NOISE EQUIVALENT TEMPERATURE DIFFERENCE OF INFRARED SYSTEMS UNDER FIELD CONDITIONS

The noise equivalent temperature difference (NETD) is one of the most convenient measures used for describing performance of infrared system s as thermographs and radiometers. The NETD expression is also contain ed as a kernel within any minimum resolvable temperature (MRT) and min imum detectable temperature (MDT) difference, so the conclusions to be reached relative to NETD apply to MRT and MDT as well. For the reason of convenience, some assumptions have been made in defining (measurin g and deriving relation for) the NETD. However, for a variety of pract ical purposes in the field these assumptions are not satisfied. Conseq uently, the conventional laboratory NETD is applicable under certain f avourable laboratory conditions. Therefore, the typical laboratory NET D expressions found in the literature cannot be simply applied to infr ared systems under field conditions. In this paper, the practical fiel d NETD expression is derived. It incorporates none of the assumptions which have been used in defining and deriving the laboratory NETD expr ession. Therefore, the given expression can be simply applied to asses sment of infrared systems capability under field conditions.