Compact multilaser TDLAS for trace gas flux measurements based on a micrometeorological technique

摘要

A novel Tunable Diode Laser Absorption Spectrometer has been developed for trace gas flux measurements based on micrometeorological techniques. Up to 2 different species can be measured simultaneously with high temporal resolution ($LS 1 sec) using individual lead-salt diode lasers. The instruments response time is ultimately determined by the gas exchange time through the compact multi-reflection cell (Aerodyne Model AMAC-36 Astigmatic Herriott Cell, 0.3 l volume, total path 36 m). The lasers are operated in a time multiplexed mode using a novel modulation scheme, which combines laser operation in a pulsed-current mode with a combination of rapid scanning and two-tone frequency modulation. The latter has the potential to improve the signal-to-noise ratio of phase-sensitive detection when compared to standard lock-in techniques because of the reduction of instrument noise at higher detection frequencies. The stability and the detection limit of the instrument will be characterized. It has been used to measure CH$-4$/ and N$-2$/O fluxes via the eddy covariance technique from rice paddies and tropical ecosystems during two recent field campaigns.