Thermal cameras are capable of providing panoramic, synthetic photographs of thermal structures, rapid and precise quantitative evaluations, and short term or long term observation periods. Theories of electromagnetic radiation are briefly reviewed and possible errors of measurement are discussed. Calibration using a black body as a reference is described. The thermal images obtained may be integrated with aerial photography and/or transcribed in colors which correspond to given levels of radiation. Data acquired in ground surveys may be combined with those derived aerially. The choice of a fixed color reference permits monitoring of temporal changes. Scanning images of the Solfatara di Pozznoli are provided, as are the thermal maps prepared from them.