Other names for this quantity are “effective differential temperature”, “radiometric delta T”, “RDT”, or “RdT”.

To achieve a given RDT, a blackbody must produce a difference in radiance between the target and the IR source which is numerically equal to the difference in radiance, integrated over the spectral band of interest, that would be produced by an ideal target at 298K and an ideal IR source maintained at an “effective” commanded temperature differential above or below 298K.

For more detail on this subject, see the application note Radiometric Temperature: Problems and Solutions.