PASSIVE ACOUSTIC IMAGING WITH THE GRANDE- OREILLE

The ''Big Ear'' is a signal processing system which permits multiple b eamforming of audio signals in real time. It may be used with any kind of arrays of microphones or hydrophones and permits to ''ear'' a sele cted point of space through instructions given to the system by a micr ocomputer. 2000 such points can be defined in the initial phase and sh ift from one to another may be done in real time so that an acoustical exploration of space is achieved in a short time. An autocalibration of the system obtained from a reference source is also an interesting opportunity. Results obtained with a first realisation which may invol ve 32 channel arrays, are shown. Aerial and submarine signals have bee n treated in collaboration with O.N.E.R.A. (Office National d'Etudes e t de Recherches Aerospatiales). The potentialities offered by a new sy stem are described. It will be more powerful : 64 sources treated simu ltaneously from a 64 channel array. The spectral acoustical image will be achieved through an integrated Fast Fourier Transform treatment. T he 64 spectral densities of the 64 sources, averaged over a duration o f one second will be continuously available at the output.