First Operational Pressure Inverted Echo Sounder Retrieved

On 24th September 2011, the Sonardyne PIES was free-fall deployed into a 960-metre-deep water channel close to the big island of Hawaii, and commanded to log average sound velocity readings every seven minutes. Now, engineers have returned to the site and recovered the unit by acoustically commanding it to float to the surface under its own buoyancy.

Pressure inverted echo sounding is a technique that works by transmitting an acoustic pulse upwards from a PIES instrument on the seabed. The pulse is reflected off the water-air boundary at the sea surface and returns back down to the seabed where it is detected by the PIES. This enables an exact measurement of the two-way signal travel time to be calculated. At the same instant, an accurate measurement of depth is made using highly precise internal pressure sensors. Average water column velocity can then be calculated directly from the depth (i.e. distance) and travel time data.