Two dimensional internal-wave spectra

Abstract

Although spatial fluctuations of the sound speed in the ocean have a variety of causes, internal waves are thought to produce most of the fluctuations over horizontal scales ranging from several tens of metres to several kilometres and vertical scales ranging from one to tens of metres. Garrett and Munk have developed a space-time in internal wave model (GM-75) which predicts temperature and velocity fluctuation spectra. This has prompted us to perform a two-dimensional experiment to provide a data set which 1) is directly applicable as input to stochastic acoustic modelling, and 2) serves to check the GM-15 model. The data is obtained from a chain towed at speeds much greater than the speed of internal waves. A spectrum in horizontal-vertical wavenumber space can then be inferred. Systematic deviations from the complete (two-dimensional) model are observed in the vertical/horizontal wavenumber model into agreement with our observed twodimensional internal wave spectrum.