We have developed, improved and deployed a Fourier transform spectrometer aboard a variety of aircraft since 1977.  This spectrometer system records the high resolution (0.06 cm^-1) infrared (2-15 micrometers, 5000-600 cm^-1) absorption of solar radiation by the atmosphere during its transit from the sun.  A description of the technique of Fourier transform spectroscopy may be found at Wolfram's Scienceworld site.

Along with the development of instrumentation to record high quality spectra we have contributed to the development of tools and techniques to retrieve gaseous constituent amounts from the spectra.  The SFIT2 multi-window, non-linear least squares fitting code has become the standard spectral fitting technique for a large part of the infrared remote sensing community.

The OT FTS experiment has been flown on numerous missions aboard NSF and NASA aircraft.  The map below shows flight paths during solar observing periods.

Observations of infrared absorption spectra have been used to derive column amounts of a number of gases important to stratospheric chemistry and global atmospheric heating, these observations have been used in a large number of scientific studies.  References to publications resulting from airborne remote sensing may be found here.

Gases Measured with the Optical Techniques FTS

Since 1999 the OT group has operated an infrared Fourier transform spectrometer (FTS) at a primary observing site of the Network for the Detection of Atmospheric Composition Change (NDACC).  The site is located at Thule, Greenland where we are able to view the sun, our source of infrared radiation, from approximately mid-February to mid-October.  The system is based around a Bruker 120M spectrometer with a spectral resolution of 0.0013 cm-1).  Custom devices acquire and track the sun, fill the detectors with liquid nitrogen, control the operation, acquisition and storage of data, all in an autonomous mode. Since 2008 we also have operated the NDACC observing site at Mauna Loa, Hawaii.   References to publications from ground-based observations may be found here.

The OT group has developed a tunable diode laser (TDL) based instrument for in situ measurements aboard aircraft of CO and N₂O.  The experiment can operate in a fully automatic mode, including self-calibration, for up to 8 hours in a package designed to occupy one half the space of a WB-57 bomb-bay pallet.  The performance goals of the diode laser experiment are to measure CO and N₂O concentrations of 1 ppbv in a measurement time of 1 second.  References to  in situ  publications  may be found here.