The North Pacific Acoustic Laboratory (NPAL) Experiment

Abstract

The North Pacific Acoustic Laboratory program augmented the existing ATOC acoustic network with a sparse, two-dimensional receiving array installed west of Sur Ridge, CA, close to an existing U.S. Navy SOSUS array, during July 1998 to receive transmissions from the 75-Hz ATOC source north of Kauai. The NPAL array consisted of four 20-element vertical arrays, each with a 700-m aperture, and one 40-element vertical array with a 1400-m aperture. The arrays were deployed transverse to the 3900-km path from the Kauai source and had a total horizontal aperture of 3600 m. Data collected with the two-dimensional array and the U.S. Navy SOSUS receivers will be used to (i) study the temporal, vertical, and horizontal coherence of long-range, low-frequency resolved rays and modes, (ii) study 3D propagation effects, (iii) examine directional ambient noise properties, and (iv) to improve basin-scale ocean nowcasts via assimilation of acoustic data and other data types into models. Environmental data along the path from the Kauai source to the two-dimensional array were acquired by two oceanographic subsurface moorings and by two XBT/CTD/ADCP transects along the path, one at the beginning and one at the end of the experiment. We describe the experiment and offer some preliminary data.