Michael Godin

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.

Using an Autonomous Underwater Vehicle to Track a Coastal Upwelling Front

Coastal upwelling is a wind-driven ocean process. It brings cooler, saltier, and usually nutrient-rich deep water upward to replace surface water displaced offshore due to Ekman transport. The nutrients carried up by upwelling are important for primary production and fisheries. Ocean life can aggregate at the boundary between stratified water and upwelling water-the upwelling front. In an upwelling water column, temperature, salinity, and other water properties are much more homogeneous over depth than in stratified water. Drawing on this difference, we set up a key measure for differentiating upwelling and stratified water columns-the vertical temperature difference between shallow and deep depths. The vertical temperature difference is large in stratified water but small in upwelling water. Based on this classifier, we developed a method for an autonomous underwater vehicle (AUV) to autonomously detect and track an upwelling front. During the Controlled, Agile, and Novel Observing Network (CANON) Experiment in April 2011, the Tethys long-range AUV ran the algorithm to autonomously track an upwelling front in a dynamic coastal upwelling region in Monterey Bay, CA. The AUV transected the upwelling front 14 times over two days, providing a very high-resolution depiction of the front.

Using an Autonomous Underwater Vehicle to Track the Thermocline Based on Peak-Gradient Detection

The thermocline plays a key role in underwater acoustics and marine ecology. 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 an autonomous algorithm for detecting and tracking the thermocline by an AUV. The key is detection and close tracking of the maximum vertical gradient of temperature. On August 31 and September 1, 2010, the Tethys AUV ran the algorithm to closely track the thermocline across a sharp temperature front in Monterey Bay, CA.

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.

ODSS: A decision support system for ocean exploration

We have designed, built, tested and fielded a decision support system which provides a platform for situational awareness, planning, observation, archiving and data analysis. While still in development, our inter-disciplinary team of computer scientists, engineers, biologists and oceanographers has made extensive use of our system in at-sea experiments since 2010. The novelty of our work lies in the targeted domain, its evolving functionalities that closely tracks how ocean scientists are seeing the evolution of their own work practice, and its actual use by engineers, scientists and marine operations personnel. We describe the architectural elements and lessons learned over the more than two years use of the system.

Ocean front detection and tracking by an autonomous underwater vehicle

In this paper we present a method of using an autonomous underwater vehicle (AUV) to detect and track an ocean front created by coastal upwelling. In an upwelling water column, temperature, salinity, and other properties are more homogeneous over depth as compared with non-upwelling water which is typically stratified. We use the vertical homogeneity of temperature as the classifier for differentiating upwelling and stratified water columns. On 27 April 2011, the Tethys long-range AUV ran the algorithm to autonomously detect and track a front in a dynamic coastal upwelling region in Monterey Bay, CA. The AUV transected the front 14 times over two days, providing a very high-resolution depiction of the front.

A Collaborative Portal for Ocean Observatories

A Collaborative Ocean Observatory Portal (COOP) has been developed to enable distributed investigators to collaboratively operate ocean observatory systems. COOP is being created within the Autonomous Ocean Sampling Network program to support the Adaptive Sampling and Prediction (ASAP) field experiment that occurred in Monterey Bay in the summer of 2006. ASAP involved the day-to-day participation of a large group of researchers with ties to geographically diverse institutions throughout North America. These investigators had to interact on a continual basis to optimize data collection and analysis. While some investigators needed to be physically present to launch and retrieve their assets, the long duration of the observatory made sustained co-location of researchers difficult. Likewise, future ocean observatories and observing systems (such as moored arrays and cabled observatories) will operate 24 hours a day, 7 days a week over many years or even decades. Since sustained co-location of researchers for situational awareness and decision-making will be impractical, there is a need for collaborative data distribution and situational awareness tools appropriate for the ASAP experiment, and eventually, for all ocean observatories. As implemented for the ASAP team, the COOP tool set consists of several components, starting with a publicly viewable, web-based tool for reviewing the days progress and proposed actions. Registered scientists are able to discuss the days progress (and attach illustrative data), propose actions (and back-up those proposed actions with supporting data), and discuss and vote upon proposed actions. The tool provides links to other system components, such as a database of data collections in both original and common formats, interactive data access and manipulation tools, and pages of automatically generated graphical summaries of observational results and model forecasts