Acoustic communications and navigation under Arctic ice

Initial results of experiments performed under Arctic ice have shown that acoustic communications and navigation can be performed on scales of 10-100 km using relatively inexpensive and compact hardware. Measurements of the impulse response at ranges of 10 and 75 km reveal extensive scatter and both resolvable and unresolvable rays. Phase coherent communication using adaptive equalization was successful up to ranges of 70-90 km at data rates of 5-10 b/s. As the SNR drops to levels too low for phase coherent communication, short FM sweeps (5-10 s), are shown to provide sufficient gain to provide lower rate communications and also support navigation.