Photon/Optical Detectors
type: Concept

GFC RADIOMETER
in scheme: instruments
definition: The Gas Filter Correlation Radiometer (GFCR) is an optoelectrical sensor able to detect airborne pollutants such as carbon monoxide, methane, and nitrogen oxides. The device makes use of a polarization modulator, in conjunction with a polarization beam splitter, to enable rapid optical-path switching without the use of moving parts. As light reflected from the atmosphere enters the instrument the light radiation passes through a polarization-sensitive beam splitter, the splitter reflects the polarized photons and transmits horizontally polarized photons. The beamis thus alternated between two optical paths: one comprised of a vacuum cell and the other a correlation cell that contains a small quantity of gas, which the sensor is calibrated to detect. The gas in the correlation cell acts as a defacto filter for incoming radiation. As radiation from the two paths is recombined and analyzed, the difference in signal strengths indicates the amount of target gas present in the outside air.
type: Concept