Knowledge Bank

Passive remote sensing using an FTIR spectrometer allows the detection and identification of pollutant/toxic gases in the atmosphere. In this paper we report a measurement method and data reduction technique that to not require a previously measured reference spectrum. Recent experimental results obtained using a new high-sensitivity mobile FTIR are presented. After a radiometric calibration of the spectrometer using reference blackbodies, the spectral radiance of the background is determined. Using the inverse function of Planck's radiation law, the brightness temperature $ϵ(\nu )$ is computed. The temperature spectrum provides a spectrally constant reference for many of the materials used as backdrops in field measurements since their emittance is high and nearly constant in the 800 to $1200cm-1$ range. Experimental results are presented to illustrate the enhancement of the signal-to-noise ratio that can be achieved by using a backdrop that provides maximal temperature difference to ambient environment.