In-situ measurement of thermal conductivity using the continuous-heating line source method and WHOI outrigged probe
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The outrigged thermal probes of a "pogo" marine geothermal probe have been adapted to measure thermal conductivity in-situ by the continuous-heating line source technique. The instrumental uncertainty in applying the analytical theory to a single-probe and double-probe configuration is found to be 3 and 6 percent, respectively. The in-situ outrigged single probe <.32 cm dia.) is essentially a scaled-up version of the needle probe (.08 cm dia.). The main advantage of the outrigged probe over a larger radius probe <e.g., violin-bow probe) is that for short-time temperatures (<2 min.), simple approximations to the exact solution for a perfectly conducting cylindrical probe are achieved. The continuous-heating compares favorably with the pulse-heating technique, the latter being more energy efficient. The continuous-heating method applied to the thin outrigged probe allows for accurate equilibrium in-situ temperature and thermal conductivity estimates in less than 15 minutes of recording time. The technique has been applied to several hundred marine heat flow stations. Comparison of in-situ measurements to needle probe measurements made on nearby piston cores indicate agreement to within 5%. The conductivity profiles of the in-situ data and core data show that the piston coring process frequently does not retrieve the upper meter of surficial sediment.