Radiation is also intimately connected to that small part of the atmosphere - the minor or variable constituents (e.g. ozone and carbon dioxide) - which actually absorb and emit radiation. Thus radiation studies and composition studies are closely connected.

We study, both theoretically and experimentally, methods of deducing atmospheric composition in space and time from measurements of radiation made from the ground, aircraft, balloons and satellites. This is possible because the atmospheric radiation field contains the spectral signature of all the interacting species, albeit weakly and sometimes with much confusion.

A major part of our current research effort is devoted to designing and testing a satellite instrument to measure carbon monoxide and methane in the lower atmosphere from space. The MOPITT (Measurements Of Pollution In The Troposphere) instrument will be launched on NASA's EOS-AM1 satellite in mid-1998. The instrument is funded by the Canadian Space Agency and is being constructed by Canadian industrial firms. It uses techniques developed as part of our research program at Toronto. In addition to the measurement program we have an active program in molecular spectroscopy for atmospheric applications using a laboratory-based difference frequency spectrometer. This spectrometer operates by mixing two visible-light lasers in a non-linear crystal to obtain a beat frequency in the infrared. The resolution of this system is high enough that we can see not only the effects of the surrounding medium on the emitting molecules, but can also learn about the details of the molecular collision dynamics through studying the spectra. This work is carried out in conjunction with Prof. A.D. May who uses almost the same apparatus to perform stimulated Raman spectroscopy for similar objectives. The interaction between these two groups is strong and students often have joint supervision.