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TRISTAR - a tracer in situ TDLAS for atmospheric research


Applied Physics. B 67 (1998), S.411-417 : Ill., Lit.
ISSN: 0340-3793
ISSN: 0721-7269
ISSN: 0946-2171
ISSN: 1432-0649
Fraunhofer IPM ()
airborne measurement; CO; N2O; pulse scan time multiplexing; TDLAS; TTFM; tunable diode laser absorption spectroscopy; two tone frequence modulation

A novel tunable diode laser absorption spectrometer (TDLAS) called TRISTAR (tracer in situ TDLAS for atmospheric research) has been developed for airborne trace-gas measurements in the upper troposphere and lower stratosphere. Up to three different species can be measured simultaneously with high temporal resolution (< 1 s) using up to three individual lead-salt diode lasers. The lasers are operated in a time-multiplexed mode using a novel modulation scheme that combines laser operation in a pulsed-current mode with a combination of rapid scanning and two-tone frequency modulation. The latter improves the signal-to-noise ratio of phase-sensitive detection when compared to standard lock-in techniques because of the reduction of instrument noise at higher detection frequencies. TRISTAR has been used in two-channel mode to measure CO and N20 during two airborne polar stratospheric campaigns in January and March 1997. These species were detected using integration periods of 1 s with a prec ision of + - 2 per cent (3 sigma) and a calibration accuracy of + - 2.8 per cent during a total of 11 measurement flights up to a maximum altitude of 12.5 km. More recently all three channels have been operated simultaneously for CO, CH4, and N2O with comparable results.