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We report the performance of a low-power one-way travel-time inverted ultra-short baseline (OWTTIUSBL) system designed specifically for use on long endurance autonomous underwater vehicles (AUVs), as deployed during trials in late 2020. The system consists of a WHOI Micromodem-2 as the acoustic processing core coupled with a MEMS attitude and heading reference system (AHRS) and bespoke four-channel array. At low tilts our system provides standalone position fixes to better than ±5° azimuth at slant ranges in excess of 1500 m. The system consumes 1.1 W when active and is capable of entering a low-power 10 mW sleep mode sufficient to maintain its time base. These specifications are based on data collected with the device lowered from a vessel and excited by a mobile source on the vessel’s small boat. We further present preliminary results from the device as installed on a Seaglider that show the potential for improved low-power navigation insensitive to temporal or depth-dependent variations in current profile. 

This paper reviews the scientific motivation and challenges, development, and use of underwater robotic vehicles designed for use in ice-covered waters, with special attention paid to the navigation systems employed for under-ice deployments. Scientific needs for routine access under fixed and moving ice by underwater robotic vehicles are reviewed in the contexts of geology and geophysics, biology, sea ice and climate, ice shelves, and seafloor mapping. The challenges of under-ice vehicle design and navigation are summarized. The paper reviews all known under-ice robotic vehicles and their associated navigation systems, categorizing them by vehicle type (tethered, untethered, hybrid, and glider) and by the type of ice they were designed for (fixed glacial or sea ice and moving sea ice). 

Vast and diverse microbial communities exist within the ocean. To better understand the global influence of these microorganisms on Earth’s climate, we developed a robot capable of sampling dissolved and particulate seawater biochemistry across ocean basins while still capturing the fine-scale biogeochemical processes therein. Carbon and other nutrients are acquired and released by marine microorganisms as they build and break down organic matter. The scale of the ocean makes these processes globally relevant and, at the same time, challenging to fully characterize. Microbial community composition and ocean biochemistry vary across multiple physical scales up to that of the ocean basins. Other autonomous underwater vehicles are optimized for moving continuously and, primarily, horizontally through the ocean. In contrast,Clio, the robot that we describe, is designed to efficiently and precisely move vertically through the ocean, drift laterally in a Lagrangian manner to better observe water masses, and integrate with research vessel operations to map large horizontal scales to a depth of 6000 meters. We present results that show howClioconducts high-resolution sensor surveys and sample return missions, including a mapping of 1144 kilometers of the Sargasso Sea to a depth of 1000 meters. We further show how the samples obtain filtered biomass from seawater that enable genomic and proteomic measurements not possible through in situ sensing. These results demonstrate a robotic oceanography approach for global-scale surveys of ocean biochemistry.