OceanScout - Developing a compact, affordable, fleet-capable autonomous glider

Christopher E. Ordoñez Haibing Wang Eric Curtiss Anders Nesheim Hefring Engineering Hefring Engineering Hefring Engineering Nortek AS Boston, USA Boston, USA Boston, USA Rud, Norway [email protected] [email protected] [email protected] [email protected]

Thore Thoresen Sotiria Lampoudi Robert Craig Nortek AS Hefring Engineering Hefring Engineering Rud, Norway Boston, USA Boston, USA [email protected] [email protected] [email protected]

Abstract— Hefring Engineering has created OceanScout, a global ocean observation network requires participation from new underwater glider designed for compactness, simplicity and countries with fewer resources [12]. Efforts to counter this affordability. The vehicle is optimized for shelf & upper ocean imbalance and to improve representation are emerging. In China measurements, low personnel requirements, long duration researchers are developing ocean gliders to address inadequate deployments, and scalable multi-vehicle operations. Affordability regional ocean observations [13] with an estimated 50 active will facilitate adoption by new glider users, and scalability will gliders [8]. Sustained glider deployments are planned in South enable established groups to deploy greater numbers of vehicles. America to study El Niño [11]. Gliders periodically run transects This paper provides a review of the design and capabilities of the between Cape Verde and the African Coast [11]. But prototype OceanScout glider. disadvantaged research groups cannot afford the cost of Keywords — Underwater Glider; AUV; Ocean Observation; acquiring and the ongoing cost of ownership of existing gliders. New, low cost technologies for measuring essential ocean I. INTRODUCTION parameters are needed [14]. Autonomous underwater gliders perform long-duration Although glider usage is far from Henry Stommel’s 1989 ocean observations without support vessels, utilizing buoyancy vision for the year 2021 of many 100s of gliders operating change and hydrodynamic lift for energy efficient propulsion, simultaneously and continuously traversing all regions of the and relaying data via satellite-based communications. The globe [15], the Argo float sensor platform is widely used for technology has been in use and commercially available since the global coverage of open ocean observations. It is worth noting early 2000s [1] [2] [3]. Gliders have been successfully utilized the aspects of Argo floats that contribute to their ubiquity and for physical, chemical, and biological oceanography at many success: simplicity, robustness, affordability, and high value for spatiotemporal scales [4], in regional observatories [5], and are the community [16]. Compared to Argo floats, gliders are more currently contributing to critical discoveries [6] [7]. technologically complex, more expensive to acquire, significantly more complicated to operate and maintain, and Most glider activity is regional and originating from more more personnel intensive. economically developed countries (MEDCs) [8]. Recently, roughly half of the Glider, AUV, and ROV assets for ocean Hefring Engineering has created OceanScout, a new vehicle observations were in the USA, UK, and France alone [9]. designed to enable broader use of gliders, to engage new users, Approximately 420 of the estimated 500 active gliders are and to scale up glider operations. These objectives have located in or operated by North America, Europe, and Oceania informed the design of all aspects of the OceanScout system: [8]. Yet, even in regions and for phenomena that are considered mechanical, electrical, controls, interface, and remote operation. well-studied, observations may still be under-sampled for The first production model will include a CTD sensor. critical research. For instance, gliders can improve hurricane Subsequent models will be developed for specific applications intensity forecasting, but “significant errors still remain in data- (e.g. Passive Acoustic Monitoring) rather than attempting to assimilative ocean analyses due to existing observations being host many sensors on one vehicle. This will keep the scarce in space and time” [10]. complexity, demand for power, and costs from multiplying. In the coming decade growth in glider use is anticipated to OceanScout is currently under development by Hefring be modest and to occur primarily in the same regions as early Engineering. At the time of publication of this paper, the adoption [8] [11]. The implications of this imbalance are that prototype model is being assembled with trials scheduled for large areas of the ocean are under-observed, and many academic Autumn 2020. The production model is slated to be ready in voices are not contributing to the global conversation. A truly Autumn 2021.

Fig. 1. OceanScout Glider

OceanScout Design Principles: • Significantly less expensive; • Easy deployment & retrieval; • Multi-vehicle control without continuous human piloting; • Target specific applications, initially only CTD. Fig. 2. OceanScout General Arrangement (units in mm)

II. GLIDER MECHANICAL & PERFORMANCE OceanScout is a 200m depth rated, buoyancy-change driven, autonomous vehicle. OceanScout, like all gliders, uses a pump to change its buoyancy, shifts a weight to change pitch angle, and uses wings to translate upward (positive buoyancy) and downward (negative buoyancy) motions into forward progress. Gliders “fly” in a sawtooth flight pattern, diving to a prescribed depth or within proximity of the seafloor, then inflecting upward, while adjusting their heading towards the commanded waypoint. After one or more dive and climb sequence, they surface to send vehicle information and sometimes collected data and also receive commands via satellite network. OceanScout is approximately 1.6m long, 16 cm in diameter, has a 0.5 m wingspan, weighs 22 kg, and displaces about 22 L. It is optimized for a 20 degree dive/climb angle. The wings have a cambered profile, providing lift to maintain a constant glide angle and stable flight. Tailfins provide additional directional stability. During inflection it rolls 180 degrees to invert the lift vector and maintain a constant glide angle back to the surface. The Variable Buoyancy Engine (VBE) is a ball-screw driven Fig. 3. OceanScout Glider, Sliced View 0.82-liter piston buoyancy pump with an approximate 80 mL/sec pump rate. The large relative displacement, combined with smart firmware, enables glider self-ballasting and operation The antenna includes Iridium, GPS, and WiFi, extending and in widely varying density ranges of coastal ocean waters. retracting with the buoyancy pump. The antenna cabling is OceanScout can dive at design speed (0.25 m/s) into 1028 g/L routed internally through the buoyancy piston to minimize density water while still surfacing in brackish plumes. external connection and maintain small vehicle diameter. As OceanScout moves the battery pack forward and aft to adjust its such, the length of the vehicle varies by about 14cm. The pitch angle for dives and climbs, and rotates the pack to induce antenna assembly is housed in a transparent pressure casing and vehicle roll for turns and inflection flips. includes LED red-yellow-green deployment indicator lights and A Nortek-designed, two-transducer altimeter senses the LED strobe recovery lights. Indicator lights aid offshore seafloor or obstacles. One dive & climb sequence to 200m takes deployment and, potentially, remote vehicle setup. Strobe lights about 80 minutes. aid recovery and some insurance requirements. TABLE I. OCEANSCOUT PARAMETERS

Fig. 5. Recovery Cart (Concept)

III. GLIDER ELECTRONICS, POWER, & CONTROL SYSTEMS The centralization of the navigation and science processors and the sensors in the Nose Cone is a key feature of OceanScout. When the sensors need to be removed for maintenance, the nose cone is easily removed and can be quickly replaced. While the prototype vehicle has no scientific sensor, the production model will have a CTD in the Nose Cone.

The vehicle mass is less than the recommended single- person safe lift at work [17]. With the tailfin handles and specially designed cart, the glider can be safely handled by one person. This reduces the personnel required offshore, an important consideration for costs, logistics, and safety.

Fig. 6. OceanScout Nose Cone with Connectors and Adjustment Weights

Fig. 4. OceanScout Wing and Deflection Test Fig. 7. OceanScout Prototype Nose Cone OceanScout electronic hardware and control systems are optimized for power efficiency, safety, processing speed, and processing power. The production vehicle will separate those functional blocks into separate processors, using a more power efficient processor to be used for navigation and user communications processor only working during deployment and recovery. The prototype currently uses a single processor for both navigation and user communications. Fig. 9. Battery Pack (empty)

Navigational sensors (AHRS, altimeter, and pressure) are packaged within the Navigational Onboard Sensor Encasement (NOSE) at the front end of the vehicle. The Nortek-designed IV. GLIDER USER INTERFACE 500kHz altimeter has two transducers, one forward-pointing Glider users must interface with the onboard vehicle (obstacle avoidance) and another angled at 25 degrees for diving computers to change settings, retrieve data, check vehicle status, (seafloor avoidance) and climbing (ice avoidance). The run tests, and perform other necessary activities. The user’s altimeter housing serves as the NOSE and can be swapped computer communicates with the glider Vehicle Management during maintenance events. Processor (VMP) primarily over WiFi or Ethernet. Glider- hosted software is primarily accessed via a web browser. For low bandwidth WiFi connections at a distance, and for Iridium connections, a simplified interface will be available. High speed download of scientific data and operational logs can be performed via the web interface (SFTP) or via the internal Ethernet port. OceanScout web software displays real-time operational data (text-based and graphical), and summarizes scientific data allowing immediate data quality checks after a test dive without the need to download / process the data. Glider-side functionality includes: function testing, compass calibration, battery usage, science & navigational data access, vehicle health parameters, mission controls, component status, and more. Automated compass calibration is built into the firmware. This may be executed during the initial test dive, where OceanScout performs maneuvers to collect magnetometer data for calibration. A web-based calibration display is also provided for shore-based calibration. The automated calibration capability may also be executed on demand during the mission, if needed, without the need to retrieve the vehicle.

Fig. 8. Navigational Onboard Sensor Encasement

A single, robust connection links the power and data between the nose and body. The vehicle computer and dive data can be accessed via WiFi or an Ethernet connection on the inside of the nose cone. Firmware parameters for the vehicle-specific components are located in the Motor & Peripheral Control Unit (MPCU) in the body, enabling use of a replacement Nose Cone without changing motor configuration settings. Battery changes only require removal of the Nose Cone and battery guard plate. The replaceable battery packs can be removed and inserted from the open front without stripping down the rest of the vehicle. The batteries are split into seven (7) identical packs, so that pack weights are lighter and easily manageable at sea. Battery packs are keyed, to ensure the correct installation orientation. Fig. 10. Vehicle Interface – Compass Calibration Page V. GLIDER DESIGN CHALLENGES AND ACCOMPLISHMENTS TABLE II. OCEANSCOUT FEATURES Designing a compact, lightweight uncomplicated, and Feature Vehicle Attribute affordable vehicle poses substantial challenges. The vehicle Easy handling • Lightweight needs low displacement volume and lighter weight for the Easy deployment • Small Diameter buoyancy engine to be fully self-ballasting, for the vehicle to be Easy recovery • Tailfin Handles single-person handleable, and to keep overall costs down. The • LED Indicator Lights size requires efficient use of internal spaces and minimizing • LED Strobe Light component weights. The light weight and narrow diameter • Recovery Cart necessitate innovations in the buoyancy pump. The pump uses a Easy Set-up • Self-Ballasting high efficiency ball screw and compact geared electric motor to • Self-Trimming drive the rolling diaphragm with a piston against hydrostatic • Compass Self-Calibration pressure. Hydrodynamics are critical to the vehicle to prevent excessive power consumption necessary to overcome drag. Drag • Simple Battery Change was minimized with close attention to the external shape (e.g. Easy Operation • Quick Data Downloads efficient cambered wing profiles, hydrodynamic handles, tail • Web-based Interface cone fairing). Maintaining affordability requires simplification • High Bandwidth WiFi of every aspect, meticulous materials selection, and precise Littoral & Open • 200m Depth Rating design for manufacturing. The simplicity of the vehicle was Ocean • Fast VBE motor achieved through conscientious design. Deployments • Large buoyancy pump Safety • Pressure Release Valve

• Carbon Fiber Reinforced Wings • Double O-ring connections • Firmware Safety Switches Performance • Cambered Wings for Stability • Iridium SBD Protocol for Critical Comms • Lithium Primary Batteries

VI. GLIDER APPLICATIONS There are immediate uses for autopiloted fleet gliders with CTDs capable of 200m dives. Examples include: tropical cyclone intensity forecasting, littoral zone water mass tracking, ocean forecast model data coverage gap filling, submesoscale lateral mixing observation, ocean mixed layer depth observations, and western boundary current following.

VII. FURTHER WORK OceanScout prototype engineering design is complete. Vehicle assembly and extensive prototype testing will be executed in Autumn 2020. Results of the lab, pool, and ocean tests will provide a clear path forward for necessary refinements to finalize the production model. Optimization will include mechanical design, firmware command and control algorithms, electrical hardware components, and user interfaces. CTD integration is the next mechanical, electrical, and data design task. Payload Capacity has been reserved for the sensor physically in the nose cone, electronically in the hardware, and data-wise in the onboard processors. Integration of the payload and optimization of the data collection will follow prototyping, trial execution, and refinement steps. Later vehicle models will include other sensors accompanying the CTD, such as passive acoustic hydrophones, and will be designed for specific applications. OceanScout is not intended as a host platform for the integration of numerous Fig. 11. VBE Ball Screw Drive adjacent sensors for simultaneous measurements. The increased complexity, size, power demand and cost would run counter to our objectives. OceanScout's piloting interfaces are still in development, but [7] Bosse, A., Fer, I., Lilly, J.M. et al. Dynamical controls on the longevity their design principles are already in place. The communication of a non-linear vortex : The case of the Lofoten Basin Eddy. Sci infrastructure for OceanScout will consist of services deployed Rep 9, 13448 (2019). https://doi.org/10.1038/s41598-019-49599-8 [8] Testor P, de Young B, Rudnick DL, Glenn S, Hayes D, Lee CM, in the Cloud. Human pilots in command (PICs) will interact with Pattiaratchi C, Hill K, Heslop E, Turpin V, Alenius P, Barrera C, Barth these services via a web-based, map-centered piloting JA, Beaird N, Bécu G, Bosse A, Bourrin F, Brearley JA, Chao Y, Chen S, interface to visualize the progress of OceanScout and issue Chiggiato J, Coppola L, Crout R, Cummings J, Curry B, Curry R, Davis commands. Shore-based, single- and multi-vehicle autopilots R, Desai K, DiMarco S, Edwards C, Fielding S, Fer I, Frajka-Williams E, will be clients of the same services, receiving telemetry, Gildor H, Goni G, Gutierrez D, Haugan P, Hebert D, Heiderich J, Henson S, Heywood K, Hogan P, Houpert L, Huh S, E. InallM, IshiiM, Ito S-i, processing it, and issuing commands. Vehicle health Itoh S, Jan S, Kaiser J, Karstensen J, Kirkpatrick B, Klymak J, Kohut J, monitoring, custom alarms, integration with computational Krahmann G, Krug M, McClatchie S, Marin F, Mauri E, Mehra A, models, third party common operational picture (COP) and Meredith MP, Meunier T, Miles T, Morell JM, Mortier L, Nicholson S, piloting software integration will all be possible using these O’Callaghan J, O’Conchubhair D, Oke P, Pallàs-Sanz E, PalmerM, Park services as the proxy to the vehicle. There will likely be a J, Perivoliotis L, Poulain PM, Perry R, Queste B, Rainville L, Rehm E, Roughan M, Rome N, Ross T, Ruiz S, Saba G, Schaeffer A, Schönau M, formalism for sequencing and conditional execution of multiple Schroeder K, Shimizu Y, Sloyan BM, Smeed D, Snowden D, Song Y, navigational and science directives, that is, a Mission. This will Swart S, Tenreiro M, Thompson A, Tintore J, Todd RE, Toro C, Venables endow OceanScout with basic rule-based decision making H, Wagawa T, Waterman S, Watlington RA and Wilson D (2019) abilities when underwater (and out of communication), and will OceanGliders: A Component of the Integrated GOOS. Front. Mar. Sci. allow OceanScout to operate for longer periods of time without 6:422. doi: 10.3389/fmars.2019.00422 PIC intervention. [9] Valdés, L., 2017. Global ocean science report: the current status of ocean science around the world. UNESCO publishing. Hefring anticipates production mode readiness in Autumn [10] Domingues, R., Kuwano-Yoshida, A., Chardon-Maldonado, P., Todd, 2021. But quality of the vehicle is paramount, and the schedule R.E., Halliwell, G., Kim, H.S., Lin, I.I., Sato, K., Narazaki, T., Shay, L.K. will be extended as needed for development, trials, and and Miles, T., 2019. Ocean observations in support of studies and forecasts of tropical and extratropical cyclones. refinement. [11] Todd, R.E., Chavez, F.P., Clayton, S., CRAVATTE, S.E., Goes, M.P., Graco, M.I., Lin, X., Sprintall, J., Zilberman, N.V., Archer, M. and VIII. CONCLUSIONS Arístegui, J., 2019. Global perspectives on observing ocean boundary Simplifying the glider design allows OceanScout to be current systems. Frontiers in Marine Science, 6, p.423. affordable for a wide community of users. Making the vehicle [12] Patricia Miloslavich, Sophie Seeyave, Frank Muller-Karger, Nicholas easy to deploy & recover, uncomplicated to maintain, and Bax, Elham Ali, Claudia Delgado, Hayley Evers-King, Benjamin Loveday, Vivian Lutz, Jan Newton, Glenn Nolan, Ana C. Peralta autonomously piloted enables smaller groups to take advantage Brichtova, Christine Traeger-Chatterjee & Edward of glider technology. Focusing on CTD initially, and targeted Urban (2019) Challenges for global ocean observation: the need for applications later, covers the main use cases of many increased human capacity, Journal of Operational researchers. We aspire for the effects of OceanScout’s Oceanography, 12:sup2, S137- technology to be new observations where there are current data S156, DOI: 10.1080/1755876X.2018.1526463 gaps, improved data coverage where glider data is already [13] Peng, S., Zhu, Y., Li, Z. et al. Improving the Real-time Marine Forecasting of the Northern South China Sea by Assimilation of Glider- collected, and democratization of ocean science through observed T/S Profiles. Sci Rep 9, 17845 (2019). affordability and accessibility. https://doi.org/10.1038/s41598-019-54241-8 [14] Linwood Pendleton, Karen Evans, Martin Visbeck, Opinion: We need a REFERENCES global movement to transform ocean science for a better world, [1] C. C. Eriksen, T. J. Osse, T. Light, R. D. Wen, T. W. Lehmann, P. L. 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