A NOTE ON HORIZONTAL-REFRACTION-MODAL TOMOGRAPHY

The use of horizontal antennas composed of long, mode-resolving, verti cal arrays is potentially useful in ocean acoustics. A scheme for acou stic tomography of the ocean based on measurements of the horizontal r efraction of horizontal rays, which are related to different acoustic modes, is discussed. The horizontal refraction angle of a given mode i s equal to the transverse gradient of the refraction index averaged ov er the depth interval embraced by this mode and integrated over the ac oustic path. The effect of internal waves is estimated. It is shown th at internal waves do not significantly blur the angular distribution o f the received field. An experiment that involves two pairs of long, v ertical arrays and a towed tonal source is proposed for the reconstruc tion of a 3-D picture of the ocean's inner structure over a 1000-x1000 -km area. (C) 1995 Acoustical Society of America.