ABSTRACT
Four different Marine Rapid Environmental Assessment (MREA) procedures are compared with a focus on underwater acoustic performance. Co-located oceanographic-acoustic data were collected during the summer of 2015 in the Northwestern Mediterranean in the framework of a sea trial led by the NATO Centre for Maritime Research and Experimentation. The data were used to link MREA procedures and ocean-acoustic validation in a seamless framework. The MREA procedures consider Conductivity Temperature Depth (CTD) data, operational products from the Copernicus Marine Service, and two dynamical downscaling systems (with and without data assimilation). A portion of the oceanographic data are used for the assimilation procedure, and the remaining portion is withheld from the assimilation system for use as an independent verifying dataset. The accuracy of modelled acoustic properties is evaluated using the sound speed estimates from the different MREA methodologies as inputs to an acoustic model, and then comparing the modelled and observed acoustic arrival intensities and temporal structure. In 95% of the studied cases, the assimilative dynamical downscaling approach provides acoustic results equaling or exceeding in skill those modelled with the sound speed extracted from CTD casts. Acoustic assessment results indicate that our implementation of dynamical downscaling has skill at oceanographic scales of 4 km, about ten times larger than the ocean model horizontal resolution.
Subject(s)
Acoustics , Sound , Electric Conductivity , Seasons , TemperatureABSTRACT
A free-surface, three-dimensional finite-difference numerical model based on the Princeton Ocean Model (POM) has been implemented in order to simulate the interannual variability of the Adriatic Sea circulation. The implementation makes use of an interactive surface momentum and heat flux computation that utilizes the European Centre for Medium-Range Weather Forecasts (ECMWF) 6-h analyses and the model predicted sea surface temperatures. The model is also nested at its open boundary with a coarse-resolution Mediterranean general circulation model, utilizing the same surface forcing functions. The simulation and analysis period spans 3 years (1 Jan 2000 to 31 Dec 2002) coinciding with the "Mucilage in the Adriatic and the Tyrrhenian" (MAT) Project monitoring activities. Model results for the simulated years show a strong interannual variability of the basin averaged proprieties and circulation patterns, linked to the atmospheric forcing variability and the Po river runoff. In particular, the years 2000 and 2002 are characterized by a weak surface cooling (with respect to the climatological value) and well-marked spring and autumn river runoff maxima. Conversely, 2001 is characterized by stronger wind and heat (autumn cooling) forcings but no river runoff autumn peak, even though the total amount of water inflow during winter and spring is sustained. The circulation is characterized by similar patterns in 2000 and 2002 but very different structures in 2001. During the latter, deep water is not formed in the northern Adriatic. A comparison with the observed data shows that the major model deficiencies are connected to the low salinity of the waters, probably connected to the missed inflow of salty Ionian waters of Aegean origin and to the numerical overestimation of the vertical mixing processes.
