effect of sea surface motion on underwater communication systems

Underwater acoustic communications are significantly affected by time-varying multipath. Time-delays induced by multiple reactors on boundaries can be compensated for through equalization, and good transmission can be achieved. However, soundwaves reflected from moving scatterers on the sea surface undergo slight variations in frequency that significantly degrade the performance of communication devices. Ocean data was collected to evaluate the amount of Doppler-spread induced by wind-driven surface waves. A model for the shallow water acoustic channel is discussed and implemented using a simplified approach to the gaussian-beam ray-tracing algorithm. This leads to the definition of the spreading function, a convenient tool to describe fading channels. The spreading function serves as a reference for the simulation of a classic digital communication setup, using baseband antipodal equalization. It is shown how frequency-spreading, a consequence of sea surface motion, affects the resulting error rate.