High-resolution digital temperature logging in areas with significant convective heat transfer Original Research Article

The Marmara region of northwestern Turkey is characterized by frequent manifestations of anomalously high temperature gradients in the underground, thermal springs, and steaming grounds. Within an interdisciplinary project, our research group measured temperature profiles in many drillholes in this region, using a digital temperature logging tool. Temperatures are measured by a PT 100 sensor; the 2 km wireline and its winch are mounted on a trailer; the data acquisition system is freely movable, weighs about 40 kg, and is transported by jeep along with a 4.7 kW power generator. This system consists of a controlling unit for the winch drive, a high-precision electrical resistance meter with a sensitivity of 100 ppm Ω and a 286 MS-DOS PC as the recording unit. All parts of the equipment are commercially available. The depth interval between two measurements is 10 cm and maximumlogging speed is 5 m/min. Using this temperature tool we were able to detect convection cells in a borehole in northern Switzerland. These cells, about 1 m in length, have a temperature amplitude range of about 0.01–0.04°C.