downhole measurement

In geology, any one of a number of experiments performed by instruments lowered down a borehole. Such instruments may be detectors that study vibrations passing through the rock from a generator, or may measure the electrical resistivity of the rock, or cosmic radiation, or radioactivity originating within the rock.

Geophysicists have measured heat flow at thousands of boreholes worldwide to gather information on climate change. Surface air temperature affects the temperature of underlying rock. Heat travels so slowly that the first 500 m/1,640 ft of the Earth's crust provides a record of the ground temperature for the last thousand years.