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Glossary

Plain-language definitions of maritime robotics terms, grouped by topic. Tip: on every page of this site, hover over an acronym (for example DVL or USBL) to see what it means.

Core Concepts

Marine Robotics / Maritime Robotics
Building and operating robots that work in, on, or underwater environments.
ROS (Robot Operating System)
Open-source software framework for building robot applications. Despite the name, it's not an operating system like Windows or Linux - it's a set of tools and libraries that run on top of an OS (usually Linux). Think of it as a toolkit that helps robots' different parts talk to each other.
ROS 2
The current generation of ROS with improved real-time behavior and security features.
Autonomy / Autonomous
The robot can make decisions and operate on its own without constant human control. An autonomous robot can navigate, avoid obstacles, and complete missions independently.
Simulation / Simulator
Software that creates a virtual environment where you can test robots without needing physical hardware or water. Like a video game for robots - you can make mistakes safely and test ideas quickly.

Vehicle Types

Surface Vehicles

ASV (Autonomous Surface Vehicle)
A boat or ship that operates on the water's surface without a crew onboard. It makes its own navigation decisions.
USV (Uncrewed Surface Vehicle)
Similar to ASV - a surface vessel with no people aboard. The terms are often used interchangeably, though USV can include both autonomous and remotely-controlled vessels.
WAM-V
Wave Adaptive Modular Vessel - a specific type of catamaran (twin-hull boat) platform used in robotics competitions and research.

Underwater Vehicles

AUV (Autonomous Underwater Vehicle)
A robot submarine that operates independently underwater. No cable to the surface - it follows pre-programmed missions or makes its own decisions.
ROV (Remotely Operated Vehicle)
An underwater robot controlled by a human operator via a tether (cable). The cable provides power and communication. Like flying a drone, but underwater.
UUV (Unmanned Underwater Vehicle)
General term for any underwater vehicle without people inside - includes both AUVs and ROVs.
Glider
A special type of AUV that doesn't have a propeller. It uses buoyancy changes to glide through the water in a sawtooth pattern. Energy-efficient for long missions.
Torpedo-shaped AUV
An AUV with a streamlined, cylindrical hull (like a torpedo). Efficient for long-distance travel in a straight line.
Hovering AUV
An AUV with multiple thrusters allowing it to move in any direction and hover in place. Good for detailed inspection work.

Sensors and Navigation

DVL (Doppler Velocity Log)
A sonar-based sensor that measures how fast the robot is moving relative to the seafloor or water. Essential for underwater navigation since GPS doesn't work underwater. Uses the Doppler effect (same physics that makes ambulance sirens change pitch as they pass you).
IMU (Inertial Measurement Unit)
A sensor that measures acceleration and rotation. Helps the robot know which way is up and how it's oriented. Contains accelerometers and gyroscopes.
INS (Inertial Navigation System)
A more advanced version of an IMU that can calculate position by tracking all movements. Higher accuracy than a basic IMU.
GPS / GNSS (Global Navigation Satellite System)
Satellite-based positioning system. Important: GPS doesn't work underwater! Only useful when a vehicle surfaces. GNSS is the generic term for all satellite navigation systems (GPS, GLONASS, Galileo, etc.).
Depth Sensor / Pressure Sensor
Measures water pressure to determine depth underwater. Deeper water = higher pressure. Simple and reliable.
CTD (Conductivity, Temperature, Depth)
A sensor package that measures three key ocean properties: - Conductivity: How well water conducts electricity (indicates salinity/saltiness) - Temperature: Water temperature - Depth: How deep the robot is
Sonar
Uses sound waves to "see" underwater (like bat echolocation). Light doesn't travel far in water, but sound does. Different types: - Imaging Sonar: Creates pictures from sound reflections - Multibeam Sonar: Maps the seafloor - Side-scan Sonar: Creates wide-area images of the seabed - Forward-looking Sonar (FLS): Detects obstacles ahead
Hydrophone
An underwater microphone. Listens to sounds in the ocean.

Control and Motion

DOF (Degrees of Freedom)
The number of independent ways a body can move. A car moves in 3 DOF on the road (forward, sideways, turning) but can control only 2 of them directly. A marine vehicle moves in 6 DOF; how many it can control depends on its thrusters: - Surge: Forward/backward - Sway: Left/right (sideways) - Heave: Up/down - Roll: Rotation around front-to-back axis (like a barrel roll) - Pitch: Rotation around left-to-right axis (nose up/down) - Yaw: Rotation around vertical axis (turning left/right)
Thruster
An underwater propeller that pushes the robot. Most marine robots have multiple thrusters to control different directions.
Thrust Allocation
The math that figures out how much power to send to each thruster to make the robot move in the desired direction.
Azimuth Thruster
A thruster that can rotate to point in different directions. More flexible than fixed thrusters.
Buoyancy
The upward force that makes things float. Submarines and AUVs carefully balance their buoyancy to neither sink nor float.
Ballast
Weight added to a robot to control buoyancy. Some robots can pump water in/out to adjust their ballast.

Control Systems

PID Controller
A common control algorithm (Proportional-Integral-Derivative). Helps the robot smoothly reach a target position or heading. Like cruise control in a car.
Waypoint
A target position or GPS coordinate the robot should navigate to. A mission might have many waypoints in sequence.
Path Planning
Algorithm that calculates the route the robot should take from start to finish, avoiding obstacles.
Localization
Figuring out where the robot is. Underwater this is hard since GPS doesn't work - robots use DVL, IMU, and sometimes acoustic beacons.
SLAM (Simultaneous Localization and Mapping)
Building a map of an unknown environment while simultaneously figuring out where you are in that map. Challenging but powerful technique.
EKF / UKF (Extended/Unscented Kalman Filter)
Mathematical techniques for combining data from multiple sensors to get a better estimate of position and velocity. Handles noisy sensor data intelligently.

Communication

Acoustic Communication / Acoustic Modem
Underwater "wireless" communication using sound waves. Much slower than WiFi (much lower data rates) but works underwater where radio doesn't.
WHOI Micro-Modem
An underwater acoustic modem developed by the Woods Hole Oceanographic Institution, widely used on research vehicles. ros_acomms supports it.
RF (Radio Frequency)
Traditional wireless communication (like WiFi, cellular, radio). Works great in air, but doesn't work underwater - water absorbs radio waves quickly.
Tether
The cable connecting an ROV to the surface. Provides power and high-bandwidth communication (like an underwater Ethernet cable). Limits how far the ROV can go.
Satellite Communication
Communication via satellites. Used by surface vehicles or AUVs when they surface. Expensive but works anywhere on Earth.
USBL (Ultra-Short Baseline)
Acoustic positioning system that uses sound to track an underwater robot's position from a surface ship. Measures range and bearing (direction).
LBL (Long Baseline)
A network of underwater acoustic beacons deployed on the seafloor. The robot triangulates its position using these beacons. More accurate than USBL but requires setup.

Software and Development

Gazebo
A widely used robotics simulator. Can simulate physics, sensors, and robot movement in a 3D environment. Free and open-source.
VRX (Virtual RobotX)
A simulated maritime robotics competition based on Gazebo.
DAVE (Dave Aquatic Virtual Environment)
An underwater vehicle simulation environment built on Gazebo. The ROS 2 version is now called POSIM.
RViz
A visualization tool for ROS. Shows you what the robot "sees" - sensor data, camera images, point clouds, etc. Helpful for debugging.
Topic
In ROS, a named channel where messages are published. For example, /camera/image might be the topic where camera images are published. Like a TV channel - anyone can tune in.
Node
In ROS, a single program or process that does one specific job. A robot might have many nodes working together (one for camera, one for navigation, one for control, etc.).
Message
In ROS, data sent over a topic. Has a specific format/structure. Like a package being delivered.
Launch File
A file that starts multiple ROS nodes at once with their configurations. Convenient for starting complex robot systems.
MCAP
An open log file format for timestamped robot data, and the default storage format of rosbag2.
QoS (Quality of Service)
ROS 2 topic settings such as reliable or best effort delivery and queue depth. Important on slow or lossy links.
Colcon / Catkin
Build tools for ROS. Colcon is used in ROS 2, Catkin was used in ROS 1. They compile your code and set up the workspace.

Organizations and Institutions

WHOI (Woods Hole Oceanographic Institution)
A major ocean research institution in Massachusetts, USA, with a long history in marine robotics and ocean engineering.
MBARI (Monterey Bay Aquarium Research Institute)
Ocean research institute in California with significant work in marine robotics.
ROS-Maritime
The ROS Maritime Community Working Group, an open group in the ROS community that maintains this site, shares interfaces, and hosts monthly meetings. See Community.

Competition and Standards

RobotX
An international maritime robotics competition for autonomous surface vehicles. Teams compete in tasks like navigation, object detection, and docking.
MBZIRC (Mohamed Bin Zayed International Robotics Challenge)
A major robotics competition that includes maritime challenges.
SAUVC (Singapore AUV Challenge)
Student-focused underwater robotics competition. Held in Singapore.
MATE ROV Competition
Popular student competition for remotely operated vehicles. Multiple divisions from high school to university.

Coordinate Frames

NED (North-East-Down)
A coordinate system where: - X points North - Y points East - Z points Down (toward Earth's center) - Common in aerospace and marine navigation
ENU (East-North-Up)
A coordinate system where: - X points East - Y points North - Z points Up (away from Earth) - The ROS standard for world frames (REP 103)
Body Frame
A coordinate system attached to the robot that moves and rotates with it. In ROS (REP 103) the body frame is FLU: x forward, y left, z up. In marine and aerospace practice it is often FRD: x forward, y right, z down. See Frames and conventions.
FLU / FRD
Forward-Left-Up and Forward-Right-Down body frames. ROS uses FLU; many marine instruments and autopilots use FRD.
Heading
The direction the bow points, measured clockwise from north (true or magnetic). Not the same as ROS yaw, which is measured counter-clockwise from east: yaw = 90° − heading.
REP 103 / REP 105
ROS Enhancement Proposals that define units and axis conventions (103) and the map, odom, and base_link frames (105).

Miscellaneous Terms

Open-source
Software where the code is freely available for anyone to use, modify, and share. ROS and most tools in this landscape are open source.
URDF (Unified Robot Description Format)
An XML format for describing a robot's physical structure (links, joints, sensors). Tells ROS what your robot looks like.
TF / TF2 (Transform)
ROS system for tracking coordinate frames. Keeps track of where different parts of the robot are relative to each other and the world.
Workspace
In ROS, a directory containing your code and packages. Where you do development.
Package
In ROS, a collection of related code, configuration files, and documentation organized together. Like an app or library.
Repository / Repo
A place where code is stored and version-controlled, usually on GitHub or GitLab.
CI (Continuous Integration)
Automated testing that runs every time code changes. Catches bugs early.

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