A Novel Empirical Orthogonal Function (EOF)-Based Methodology to Study the Internal Wave Effects on Acoustic Propagation

This paper presents a novel approach to synthesize realistic environment for ocean-acoustic parametric studies. In its current form, this methodology applies to internal waves and tides. Empirical orthogonal function (EOF) decomposition is applied to a temporal series of temperature profiles. It can be observed that the first two time-dependent expansion coefficients are dynamically linked. When they are plotted one versus another in a scatter diagram, the cloud of points consists of a crescent shape that can easily be represented by a polynomial fit. If the first two expansion coefficients capture enough variability in the temperature profiles, the EOF modes plus the polynomial can be used to reconstruct temperature profiles independently from the set of data. This realistic synthesized environment can then be input to acoustic propagation models. This approach is applied to the case of the Messina Strait in which internal waves are known to be intensive. From a short-term series of temperature profiles collected on a thermistor string, range-dependent profiles along and across the strait are reconstructed. The acoustical impact study is conducted with the range-dependent acoustic model (RAM) parabolic equation (PE) model. The methodology presented in this paper is simple to run and requires a very affordable set of data. It could be used as an efficient alternative to ocean and acoustic model coupling for process studies or for regional studies especially in poorly known areas or highly variable areas, where it is difficult to obtain good sound-speed profile prediction from ocean models.