TRISTAR - a tracer in situ TDLAS for atmospheric research

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 N2O during two airborne polar stratospheric campaigns in January and March 1997. These species were detected using integration periods of 1 s with a precision of +/-2%(3 sigma) and a calibration accuracy of +/-2.8% during a total of Il 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.