INTERVIEW – The ADCP and CTD are two classical instruments for measuring oceanic physical characteristics. Stéphanie Barrillon, researcher at MIO, explains how they work.
THE INSTRUMENTS OF OCEANOGRAPHERS – Stéphanie Barrillon, is a researcher at the Mediterranean Institute of Oceanography (MIO) CNRS/INSU in Marseille, France. Her research focuses on the investigation of the oceanic vertical velocities and their impact. During the BioSWOT-Med campaign she will be in charge, among others, to deploy and analyze data from the ADCP and CTD. She explains what they are and how they work.
What are your research interests?
I’m interested in understanding the oceanic vertical velocities and their impact. These vertical velocities are present everywhere in the ocean but still largely undetermined. Their in situ measurement is very challenging, in particular because of their low intensities. How to measure them in situ and with which precision? How do they structure the ocean vertical dynamics? What IS their impact on nutrients’ transport upward the surface and on the carbon sequestration to the bottom of the ocean? The BioSWOT-Med cruise will certainly bring some building blocks towards the answers to these questions…
The FF-ADCP was developed at MIO. What is the difference with other existing ADCP?
The ADCP (Acoustic Doppler Current Profiler) is a classical instrument for measuring oceanic currents using acoustic beams and the Doppler effect. ADCPs are usually used for the horizontal components measurements, but we are now exploiting them for the vertical component. In particular, the new generation ADCPs can have an additional vertical beam dedicated to this component.
ADCPs are either fixed on the bottom of the ship or deployed with a package attached to the ship, their measurements are thus largely influenced by the ship movement.
The idea of the FF-ADCP (ADCP in Free Fall) is to decouple the ADCP from the vertical movement of the ship: attached to the ship by a loose rope, the FF-ADCP falls freely, independently from the ship movements. Thanks to this decoupling, and using the vertical beam of the new generation ADCPs, the measurement of the vertical velocities reaches a precision of a few mm/s.
In the BioSWOT-Med campaign, among other things, you will be in charge of the CTD. Can you explain what it is?
The CTD (Conductivity, Temperature, Depth) probe is yet another classical instrument in oceanography that measures pressure, conductivity and temperature of the water. It is usually fixed on a vertical moving package electrically connected to the ship. This package contains a lot of other instruments to measure physics and biological observables through the water column, as well as Niskin bottles to sample water at different depths. A lot of profiles will be performed using this package during the BioSWOT-Med cruise.
Contact: Tosca Ballerini (news@swot-adac.org)
