Effect of array tilt on estimates of vertical ambient noise spectrum

The vertical spectrum of ambient noise in the SOFAR channel carries useful information about noise sources and trapped modes in the channel. Measuring the directionality of low frequency ambient noise requires very long hydrophone arrays. Array motion can obscure the measurements of vertical spectra. This paper is motivated by the need to characterize the ambient noise spectrum using moored arrays such as those deployed in the North Pacific [1] and the Philippine Sea [2]. Using a straight-line model for array motion, this paper derives an approximate expression for the vertical spectrum measured by a tilted array. Analysis show that array tilt broadens the measured spectrum and reduces the noise notch at broadside. Numerical simulations using transport theory confirm the results.