Gas Filter Correlation Radiometry (GFCR)
GFCR is a well-established, simple but efficient, remote sensing spectroscopy technique for the detection of trace gases with high sensitivity and selectivity. This technology, first developed in the 1960s was first employed for atmospheric remote sensing of the atmosphere from space in 1970.
As the name suggests, a sample of the target gas fills a container, usually named correlation cell, located within the path of the incoming electromagnetic radiation and acts as a spectral filter. The radiation incident upon the cell is only the part of total incoming radiation that passes through a narrow band-pass filter matching the instrument spectral sensitivity range. This range is chosen so that it contains the absorption lines of the gas, which is the reason why filtering takes place. When the radiation passes through the cell containing the gas sample, the part of it corresponding to the wavelengths of absorption lines is partially absorbed. What remains is measured by a detector and associated electronics.