James H. Miller Ching-Sang Chiu
Code EC/Mr, Naval Postgraduate School, Monterey, CA 93943
James F. Lynch
Woods Hole Oceanogr. Inst., Woods Hole, MA 02543
Philip McLaughlin Christopher W. Miller
Naval Postgraduate School, Monterey, CA 93943
Keith Von Der Heydt John Kemp
Woods Hole Oceanogr. Inst., Woods Hole, MA 02543
In the 1992 Barents Sea Polar Front Experiment, bandpass acoustic tomography signals centered at 224 Hz were received with very high SNR on a 16-element vertical hydrophone array at a range of 35 km from the source. The depth of the ocean varied from 120 m at the source to 280 m at the vertical array. A critical part of travel time tomography is the measurement of the arrival time of individual modes and rays. Identifying and tracking these mode and rays can be extremely difficult using a single hydrophone in coastal waters due to signal interference. A vertical array has the potential to solve these problems. An efficient signal processing scheme is described, written in MATLAB, that simultaneously (1) beamforms for the bandpass modes or rays, (2) compensates for clock drift, sampling skew, and array tilt, and (3) compresses the maximal-length, phase-encoded signal. Data are presented that show that the beamforming along with acoustic modeling provides identification of the arrivals with a high degree of confidence. Errors in measuring the arrival times are estimated to range from 2 ms for low modes to 10 ms for high angle rays making the arrivals useful for inversions. [Work supported by ONR, Code 1125AR.]