3,594 research outputs found
An Underwater SLAM System using Sonar, Visual, Inertial, and Depth Sensor
This paper presents a novel tightly-coupled keyframe-based Simultaneous
Localization and Mapping (SLAM) system with loop-closing and relocalization
capabilities targeted for the underwater domain. Our previous work, SVIn,
augmented the state-of-the-art visual-inertial state estimation package OKVIS
to accommodate acoustic data from sonar in a non-linear optimization-based
framework. This paper addresses drift and loss of localization -- one of the
main problems affecting other packages in underwater domain -- by providing the
following main contributions: a robust initialization method to refine scale
using depth measurements, a fast preprocessing step to enhance the image
quality, and a real-time loop-closing and relocalization method using bag of
words (BoW). An additional contribution is the addition of depth measurements
from a pressure sensor to the tightly-coupled optimization formulation.
Experimental results on datasets collected with a custom-made underwater sensor
suite and an autonomous underwater vehicle from challenging underwater
environments with poor visibility demonstrate performance never achieved before
in terms of accuracy and robustness
An Underwater Vehicle Navigation System Using Acoustic and Inertial Sensors
Unmanned Underwater Vehicles (UUVs) have become an essential tool for different underwater tasks. Compared with other unmanned systems, the navigation and localization for UUVs are particularly challenging due to the unavailability of Global Positioning System (GPS) signals underwater and the complexity of the unstable environment. Alternative methods such as acoustic positioning systems, Inertial Navigation Systems (INS), and the geophysical navigation approach are used for UUV navigation. Acoustic positioning systems utilize the characteristics of acoustic signals that have a lower absorption rate and a more extended propagation distance than electromagnetic signals underwater. The significant disadvantage of the INS is the “drift,” the unbounded error growth over time in the outputs. This thesis is aimed to study and test a combined UUV navigation system that fuses measurements from the INS, Doppler Velocity Log (DVL), and Short Baseline (SBL) acoustic positioning system to reduce the drift. Two Kalman filters are used to do the fusion: the Extended Kalman Filter (EKF) and the Unscented Kalman Filter (UKF). After conducting the experiments and simulation, the results illustrated the INS/SBL fusion navigation approach was able to reduce the drift problems in the INS. Moreover, UKF showed a better performance than the EKF in the INS
Advances in Decentralized Single-Beacon Acoustic Navigation for Underwater Vehicles: Theory and Simulation
This paper reports the theory and implementation
of a decentralized navigation system that enables simultaneous
single-beacon navigation of multiple underwater vehicles. In
single-beacon navigation, each vehicle uses ranges from a single,
moving reference beacon in addition to its own inertial navigation
sensors to perform absolute localization and navigation. In this
implementation the vehicles perform simultaneous communication
and navigation using underwater acoustic modems, encoding
and decoding data within the acoustic broadcast. Vehicles calculate
range from the time of flight of asynchronous acoustic
broadcasts from the reference beacon. Synchronous clocks on
the reference beacon and the vehicles enable the measurement
of one-way travel-times, whereby the time of launch of the
acoustic signal at the reference beacon is encoded in the acoustic
broadcast and the time of arrival of the broadcast is measured
by each vehicle. The decentralized navigation algorithm, running
independently on each vehicle, is implemented using the
information form of the extended Kalman filter and has been
previously shown to yield results that are identical to a centralized
Kalman filter at the instant of each range measurement. We
summarize herein the architecture and design of the acoustic
communications (Acomms) system consisting of an underwater
acoustic modem, synchronous clock, and the software necessary
to run them, and salient results from the validation of the
decentralized information filter using a simulated data set.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86057/1/swebster-4.pd
Uncertainty Modeling for AUV Acquired Bathymetry
Abstract
Autonomous Underwater Vehicles (AUVs) are used across a wide range of mission scenarios and from an increasingly diverse set of operators. Use of AUVs for shallow water (less than 200 meters) mapping applications is of increasing interest. However, an update of the total propagated uncertainty TPU model is required to properly attribute bathymetry data acquired from an AUV platform compared with surface platform acquired data. An overview of the parameters that should be considered for data acquired from an AUV platform is discussed. Data acquired in August 2014 using NOAA’s Remote Environmental Measuring UnitS (REMUS) 600 AUV in the vicinity of Portsmouth, NH were processed and analyzed through Leidos’ Survey Analysis and Area Based EditoR (SABER) software. Variability in depth and position of seafloor features observed multiple times from repeat passes of the AUV, and junctioning of the AUV acquired bathymetry with bathymetry acquired from a surface platform are used to evaluate the TPU model and to characterize the AUV acquired data
Observations of High Frequency, Long Range Acoustic Propagation in a Harbor Environment
The positioning and navigation of AUV\u27s in harbor environments using underwater acoustics is complicated by shallow waters, long propagation distances, and complex oceanographic features. This paper reports on high frequency (40 kHz) acoustic measurements made in Portsmouth Harbor, NH, USA, which is an estuary containing several riverine inputs and a strong tidal flow (2+ knots). A one-way propagation experiment was conducted at the mouth of the harbor for propagation distances up to 100 water depths. Strong signatures of a variety of phenomenon were observed in the acoustic signal levels, including tidal heights and currents, turbulent mixing, and wind/wave action. The relative importance of each of these will be discussed in terms of signal to noise level and the associated constraints on acoustic positioning systems
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