The estimated detection, recognition, and identification (DRI) ranges for each of the Tau2 and Quark2 lens versions are given at their respective web pages. There is a tab labeled `DRI` that provides both conservative detection, recognition, and identification ranges for each lens version, as well as best case values. DRI ranges can be influenced by many factors, including ambient environmental conditions such as humidity, temperature, solar loading, precipitation (rain, snow, fog, etc.), and background clutter, as well as camera sensitivity, setup parameters, and operator experience.
NOTE: This question has many variables that must be considered, and some of those variables are interrelated. FLIR makes some assumptions to simplify the problem, but it is important to note that this type of question (what can be seen at what distance with an particular IR camera system) is typically approached in terms of target detection, recognition & identification ranges, along with an associated probability of success. Typically the result will be communicated in terms of a percentage probability of a particular target being detected, recognized and identified and certain ranges. There is a standard set of conditions regarding targets and defined meaning for the results that allows some simple test measurements to be fed into models that provide range outputs. Where applicable, our assumptions are consistent with standard range modeling.