Abstract

Most active open-path FTIR measurements are made using a bistatic configuration in which an infrared source is set up in the field at one side of the parcel of atmosphere to be measured and the Michelson interferometer and detector is placed on the other side. In order to maintain efficient collection of light at the detector, the source may be placed at the optical focus of a transmitting telescope and a receiver telescope may be optically coupled to the interferometer and detector. In this configuration, the infrared radiation emitted from objects in the field of view of the detector (objects behind or around the source, the receiver optics and the interferometer beamsplitter) passes through the interferometer and contributes to the interferogram and thus to the Fourier transformed single beam spectrum. The gray-body emission curve for the terrestrial temperature range (260 °K to 315 °K) extends through the entire fingerprint window of the atmospheric infrared spectrum (700 to 1200 cm^-1).

© 1995 Optical Society of America