This instrumentation development project will develop an acoustic data/command link for complex hydrographic profiling and related underwater hardware. It builds upon extensive work at Woods Hole Oceanographic Institution on acoustic telemetry and an acoustic modem that has resulted from these efforts. The acoustic data link is intended to replace or augment the standard data communications link that utilizes conducting wires within the oceanographic cable suspending the CTD package. Given the large number of hydrographic stations planned for Global Ocean studies and the potential for data loss resulting from broken conducting cables, a back-up acoustic data link providing real-time information to the ship, would be highly beneficial. The new data link would also have application on ships of opportunity when standard oceanographic cables are not available. The proposed system would also be compatible with control systems and data loggers in use at other institutions.