Terrestrial heat flow through the ocean floor is determined by measuring the temperature gradient and thermal conductivity in the upper few meters of sediment with an instrument lowered on hydrographic wire. The chief novel feature of the device is that the thermal conductivity is measured in situ simultaneously with the temperature gradient instead of in a cored specimen of sediment in the laboratory.
Corry, Charles, Carl Dubois, and Victor Vacquier. 1968. "Instrument far measuring terrestrial heat flow through the ocean floor." Journal of Marine Research 26, (2). https://elischolar.library.yale.edu/journal_of_marine_research/1124