A vertical array of 20 vibration isolated hydrophones was suspended from the Research Platform FLIP at various depths from 713 to 4816 m. Preformed sets of beams were formed with a digital beamformer to observe the vertical noise distribution at several frequencies between 23 and 100 Hz. Directional spectra derived from 10-min samples of digital records are presented. Interpretation of the data set leads to a model for the vertical noise directional spectrum as a function of depth which indicates a reduction of a factor of 2 in the vertical extent of the noise window as depth increases from the sound channel axis to the critical depth. This reduction in width is accompanied by a reduction in the maximum level of about 4 dB. The effect is essentially independent of frequency over the observed range of 23 to 100 Hz. No horizontal null in the directional spectrum of the noise, as predicted by ray theory for a horizontally homogeneous ocean, was observed in the data. © 1979, Acoustical Society of America. All rights reserved.
