![]() ![]() ![]() Some examples of 3D acoustics studies using these two methods are cited below. The PE method can provide a 3D full field solution, whereas the normal mode method sheds light on the propagation physics. These two modeling methods, in fact, complement each other. The primary methods used in this study are normal mode and PE methods, and they will be reviewed in Sec. These 3D propagation effects are investigated in this study to explain the observed data near Block Island, RI, USA. There is also limited documented evidence of horizontal diffraction, another 3D propagation effect observed as the bending of sound energy around an obstacle into the region of geometrical shadow, which can be described by Huygens' principle. Effects of this type of propagation include the repeating 3D reflections of sound off a sloping bottom that manifest themselves as horizontal refraction, the formation of an acoustic shadow zone with a leading edge caustic, intermodal interference and focusing, as well as the selective cutoff of acoustic normal modes with water depth. For example, few studies have analyzed the propagation in the coastal wedge environment, where acoustic rays or equivalent normal modes interact intensively with the bottom features ( Doolittle et al., 1988 Heaney and Murray, 2009 Ballard, 2012 Heaney et al., 2017). However, only a limited number of field observations can be found in the published literature. The phenomenon of three-dimensional (3D) acoustic propagation, including horizontal refraction and diffraction along a sloping bottom or around physical obstructions, is well understood both theoretically and from a numerical modeling perspective. The arrival angle measurements on the tetrahedral array show the complex propagation patterns, including the diffracted energy in the island shadow and acoustic energy refracted away from the island. The evidence of horizontal caustics of the sound was shown in the parabolic equation and modal ray models by comparing to the arrival pattern observed in the data. This analysis found that the modes at higher frequencies can propagate closer to the coast of the island with shallower modal cutoff depths, where the sound energy penetrates the sloping seafloor at supercritical incidence. The 3D modal ray calculation provided additional insight into the frequency dependence of the signal spreading. The observed shadow zone boundary was consistent with the prediction made by a 3D sound propagation model incorporating high-resolution bathymetry and realistic sound speed obtained from a data-assimilated regional ocean model. Linear frequency modulated chirp signals, centered at 1 kHz with a 400 Hz bandwidth, were transmitted from a ship moving out of the acoustic shadow zone blocked by the island from the perspective of the hydrophone array. The three-dimensional (3D) propagation effects of horizontal refraction and diffraction were measured on a tetrahedral hydrophone array deployed near the coast of Block Island, RI. ![]()
0 Comments
Leave a Reply. |
AuthorWrite something about yourself. No need to be fancy, just an overview. ArchivesCategories |