink"><tex-math notation="LaTeX">$^{\circ}$</tex-math></inline-formula> flight envelope. Such AUVs can be beneficial in novel use cases in ocean production, environmental sensing, and security, by enabling new capabilities for docking, inspection, or under-ice operations. To further explore their capabilities in such scenarios, it is crucial to be able to model their flight dynamics over the full envelope, which includes strong nonlinear effects and turbulence at high angles of attack. With accurate and efficient simulation models, new hydrobatic maneuvers can be generated and control strategies can be developed. Therefore, this article contributes with a strategy to perform efficient and accurate simulations of hydrobatic maneuvers in real time. A multifidelity hydrodynamic database is synthesized by combining analytical, semiempirical, and numerical methods, thereby capturing fluid forces and moments over the full envelope. A component buildup workflow is used to assemble a nonlinear flight dynamics model using lookup tables generated from the database. This simulation model is used to perform real-time simulations of advanced hydrobatic maneuvers. Simulation results show agreement with literature and experiment, and the simulator shows utility as a development tool in designing new maneuvers and control strategies.

A Bayesian Approach to Supervisory Risk Control of AUVs Applied to Under-Ice Operations

AbstractAutonomous underwater vehicles (AUVs) are efficient sensor-carrying platforms for mapping and monitoring undersea ice. However, under-ice operations impose demanding requirements to the system, as it must deal with uncertain and unstructured environments, harsh environmental conditions, and reduced capabilities of the navigational sensors. This paper proposes a Bayesian approach to supervisory risk control, with the objective of providing risk management capabilities to the control system. First, an altitude guidance law for following a contour of an ice surface via pitch control using measurements from a Doppler velocity log (DVL) is proposed. Furthermore, a Bayesian network (BN) for probabilistic reasoning over the current state of risk during the operation is developed. This is then extended to a decision network (DN) for autonomously adapting the behavior of the AUV in order to maximize the mission utility, subject to a constraint on the predicted risk from the risk model. The vehicle is thus able to autonomously adapt its behavior in response to its current belief about the risk. The goal of this work is to improve the AUV performance and likelihood of mission success. Results from a simulation study are presented in order to demonstrate the performance of the proposed method.

A very practical requirement: under-ice operations in the Canadian Arctic, 1960–1986

In May 1986 three American nuclear attack submarines (SSNs) surfaced at the North Pole. Their mission was routine – weapons tests, environmental studies, and data collection – similar to dozens of ...