Pressure Inverted Echo Sounder (PIES) is an oceanographic instrument for measuring average sound speed in the water column. The instrument has been developed for marine seismic and ocean science applications to gather valuable physical oceanography data. PIES can be configured for autonomous monitoring over periods of several months or years. One key operational advantage for users is that minimal conductivity and temperature profiling is needed over the seismic survey period.
Pressure Inverted Echo Sounder
PIES uses an up chirp to accurately measure two-way travel-time through the water column. It simultaneously measures pressure at the seabed. Pressure measurements are converted to depth to find the acoustic distance travelled from the seabed to the surface and back again. By combining the depth and travel time the average sound speed in the water column can be calculated.
The user can retrieve two-way travel-time in seconds and pressure in kilo Pascals via an embedded acoustic modem. Alternatively the PIES unit can be retrieved to the surface. The SD Card Extractor software gives the user access to the raw data gathered by the instrument. Accurate conversion from pressure to depth can be achieved by allowing the user to include local barometric pressure, sea water density and gravity with the PIES data. The PIES unit is user configurable to capture at a programmable ping rate ranging from one minute to many minutes or even hours. The choice of ping rate enables the user to balance the conflicting demands of battery life with the need to average out effects from the instantaneous sea state at the time of acoustic measurement.
Logged data is typically retrieved once the survey is completed and PIES unit recovered. The PIES data is retrieved using the SD Card Extractor software and the raw measurements are post processed with geophysical data. The set-up for the SD Card Extractor is partially automatic and guides the user through the process. It can detect the current baud rate and minimise the time spent completing the extraction process.