Modeling hydrophone array directivity effects for sonar system performance prediction

Directivity effects of large arrays are the result of array geometry and element directivity. Directivity index for a transmitter and array gain for a receiver are the directivity effects included in the sonar performance equations. Using models to predict directivity index and array gain is useful for performance analysis of conceptual arrays as well as existing arrays where measurements cannot be made readily or conveniently. Array gain reduces to directivity index for the case where ambient noise is isotropic. Arrays of directional elements are more difficult to model, except in the case where all elements in array have parallel principal axes whereby pattern multiplication can be applied. An example is presented of a large existing array whose vertical patterns and directivity index are not readily measurable. Directivity effects of this array are predicted using pattern multiplication with models for elements, array, and baffling. Models are validated using measured directivity patterns and directivity index is predicted over a frequency range of two decades to be used for performance analysis of conceptual sonar systems.