Sound velocity profiling from a moving vessel

Paul Boughton
A partnership between a well-established UK instrument manufacturer and a USA developer of oceanographic deployment systems has resulted in an innovative system which can produce sound velocity profiles from a moving vessel.

Valeport Ltd (UK) and The Oceanscience Group (USA) have produced a package that could save surveyors both time and money when surveying.

Hydrodynamic nose

Traditionally performed profiles using SVPs or XBTs are the accepted method, but stopping or slowing vessels for sound velocity profiles is both expensive and time consuming.

The Underway SV allows vertical sound velocity profiles in minutes without ever having to stop the vessel with the ability to cast down to 1000m @ 4 knots vessel speed, or up to 10 Knots and 600m depth.

The Underway SV system approach utilises the best in sound velocity probe technology from Valeport and a winch deployment system from The Oceanscience Group. The Rapid SV probe has been designed to freefall through the water column at up to 5m/s whilst sampling at 32Hz.

The transducer is mounted in a hydrodynamic nose section to ensure good water flow and the electronics are housed in a 2000m rated titanium casing. A Bluetooth module allows fast and easy data recovery once the probe is out of the water.

The Underway SV winch features a large capacity reel with a high-torque dc drive unit and motorised level wind, for fast and safe probe deployment and retrieval.

The reel holds up to 2000m of high strength line for maximum profiling flexibility.

The main winch not only pays out line during deployment as the probe drops through the water column, but is rotated to provide line for re-spooling onto the probe using a tail re-winder for deep profiling.

The microprocessor controlled Underway SV tail spool re-winder precisely loads the profiler tail spool with high strength line; typically 350 to 550m of line is added from the main winch for each deployment. The unit may be programmed for different profile depths and is automated for quick turnaround.

Freshwater intrusion

The Underway SV is suitable for surveys where fluctuations in temperature or freshwater intrusion may create highly complex sound speed patterns.

The rapid profiling afforded by the Underway SV results in minimisation of downtime and reduced costs to quantify these sound velocity features.

Operating costs for the Underway SV are also minimal. The system uses no expendable components which makes it environmentally friendly and it also requires little maintenance as the profiler returns to the vessel after every cast, leaving no trace in the environment.

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Kevin Edwards is with Valeport Limited, Totnes, Devon, UK.

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