Brett Hobson

Docking Control System for a 54-cm-Diameter (21-in) AUV

The Monterey Bay Aquarium Research Institute (MBARI, Moss Landing, CA) has developed a 54-cm-diameter (21-in) docking AUV and companion docking station. This program resulted in four consecutive successful autonomous homing and docking events in the open ocean, which included downloading data, uploading a new mission plan, recharging the battery, and complete power cycling of the AUV. We describe the design, simulation, and at-sea test of the homing and docking control system.

Efficient propulsion for the Tethys long-range autonomous underwater vehicle

The Tethys autonomous underwater vehicle (AUV) is a 110 kg vehicle designed for long-range, high- endurance operations. Performance goals include supporting a payload power draw of 8 W for a range of 1000 km at 1 m/s, and a power draw of 1 W for 4000 km at 0.5 m/s. Achieving this performance requires minimizing drag and maximizing propulsion efficiency. In this paper, we present the design of the propulsion system, explore the issues of propeller-hull interactions, and present preliminary test results of power consumption and efficiency. In recent underwater experiments, the propulsion systems power consumptions were measured in both Bollard pull tests and during the vehicles flights. Preliminary results of power consumptions and efficiency are shown to be close to the theoretical predictions.

Tethys-class long range AUVs - extending the endurance of propeller-driven cruising AUVs from days to weeks

Most existing propeller-driven, cruising AUVs operate with a support ship and have an endurance of about one day. However, many oceanographic processes evolve over days or weeks, requiring propeller-driven vehicles be attended by a ship for complete observation programs. The Monterey Bay Aquarium Research Institute (MBARI) developed the 105 kg propeller-driven Tethys AUV to conduct science missions over periods of weeks or even months without a ship [1]. Here we describe a three week deployment covering 1800 km at a speed of 1 m/s, supporting sensor power levels averaging 5 watts. Unlike buoyancy driven gliders, Tethys uses a propeller that allows level flight and a variable speed range of 0.5 - 1.2 m/s. The extended endurance enables operations in remote locations like under the ice, across ocean basins in addition to enabling continuous presence in smaller areas. Early success led to the construction of a second Tethys-class AUV with a third in planning. An AUV docking station that can be mated to a cabled observatory or standalone mooring is in development to further extend Tethys endurance.

The Development and Ocean Testing of an AUV Docking Station for a 21" AUV

The Monterey Bay Aquarium Research Institute (MBARI) has developed an AUV docking station for a 21-inch (54 cm) diameter AUV. The system was designed for operation with cabled undersea observatories in water depths up to 4 km deep and has been demonstrated in the open ocean, though at much shallower depths. The program demonstrated successful autonomous homing and docking, data downloads, uploading of new mission plans, battery recharging, and complete power cycling of the AUV. We describe the design, and at-sea tests.

Genesis of a submarine sinkhole without subaerial exposure: Straits of Florida

A sinkhole has been identified on side-scan sonar images and from near-bottom echo sounder data in the southern Straits of Florida in 575 m of water. Sinkholes are often thought to form exclusively in subaerial environments and for this reason have been used as indicators of sea level. This sinkhole exists within a Quaternary sediment apron in water depths too great to have been subaerially exposed by Neogene sea-level lowstands, thus indicating that sinkholes can develop within the submarine environment.

Thermocline tracking based on peak-gradient detection by an autonomous underwater vehicle

Thermoclines play a key role in ocean circulation, marine ecology, and underwater acoustics. In oceanographic surveys, it is often desirable to detect the thermocline and track its spatio-temporal variation. Mobility of an autonomous underwater vehicle (AUV) makes it an efficient platform for thermocline tracking. In this paper, we present a fully autonomous algorithm for detecting and tracking the thermocline by an AUV. The key is detection of the peak gradient of temperature. We have tested the algorithm by post-processing data from a previous Dorado AUV survey over the northern Monterey Bay shelf. We are in preparation for field tests of the algorithm on the newly developed long-range AUV Tethys.

MARS Benthic Rover: In-situ rapid proto-testing on the Monterey Accelerated Research System

The Benthic Rover is an autonomous, bottom-crawling vehicle being developed at the Monterey Bay Aquarium Research Institute (MBARI) to conduct long-term deep-ocean ecological research. In 2009 MBARI researchers deployed the Rover on the Monterey Accelerated Research System (MARS) cabled observatory for component and operational testing. MARS is located near-shore in the Monterey Bay near Monterey, CA, at a depth of approximately 900 meters, providing the power reliability and network accessibility similar to an on-shore laboratory. By enabling immediate feedback and the ability to quickly re-program control software and re-configure mission scripts, MARS facilitates a kind of “in-situ rapid proto-testing”. MBARI researchers were able to run numerous experimental procedures and analyze results in a relatively short timeframe, converging on desired operational profiles quickly and at very low cost. This paper will cover recent development work on the Benthic Rover with emphasis on the deployment and testing on MARS.

Return-to-site of an AUV using terrain-relative navigation: Field trials

This paper presents the results from recent field trials in Monterey Bay, CA which demonstrate the use of Terrain-Relative Navigation (TRN) to perform return-to-site missions using a 53cm diameter Dorado-class Autonomous Underwater Vehicle (AUV). For these tests, a series of targets were identified on a bathymetry map that were recognizable features (e.g. large boulders and outcroppings), and a trajectory was constructed for the AUV to fly over those targets (i.e. the latitudes and longitudes as defined on the map). Multiple missions were flown using a real-time TRN algorithm to identify and correct for georeferencing errors in the bathymetry map. The results were repeatable. They demonstrated that there was a 20m georeferencing error in the map. Without TRN, the targets were missed. With TRN, the AUV flew directly over the targets. Performance was independently validated using acoustic imagery from an on-board mapping multibeam sonar. These field results are presented and described. The TRN algorithm is also discussed.

Tracking and sampling of a phytoplankton patch by an autonomous underwater vehicle in drifting mode

Phytoplankton patches in the coastal ocean have important impacts on the patterns of primary productivity, the survival and growth of zooplankton and fish larvae, and the development of harmful algal blooms (HABs). We desire to observe microscopic life in a phytoplankton patch in its natural frame of reference (which is moving with the ocean current), thereby permitting resolution of time-dependent evolution of the population. To achieve this goal, we have developed a method for a Tethys-class long range autonomous underwater vehicle (AUV) (which has a propeller and a buoyancy engine) to detect, track, and sample a phytoplankton patch in buoyancy-controlled drifting mode. In this mode, the vehicle shuts off its propeller and actively controls its buoyancy to autonomously find the peakchlorophyll layer, stay in it, and trigger water sampling in the layer. In an experiment in Monterey Bay, CA in July 2015, the Makai AUV, which was equipped with a prototype 3rd-generation Environmental Sample Processor (3G-ESP), ran the algorithm to autonomously detect the peak-chlorophyll layer, and drifted and triggered ESP samplings in the layer.

Acoustic tracking and homing with a long-range AUV

This paper presents the development effort toward demonstrating acoustic tracking and homing with a long-range AUV (LRAUV) at the Monterey Bay Aquarium Research Institute (MBARI). The acoustic tracking system uses a directional acoustic transponder (DAT) from Teledyne Benthos, backed by an acoustic baffle made from syntactic acoustic damping material (SADM). We discuss sensor integration into the LRAUV system, procedures and results from an in-house calibration, and field tests with both anchored and towed transponders.