With the increase on the use of thermal infrared sensor systems onboard airplanes and more recently in RPAs (Remotely Piloted Aircrafts), also known as Drones, it is of fundamental importance to know the radiometric, spectral and spatial characteristics of these cameras, in order to optimize its use. In this study, these characteristics of 2 cameras were analyzed in laboratory conditions, to evaluate its capacities and limitations, regarding the specifications from the respective manufacturers. Furthermore the similarities and differences between the OPTRIS PI Lightweight (A) and FLIR A 310 (B) cameras are presented and discussed. Through the methodological procedures described in this work, the spectral response function curve of the two sensors was obtained. The uncertainties of the radiometric measurement of the sensors were analyzed and it was found that the sensor A presents uncertainties greater than those specified by the manufacturer and that the measurements carried out by the sensor B have remained within the specified uncertainties. In both sensors, the Effective Instantaneous Field of View (EIFOV) was found to be larger than the Instantaneous Field of View (IFOV) values reported by the manufacturers. The observed results demonstrated the importance of the characterization procedures in order to recognize the real capacities and limitations of a thermal sensor system.