On monitoring depth variations of the main thermocline acoustically

It is shown that depth variations over weeks and months of the main thermocline may be resolved effectively by means of an inverted echo sounder that measures precisely the time for an acoustic signal to travel from the sea bottom to the surface and back. Calculations with hydrographic data show that depth changes as small as 10 meters may be resolved. Preliminary experiments off Bermuda show that apart from a variation due to the surface and internal semidiurnal tides, the travel time is stable for more than a week, which is consistent with the observation that the thermocline depth does not change substantially on this short a time scale.