Sonardyne International has retrieved its first Pressure Inverted Echo Sounder (PIES) off the coast of Hawaii. This new long life sensor logging node is designed to accurately measure the average sound velocity through a column of water from the seabed to the sea surface. The information gathered will help oceanographers to better understand the dynamics of the ocean and atmosphere-ocean coupling.
On the 24th of September, 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 from a PIES instrument on the seabed upwards. 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.
“We were keen to evaluate the performance of PIES so our team began the analysis of its data as soon as it was recovered,” said Shaun Dunn, Engineering Business Development Manager at Sonardyne speaking on the first day of the Oceanology International exhibition and conference in London where the Hawaii PIES data is being presented for the first time.
He continued, “Initial analysis suggests that there was very little variation in the sound velocity during the 39 day recording period with a fairly stable average of around 1500m/s throughout the deployment. This figure correlates well with independent measurements made at the deployment site. The data demonstrates the ability to accurately track the average water column sound velocity over long periods and this is thought to be of significant interest to oceanographers to enable them to better understand the physical processes that occur in the deep ocean. Sonardyne’s Wideband®2 PIES instrument provides an ideal platform from which these measurements can be made with a high degree of accuracy and repeatability”
Subsea World News Staff , March 20, 2012; Image: Sonardyne