Abstract
Acoustic path lengths in the Heard Island Feasibility Test ranged from under 1 Mm to 18 Mm (1 Mm is 1000 km). The signal set consisted of three basic waveforms: cw, pentaline, and M-sequence-modulated carrier. This set offered the opportunity for successful measurements given the large uncertainty in prior estimates of propagation loss, stability, and arrival spread. Receivers ranged from simple sonobuoy systems to elaborate horizontal and vertical arrays. International collaborators acquired data at a variety of sites worldwide. The resulting data has been collected and subjected to a summary form of frequency domain processing. Variations in the recorded spectral phases are largely the result of nonuniformity in the speed of the source ship as determined by GPS comparison. Time domain processing has shown that at all ranges the receptions exhibit exceptional stability.
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