Measurements of the ambient noise background have been made with a string of seven hydrophones 200 ft long. Data were collected at a number of depths throughout the water column at a deep water site north of St. Croix, Virgin Islands. The time delay correlograms obtained confirm a binary model for the sources of ambient noise: a low‐frequency type arriving preferentially from near‐horizontal directions, and a high‐frequency type arriving from near‐vertical directions. No variation in coherence with depth was observed. The correlograms constantly fluctuate in amplitude and peak time delay, indicating that the coherence and therefore the directionality are time‐variable properties of the ambient background. Coherence measurements are an alternate, and in some ways a preferable, approach to obtaining the data needed for the optimum design of arrays to operate in the real‐world noise background.