Shallow Water Communications for Mine Warfare

Acoustic communication near shorelines is frequently problematic because of high ambient noise and poor propagation conditions. AD&D is proposing a low-cost, lightweight, Magneto-Inductive Modem which will provide reliable short range communications to ranges of 1000 meters near a shoreline in a secure manner.Exponential absorption loss in seawater is fierce, over 0.8 dB per meter at 575 Hz with 4 S/m conductivity, precluding a direct path through the water at anywhere near the required maximum range. Our approach makes use of either up-over-down or down-over-up propagation paths, which takes advantage of negligible absorption loss in the air or potentially much lower absorption loss in the ocean floor to allow communications at a range of 1000 meters.During this effort, AD&D will demonstrate geometries that maximize MI communication ranges and will demonstrate a low cost loop antenna sensitive to only low frequency H-fields, a low cost, efficient power amplifier with integrated waveform generation capability, and a low-noise preamp-digitizer which will be used to collect data for analysis. Proof-of-Concept demonstrations will be performed to show that the hardware is effective and the concepts are sound. Collected data will be analyzed to demonstrate antenna performance, transmitter radiation efficiency, and the receiver noise floor.