TRISTAR - A TRACER IN-SITU TDLAS FOR ATMOSPHERIC RESEARCH

A novel tunable diode laser absorption spectrometer (TDLAS) called TRI STAR (tracer in situ TDLAS for atmospheric research) has been develope d for airborne trace-gas measurements in the upper troposphere and low er stratosphere. Up to three different species can be measured simulta neously with high temporal resolution (< 1 s) using up to three indivi dual lead-salt diode lasers. The lasers are operated in a time-multipl exed mode using a novel modulation scheme that combines laser operatio n in a pulsed-current mode with a combination of rapid scanning and tw o-tone frequency modulation. The latter improves the signal-to-noise r atio of phase-sensitive detection when compared to standard lock-in te chniques because of the reduction of instrument noise at higher detect ion frequencies. TRISTAR has been used in two-channel mode to measure CO and N2O during two airborne polar stratospheric campaigns in Januar y and March 1997. These species were detected using integration period s 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 a ltitude of 12.5 km. More recently all three channels have been operate d simultaneously for CO, CH4, and N2O with comparable results.