Scientific seabed surveys often require the use of multiple sensing modalities with different capabilities and operational requirements. When using AUVs, this is often accomplished via a series of dives, between which operators examine collected data and plan the subsequent survey. Planning a follow-up survey while the vehicle is still in the water dramatically improves operational efficiency, but requires that topside scientists receive information from the initial survey during the dive. With this motivation, we developed a toolbox for CoExploration that is designed to acoustically transmit scientifically-actionable data, making use of any bandwidth that is not required for safe vehicle operation. This paper describes utilities for incrementally transmitting a multi-resolution multibeam map and for progressive transmission of camera imagery, along with field results from their first use on the NUI hybrid AUV/ROV.

This letter presents a precise navigation technique for a scuba diver using an autonomous underwater vehicle (AUV) as a positioning aid. We develop and evaluate the state estimation algorithms and communication architecture for diver navigation based on subsurface human-AUV teaming with no requirement for ocean current data or exact diver speeds. By depending on acoustic communication and commercial AUV navigation capabilities, our method provides a unique capability for localizing a diver's position during an extended mission, without the requirement to maintain visual contact with the diver during the mission, or to deploy acoustic beacons. We utilize the Woods Hole Oceanographic Institution Micromodem 2 for range-only single-beacon navigation between two kayaks serving as proxies for the diver and REMUS 100 AUV. Range and odometry measurements are fused in a factor graph using incremental smoothing and mapping 2 (iSAM2) with appropriate motion and measurement models to provide real-time diver position estimates given unknown ocean currents. Field experiments demonstrate an average online endpoint error of 4.53 meters after 400-meter transits.

Autonomous systems, including gliders, floats, and propeller-driven AUVs, require navigation under Arctic ice to be able to geolocate during their missions. In addition, acoustic communications provides for unidirectional or bidirectional data and command flow with the autonomous systems. Over the past ten years, steady progress has been made on implementing and demonstrating these acoustic systems in the Beaufort Sea north of Alaska. The eventual goal is a multi-frequency capability that uses 35 Hz for very long range navigation, 900 Hz for long-range navigation and communications, plus 10 kHz for close-range use. The different frequencies offer different advantages, and each is used accordingly. At 35 Hz, navigation transmissions span the water-column and survive reflection from the underside of the ice, allowing pan-Arctic ranges. The 900 Hz navigation and communications signals persist in the shallow (150 m) duct in the Beaufort at ranges up to several hundred kilometers, which is useful for under-ice survey transits. Finally, at 10 kHz, compressed data can be off-loaded and new mission files transferred via buoys on the ice. Recent work in 2021 and 2022 has continued to develop these capabilities, and this talk summarizes results and describes future directions.

A software framework, “ros_acomms,” has been developed to enable transport of ROS messages and other data across low-throughput and high-latency underwater acoustic links. Messages are efficiently marshalled using user-provided configuration data, if available, or automatically via message introspection. A modular set of modem drivers, media-access-control engines, and message queues transport messages from one system to another via a modem. It supports message fragmentation, positive acknowledgment, and custody-transfer routing. It also includes an acoustic link simulator that uses a raytracing model to estimate link performance and latency. While it targets the WHOI Micromodem family of acoustic modems, the modular modem driver implementation has been leveraged to support low-throughput Iridium satellite links and other acoustic modems. It has been tested and used operationally at sea for remote redirection of autonomous underwater vehicles while providing operators with near real time vehicle telemetry and sensor data.

This paper presents improved algorithms for localization and navigation in which an autonomous underwater vehicle (AUV) supports a human diver. Our initial efforts validated state estimation algorithms and communication protocols for accurate diver navigation based on subsurface teaming with no ocean current data or exact diver speeds. By leveraging acoustic modem messaging and iterative ranging between the AUV and diver, this collaborative team maintains a loosely-coupled support structure that does not rely on close proximity or maintaining sight of a teammate. Range and odometry measurements comprise a factor graph structure that leverages the incremental smoothing and mapping 2 (iSAM2) algorithm for state estimation. However, this approach suffers from decreased accuracy in environments with heavy ocean currents. This requires an updated measurement strategy for ocean currents and new communication protocols to allow a diver to compensate for ocean currents. Extensive simulation results and comparisons to previous non-adaptive techniques show that these updates enable more efficient diver paths to a known target, decreased workload on the diver, and increased accuracy and robustness to ocean currents at the limits of human diver capability.

A scalar magnetometer payload has been developed and integrated into a two‐man portable autonomous underwater vehicle (AUV) for geophysical and archeological surveys. The compact system collects data from a Geometrics microfabricated atomic magnetometer, a total‐field atomic magnetometer. Data from the sensor is both stored for post‐processing and made available to an onboard autonomy engine for real‐time sense and react behaviors. This system has been characterized both in controlled laboratory conditions and at sea to determine its performance limits. Methodologies for processing the magnetometer data to correct for interference and error introduced by the AUV platform were developed to improve sensing performance. When conducting seabed surveys, detection and characterization of targets of interest are performed in real‐time aboard the AUV. This system is used to drive both single‐ and multiple‐vehicle autonomous target reacquisition behaviors. The combination of on‐board target detection and autonomous reacquire capability is found to increase the effective survey coverage rate of the AUV‐based magnetic sensing system.

The development of a synthetic baseline navigation technique that self-localizes an autonomous underwater vehicle (AUV) using intermittent acoustic communications signals received by a single transducer is described, along with field results from in-ocean tests. The method uses the phase measurement at the output of a second-order phase-locked loop to create fine-scale pseudorange estimates in addition to, or in the absence of, a one-way travel time measurement based on the arrival time of the acoustic data packet. These range measurements are incorporated by an adaptive particle filter. This technique allows the vehicle navigation system to take advantage of multiple phase-derived range measurements made over the duration of a communication packet. These measurements, when incorporated with an appropriate filter and vehicle kinematic model, improve vehicle navigation at no additional cost in navigation-specific acoustic transmissions. This approach was demonstrated and evaluated with data collected at-sea using a REMUS 100 AUV (Hydroid, Inc., Pocasset, MA).

Author(s): Gallimore, Eric Curtis | Advisor(s): Terrill, Eric; Gee, Jeffrey | Abstract: Research results that advance the capabilities of autonomous underwater vehicles (AUVs) to conduct seabed surveys are described. These include the creation of a software framework to enable research and development in sensing and adaptive autonomy, a novel synthetic baseline navigation technique, and a magnetic sensing system that incorporates sense and react behaviors. Field experiments were conducted globally in a wide range of littoral environments to test hypotheses associated with the emerging field of autonomy as applied to underwater systems.To facilitate sensor integration and provide a testbed for autonomous sense and react research, an onboard sensor processing and autonomy system was developed for the REMUS AUV using the Robot Operating System (ROS) that provides high-level control of the vehicle. Multiple vehicles outfitted with this system were used for seabed surveys, sensor evaluation, and engineering tests. This framework enabled the development of novel techniques for undersea navigation and magnetic sensing.A synthetic baseline navigation technique that self-localizes an AUV using intermittent acoustic communications signals received by a single transducer is presented. The methodology is found to offer advantages over traditional acoustic-based navigation, in that it can operate with or without synchronized clocks, does not require acoustic transmissions dedicated to navigation, and can provide faster navigation solution convergence. The method uses the phase measurement at the output of a second-order phase-locked loop (PLL) to create fine-scale pseudo-range estimates in addition to, or in the absence of, a one-way travel time (OWTT) measurement based on the arrival time of the acoustic data packet. These range measurements are incorporated by an adaptive particle filter. This technique allows the vehicle navigation system to take advantage of multiple phase-derived range measurements made over the duration of a communication packet. To enable geophysical and archaeological survey capabilities, a scalar magnetometer system has been developed and integrated into an AUV. Real-time signal processing mitigates platform effects of the vehicle. Development of autonomy for on-board processing and target detection, coupled with reacquisition behaviors, is found to increase the effective survey coverage rate by nearly 300% when searching for magnetic dipole targets. The compact system collects data from a Micro-Fabricated Atomic Magnetometer (MFAM, Geometrics Corporation, San Jose, CA, USA), a total-field atomic magnetometer, and data from the sensor is both streamed to storage and made available to an onboard autonomy engine for real-time sense and react behaviors. Following characterization both in controlled laboratory conditions and at sea to determine its performance limits, methodologies for processing the magnetometer data to correct for interference and error introduced by the AUV platform were developed to improve sensing performance. When conducting seabed surveys, the developed autonomy is found to reliably detect and characterize targets of interest using physics-based algorithms designed to operate in real-time within the computational constraints of the AUV. Over the course of this research, the system was advanced to drive both single- and multiple-vehicle autonomous target reacquisition behaviors. Detailed results from surveys searching for submerged World-War II aircraft wrecks at locations worldwide are presented.

To facilitate sensor integration and provide a testbed for autonomous sense and react research, an onboard sensor processing and autonomy system has been developed for the REMUS 100 AUV using the Robot Operating System (ROS) and the REMUS RECON interface, which provides backseat control of the vehicle. An interface library, pyREMUS, has been developed to handle the REMUS RECON interface, and a ROS package, ros_remus, uses this library to provide a deep level of interoperability between the REMUS vehicle computer and other ROS-based subsystems. This system has been deployed on multiple REMUS 100 vehicles and it is currently used operationally for field research programs. Vehicles outfitted with this system have seen numerous deployments, where they have been used for seabed surveys, sensor evaluation, and engineering tests.

“Chirp”-style sidescan sonar systems, which use pulse-compressed signals, provide advantages over pulsed continuous-wave sidescan sonar systems, including increased imaging range, resolution, and image fidelity. Marine Sonics (Yorktown, VA) has recently released a system, the “Arc Scout”, using modern electronics in a form factor suitable for installation on small autonomous underwater vehicles (AUVs). A number of these systems have been integrated into REMUS 100 AUVs, and their performance imaging archaeological targets on the seabed has been evaluated. Targets were surveyed under a variety of conditions at four different sonar center frequencies: 600 kHz, 900 kHz, 1200 kHz, and 1800 kHz. The results were analyzed to provide performance assessments for selecting the sonar operating characteristics based on area search rate and target size. The hardware and software integration required for the retrofit installation of these sonar systems the REMUS 100 vehicle is detailed.

An estimated 70,000 US servicemen remain missing from World War II, with approximately two-thirds of those losses from the Pacific Theater. Many of the missing were lost in the maritime environment. Historically, attempts to locate remains in this environment were deemed too difficult, as water-based searches can be labor intensive, logistically cumbersome, and technically difficult to execute. Ironically, despite these challenges, underwater sites are often better preserved than terrestrial sites, as they are less subject to human disturbance and negative environmental conditions. Technological advances in unmanned platforms, autonomy, sensors, underwater navigation and communications, forensic oceanography, search methodologies, and data processing are now enabling the discovery of crash sites associated with losses and stimulating new research that combines oceanography, unmanned systems, historical research, and forensic archaeological methods. Project Recover began as a two-year program funded by the US Office of Naval Research, designed to serve as a testbed for unmanned technologies and public outreach. Now, through public and private sponsorship, it has grown into providing a global survey capability.

The recently developed wave glider has the potential to be an effective unmanned platform for acoustic applications. We present the results of a variety of experiments that quantify this potential. The radiated self‐noise of the autonomous platform is evaluated using an integrated passive acoustic recorder during a set of field trials off the coast of Hawaii. We present the radiated noise spectra from these trials to illustrate the dependence on hydrophone location and sea state. Using the same instrumentation, we demonstrate the ability of a modified wave glider to detect marine mammals using passive acoustic monitoring techniques. We also evaluate the performance of the wave glider operating as an active acoustic gateway, highlighting the potential of this platform to serve as a navigation reference and communications relay for scientific, industrial, and military subsea assets. To demonstrate the potential of the wave glider platform to support acoustic navigation, we assess the performance of time‐of‐flight range estimation and seafloor transponder localization. These tests were performed using commercial off‐the‐shelf acoustic positioning hardware integrated with the wave glider to illustrate that the low self‐noise of the wave glider makes it possible to achieve acoustic positioning performance similar to previously reported results. Finally, we show that the glider can operate as a station‐keeping surface communications gateway and provide recommendations for its use. © 2012 Wiley Periodicals, Inc.

A successor to the WHOI Micromodem-1 underwater acoustic modem has recently been developed. The Micromodem-2 has the same compact form-factor as the Micromodem-1 and will support all of the existing applications for the Micromodem-1, as well as interoperate with the Micromodem-1. Existing acoustic communications protocols using phase-shift keying (PSK) as well as frequency-hopping frequency-shift keying (FH-FSK) are supported, as are navigation features including narrow-band and broadband long-baseline (LBL) navigation. The Micromodem-2 is significantly more capable than the Micromodem-1 in computational ability and memory, bandwidth, non-volatile data storage, user expansion interfaces, and real-time clock precision. The expanded capabilities will allow new communications algorithms, modulation, errorcorrection methods, navigation features, and networking capabilities to be implemented. The improvements in processing capability and acoustic interfaces on the Micromodem-2 allow it to operate at acoustic frequencies from approximately 1kHz to 100kHz. The significant increases in available non-volatile storage enable the Micromodem-2 to capture data in-situ for diagnostic and research purposes. The Micro mo dem-2's firmware architecture is similar to the Micromodem-1's firmware architecture, using a real-time operating system based on modular signal processing blocks. It has been improved to increase modularity and facilitate future portability, and it offers significant improvements in timing for use with navigation and networking applications.

Work at Woods Hole in underwater acoustic networks in focused on several aspects of development with the goal of creating a general-purpose framework that facilitates research for multiple applications. These applications include fixed sensor networks for environmental or naval use, as well as mobile ad-hoc networks and mixed systems that include both stationary nodes and mobile underwater vehicles. Common to research in all of these areas is a need for a hardware and software test-bed that facilitates prototyping of approaches to networking. Our work in this area includes a complete approach: modems for the physical layer, general-purpose processor for networking and sensor interface, and a modular software environment.