A concentration correction system includes an infrared detector and components that produce an aggregate emission of infrared radiation. A mirror assembly includes a mirror and is changeable between a correcting configuration and a measuring configuration. In the correcting configuration, the mirror produces a mirror signal incident on the detector. The mirror assembly also obstructs external body infrared radiation from reaching the detector. In the measuring configuration, the mirror assembly allows the external body infrared radiation onto the detector. A concentration correction method includes receiving external body infrared radiation and simultaneously receiving a first portion of the aggregate emission. A measurement value indicative of concentration is recorded from the detector. A second portion of the aggregate emission reflected with the mirror and produces a mirror signal incident on the detector. A correction value corresponding to the mirror signal is recorded from the detector and used to correct the measurement value.
