What is an Attitude and Heading Reference System (AHRS)?
When navigating the complexities of motion sensing and navigation systems, it is essential to understand the distinctions between devices and systems like Inertial Measurement Units (IMUs), Inclinometers, Roll & Pitch sensors, Vertical Reference Units (VRU), Attitude and Heading Reference Systems (AHRS), Motion Reference Units (MRUs), Gyrocompasses, and GNSS-Aided Inertial Navigation Systems (GNSS/INS). Each serves specific purposes and offers different levels of functionality, accuracy, and application scope.
Attitude and Heading Reference System (AHRS)
Definition: An Attitude and Heading Reference System (AHRS) is an integrated system that builds on the capabilities of a Roll & Pitch sensor, offering complete orientation information—roll, pitch, and yaw (heading). It achieves this by processing data from an IMU combined with additional sensors, such as magnetometers or, in some cases, a north-seeking gyro (commonly referred to as a gyrocompass). An AHRS features an onboard processing unit that calculates attitude (roll and pitch) and heading using sensor fusion algorithms such as Kalman filters. It integrates data from accelerometers, gyroscopes, and magnetometers, applying these algorithms to correct sensor errors, biases, and drift, ensuring accurate and drift-free orientation. While combining sensors in an AHRS addresses many limitations, magnetic disturbances can still pose a challenge. Both internal and external disturbances may affect the magnetometer, potentially impacting the accuracy of the system's heading estimation.
Key Features:
- Sensors Included: Accelerometers, gyroscopes, and magnetometers.
- Output: Orientation data (roll, pitch, and heading).
- Functionality: Incorporates an onboard processing unit that utilizes sensor fusion algorithms (e.g., Kalman filters) to accurately compute orientation data.
- Applications: Provides real-time, accurate orientation data for navigation and control systems.
Example Uses:
- Maritime navigation systems
- Ship Stabilization Systems
- Aviation and drones
Selecting the appropriate sensor depends on the required measurements, environmental conditions, and budget.
- Use an IMU when you need raw acceleration and rotational data.
- Use an Inclinometer for simple, static tilt measurements.
- Use a Roll & Pitch Sensor for lower-level attitude measurements in a dynamic setting.
- Use a VRU when precise roll and pitch measurements are needed in a dynamic environment.
- Use an AHRS for roll, pitch, and heading data.
- Use an MRU for comprehensive motion data in dynamic marine environments.
- Use a Gyrocompass for accurate true north heading.
- Use a GNSS/INS for continuous, absolute position, velocity, and orientation data.
Related products
Usage area
50 m depth, IP 68
Connectors
Lemo or SubConn 8 or SubConn 16
Roll & Pitch accuracy
- 3000±0.05°
- 6000±0.02°
- 9000±0.01°
Heave accuracy
5 cm or 5.0%
Usage area
IP 65
Connectors
RJ45 or RJ50
Roll & Pitch accuracy
- 3000±0.05°
- 6000±0.02°
- 9000±0.01°
Heave accuracy
5 cm or 5.0%
Usage area
6000 m depth
Connectors
SubConn 8
Roll & Pitch accuracy
- 3000±0.05°
- 6000±0.02°
- 9000±0.01°
Heave accuracy
5 cm or 5.0%
Usage area
Hazardous areas
Connectors
Pigtail cable
Roll & Pitch accuracy
- 3000±0.05°
- 6000±0.02°
- 9000±0.01°
Heave accuracy
5 cm or 5.0%
Further reading
Advanced motion compensation for sonars introduced at Ocean Business 2025
MRUs for vessel performance optimisation in focus at Europort 2025
Research Project to Test Value of MRU Data for Vessel Performance and Carbon Reduction
Related questions
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What is the difference between the MRU Marine and MRU Marine SW?
- The MRU Marine has an IP-68 rating, uses a Lemo 16-pin connector and has indicator lights.
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When navigating the complexities of motion sensing and navigation systems, it is essential to understand the distinctions between devices and systems like Inertial Measurement Units (IMUs), Inclinometers, Roll & Pitch sensors, Vertical Reference Units (VRU), Attitude and Heading Reference Systems (AHRS), Motion Reference Units (MRUs), Gyrocompasses, and GNSS-Aided Inertial Navigation Systems (GNSS/INS). Each serves specific purposes and offers different levels of functionality, accuracy, and application scope.
Gyrocompass
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The MRU Compact uses a standard RJ45 ethernet cable where power is supplied through Passive PoE (Power over Ethernet). In most cases you cannot connect the MRU directly to a an ethernet switch with PoE, since most of these are Active PoE.
We normally supply your first MRU Compact with a start kit containing a POE RJ45 spliter socket. You will only need standard RJ45 cat5 ethernet cables to connect the MRU to the spliter socket and the spliter socket to your PC or ethernet switch.
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