Inference of source–receiver motion from phase measurements in the Modal Mapping Experiment

Abstract

In March 1997, the Modal Mapping Experiment (MOMAX) was conducted aboard the R/V Endeavor in about 70 m of water off the New Jersey coast. Three drifting MOMAX buoys, each containing a hydrophone, GPS navigation, and radio telemetry received signals up to ranges of 10 km from a NUWC J15-3 source suspended from the moving ship and transmitting pure tones at 50, 75, 125, and 175 Hz. A striking feature of the data is the remarkable stability and regularity of the phase, even though the magnitude displays a complex multimodal interference pattern. This phase behavior occurs even at the higher frequencies and higher source/receiver speeds (up to 3 kts) measured in the experiment. A phase model is developed which indicates that the leading-order behavior of the time rate-of-change of the phase is simply equal to the product of a typical wave number in the water column and the source-receiver speed. This model accurately predicts the source-receiver speed from the phase measurements obtained in MOMAX. The implications of this model for other scenarios, such as long-range, deep-water situations are also discussed. [Work supported by ONR.]