1. A method of maintaining image quality in presence of temperature drift for an infrared (IR) imaging system comprising: a) taking base measurements from the IR imaging system while a shutter of the IR imaging system is closed, the base measurements comprising temperature with regard to the shutter and outputs of detector elements of a focal plane array (FPA) of the IR imaging system; b) determining an offset output for the IR imaging system from the base temperature with regard to the shutter; c) taking present measurements from the IR imaging system while the shutter is open and the IR imaging system is directed at a target scene, the present measurements comprising temperature with regard to the shutter and outputs of the FPA detector elements; d) calculating thermal drift components with regard to the present outputs of the FPA detector elements in light of differences between the base and present measurements; e) calculating outputs of the FPA detector elements attributable to the target scene in light of the present outputs of the FPA detector elements, the respective drift components of the FPA detector elements, and the offset output; f) determining temperatures of the target scene from the output portions of the FPA detector elements attributable to the target scene; and g) repeating steps (c) through (f) while the shutter is open during continued use of the IR imaging system.