PIES stands for Pressure Inverted Echo Sounder and the Origin 65 has one integrated as standard for accurately measuring two-way travel time (tau) and average sound velocity through the water column.
What is the requirement for two-way travel time data?
Robust relationships have been found to exist between two-way travel time and historical water column structure. As a result, two-way travel time data can be used to derive density profiles. Based on the concept of geostrophy, vertical profiles of seawater density can then be used to infer ocean currents (Watts and Rossby, 1977). More specifically, by combining current velocity data with water column density profile data, currents can be characterised in terms of strength and direction throughout the full water column over an extended area.
Networks of PIES instruments and current meters are ideal for physical oceanography studies of geostrophic currents, with this methodology applied by the University of Rhode Island for monitoring the Gulf Loop Current (Griffiths, 2018).
What is the requirement for average in situ sound velocity data?
Sound velocity data is used in seismic applications, and the Sonardyne PIES instrument has specifically been used in marine seismic acquisition to measure average sound velocity and tidal variation. The requirement for this data is due to the effects of sound velocity and tides, and their significant contributions to the non-repeatability of marine time-lapse seismic data (Wang et al., 2015).
What is the benefit of Origin 65’s integrated PIES?
As an ADCP with integrated PIES, Origin 65 can not only support but augment density mapping projects. The aforementioned project investigating the Gulf Loop Current used a separate single point current meter to provide a reference velocity for the calculated geostrophic currents. However, the ADCP has advantages over the single point current meter by measuring a whole profile over a greater range. Being an all-in-one instrument, Origin 65 also removes the risk and/or expense of combining separate devices for a single application, and what’s more, Origin 65’s PIES data is time-synchronised and fused with the ADCP measurements for simpler analysis.
Origin 65 can also lend itself to marine seismic acquisition programmes, generating the required sound velocity and tidal height data for accurate seismic processing whilst also providing the additional parameter of currents.
Contact [email protected] for more information.