Noise equivalent temperature difference (NETD) or thermal sensitivity is considered to be of great importance for the process of evaluating and comparing performances of thermal imagers which are essentially non-contact temperature measurement devices. This paper describes an NETD calculation application based on the detector specific detectivity. The NETD for several types of thermal imagers was estimated and compared with the declared values provided by the producers. The mathematical model used in this process is strongly dependent on the specific detectivity of the detector QUOTE  QUOTE   . For this reason, a number of geometrical curves are introduced to approximate the various shapes of specific detectivity curves in different spectral domains. Moreover, the effect of the chosen spectral band and the change of the NETD inside the whole spectral domain are studied taking into account two cases: overlapping subintervals and non-overlapping subintervals.

Keywords: thermal imager, thermal sensitivity, thermal noise, mathematical model, parameter analysis.