Abstract

We discuss the development of two open path IR absorption instruments for eddy correlation measurements of fluxes of atmospheric trace gases which impact greenhouse and acidic dry deposition problems. One instrument, designed for CH₄ measurements, uses a tunable IR He-Ne laser operating at 3.39/µm. The second, based on a tunable diode laser system, will be used to detect a variety of molecules including N₂O, O₃, and HNO₃. Since these measurements are made in the free atmosphere, the instrument must discriminate against spectral features of the atmospheric background, especially water vapor. The chosen approaches to this problem are described, including the use of a frequency-modulated source and detection at both the first and second harmonic of the modulation frequency. The multipass cell must exhibit minimal sensitivity to the expected vibration of its supporting structure; methodsof achieving this are described.

© 1986 Optical Society of America