[Behind the scenes in oceanography (4/12)]. Andrea Garcia Juan, a research engineer in physical oceanography, is an underwater ambient noise measurement technician at the Shom (national hydrography and oceanography service) in Brest. She is responsible for the deployment and maintenance of the Mambo network (Acoustic Monitoring and Noise Measurement by Opportunity) in French marine waters (mainland France) in support of the Marine Strategy Framework Directive (MSFD). The measurements collected by underwater hydrophones are then analysed by the Shom’s marine acoustics engineers in order to study the soundscapes at different geographical points, both inshore and offshore. The aim is to observe the sound pollution and masking that is affecting marine animal populations.
Each month, Océans connectés meets the men and women who make oceanography work. They are laboratory technicians, surveyors, engineers, sailors or meteorologists, and they are all essentials to the smooth running of marine research. In this fourth episode, we delve into the day-to-day life between sea and land of Andrea Garcia Juan, an underwater ambient noise measurement technician.
by Marguerite Castel
Cover photo: Andrea Garcia Juan, discovering marine acoustic observation with great interest at the Shom, adjusting and programming the hydrophones deployed for the recordings. © Marguerite Castel
The Spanish-born woman in her thirties seems to juggle easily between her office, the Shom workshop in Brest, microphones, recorders, mooring devices and the areas where she deploys hydrophones. In early November, she was in Normandy waters with the Cotentin cetacean study group. However, she is just starting out in marine acoustic observation.
Andrea wanted her studies in the physical sciences to help her understand the world. Having come from the land, she discovered the gigantic field of observation that is the ocean. First by observing currents and studying wave modelling, then by acquiring a wealth of experience within the Euro-Argo network. Meet Andrea Garcia Juan.
What is your background?
Andrea Garcia Juan: I graduated with a degree in general physics from the University of Oviedo in Spain and then came to France to study for a master’s in oceanography, meteorology and climate sciences in Toulouse. In 2018, I started my career as a research engineer at Euro-Argo in Brest. I carried out analyses on the behaviour of Argo floats at sea, took part in tests in the Ifremer basin and monitored the floats at sea.
I then worked at Ifremer’s LOPS (Physical and Spatial Oceanography Laboratory), where I applied machine learning algorithms to oceanographic data, particularly that from Argo floats.
What is your current mission?
AGJ : In September 2024, I joined the scientific equipment engineering department (oceanographic systems) at Shom as an underwater noise measurement technician. My mission is part of the Marine Strategy Framework Directive, which aims to monitor ambient underwater noise levels in European waters. Anthropogenic ocean noise is recognised as a potential threat to many marine species. I’m in charge of deploying and maintaining the network of twelve Mambo acoustic moorings in mainland France, the aim of which is to collect time series of long-term acoustic data.
The MAMBO system consists of 12 acoustic acquisition stations deployed throughout the marine sub-regions. © shom.
In practical terms, what does this involve?
AGJ : It’s an operational job; I coordinate the mission in liaison with the mooring workshop and the scientists and other different players (study groups, customs, etc.). I prepare the acoustic moorings before they are launched, i.e. I adjust and programme the hydrophones precisely according to the research. The settings vary according to buoyancy, depth and also the duration of the recording and the rotation of the instruments. I also take care to reduce the noise from the mooring itself by positioning the microphone and recorder differently. It’s a very precise job because I have to ensure that the instruments are working properly and that the time series are reliable in order to optimise the experiment and obtain the best acquisition. The aim of Mambo is to measure underwater decibels around France at 12 precise geographical points, both inshore and offshore, and to identify man-made noise. The listening radius depends on the environment, depending on the proximity or distance from the coast, the depth in the water column (from 20 metres to 4783 metres below the surface) etc. These are long recordings, sampled at high frequency.
Then it’s not me who listens, that’s the role of the acoustic engineers once they’ve been given the data. They then compare them with their digital models, which gives them greater precision.
What are the challenges of marine acoustic observation?
AGJ : It’s a rapidly evolving discipline, thanks to advances and innovations in instrumentation. It used to be a military field of expertise, but has gradually been opened up to scientists. The growth in maritime traffic has generated a great deal of noise pollution in the ocean. This has become a major concern in Europe and for the International Maritime Organisation (IMO).
Annual maximum of continuous noise in the 63 Hz third octave band in French waters for the year 2016 (dB re 1 µPa²). © Map source Shom.
Anthropogenic noise disturbs the communication of marine animals. They are assessed according to criteria of spatial distribution, temporal extent, level, duration, sources of continuous noise or impulsive noise (2). Noise can range from slightly harmful to harmful, indicating excess mortality and disturbance. For example, there are communication masking phenomena – where anthropogenic noise drowns out the natural sounds of the ecosystem – which cause accidental excess mortality and area desertions in marine animals (including fish). Cetaceans in particular depend on sound for their social and environmental learning, their search for food and their reproduction.
It’s fascinating, and I’m discovering this notion of soundscapes with great interest. Sound illustrates the life of the ocean, it bears witness to its health. For me, it’s a good way of applying physics to understanding the world.
(1) – Shom : The national hydrography and oceanography service, has been a public administrative establishment (EPA) since 2007, under the supervision of the Ministry of the Armed Forces and Veterans.
(2) – Continuous noise and impulsive noise: sources of impulsive noise include pile-driving in underwater or coastal constructions (port developments, wind turbine installations), seismic surveys (to locate oil or gas deposits), underwater explosions (destruction of munitions carried out underwater at high tide, military exercises), and sonar in particular. Continuous sources come mainly from maritime traffic, and also include foghorns on buoys and permanent industrial installations (oil platforms, etc.).