Distance and Cable Length Measurement System

A simple, economic and successful design for distance and cable length detection is presented. The measurement system is based on the continuous repetition of a pulse that endlessly travels along the distance to be detected. There is a pulse repeater at both ends of the distance or cable to be measured. The endless repetition of the pulse generates a frequency that varies almost inversely with the distance to be measured. The resolution and distance or cable length range could be adjusted by varying the repetition time delay introduced at both ends and the measurement time. With this design a distance can be measured with centimeter resolution using electronic system with microsecond resolution, simplifying classical time of flight designs which require electronics with picosecond resolution. This design was also applied to position measurement

Synchronous-Clock, One-Way-Travel-Time Acoustic Navigation for Underwater Vehicles

This paper reports the development and deployment of a synchronous-clock acoustic navigation system suitable for the simultaneous navigation of multiple underwater vehicles. Our navigation system is composed of an acoustic modem–based communication and navigation system that allows for onboard navigational data to be broadcast as a data packet by a source node and for all passively receiving nodes to be able to decode the data packet to obtain a one-way-travel-time (OWTT) pseudo-range measurement and navigational ephemeris data. The navigation method reported herein uses a surface ship acting as a single moving reference beacon to a fleet of passively listening underwater vehicles. All vehicles within acoustic range are able to concurrently measure their slant range to the reference beacon using the OWTT measurement methodology and additionally receive transmission of reference beacon position using the modem data packet. The advantages of this type of navigation system are that it can (i) concurrently navigate multiple underwater vehicles within the vicinity of the surface ship and (ii) provide a bounded-error XY position measure that is commensurate with conventional moored long-baseline (LBL) navigation systems [i.e., ] but unlike LBL is not geographically restricted to a fixed-beacon network. We present results for two different field experiments using a two-node configuration consisting of a global positioning system–equipped surface ship acting as a global navigation aid to a Doppler-aided autonomous underwater vehicle. In each experiment, vehicle position was independently corroborated by other standard navigation means. Results for a maximum likelihood sensor fusion framework are reported.Peer Reviewedhttp://deepblue.lib.umich.edu/bitstream/2027.42/86046/1/reustice-2.pd

Cooperative AUV Navigation using a Single Maneuvering Surface Craft

In this paper we describe the experimental implementation of an online algorithm for cooperative localization of submerged autonomous underwater vehicles (AUVs) supported by an autonomous surface craft. Maintaining accurate localization of an AUV is difficult because electronic signals, such as GPS, are highly attenuated by water. The usual solution to the problem is to utilize expensive navigation sensors to slow the rate of dead-reckoning divergence. We investigate an alternative approach that utilizes the position information of a surface vehicle to bound the error and uncertainty of the on-board position estimates of a low-cost AUV. This approach uses the Woods Hole Oceanographic Institution (WHOI) acoustic modem to exchange vehicle location estimates while simultaneously estimating inter-vehicle range. A study of the system observability is presented so as to motivate both the choice of filtering approach and surface vehicle path planning. The first contribution of this paper is to the presentation of an experiment in which an extended Kalman filter (EKF) implementation of the concept ran online on-board an OceanServer Iver2 AUV while supported by an autonomous surface vehicle moving adaptively. The second contribution of this paper is to provide a quantitative performance comparison of three estimators: particle filtering (PF), non-linear least-squares optimization (NLS), and the EKF for a mission using three autonomous surface craft (two operating in the AUV role). Our results indicate that the PF and NLS estimators outperform the EKF, with NLS providing the best performance.United States. Office of Naval Research (Grant N000140711102)United States. Office of Naval Research. Multidisciplinary University Research InitiativeSingapore. National Research FoundationSingapore-MIT Alliance for Research and Technology. Center for Environmental Sensing and Monitorin

Motion-aided Network SLAM

Summary. A key problem in the deployment of sensor networks is that of determining the location of each sensor such that subsequent data gathered can be registered. We would also like the network to provide localization for mobile entities, allowing them to navigate and explore the environment. In this paper, we present a thorough evaluation of our algorithm for localizing and mapping the mobile and stationary nodes in a sparsely connected sensor network using range-only measurements and odometry from the mobile node. Our approach utilizes an Extended Kalman Filter (EKF) in polar space allowing us to model the nonlinearities within the range-only measurements using Gaussian distributions. We demonstrate the e ectiveness of our approach using extensive real-world experiments with sparse connectivity and little to no prior information about the node locations.