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  • Author or Editor: Mark A. Moline x
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Mark A. Moline and Oscar Schofield

Abstract

One of the key challenges in the development and implementation of ocean observatories is sustained observations over relevant temporal and spatial scales. Autonomous underwater vehicles (AUVs) have demonstrated their potential for synoptic spatial coverage of regions of scientific and strategic interest. The range and duration of these systems are limited, however, to the capabilities of a single charge. A few efforts have been made to develop docking systems for propeller-driven vehicles; however, these systems are not applicable for buoyancy-driven gliders and cannot be universally applied to AUVs. Here the authors introduce an alternative strategy for AUV docking, demonstrate feasibility with a series of field tests using a remotely operated vehicle (ROV) to remotely recover an AUV, and comment on the scalability within the framework of the evolving global ocean observatory initiatives. Implementation of simple strategies such as this has the potential to reduce the chronic problem of undersampling in the ocean and may facilitate addressing some outstanding scientific questions related to the ocean.

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Mark A. Moline, Kelly Benoit-Bird, David O’Gorman, and Ian C. Robbins

Abstract

Acoustic echo sounders designed to map and discriminate organisms in the water column have primarily been deployed on ships. Because of acoustic attenuation of higher frequencies used to detect and discriminate micronekton and nekton, this has effectively restricted the range of this information to the upper water column. In an effort to overcome these range limitations by reducing the distance between the transducer and the targets of interest, dual-frequency (38 and 120 kHz) split-beam echo sounders were integrated into a Remote Environmental Monitoring Units (REMUS) 600 autonomous underwater vehicle (AUV), effectively doubling the range of quantitative acoustic data into the mesopelagic zone (600–1200 m). Data from the first set of missions in a range of conditions revealed that the AUV provided a stable platform for the echo sounders and improved vertical and horizontal positional accuracy over echo sounders towed by ships. In comparison to hull-mounted echo sounders, elimination of ship noise and surface bubbles provided a 17- and 19-dBW decrease in the noise floor for the 38- and 120-kHz echo sounders, respectively, effectively increasing the sampling range by 30%–40%. The extended depth range also increased the resolution of the acoustic horizontal footprint from 37–40 to 0.6–3.7 m, enabling discrimination of individual targets at depth. Also developed here is novel onboard echo sounder data processing and autonomy to allow sampling not feasible in a surface ship or towed configuration. Taken together, these data demonstrate an effective new tool for examining the biology of animals in the mesopelagic zone (600–1200 m) in ways previously only possible in the upper ocean.

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Mark A. Moline, Shelley M. Blackwell, Chris von Alt, Ben Allen, Thomas Austin, James Case, Ned Forrester, Robert Goldsborough, Mike Purcell, and Roger Stokey

Abstract

In oceanography, there has been a growing emphasis on coastal regions, partially because of their inherent complexity, as well as the increasing acknowledgment of anthropogenic impacts. To improve understanding and characterization of coastal dynamics, there has been significant effort devoted to the development of autonomous systems that sample the ocean on relevant scales. Autonomous underwater vehicles (AUVs) are especially well suited for studies of the coastal ocean because they are able to provide near-synoptic spatial observations. These sampling platforms are beginning to transition from the engineering groups that developed and continue to improve them to the science user. With this transition comes novel applications of these vehicles to address new questions in coastal oceanography. Here, the relatively mature Remote Environmental Monitoring Units (REMUS) AUV system is described and assessed. Analysis of data, based on 37 missions and nearly 800 km of in-water operation, shows that the vehicle’s navigational error estimates were consistently less than 10 m, and error estimates of mission duration, distance, velocity, and power usage, once the vehicle was properly ballasted, were below 10%. An example of the transition to science is demonstrated in an experiment conducted in 2002 in Monterey Bay, California, where the vehicle was used to quantify critical horizontal length scales of variability. Length scales on the order of tens to hundreds of meters were found for the region within 25 km of the coastline, which has significant implications for designing proper sampling approaches and parameterizing model domains. Results also demonstrate the overall utility of the REMUS vehicle for use by coastal oceanographers.

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