INTERVIEW – Anne Petrenko is in charge of analysis of hull mounted ADCP and of deployment of L-ADCP and FF-ADCP in the BioSWOT-Med campaign. Here, she describes how these instruments work and what are the differences among them.
THE INSTRUMENTS OF OCEANOGRAPHERS – Anne Petrenko is a Professor at Aix-Marseille University, in the Mediterranean Institute of Oceanography. She’s a physical oceanographer with interdisciplinary competences and interests.
What are your research interests besides BioSWOT-Med?
Science-wise, for a while I have concentrated my research on coastal circulation, coast-offshore gradients, using multidisciplinary approaches : in situ data, modeling outputs, satellite. Apart from currents, the data include classical temperature, salinity, depth but also all kind of optical data providing information on phytoplankton and particles present in the water column. I generally measure currents with ADCPs as described below.
Lately, with our PhD student Caroline Comby, and colleagues Stephanie Barrillon and Jean-Luc Fuda and others, we have focused on the challenge to estimate vertical velocities. We re doing it either theoretically (with equations) or by measurements. In the latter case, we have two types of approaches: either using a flight model as in the case of VVP, or with 5-beam ADCPs (ADCPs with a special vertical beam). We have been doing these measurements in low energy regions (with relatively small vertical velocities) to challenge our results and are also aiming at measuring these velocities in areas with stronger ascending or descending velocities. The aim afterwards is to connect the results with biology, and in the future HOPE-VV program (starting at the end of 2023) to connect it with carbon export due to trichodesmium in the South Pacific.
Aside from science, I love swimming, walking/hiking, singing, reading, doing yoga and teaching hatha yoga. Teaching yoga is completely different from teaching science but, in both cases, it is great to either sow seeds or, even better, see “plants” growing. I really enjoy teaching, love to see people/student understand new concepts. Maybe it is linked to the fact that I bloom on learning new things myself. I am very curious, enthousiastic at discovering new ways of thinking. I suppose that’s why I am a scientist. I am never bored in our job.
In the BioSWOT-Med campaign, among other things, you will be in charge of analysis of hull mounted ADCP and of deployment of L-ADCP and FF-ADCP. What are they and how do they work?
An acoustic Doppler current profiler (ADCP) is an instrument used to measure water current velocities over a depth range using the Doppler effect of sound waves, scattered back from particles within the water column. If a sound is emitted and there is a receiver, the Doppler effect consists in having the sound pitch getting higher (lower) when the distance transmitter/receiver shortens (lengthens). The quicker the distance changes, the quicker the sound pitch changes. Reversely, if we measure the pitch drift from its initial value, we can evaluate the relative displacement between the transmitter and the receiver. That is what we are using with ADCPs with the hypothesis that the particles -on which the sound backscatters- are drifting passively with the ocean currents. Hence the velocities, measured by the frequency shift of the backscattered sound waves, are taken to be oceanic velocities.
These ADCP can be put at a fixed point (for example on a mooring or oceanic fixed structure), in the hull of a vessel (hereafter called VM-ADCP as vessel-mounted ADCP), attached to a CTD rosette (called L-ADCP for lowered ADCP) or to a free-falling cage (hence called FF-ADCP).
Tosca Ballerini (firstname.lastname@example.org)