A process for converting signal to temperature for a set of production thermal imaging systems, each thermal imaging system of the set of thermal imaging systems including an array of photodetectors each configured to output a signal S x,y corresponding to a temperature of a portion of an imaged scene, and an ambient temperature sensor, the process comprising: performing a scene temperature calibration on all thermal imaging systems of the set of thermal imaging systems, the calibration comprising: exposing each thermal imaging system, at a calibration ambient temperature, to n known temperature scenes, each known temperature scene having a unique scene temperature T si, from T s1 to T sn, wherein n is at least 2; developing, based on the signal S x, y, a unit-specific function F(S x,y) i = T si that fits the observed signal to the known scene temperatures for each thermal imaging system; and storing an ambient temperature sensor value Tsens corresponding to the calibration ambient temperature; performing a scene temperature/ambient temperature qualification test on a portion of previously calibrated thermal imaging systems of the set of thermal imaging systems, the portion comprising at least one unit but less than all units of the set, and the qualification test comprising: exposing each thermal imaging system of the subset to a plurality of known ambient temperatures and, at each ambient temperature, exposing the unit to a plurality of known temperature scenes at different known scene temperatures, calculating F(S x,y) for each combination of ambient temperature and scene temperature; correlating the ambient temperature sensor output to the known ambient temperatures; creating a two-dimensional table of at least one of an error Δ T between F(S x,y) and the known scene temperature for each known scene at each ambient temperature, or the known scene temperature T act; and loading the table into all units of the set; and for individual thermal imaging systems of the set of thermal imaging systems, adjusting F(S x,y) during subsequent operational use by extracting at least one of actual scene temperature or error information from the two-dimensional table based on S x,y and the ambient temperature sensor value. performing a scene temperature calibration on all thermal imaging systems of the set of thermal imaging systems, the calibration comprising: exposing each thermal imaging system, at a calibration ambient temperature, to n known temperature scenes, each known temperature scene having a unique scene temperature T si, from T s1 to T sn, wherein n is at least 2; developing, based on the signal S x, y, a unit-specific function F(S x,y) i = T si that fits the observed signal to the known scene temperatures for each thermal imaging system; and storing an ambient temperature sensor value Tsens corresponding to the calibration ambient temperature; exposing each thermal imaging system, at a calibration ambient temperature, to n known temperature scenes, each known temperature scene having a unique scene temperature T si, from T s1 to T sn, wherein n is at least 2; developing, based on the signal S x, y, a unit-specific function F(S x,y) i = T si that fits the observed signal to the known scene temperatures for each thermal imaging system; and storing an ambient temperature sensor value Tsens corresponding to the calibration ambient temperature; performing a scene temperature/ambient temperature qualification test on a portion of previously calibrated thermal imaging systems of the set of thermal imaging systems, the portion comprising at least one unit but less than all units of the set, and the qualification test comprising: exposing each thermal imaging system of the subset to a plurality of known ambient temperatures and, at each ambient temperature, exposing the unit to a plurality of known temperature scenes at different known scene temperatures, calculating F(S x,y) for each combination of ambient temperature and scene temperature; correlating the ambient temperature sensor output to the known ambient temperatures; creating a two-dimensional table of at least one of an error Δ T between F(S x,y) and the known scene temperature for each known scene at each ambient temperature, or the known scene temperature T act; and loading the table into all units of the set; and exposing each thermal imaging system of the subset to a plurality of known ambient temperatures and, at each ambient temperature, exposing the unit to a plurality of known temperature scenes at different known scene temperatures, calculating F(S x,y) for each combination of ambient temperature and scene temperature; correlating the ambient temperature sensor output to the known ambient temperatures; creating a two-dimensional table of at least one of an error Δ T between F(S x,y) and the known scene temperature for each known scene at each ambient temperature, or the known scene temperature T act; and loading the table into all units of the set; and for individual thermal imaging systems of the set of thermal imaging systems, adjusting F(S x,y) during subsequent operational use by extracting at least one of actual scene temperature or error information from the two-dimensional table based on S x,y and the ambient temperature sensor value.