James G. Bellingham

Robotics in Remote and Hostile Environments

In our continuing quest for knowledge, robots are powerful tools for accessing environments too dangerous or too remote for human exploration. Early systems functioned under close human supervision, effectively limited to executing preprogrammed tasks. However, as exploration moves to regions where communication is ineffective or unviable, robots will need to carry out complex tasks without human supervision. To enable such capabilities, robots are being enhanced by advances ranging from new sensor development to automated mission planning software, distributed robotic control, and more efficient power systems. As robotics technology becomes simultaneously more capable and economically viable, individual robots operated at large expense by teams of experts are increasingly supplemented by teams of robots used cooperatively under minimal human supervision.

A second generation survey AUV

Odyssey class autonomous underwater vehicles (AUVs) are designed to be small, high performance survey platforms. The logistical complexities of operating off of oceanographic vessels or in hostile environments, such as the Arctic, make a small vehicle with minimal support requirements extremely attractive. Although built for great depths and endurances of up to two days, Odyssey class vehicles are small by the standards of existing AUVs. This paper describes Odyssey II, the second generation of Odyssey class AUV, and presents the results of under-ice field trials in New Hampshire and the Arctic.

Docking for an autonomous ocean sampling network

In this paper, we examine the issues associated with docking autonomous underwater vehicles (AUVs) operating within an Autonomous Ocean Sampling Network (AOSN). We present a system based upon an acoustic ultrashort baseline system that allows the AUV to approach the dock from any direction. A passive latch on the AUV and a pole on the dock accomplish the task of mechanically docking the vehicle. We show that our technique for homing is extremely robust in the face of the two dominant sources of error-namely the presence of currents and the presence of magnetic anomalies. Our strategy for homing is independent of the initial bearing of the dock to the AUV, includes a method for detecting when the vehicle has missed the dock, and automatically ensures that the AUV is in a position to retry homing with a greater chance of success. Our approach is seen to be extremely successful in homing the vehicle to the dock, mechanically attaching itself to the dock, aligning inductive cores for data and power transfer, and undocking at the start of a fresh mission. Once the AUV is on the dock, we present a methodology that allows us to achieve the complex tasks with ensuring that the AUV is securely docked, periodically checking vehicle status, reacting to a vehicle that requires charging, tracking it when it is out on a mission, archiving and transmitting via satellite the data that the AUV collects during its missions, as well as providing a mechanism for researchers removed from the site to learn about vehicle status and command high-level missions. The dock is capable of long-term deployments at a remote site while respecting the constraints - low power, small size, low computational energy, low bandwidth, and little or no user input - imposed by the amalgamation of acoustic, electronic and mechanical components that comprise the entire system.

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.

Optimizing AUV oceanographic surveys

The objective of an oceanographic survey is to obtain the best understanding of the phenomena under study for a given amount of expended effort. This problem is complicated by the fact that the ocean usually evolves on a time scale comparable to (or faster than) the survey time. The ideal survey would be accomplished instantaneously and with infinite resolution. However, as platform limitations preclude such synoptic surveys, compromises between resolution, total survey time, and vehicle speed must be made. This paper presents a framework for optimizing uniform surveys of temporally evolving scalar fields under platform introduced constraints. Knowledge of the statistical characteristics of the ocean and the dominant physical processes are assumed. Advection is assumed to be negligible as a driving factor in temporal variations. The survey error, given by the squared difference between the true and reconstructed field, is determined as a function of the survey parameters. These in turn are subject to the physical limitations of the vehicle. Combining these constraints, we arrive at a tool which can be used to maximize survey efficiency and to assess relative efficiencies of various adaptive sampling techniques.

Outlier rejection for autonomous acoustic navigation

Navigation is a critical requirement for the operation of autonomous underwater vehicles (AUVs). In this paper we present acoustic navigation results for the Odyssey II AUV obtained by using a Kalman filter that integrates dead-reckoning with acoustic range measurements made to an array of acoustic beacons pre-deployed in the operating environment. Because spurious acoustic measurements due to multipath propagation are common, initialization and outlier rejection techniques are addressed. The navigation algorithm has been extensively tested by post-processing of real data acquired by Odyssey II during field operations in a variety of environments. These include the Charles River Basin, the Atlantic Ocean (1.5 km off the Florida coast), and the Pacific Ocean (375 km off the Oregon coast). Our results show improved performance over prior techniques based exclusively on fix computation and dead reckoning.

An integrated approach to multiple AUV communications, navigation and docking

In this paper we report on our progress in two topics related to the development of an autonomous oceanographic sampling network. The first topic deals with the use of a flexible DSP system on the Odyssey class AUV which provides acoustic communications and ultra-short baseline navigation, while the second topic details our efforts in integrating these capabilities for the purpose of autonomous vehicle docking. We present an algorithm for homing in on a beacon and our results of testing this approach at sea. We show how our docking approach may be extended to allow coordinated multiple vehicle operations and demonstrate this approach for the case of two vehicles conducting a coordinated survey. We also include results from the at-sea tests of our acoustic communications system.

The application of autonomous underwater vehicles for interdisciplinary measurements in Massachusetts and Cape Cod Bays

An ODYSSEY autonomous underwater vehicle (AUV) was deployed in Massachusetts and Cape Cod Bays in September 1998 to collect chlorophyll fluorescence, optical backscattering (880 nm), and physical data. It sampled the region mainly in a sawtooth pattern with horizontal resolution between B120 m at the middle of the water column and with vertical resolution of 0.1 m. The data were used to quantify various features in both physical and bio-optical properties in the Bays. In particular, an upwelling front with enhanced chlorophyll fluorescence was found off the coast of Race Point. Chlorophyll patches with along-track spatial scales less than 3.6 km were found southeast of Plymouth and southwest of Race Point. Southeast of Plymouth, strong sediment re-suspension was also evident. In the early fall, the water column was characterized by three layers: warm and fresh surface water; cold and salty bottom water; and a transition (pycnocline) layer with sharp vertical temperature and salinity gradients. A relatively thin chlorophyll maximum layer was evident in the strong pycnocline. This work represents one of the first successful applications of AUVs for interdisciplinary coastal research. Our results demonstrate that AUVs can provide high-quality, concurrent measurements of physical and bio-optical properties in a very effective manner. Some future uses of AUVs are suggested.

Comparison of fix computation and filtering for autonomous acoustic navigation

Oceanographic data acquired by an autonomous underwater vehicle (AUV) must he correlated with accurate position information in order to he of value to scientists. Accurate navigation is therefore an essential requirement which can he fulfilled by use of acoustic long-baseline navigation systems and dead-reckoning sensors. Two approaches are presented in this paper. The fix computation approach consists of dead reckoning between fixes computed from a set of acoustic travel times. The filtering approach consists of correcting the vehicle dead-reckoned motion by taking into account the influence of the measured travel times. Fix computation is widely used for the positioning of manned submersibles and there seems to be some reluctance to switch to a filler-based approach, mainly because of the fear for divergence. After a detailed description of these two approaches, their advantages and drawbacks are compared by applying both algorithms to real data sets collected by the Odyssey II AUV developed at Massachu...

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.