Stefano Suman

Influence of ice thickness and surface properties on light transmission through Arctic sea ice

Abstract The observed changes in physical properties of sea ice such as decreased thickness and increased melt pond cover severely impact the energy budget of Arctic sea ice. Increased light transmission leads to increased deposition of solar energy in the upper ocean and thus plays a crucial role for amount and timing of sea‐ice‐melt and under‐ice primary production. Recent developments in underwater technology provide new opportunities to study light transmission below the largely inaccessible underside of sea ice. We measured spectral under‐ice radiance and irradiance using the new Nereid Under‐Ice (NUI) underwater robotic vehicle, during a cruise of the R/V Polarstern to 83°N 6°W in the Arctic Ocean in July 2014. NUI is a next generation hybrid remotely operated vehicle (H‐ROV) designed for both remotely piloted and autonomous surveys underneath land‐fast and moving sea ice. Here we present results from one of the first comprehensive scientific dives of NUI employing its interdisciplinary sensor suite. We combine under‐ice optical measurements with three dimensional under‐ice topography (multibeam sonar) and aerial images of the surface conditions. We investigate the influence of spatially varying ice‐thickness and surface properties on the spatial variability of light transmittance during summer. Our results show that surface properties such as melt ponds dominate the spatial distribution of the under‐ice light field on small scales (<1000 m2), while sea ice‐thickness is the most important predictor for light transmission on larger scales. In addition, we propose the use of an algorithm to obtain histograms of light transmission from distributions of sea ice thickness and surface albedo.

A long term vision for long-range ship-free deep ocean operations: Persistent presence through coordination of Autonomous Surface Vehicles and Autonomous Underwater Vehicles

We outline a vision for persistent and/or long-range seafloor exploration and monitoring utilizing autonomous surface vessels (ASVs) and autonomous underwater vehicles (AUVs) to conduct coordinated autonomous surveys. Three types of surveys are envisioned: a) Autonomous tending of deep-diving AUVs: deployed from a research vessel, the ASV would act as a force-multiplier, watching over the AUV to provide operators and scientists with real-time data and re-tasking capabilities, while freeing the ship to conduct other over-the-side operations; b) Ridge-segment-scale (100 km) autonomous hydrothermal exploration: combined with conventional gliders or long-endurance AUVs, an ASV could tend a fleet of underwater assets equipped with low-power chemical sensors for mapping hydrothermal plumes and locating seafloor hydrothermal venting. Operators would control the system via satellite, such that a support ship would be needed only for initial deployment and final recovery 1-2 months later; and c) Basin-scale (10,000 km) autonomous surveys: a purpose-built autonomous surface vessel (mother-ship) with abilities up to and including autonomous deployment, recovery, and re-charge of subsea robots could explore or monitor the ocean and seafloor on the oceanic basin scale at a fraction of the cost of a global-class research vessel. In this paper we outline our long term conceptual vision, discuss some preliminary enabling technology developments that we have already achieved and set out a roadmap for progress anticipated over the next 2-3 years. We present an overview of the system architecture for autonomous tending along with some preliminary field work.

Toward ice-relative navigation of underwater robotic vehicles under moving sea ice: Experimental evaluation in the Arctic sea

This paper addresses the problem of ice-relative navigation of underwater robotic vehicles for oceanographic missions under moving sea ice. We define the ice-relative navigation problem and report a novel underwater robot vehicle, Nereid-UI, and its navigation system designed for under-ice oceanographic operations in ice-covered seas. The goal of Nereid-UI is to enable deployments in polar ocean regions traditionally considered difficult or impossible to access such as the ice-ocean interface in marginal ice zones, the water column of ice-covered seas, and the water column underlying ice shelves. This paper also reports the navigation results of Nereid-UIs first under-ice sea trials and science operations conducted under moving multi-year sea ice off the ice breaker Polarstern in the Arctic Ocean at 83° N 6° W - about 200 km NE of Greenland.

Design of Nereid-UI: A remotely operated underwater vehicle for oceanographic access under ice

This paper reports the development of a new underwater robotic vehicle, Nereid-UI, with the goal of being capable of deployments in polar ocean regions traditionally considered difficult or impossible to access such the ice-ocean interface in marginal ice zones, in the water column of ice-covered seas, and the seas underlying ice shelves. The vehicle employs a novel lightweight fiber-optic tether that will enable it to be deployed from a ship to attain standoff distances of up to 20 km from an ice-edge boundary under the real-time remote-control of its human operators, providing real-time high-resolution optical and acoustic imaging, environmental sensing and sampling, and, in the future, robotic intervention.

Integration and algorithm development for forward looking imaging sonars on hybrid and autonomous underwater robots

We present the integration of Blueviews P900 2D forward looking imaging sonars on two vehicles developed at WHOIs Deep Submergence Laboratory and the software to support them. For the Sentry AUV, a 6000m AUV, we developed a software system designed to run on low-power embedded Linux platforms that applies real-time computer vision techniques on acoustic returns intensity images to detect threats to vehicle safety. The system operates in the horizontal plane to simultaneously allow the collection of forward looking data that would be relevant to science. It can autonomously inform the vehicle control system to avoid threats that would otherwise result in a collision. Simultaneously, the system logs forward looking acoustic returns data for subsequent use in post processed science products. We developed a data pipeline that injects the post-processed vehicle navigation, with fused USBL and DVL navigation, in the sonar logs that the system generates and creates maps. We present results from the June 2014 R/V Atlantis expedition in the Gulf of Mexico. During this expedition we used Sentrys forward looking sonar to generate very high resolution maps of steep slope subsea escarpments sections. We also present results from our new HROV Nereid Under Ice (nUI) a 2000m depth rated fiber tethered ocean robot. First, deployed from the R/V Polarstern in a July 2014 expedition in the Arctic Ocean, nUI provided observations at the ice-sea interface. We developed software for the vehicles Blueview P900 forward looking imaging sonar to improve under-ice precision localization and science under drifting and fragmented sea ice. Navigation under through-ice GPS-referenced poles was improved by developing software that could track the vehicle-relative position of the poles. This enabled the generation of a high-accuracy, highfrequency floe-relative vehicle position estimate. Ice floe-relative vehicle velocity, when in open water surrounded by ice floes without DVL ice lock, could be estimated by applying optical flow computer vision techniques to forward looking sonar images.

Closed‐loop one‐way‐travel‐time navigation using low‐grade odometry for autonomous underwater vehicles

This paper extends the progress of single beacon one‐way‐travel‐time (OWTT) range measurements for constraining XY position for autonomous underwater vehicles (AUV). Traditional navigation algorithms have used OWTT measurements to constrain an inertial navigation system aided by a Doppler Velocity Log (DVL). These methodologies limit AUV applications to where DVL bottom‐lock is available as well as the necessity for expensive strap‐down sensors, such as the DVL. Thus, deep water, mid‐water column research has mostly been left untouched, and vehicles that need expensive strap‐down sensors restrict the possibility of using multiple AUVs to explore a certain area. This work presents a solution for accurate navigation and localization using a vehicles odometry determined by its dynamic model velocity and constrained by OWTT range measurements from a topside source beacon as well as other AUVs operating in proximity. We present a comparison of two navigation algorithms: an Extended Kalman Filter (EKF) and a Particle Filter(PF). Both of these algorithms also incorporate a water velocity bias estimator that further enhances the navigation accuracy and localization. Closed‐loop online field results on local waters as well as a real‐time implementation of two days field trials operating in Monterey Bay, California during the Keck Institute for Space Studies oceanographic research project prove the accuracy of this methodology with a root mean square error on the order of tens of meters compared to GPS position over a distance traveled of multiple kilometers.

The design and 200 day per year operation of the Autonomous Underwater Vehicle Sentry

The Autonomous Underwater Vehicle (AUV) Sentry has been in routine operation since 2009. It is a 6000m depth rated autonomous survey and sampling platform and is a “fly-away” system meaning it transports easily anywhere in the world to utilize vessels of opportunity. Sentry, initially a radical concept and experiment in AUV design, is now the AUV component of the National Deep Submergence Facility (NDSF) operated by Woods Hole Oceanographic Institution and as such spends up to 200 days per year in the field conducting operations for ocean scientists. Accordingly, Sentry must be reliable enough for a customer focused mission, but flexible enough to undertake previously unconceived missions on very short notice and with a high success rate. Field operations on a “Global Class” research vessel can easily exceed

Distribution and composition of thiotrophic mats in the hypoxic zone of the Black Sea (150-170m water depth, Crimea margin)

100,000 per day placing a premium on efficiency. Here we describe not only the vehicle Sentry, but also, the systems and infrastructure which supports Sentry and the unique nature of operations within the NDSF.