Balloon-borne diode-laser absorption spectrometer for measurements of stratospheric trace species

A stratospheric trace species measurement concept is presented which utilizes tunable infrared diode lasers as sources for sensitive in situ absorption spectroscopy in selected wavelength regions. As an embodiment of this concept, the Balloon-Borne Laser In Situ Sensor (BLISS) is a high-resolution absorption spectrometer designed to provide measurements of the concentrations of stratospheric species and their diurnal variations. The instrument uses second-harmonic detection of the absorption of tunable diode laser (TDL) radiation (3–30 μm) in a 1-km path length defined by a retroreflector lowered 0.5 km below the BLISS gondola. A He–Ne laser and co-aligned TV camera with CID imaging are used for retroreflector tracking under microprocessor control. Four TDLs will provide simultaneous measurements of molecular species in the 20–40-km altitude range, the predicted minimum-detectable mixing ratio at 30 km being typically ≤0.1 ppbv.