Remote sensing of gas concentrations in smokestack emissions.

A measurement technique is discussed that allows for remote sensing of polluting gases that are emitted together with the water droplets in a steam plume. Infrared laser radiation is backscattered from the droplets. As wavelength of the radiation is varied, resonant absorption in the gases diminishes the backscatter signal; this may be quantitatively related the Concentration of specific gases. The backscatter arrangement makes possible the construction of a compact, single-ended, remote sensing instrument. Feasibility of this concept has been demonstrated in a laboratory experiment where a laser beam at 3.391 microm and 4.217 microm was scattered from a steam plume containing controlled amounts of CH(4) and CO(2).