Michael J. Buckingham
Marine Phys. Lab., Scripps Inst. of Oceanogr., La Jolla, CA 92093-0213
In the polar seas the spatial structure of the ambient noise is often determined by the upward refracting sound-speed profile. Such a profile supports normal modes, even in the absence of bottom interactions. A full theoretical (analytical) model of ambient noise in an inverse-square profile---representative of polar waters---has been developed [Buckingham, Philos. Trans. R. Soc. (in press)], which yields expressions for the auto and cross spectral densities of the noise that are valid at infrasonic frequencies (VLF) and low frequencies (LF) up to several kilohertz. Three terms appear in these expressions, representing the modal and continuous components of the noise. When the theoretical spectra are compared with ambient noise data taken in the marginal ice zone off the east coast of Greenland, a crude distribution of noise sources at the ice edge can be inferred and bottom effects in the observed spectra become apparent. The spatial inhomogeneity of the noise is also very evident from the theory, which has implications concerning beamforming for obtaining noise directionality information. [Research supported by ONR.]