Applying an alternative methodology to evaluate acoustic responses from copepods and suspended sediments in the Bahia Blanca estuary

BAQUÉS, M., GARIBOTTI, E.J., ALBERDI, E., BLANC, S., PICCOLO, M. C., CERVELLINI, P.M.

Bahía Blanca

Simposio; II Simposio de Métodos Experimentales en Hidráulica; 2011

IADO - CONICET - UNS - AGENCIA - UNC - FICH - University of Illinois

Recent advances on the application of an acoustic methodology based upon ADCP registered echo-signals processing and modelling of volume sound scattering parameters to simultaneously evaluate Numerical Abundance estimation of zooplankton and suspended sediments, are presented. The assumption of the validity of a generalised extended version of the well known Superposition Principle for scattered sound waves enabled the computation of the Volume Backscattering Acoustic Coefficients for scatterers of different nature, for a very shallow water area in the Bahía Blanca Estuary. ADCP measurements at 614 kHz, suspended sediment concentration data, sediment particles granulometry and classification, zooplankton net samples and CTD data were employed for an oceanographic-acoustic correlated analysis. Absolute values of Acoustic Volume Backscattering Strengths, Sv (dB) and their corresponding Coefficients, v (m-1), versus depth, were computed from the recorded ADCP’s echo intensities, using factory calibration values. v profiles and theoretical modelling of the Acoustic Backscattering Cross Section, (m2), using a modified High-Pass Johnson’s Model, led to the computation of Numerical Abundances. A generalized least squares estimation method was used to validate the hypothesis assumed as a first attempt to estimate Numerical Abundances by means of acoustics methods, for the copepod Acartia tonsa and silt and fine sand suspended sediments. Comparisons with optical determinations provided reasonable results. Further work has been planned, including in-situ ADCP calibration and development of more realistic models for the Acoustic Backscattering Cross Section of each particular scatterer, responsible of the recorded echo signals.