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IEEE International Conference on Acoustics, Speech, and Signal Processing

作者： Atulya Yellepeddi James C. Preisig Electrical Eng./Applied Ocean Physics and Eng. MIT-WHOI Joint Program Applied Ocean Physics and Engineering Woods Hole Oceanographic Institution

ISBN: (纸本)9781479903573

Adaptation of the coefficients of an equalizer usually takes place in the decision directed mode. The decision used for adaptation has a profound influence on the performance of the equalizer. In this work, we consider the influence of the probabilistic model used by a soft information decision device on the performance of the equalizer. It is shown that the equalizer output is distributed as a Gaussian Mixture, and these statistics are used to form a soft-decision device. We show that this is very near optimal in the sense of the Recursive Expected Least Squares algorithm introduced in prior work. Sub-optimal decision devices that are often more practical are also introduced and the loss of performance as a result of using these is considered.

关键词： Equalizers adaptive signal processing adaptive equalizers time-varying channels

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APPROXIMATE LEAST SQUARES PARAMETER ESTIMATION WITH STRUCTURED OBSERVATIONS

APPROXIMATE LEAST SQUARES PARAMETER ESTIMATION WITH STRUCTUR...

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IEEE International Conference on Acoustics, Speech and Signal Processing

作者： Atulya Yellepeddi James C. Preisig Electrical Eng./Applied Ocean Physics and Eng. MIT-WHOI Joint Program Applied Ocean Physics and Engineering Woods Hole Oceanographic Institution

ISBN: (纸本)9781479928941

The solution of inverse problems where the parameter being estimated has a known structure has been widely studied. In this work, we consider the situation where it is not appropriate to assume a structure for the parameter, but the observations on which the estimate are based are structured;specifically, when the observations are parametrized by a decomposable graphical model. This translates to structured sparsity of the inverse covariance matrix for Gaussian distributed observation vectors. We present an approximate least squares method which takes advantage of the structure to reduce the complexity of least squares. The approximate least squares method can be implemented recursively for even lower complexity. It is shown that the proposed method is asymptotically equivalent to least squares parameter estimation for a large number of observations. The properties of the algorithm are verified by simulation.

关键词： Least squares method variance covariance matrix Asymptotically equivalent Inverse method Parameter estimation Approximate

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Soft-adaptive turbo equalization: Using soft information in adaptation

Soft-adaptive turbo equalization: Using soft information in ...

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Asilomar Conference on Signals, Systems & Computers

作者： Atulya Yellepeddi James C. Preisig Electrical Engineering/Applied Ocean Science and Engineering WHOI Joint Program MIT USA Applied Ocean Science and Engineering Woods Hole Oceanographic Institution Woods Hole MA USA

ISBN: (纸本)9781467350501

Turbo equalizers have been exploited for underwater wireless communication due to their excellent practical performance. As the equalizer is adaptive, it is possible to take advantage of the soft information available from the decoder in the adaptation process. In this paper, we consider a method to do this and compare it with the use of soft information in feedback, which is a method that has been considered in the past. Data from the KAM11 experiment demonstrates that using soft information in adaptation can improve performance over using it only in feedback. We also consider combining these different approaches and how this affects performance.

关键词： Using how this soft information Equalizers Worm gears Turbo CARRIER SYSTEM Feedback Equalization decoders

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Experiments in dynamic control of autonomous marine vehicles using acoustic modems

Experiments in dynamic control of autonomous marine vehicles...

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IEEE International Conference on Robotics and Automation (ICRA)

作者： Eric Gilbertson Brooks L. Reed Josh Leighton Mei Yi Cheung Franz S. Hover Department of Mechanical Engineering Massachusetts Institute of Technology USA WHOI Joint Program in Oceanographic Engineering Massachusetts Institute of Technology USA

ISBN: (纸本)9781467356404

Marine robots are an increasingly attractive means for observing and monitoring in the ocean, but underwater acoustic communication (“acomms”) remains a major challenge, especially for real-time control. Packet loss occurs widely, bit rates are low, and there are significant delays. We consider here strategies for feedback control with acomms links in either the sensor-controller channel, or the controller-actuator channel. On the controller-actuator side we implement sparse packetized predictive control (S-PPC), which simultaneously addresses packet-loss and the data rate limit. For the sensor-controller channel we study a modified information filter (MIF) in a Linear Quadratic Gaussian (LQG) control scheme. Field experiments were carried out with both approaches, regulating crosstrack error in a robotic kayak using acomms. Outcomes with both the S-PPC and MIF LQG confirm that good performance is achievable.

关键词： Acoustics Packet loss Sensors Delays Vehicles Trajectory

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Adaptive multi-altitude search and sampling of sparsely distributed natural phenomena

Adaptive multi-altitude search and sampling of sparsely dist...

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IEEE/RSJ International Conference on Intelligent Robots and Systems (IROS)

作者： Jessica E. Todd Seth McCammon Yogesh Girdhar Nicholas Roy Dana Yoerger Department of Aeronautics and Astronautics MIT-WHOI Joint Program in Applied Ocean Science and Engineering at the Woods Hole Oceanographic Institution (WHOI) Massachusetts Institute of Technology (MIT) Applied Ocean Physics and Engineering Department Woods Hole Oceanographic Institution Woods Hole MA USA Department of Aeronautics and Astronautics Massachusetts Institute of Technology

ISBN: (数字)9798350377705

ISBN: (纸本)9798350377712

In this paper, we propose a novel method for autonomously seeking out sparsely distributed targets in an unknown underwater environment. Our Sparse Adaptive Search and Sample (SASS) algorithm mixes low-altitude observations of discrete targets with high-altitude observations of the surrounding substrates. By using prior information about the distribution of targets across substrate types in combination with belief modelling over these substrates in the environment, high-altitude observations provide information that allows SASS to quickly guide the robot to areas with high target densities. A maximally informative path is autonomously constructed online using Monte Carlo Tree Search with a novel acquisition function to guide the search to maximise observations of unique targets. We demonstrate our approach in a set of simulated trials using a novel generative species model. SASS consistently outperforms the canonical boustrophedon planner by up to 36% in seeking out unique targets in the first 75-90% of time it takes for a boustrophedon survey. Additionally, we verify the performance of SASS on two real world coral reef datasets.

关键词： Surveys Adaptation models Monte Carlo methods Adaptive systems Marine vegetation Substrates Intelligent robots

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The Ceres Human Exploration and Transit Architecture (CHEATA): A Mission Architecture for Small Bodies Exploration 73

The Ceres Human Exploration and Transit Architecture (CHEATA...

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73rd International Astronautical Congress, IAC 2022

作者： Todd, Jessica Gentgen, Chloe Porter, Allison Bellisle, Rachel Martell, Benjamin Hoffman, Jeffrey Department of Aeronautics and Astronautics Massachusetts Institute of Technology 77 Massachusetts Ave CambridgeMA02139 United States MIT-WHOI Joint Program in Oceanography/Applied Ocean Science and Engineering Woods Hole Oceanographic Institution Woods HoleMA United States Harvard-MIT Health Sciences and Technology Massachusetts Institute of Technology 77 Massachusetts Ave CambridgeMA02139 United States

The Ceres Human Exploration and Transit Architecture (CHEATA) is a conceptual mission developed to enable human exploration of Ceres and other small bodies in the asteroid belt. These small bodies present tempting targets for future human exploration, providing insight into the evolution of our solar system, potentially containing environments of interest to astrobiologists, and acting as water- and mineral-rich stepping stones for outer solar system exploration. Minimizing radiation exposure and mission duration while maximizing surface science operations on the surface of Ceres was the critical driving requirement for this design reference mission. Key elements of the design include (1) a low gravity hopping vehicle using vacuum retro-propulsion and LOX/Methane propellant, taking advantage of the low gravity environment for regional exploration and surface operations on Ceres, (2) a bimodal nuclear thermal propulsion (NTP) system that utilizes liquid hydrogen and a reusable CERMET core, and (3) an active high-temperature superconducting magnet system, complemented by a passive high-density polyethylene system, to mitigate crew exposure to galactic cosmic radiation and solar energetic particle events. A transit habitat vehicle is assembled in cislunar space and used to ferry astronauts to Ceres orbit. The study also details breakdowns of the human countermeasures employed to address the effects of microgravity and isolation. The CHEATA mission concept was initially presented at the IEEE Aerospace Conference in 2022. The mission architecture has been updated to now include the design of additional spacecraft and habitation subsystems. These include the design of an Environmental Control and Life Support System, secondary propulsion for corrections, small maneuvers, and attitude control, but also more in-depth power and thermal management systems. The propellant storage was refined with the inclusion of zero boil-off technology for the Liquid Hydrogen tanks. A detail

关键词： Liquefied gases

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Correction: Oceanic bottom mixed layer in the Clarion-Clipperton Zone: potential influence on deep-seabed mining plume dispersal

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Environmental Fluid Mechanics 2024年第6期24卷 1443-1444页

作者： Chen, Si-Yuan Sean Ouillon, Raphael Muñoz-Royo, Carlos Peacock, Thomas Department of Mechanical Engineering Massachusetts Institute of Technology Cambridge USA Department of Physical Oceanography Woods Hole Oceanographic Institution Woods Hole USA MIT-WHOI Joint Program in Oceanography Massachusetts Institute of Technology Cambridge USA

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A Low-Cost Entangling Drifter for Sargassum Tracking: Design and Experimental Evaluation

A Low-Cost Entangling Drifter for Sargassum Tracking: Design...

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OCEANS

作者： Chase Pixa Kevin Manganini Alyson Myers Anna PM Michel MIT-WHOI Joint Program in Applied Ocean Science and Engineering Cambridge USA Applied Ocean Physics and Engineering Woods Hole Oceanographic Institution USA Fearless Fund Washington D.C. USA

Since 2011, Sargassum, a free-floating macroalgae, has been causing significant ecological and economic damage to coastal regions in the Northern Equatorial Atlantic due to its voluminous blooms. To better understand the fate and effects of Sargassum, approaches are needed to track its transport. Here we developed a low-cost drifter, designed to entangle with Sargassum, to aid in its tracking providing in situ movement data to ground-truth models and supplementing gaps in satellite imaging. The results of 27 drifter designs and five days of field trials are presented. The successful entanglement and tracking with the Sargassum demonstrated here can guide future studies to further our understanding of the movement of Sargassum in the great Atlantic Sargassum belt (GASB).

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Improved vehicle based multibeam bathymetry using sub-maps and SLAM

Improved vehicle based multibeam bathymetry using sub-maps a...

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2005 IEEE/RSJ International Conference on Intelligent Robots and Systems

作者： C. Roman H. Singh MIT/WHOI Joint Program in Applied Ocean Science and Engineering Massachusetts Institute of Technology Cambridge MA USA Department of Applied Ocean Physics and Engineering Woods Hole Oceanographic Institution Woods Hole MA USA

This paper presents an algorithm to improve sub-sea acoustic multibeam bottom mapping based on the simultaneous mapping and localization (SLAM) methodology. Multibeam bathymetry from underwater water vehicles can yield valuable large scale terrain maps of the sea door, but the overall accuracy of these maps is typically limited by the accuracy of the vehicle position estimates. The solution presented here uses small bathymetric patches created over short time scales in a sub-mapping context. These patches are registered with respect to one another and assembled in a single coordinate frame to produce a more accurate terrain estimate and provide improved renavigation of the vehicle trajectory. The mapping is implemented using a delayed state extended Kalman filter (EKF) and results are shown for a real world multibeam data set collected at the mid-Atlantic ridge using the JASON ROV.

关键词： Simultaneous localization and mapping Terrain mapping Marine vehicles Underwater vehicles Underwater acoustics Large-scale systems Yield estimation Assembly Delay Remotely operated vehicles

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Visually augmented navigation in an unstructured environment using a delayed state history

Visually augmented navigation in an unstructured environment...

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IEEE International Conference on Robotics and Automation (ICRA)

作者： R. Eustice O. Pizarro H. Singh MIT/WHOI Joint Program in Applied Ocean Science and Engineering Massachusetts Institute of Technology Cambridge MA USA Department of Applied Ocean Physics and Engineering Woods Hole Oceanographic Institution Woods Hole MA USA

This work describes a framework for sensor fusion of navigation data with camera-based 5 DOF relative pose measurements for 6 DOF vehicle motion in an unstructured 3D underwater environment. The fundamental goal of this work is to concurrently estimate online current vehicle position and its past trajectory. This goal is framed within the context of improving mobile robot navigation to support sub-sea science and exploration. Vehicle trajectory is represented by a history of poses in an augmented state Kalman filter. Camera spatial constraints from overlapping imagery provide partial observation of these poses and are used to enforce consistency and provide a mechanism for loop-closure. The multi-sensor camera + navigation framework is shown to have compelling advantages over a camera-only based approach by: 1) improving the robustness of pairwise image registration, 2) setting the free gauge scale, and 3) allowing for a unconnected camera graph topology. Results are shown for a real world data set collected by an autonomous underwater vehicle in an unstructured undersea environment.

关键词： Navigation Delay History Cameras Underwater vehicles Robot vision systems Sensor fusion Motion measurement Mobile robots Robustness

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