Abstract
In November 1995 an experiment was performed in San Diego harbor, in which the Acoustic Daylight Ocean Noise Imaging System (ADONIS) was used to produce images of a variety of targets in the ocean. ADONIS operates in the frequency range 8 – 80 kHz, and relies on ambient noise to provide the acoustic contrast between look angles on- and off-target. No dedicated sound source is used to provide illumination. Thirty-gallon PVC oil drums filled with sand and syntactic foam were imaged at a range of 40 m in the water column, and at a range of 20 m when lying on the seafloor (silt). The primary sources of illumination were snapping shrimp (high frequency) and small-boat noise (low frequency), with the directionality and intensity of the latter varying greatly over time. The spectral, temporal, and azimuthal variations in the noise field will be discussed in relation to shadowing features in the images. Small-scale fluctuations in the medium gave rise to scintillation effects, with spatial and temporal scales that can be investigated with the ADONIS receiver. [Work supported by ONR.]
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