Methane analyzer based on TDL's for measurements in the lower stratosphere: design and laboratory tests

This paper describes a tunable diode laser spectrometer for the in situ measurement of methane by high resolution absorption spectroscopy of roto-vibrational lines, using a distributed feedback laser emitting in the near infrared (1.65 ?m) and a multi-pass cell, with a two-tone detection scheme. The instrument was designed to be installed on the high-altitude aircraft M55 Geophysica, for high-sensitivity and high-temporal-resolution measurement of CH4, both as a greenhouse gas and as a tracer of air-mass motion. The instrument design criteria to achieve the compactness, low weight, and ruggedness necessary for automatic operation on an unpressurized high-altitude aircraft are reported. Results of the laboratory testing are also shown and discussed.