Accuracy of acoustic multipath timing and ranging predictions over extended ranges

An at-sea experiment was conducted to verify a long range acoustic timing and ranging concept. A spread spectrum signal was transmitted and received at ranges of 1 to 75 nautical miles. Processing this data gave thousands of multipaths profiles which were compared with profiles generated by existing long range acoustic propagation models. Agreement between the models and the experimental data was inconsistent throughout the test geometry. Hydrophone array receivers were suspended atdepths of 2500, 3750 and 4750 meters during the test. The frequency band of interest was 850 to 1325 Hertz. The results of this paper show that long range acoustic performance cannot always be predicted with current modeling techniques. New technologies and modeling concepts are needed to raise the accuracy and reliability of predicted performance.