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Basic principles - Underwater positioning and navigation

40 years of experience

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We have more than 40 years of experience within underwater positioning based on acoustics, or hydroacoustics as we call it. Hydroacoustic underwater positioning is based on sound waves in water. The systems use an antenna (the transducer) fitted into the vessel hull containing both a transmitter and a receiver. A signal (pulse) is transmitted aimed at a seabed transponder. The pulse activates the transponder, which will respond with a replay. The vessel transducer with corresponding electronics will calculate an accurate position of the transponder relative the vessel.

Typical problems for underwater positioning and navigation

Sound waves do not follow a straight path. Deflection occurs when the sound passes through different thermo clines in the sea. Thermo clines are a result of differences in temperature and salinity. The velocity of sound varies accordingly to these factors, and shadow zones can occur. Another problem with sound in water is noise generated from the vessel itself and surrounding objects.

Three principles

Our family of underwater positioning and navigation systems use three different principles for measurements and calculations.

SSBL - Super Short Base Line

Here the calculation of positioning is based on range, and on vertical and horizontal angle measurements, from a single multi element transducer. The system provides three-dimensional transponder positions relative to the vessel.

SBL - Short Base Line

The calculation of position is based on range, and vertical and horizontal angle measurements from a minimum of three hull mounted transducers. The system provides three-dimensional transponder positions relative to the vessel.

LBL - Long Base Line

The calculation of position is based on range measurements only. The vessel is positioned relative to a calibrated array of transponders.

Combined mode systems

Any combination of the three principles above secures flexibility as well as a high degree of redundancy and accuracy.