A Survey of Underwater Vehicle Navigation: Recent Advances and New Challenges
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A SURVEY OF UNDERWATER VEHICLE NAVIGATION: RECENT ADVANCES AND NEW CHALLENGES James C. Kinsey ∗ Ryan M. Eustice ∗∗ Louis L. Whitcomb ∗ ∗ Department of Mechanical Engineering The Johns Hopkins University Baltimore, Maryland USA ∗∗ Department of Naval Architecture and Marine Engineering University of Michigan Ann Arbor, Michigan USA Abstract: The paper surveys recent advances in underwater vehicle navigation and identifies future research challenges. Improvements in underwater navigation sensor technology and underwater navigation algorithms are enabling novel un- derwater vehicles and novel underwater vehicle missions. This paper first reviews advances in underwater navigation sensor technology. Second, advances in deter- ministic and stochastic underwater navigation methodologies and algorithms are reviewed. Finally, future challenges in underwater vehicle navigation are articu- lated, including near-bottom navigation, vehicle state estimation, optimal survey, environmental estimation, multiple-vehicle navigation, and mid-water navigation. Advances in vehicle navigation will enable new missions for underwater vehicle (commercial, scientific, and military) which were previously considered impractical or infeasible. 1. INTRODUCTION eras, have served as a catalyst for the develop- ment of novel navigation methodologies. Many of This paper reviews recent advances in under- these methodologies supplement sensor data with water vehicle navigation sensing and algorithm information from dynamic or kinematic models. research, and identifies future challenges in un- This paper concludes with a discussion of current derwater vehicle navigation. Within the last ten research problems that will improve our ability to years, the development of commercially available, navigate oceanographic submersibles and increase precise, high update rate navigation sensors such the value of these vehicles to the oceanographic as Doppler sonars, optical gyrocompasses, and community. inertial measurement units (IMUs), have served to complement traditional underwater sensors such The motivation for improving underwater vehi- as acoustic positioning systems, magnetic com- cle navigation arises from the need to expand passes, and pressure depth sensors. Data from the capabilities of these vehicles and further in- these sensors, along with data from scientific sen- crease their value to oceanography. All classes of sors such as bathymetric sonars and optical cam- oceanographic vehicles have progressed remark- ably and the data collected with these vehicles contributes to our knowledge of the oceans. For 1 The Authors gratefully acknowledge the support of the example, over the last decade the Autonomous National Science Foundation. Benthic Explorer (ABE), an autonomous under- the experimental reports of undersea robotic ve- water vehicle (AUV), has conducted 191 benthic hicle tracking controllers e.g. (Yoerger and Slo- surveys at mid-ocean ridge sites at an average tine, 1991; Choi and Yuh, 1996; Whitcomb and depth of 2000 meters and a navigation precision Yoerger, 1996; Fossen, 1994), which have his- on the order of a few meters (Yoerger et al., 2006). torically focused primarily on heading, altitude, These surveys have provided bathymetric and depth, or attitude control. Less common is the magnetic maps of the seafloor, photographed bi- experimental reports of XY controllers in the ological and geological features, and mapped hy- horizontal degrees of freedom. However, recent drothermal plumes (Karson et al., 2006; Kelley improvements in commercially available sensors, et al., 2005). A critical factor in ABE’s success, particularly Doppler sonars and IMUs, have en- and that of other oceanographic submersibles, abled significant improvements in XY navigation. had been continued research in underwater vehicle This section reports a survey of recent advances navigation. For example, improvements in the pre- in navigation sensor technology. Navigation tech- cision and update rate of navigation have (i) en- nologies surveyed in this section include depth abled closed-loop feedback control of underwater sensing (Sections 2.1), orientation sensing (Sec- robotic vehicles; and (ii) allowed oceanographers tion 2.2), time-of flight acoustic navigation (Sec- to more fully exploit quantitative data from high- tion 2.3), Doppler navigation (Section 2.4), iner- resolution sensors such as high-frequency bathy- tial navigation (Section 2.5), and satellite naviga- metric sonars and optical cameras. Future im- tion (Section 2.6). provements in underwater vehicle navigation will enable us to optimize the infrastructure necessary for navigation and enable submersibles to opti- 2.1 Depth mally achieve specific objectives. These improve- ments will increase the value, quantity, and cost- Vehicle depth is computed from the direct mea- effectiveness of scientific data obtained with these surements of ambient sea water pressure via stan- vehicles. dard equations for the properties of sea water, e.g. (Fofonoff and Millard Jr., 1983). The two This paper is organized as follows: Section 2 re- most common pressure sensors technologies for views advances in navigation sensors and method- deep ocean applications are (i) strain gauges and ologies that primarily employ data from a single (i) quartz crystals. Strain gauge pressure sensors sensor. Section 3 surveys state estimators that employ metal alloys (e.g. constantin) or silicon employ kinematic or dynamic models along with crystal sensing elements whose resistance changes sensor data to estimate the vehicle state (posi- linearly with total strain, mounted on an elas- tion and velocity). Section 4 identifies current re- tic pressure diaphragm in a Wheatstone Bridge. search problems that have the potential to further Strain gauges pressure sensors can typically attain advance underwater vehicle navigation, and, in overall accuracies of up to about 0.1% of full-scale consequence, improve oceanographic submersibles and resolutions of up to about 0.01% of full-scale. and the value of scientific data collected with these Attaining full accuracy requires calibration and platforms. compensation for thermal variation in sensor gain None of the techniques reported within is a perfect and offset. Quartz crystal pressure sensors employ solution to the challenges of underwater vehicle quartz crystals whose resonant frequency varies navigation, and in practice it is common for a with stress induced by being subject to ambient vehicle to employ a combination of these meth- ocean pressure. Quartz crystal pressure sensors ods. The selection of sensors and techniques that can typically attain overall accuracies of about are employed on a specific vehicle depends on 0.01% of full-scale and overall resolution of up numerous factors including the required precision to about 0.0001% of full-scale — i.e. a resolution and update rate of navigation and scientific mea- of one part per million. Attaining full accuracy surements, sensor cost, power, depth, range, and requires calibration and compensation for thermal time necessary to setup and calibrate requisite variation in gain and offset. The computation of infrastructure. geodetic vehicle altitude from depth is compli- cated by variation (due to tide, weather, or other 2. NAVIGATION SENSOR SYSTEMS factors) of the ocean’s free-surface. Table 1 lists navigation sensors commonly used 2.2 Orientation aboard oceanographic submersibles. Depth, head- ing, pitch, and roll are instrumented with strap- Rapid innovation in the the technology of atti- down high update rate sensors which provide di- tude sensing over the past two decades has re- rect measurement of the state (position and ve- sulted in new families of attitude sensors that offer locity) of these four degrees of freedom (DOF). dramatic improvement in accuracy, size, power The lack of a single equivalent sensor for the XY consumption, interfaces, and operational lifetime. horizontal degrees of freedom complicates navi- This section briefly reviews some of the technolo- gation in this plane. This lacuna is apparent in gies commonly employed for attitude sensing of underwater vehicles. Table 1. Commonly Used Underwater Vehicle Navigation Sensors INSTRUMENT VARIABLE UPDATE RATE PRECISION RANGE DRIFT Acoustic Altimeter† Z - Altitude varies: 0.1-10Hz 0.01-1.0 m varies with frequency — Pressure Sensor† Z - Depth medium: 1Hz 01% - .01% full ocean depth — Inclinometer† Roll, Pitch fast: 1-10Hz 0.1◦ - 1◦ +/ − 45◦ — Magnetic Compass† Heading fast: 1-10Hz 1 − 10◦ 360◦ — Gyro: (mechanical)† Heading fast: 1-10Hz 0.1◦ 360◦ 10◦/h Gyro: Ring-Laser and Fiber- Heading fast: 1-1600Hz 0.1◦ - 0.01◦ 360◦ 0.1 − 10◦/h optic† Gyro: North Seeking† Heading, Pitch, fast: 1-100Hz 0.1◦ - 0.01◦ 360◦ — Roll,x ¨,ω 12 kHz LBL XYZ Position varies: 0.1-1.0 Hz 0.1-10 m 5-10 Km — 300 kHz LBL XYZ Position varies: 1.0-10.0 Hz +/-0.007 m 100 m — IMU† x,¨ ω, ω˙ fast: 1-1000Hz 0.01m varies varies Bottom-Lock x˙ body fast:1-5Hz 0.3% or less varies: 18 - 100 m Doppler† Global Positioning XYZ Position fast: 1-10 Hz 0.1-10 m In water: 0 m — System in air † — Internal Sensor 2.2.1. Two-Axis and Three-Axis Magnetic Sen- Despite the noted limitations in accuracy and pre- sors A great variety of commercially available cision, most underwater vehicles employ a mag- single-axis (heading only) and three-axis flux-gate netic heading sensor either as a primary or sec- magnetometers provide heading accuracies (when ondary heading sensor. properly calibrated) on the order of 1◦–3◦ with 2.2.2. Roll and Pitch Low-cost roll and pitch