John Canning

Synchronous navigation of AUVs using WHOI micro-modem 13-bit communications

This paper presents the development and testing of a synchronous one-way travel time (OWTT) navigation system for autonomous underwater vehicles (AUVs). Synchronous OWTT navigation is important for multiple vehicle applications as it preserves the range update rate independent of fleet size. The presented approach is based on the use of ranges generated by 13-bit acoustic messages and an a priori temporal communications cycle. The accuracy of the 13-bit acoustic ranges was experimentally compared to independent ground truth measurements. In addition, the presented synchronous OWTT approach was successfully used for real-time navigation of an AUV in field testing. The results show comparable performance to traditional two-way travel time (TWTT) navigation.

Measurement of magnetic field using collaborative AUVs

This paper describes an effort to adapt a fleet of autonomous underwater vehicles (AUVs) for the measurement of the magnetic signature of surface ships. Currently, two such vehicles have been upgraded with the necessary navigation and measurement hardware to perform magnetic measurements. Initial testing has been performed at the Naval Acoustic Research Detachment at Lake Pend Oreille, Idaho. Two vehicles have leveraged formation control algorithms originally developed for mine countermeasure missions to operate collaboratively. In the testing area, changes in ambient field were measured to be ∼1,000–2,000 nT. Over one square meter area segments, the standard deviation of total field measurements was below 25 nT. When a steel barge was located in the testing area, localized fields of ∼50,000 nT to ∼62,000 nT were observed.

A versatile tracking system for AUV testing

Testing and development of AUVs and AUV-based systems can be greatly accelerated with access to a suitable underwater tracking range area. A tracking system was recently developed jointly by the NSWCCD Acoustic Research Detachment (ARD) and the University of Idaho (UI). Located on Lake Pend Oreille, the system is used routinely to test AUVs being developed at UI. The system includes four acoustic tracking nodes which are held stationary near the lake floor. Three transducers are mounted on each node and cabled to a dockside tracking and control station. Acoustic pings are emitted from the test vehicle at periodic intervals. These pings are received at multiple tracking nodes allowing 3-D tracking solutions to be computed. The test area covers approximately 23,000 square meters, with a nominal water depth of 15 meters.

DEVELOPMENT OF A FUZZY LOGIC CONTROLLER FOR AUTONOMOUS FOREST PATH NAVIGATION

We describe the application of fuzzy logic to the control of a robot intended to navigate forest paths. Robots could improve the safety of forest operations by removing the operator from the vehicle and also reduce costs by automating these operations. The controller was organized into three modules, each of which was capable of providing a heading recommendation for the robot. Sensory information was provided by shaft encoders and three ultrasonic rangefinders. The controller required a set of sensory data acquired from one training run down the path. Two of the modules provided heading recommendations from the shaft encoder and ultrasonic rangefinder data, respectively. A third module arbitrated the recommendations of the first two modules and provided a final heading recommendation. Decisions made by the operator during the training run were used in the arbitration to weight the recommendations of the individual modules. It was observed that the combination of modules performed better than the individual modules alone. Despite the simplicity of the controller, a test vehicle was able to consistently navigate 152 m (500 ft) down a forest path. It was concluded that the approach is feasible, and further development of the control algorithm is warranted.

Developing a Radio-controlled Log Skidder with Fuzzy Logic Autonomous Control

This article presents the development of a small, radio-controlled (RC) log skidder and also discusses the results of a preliminary investigation into using fuzzy logic for autonomous control of the skidder. Small skidders can reduce the environmental impact of logging and help improve timber stands. With previous small skidders, the operator walked in front of the skidder and reached back with one hand to operate the controls on a handle. The RC skidder allows the operator to be removed from the immediate vicinity of the skidder, thus making a safer operating environment. Field trials of the RC skidder were conducted and are discussed.

Hybrid Baseline Localization for Autonomous Underwater Vehicles

This paper presents a hybrid baseline (HBL) navigation method for autonomous underwater vehicles (AUVs). In this approach, a floating acoustic transponder is used to augment moving short baseline (MSBL) navigation, in which two transponders are mounted on a source ship. Kinematic information regarding the floating buoy and source ship are communicated via acoustic messages to the AUV fleet. Simultaneously, clock synchronization and a predefined broadcast cycle enables transponder-to-AUV range estimates based on the acoustic message time-of-flight. Using the extended Kalman (EKF) filter formulation, the broadcasted kinematic information and acoustic ranges are combined onboard each AUV in the fleet to estimate the states of the source ship, the floating transponder, and the AUV itself. Simulation was used to optimize the configuration and performance of the HBL navigation, and field tests were performed to evaluate the navigational performance. In post-processing, high-accuracy position and timing data for the source ship and floating buoy was added to the onboard navigation data in an EKF to recreate the path of the AUV. The accuracy of this post-mission localization was evaluated relative to AUV positions independently measured by an acoustic tracking array at the test facility. The resulting AUV position estimation showed a mean error of 1.59 m, an improvement over the previous result (using MSBL navigation only) of 3.30 m.

Field Testing of Moving Short-baseline Navigation for Autonomous Underwater Vehicles using Synchronized Acoustic Messaging

This paper presents the results from field testing of a unique approach to the navigation of a fleet of autonomous underwater vehicles (AUVs) using only onboard sensors and information provided by a moving surface ship. The approach, considered moving short-baseline (MSBL) navigation, uses two transponders mounted on a single surface ship that alternately broadcast acoustic messages containing one of the parameters of the kinematic state of the surface ship. The broadcasts are initiated according to a predefined schedule so that the one-way travel time (OWTT) of the acoustic messages may be used to determine the range to the transponder. Each AUV in the fleet uses the surface ship state measurements and ranges provided by the acoustic messages in two extended Kalman filters (EKFs) for state estimation. The first EKF merges the intermittent surface ship state measurements with a kinematic model to estimate the state of the surface ship. This is necessary because the presented approach uses 13-bit acoustic messages as opposed to the more commonly used 32-byte messages, which allow the full state to be encoded in a single broadcast. The second EKF uses the current surface ship state estimate to properly interpret the acoustic ranges, combining them with a kinematic model to estimate the state of the AUV itself. Numerous MSBL navigation experiments were compared against a more traditional approach using a long-baseline (LBL) array of transponders and OWTT acoustic ranging. The results of all tests were verified by independent LBL measures of position.

Calibration and localization of AUV-acquired magnetic survey data

A system is being developed to enable the measurement of the magnetic signature of a surface vessel at forward locations. The system consists of a fleet of AUVs (Autonomous Underwater Vehicles) each equipped with a magnetometer. A magnetic signature measurement would be performed in a coordinated relative movement between the fleet and the surface vessel. The precision of the magnetometer system and the precision of each position associated with magnetic measurements in a survey are crucial to the value of this measurement. Results of experiments on these two issues are reported. Calibrations of the AUV/magnetometer systems are performed in-situ and on land and are characterized by a noise floor of less than 10 nT. In experiments performed at a deepwater facility free from extraneous ambient magnetic sources, an AUV passed near a known magnetic source at a fixed location and orientation. Measurements of magnetic field and position estimates based upon navigation data acquired by the AUV were associated. An independent, high-accuracy acoustic tracking system was used during the experiments to determine a ground truth position for the AUV. The predicted magnetic field at the AUV estimated position was compared to the magnetic field acquired by the AUV near the source and found to have an error of 15 nT.

AUV state estimation and navigation to compensate for ocean currents

This paper presents a novel approach to water-current compensation for autonomous underwater vehicle (AUV) state estimation and navigation. The approach is twofold: first, an extended Kalman filter estimates both the AUV state and water-currents in the north and east directions; second, these water-current estimates are used in a modified heading controller to calculate a current-compensated desired heading for the AUV to follow. Both the extended Kalman filter and modified heading controller are presented and simulated using historical experimental data for noise estimation. The presented results are a promising first step towards further testing and real-time implementation on the AUVs for localization and navigation in ocean environments.

Estimating and compensating for water currents: Field testing

This paper describes field testing of state estimation and navigation for autonomous underwater vehicle (AUV) operation in the presence of water currents. In the presented approach, an extended Kalman filter (EKF) is used to estimate the water currents in the north and east directions in real-time during AUV missions. These water current estimates are then used to compensate the desired AUV heading so that the resultant velocity vector of the AUV achieves proper waypoint path following behavior. This work builds on previous evaluation of the approach in simulation; here, we present results from preliminary field testing.