Abstract
Abstract. This paper presents an analysis of sound speed distribution in the Mediterranean Sea based on climatological temperature and salinity data. In the upper layers, propagation is characterised by upward refraction in winter and an acoustic channel in summer. The seasonal cycle of the Mediterranean and the presence of gyres and fronts create a wide range of spatial and temporal variabilities, with relevant differences between the western and eastern basins. It is shown that the analysis of a climatological data set can help in defining regions suitable for successful monitoring by means of acoustic tomography. Empirical Orthogonal Functions (EOF) decomposition on the profiles, performed on the seasonal cycle for some selected areas, demonstrates that two modes account for more than 98% of the variability of the climatological distribution. Reduced order EOF analysis is able to correctly represent sound speed profiles within each zone, thus providing the a priori knowledge for Matched Field Tomography. It is also demonstrated that salinity can affect the tomographic inversion, creating a higher degree of complexity than in the open oceans.Key words. Oceanography: general (marginal and semi-enclosed seas; ocean acoustics)
Highlights
Acoustic methods have been widely applied for underwater communication and for the remote observation of ocean interiors
The aim of this paper is to provide a description of sound speed characteristics in the Mediterranean Sea, its seasonal variability and spatial distribution, starting from a climatological data set of temperature and salinity
3.1 Sound speed distribution: annual mean and seasonal variability. This analysis focuses on the layer between 50 and 400 m, since – in terms of acoustic propagation – in the upper mixed layer the acoustic wave undergoes a near-surface upward refraction; and it is not exploitable for tomographic applications, while in the deeper layers sound speed differences are not strong enough to be resolved by this methodology
Summary
Acoustic methods have been widely applied for underwater communication and for the remote observation of ocean interiors. In the Western Mediterranean Sea, the ninemonths-long experiment THETIS-2 (Send et al, 1997) has estimated the seasonal heat budget, but this experience remains an unicum among tomographic Mediterranean basinscale studies. Ocean acoustic tomography has proved to be a methodology for the observation of currents and internal tides (Shang and Wang, 1994; Demoulin et al, 1997). These successful applications propose ocean tomography as a tool for large-scale monitoring of the oceans in the frame of the development of Global Oceans Observing Systems (GOOS)
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