Correlation Velocity Log (CVL) for Underwater Navigation

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Energy, Engineering

AquaTrak™ is a state-of-the-art correlation velocity log that provides long range robust bottom tracking, even in rapidly changing topography.

With long-term accuracy exceeding a typical 1200kHz Doppler Velocity Log (DVL) and the range of a 300kHz DVL, AquaTrak™ represents a leap forward in velocity log technology, all from a single 3000m depth rated unit.

A DVL relies on the Doppler Effect to calculate velocity, which requires knowing the speed of sound. AquaTrak™ differs by using an advanced acoustic cross-correlation technique to calculate the distance moved between two very closely spaced pulses transmitted from a single transmitter and is thus, independent from knowing the speed of sound. With a wide vertical beam, as opposed to the tilted beams of a DVL, there is no error from the speed of sound mismatch and the majority of the transmitted energy is returned from the seabed rather than being scattered out to the sides, which results in the AquaTrak™ having a reduced source level to achieve the comparable range of DVL.

AquaTrak™ provides accurate velocity estimates at low speeds, as it does not rely on a Doppler shift, which in turn requires movement to provide a robust velocity estimate. Therefore, AquaTrak™ is the ideal navigation tool for complex, low-speed manoeuvres, which are common operations for Workclass ROVs.

Designed as a drop-in replacement for industry standard DVLs, AquaTrak™ provides the same level of performance irrespective of altitude with a class-leading range of 0.5m to 300m. With simultaneous data outputs over Ethernet and Serial, the standard PD 4 / 6/ 11 outputs from the AquaTrak™ CVL can be used to satisfy the requirements of both the ROV crew and survey team at the same time. With a flat transducer face, cavitation and turbulence (common issues with Janus configured DVLs), are kept to a minimum.

Deployed on ROVs or AUVs, AquaTrak™ provides high altitude bottom lock that dramatically improves long-term accuracy, reducing overall drift with or without USBL aiding. Furthermore, by removing the reliance on the speed of sound input to calculate velocity, any system errors and biases are further reduced.

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