ASA 127th Meeting M.I.T. 1994 June 6-10

2aUW7. A new scheme of the acoustic tomography of the ocean.

A. G. Voronovich

E. C. Shang

NOAA/EFL/Environmental Technol. Lab. R/E/WP1, 325 Broadway, Boulder, CO 80303

Using horizontal antennas composed out of mode resolving long vertical arrays has powerful potentials in the study of ocean acoustics. The new scheme for acoustic tomography of the ocean is presented based on the measurements of horizontal refraction of horizontal rays related to different acoustic modes. The horizontal refraction angle (HRA) of a given mode equals the transverse gradient of the refraction index averaged over the depth interval embraced by this mode and integrated over the acoustic path. Using HRA offers the following advantages. (a) Only simple tonal signals are involved. (b) There is no need for exact positioning of the source. (c) As rays are straight lines with great accuracy, the linear procedures of inversion are adequate in the 2-D stage. (d) Since tomography reconstruction is two dimensional for any given mode number, the processing and interpretation of the data are greatly simplified; a precise 3-D picture of inhomogeneities is calculated as the next stage after 2-D reconstruction. An experiment involving two pairs of LVA and a towed tonal source which allowed the reconstruction of a 3-D picture of the ocean inner structure in the area of 1000 nmx1000 nm for about 2 weeks, is discussed. [Work partly supported by NRC and ARPA.]