Acoustic remote sensing: 5 MHz backscattering response by phytoplankton in waters off the southeast Argentinian coast.

IGOR PRARIO; MARIANO CINQUINI; SILVIA BLANC; PATRICIO BOS; ANALÍA TOLIVIA

Ciudad del Cabo

Congreso; IAPSO/IAMAS/IAGA Joint Assembly; 2017

IAPSO (International Association for the Physical Sciences of the Oceans)

Acoustics is considered an important tool for remote sensing of the marine environment. Its application realm spans over a wide spectrum of signal frequencies (from less than 1 Hz to 10 MHz) with its consequent very different fields of interest for scientific research purposes. The present work is motivated by the fact that phytoplankton is generally the most important primary producer in the aquatic systems. Therefore, it plays an undoubtedly relevant role in the oceanic ecosystem. A long-term research programme to investigate the acoustic response of phytoplankton has been developed. Its aim is to use the remote sensing capability of high-frequency acoustic scattering techniques as a tool for contributing to phytoplankton biomass? estimation and harmful algae blooms detection. It includes insonification of single-species algae aqueous culture media during laboratory experiments as well as examination of nearly real-time acoustic responses of seawater samples collected with a vertical trawl phytoplankton net or Niskin bottles. Recently, acoustic measurements in waters off the southeast Argentinian coast were conducted at thirteen CTD stations within the San Jorge Gulf. Seawater samples were insonified with a 5 MHz narrowband transducer driven by a pulse-receiver system. Analysis, signal processing, simulation and modelling of the scattered signals have been carried out in order to correlate measured backscattered power with scatterers? type and concentrations. For that purpose, optical observation, taxonomic classification, sample cells counting were also accomplished. Unmasking of undesirable acoustic responses from spurious scattering was performed through ad-hoc signal processing techniques. The power backscattered by the at-sea samples from the whole water column collected with the phytoplankton net showed an increment of about 20 dB - 25 dB referred to surface samples at the stations with high fluorescence values.  A detailed analysis of the time dependence of the backscattered signals is fulfilled. Measurements of backscattered power, generated by the insonified collected seawater samples are compared with simulations using theoretical models.