In 2002, AML Oceanographic was approached to create a sound velocity sensor specifically designed for deployment with a helicopter dipping sonar system in support of ASW (anti-submarine warfare) activities.

Dipping sonar allows the helicopter to listen for and transmit underwater electronic signals while in a “hover” or stationary mode. The active sonar package can detect and maintain contact with underwater targets through a transducer lowered into the water. The system provides target identification clues and through active echo-ranging determines a target's range and bearing and opening or closing rate relative to the aircraft.  Sound Velocity was required for determining the SV profile through the water column and for acoustic beam steering.

The project presented some design challenges to overcome in order to facilitate the integration and operation of the sound velocity sensor on the helicopter deployed sonar head.  They include:

• Minimization of drag
• Impact protection as the package is immersed
• No acoustic interference with the sonar
• Concerns over EMI and RF interference
• Drag Reduction and Impact Protection

 A custom right angle (R/A) titanium sensor header was designed to mount the carbon composite SV sensor parallel to the sonar head thus reducing drag. To compensate for the close proximity to the end cap, grooved were designed in the face to ensure adequate water flow past the sensor.  This design combined with the strong materials chosen met the requirements for both drag reduction and impact protection.

The potential for EMI (electromagnetic interference) or RFI (radio frequency interference) on helicopter deployments is a strong concern.  EMI or RFI are unwanted disturbances that affect an electrical circuit due to electromagnetic radiation emitted from an external source.  The disturbance may interrupt, obstruct, or otherwise degrade or limit the effective performance of the circuit.  A custom aluminum enclosure was designed to protect the electronics from this harsh environment ensuring optimal performance of the SV dipping sonar.

The prototypes were shipped in 2002 and 2003 with ongoing orders being fulfilled.