Testing the applicability of a non-contact IR thermometer for wall surface temperature measurements in a cave environment: A case study from the dynamic Císařská Cave (Moravian Karst)

Abstract

The surface temperature of cave walls is important, particularly as a factor controlling water condensation and calcite corrosion, as well as in paleoclimatic reconstructions of external annual temperatures. The use of a non-contact IR thermometer (NCT) could provide an alternative method for monitoring wall surface temperature in inaccessible passages of the cave. However, temperatures obtained by the standard NCT showed increased error. The accuracy of the NCT was tested by comparison with a calibrated contact thermometer (CCT), which revealed a systematic error of –8.2 ± 1.2 °C for the right wall and –8.3 ± 0.9 °C for the left wall. Calibration with the equations T = 0.478×NCT + 8.254 (right wall) and T = 0.554×NCT + 8.308 (left wall) corrected this error. Uncertainty was tested by repeated measurements on a calibration area of 1.7 m2 in the cave, resulting in a random relative error of 4.25 % for dry wall surfaces and 4.95 % for wet wall surfaces. Although a relative error of 5 % is common for major instrumental methods, it is near the applicability limit for karstological interpretations.