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Hydroacoustic Aided Inertial Navigation, DP applications

HAIN Reference

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The complementary solution

HAIN Positioning Refrence
The HAIN Positioning Reference Hydroacoustic Aided Inertial Navigation system is ideal for use with Dynamic positioning systems.

Acoustic and Inertial positioning principles in combination is ideal, since they have complementary qualities. Acoustic positioning is characterised by relatively high and evenly distributed noise and no drift in the position, whilst Inertial positioning has very low short-term noise and relatively large drift in the position over time.

Easy installation

A HAIN computer onboard the vessel interfaces the Inertial Measurement Unit (IMU) via a serial line, and the Acoustic Positioning system (HiPAP or HPR) via an Ethernet interconnection. The HAIN position reference system provides:

  • Improved acoustic position accuracy The HAIN system will typically improve the accuracy some 2-3 times. Example: If the "ping to ping" deviation is 6 meters, the HAIN will reduce this to approximately 2 meters.
  • Higher position update rate The HAIN calculates a new position every 1 second regardless of water depth.
  • Extends operational depth capabilities Since both the accuracy and the position update rate are improved, the HAIN allows operation in deeper waters.
  • Longer transponder-battery lifetime The HAIN position update rate allows slowing down the acoustic update frequency. This will result in less "ping" per hour, and thereby longer battery duration.
  • Position update during acoustic drop-out The HAIN gives continuity in position output, even though the acoustic position should fail to operate in periods of limited time.

Hydroacoustic Aided Inertial Navigation - HAIN

The HAIN positioning system can be used on any vessel equipped with an acoustic positioning system. Inertial Measurement Unit - IMU The IMU contains three accelerometers and three Fibre Optic Gyro that measure the vessel’s accelerations and rotation in three axes very accurately.

HAIN computer

The HAIN computer executes the navigation algorithm, which consists of strap-down navigation equations and a Kalman filter. The unit is interfaced to an IMU and to an acoustic positioning operator station. The HAIN computer receives the aiding positions (latitude and longitude) from the acoustic positioning operator station and will limit the position drift that is inherent in inertial navigation systems. Vessel position, attitude, speed and expected accuracy of the data are sent back to the operator station at a 1 Hz update rate.

Operator station

The HAIN system is operated from an acoustic positioning operator station. The information received from the HAIN computer is displayed and sent to external computer(s). The operator station can request status information from the HAIN computer to be displayed, which helps the operator to check the system in real-time.

Data Logging

HAIN system interconnection
HAIN Positioning Reference system interconnection to external systems

Data logging can be done on two levels:

  • The HAIN computer is logging all measurements on its hard disk. These data can be post-processed.
  • The APOS can log measured and calculated vessel positions, attitude and velocity on its hard disk.

All measurements and positions in the log files are time stamped. The operator station clock and the HAIN computer clock are both synchronised with the GPS clock (1pps).

Accuracy

HAIN accuracy
Accuracy as a function of depth for HAIN Positioning Reference - Hydroacoustic Aided Inertial Navigation system.

HAIN combines the acoustic measurements and the readings from the IMU sensor installed onboard in an optimum way. The navigation equations update the vessel position, velocity, heading and attitude almost continuously based on the readings from the IMU. The Kalman filter corrects these values when new acoustic positions are available. This gives improved position accuracy compared to the acoustic measurements, as illustrated in the figure below.

The simulation parameters used in the figure are:

  • HiPAP SSBL angle accuracy: 0.1° in x and y
  • dGPS position white / coloured noise: 0.15 m / 0.1 m North and East

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