Airborne Laser Infrared Absorption Spectrometer (ALIAS-II) for in situ atmospheric measurements of N2O, CH4, CO, HCl, and NO2 from balloon or remotely piloted aircraft platforms

The Airborne Laser Infrared Absorption Spectrometer II (ALIAS-II) is a lightweight, high-resolution (0.0003-cm(-1)), scanning, mid-infrared absorption spectrometer based on cooled (80 K) lead-salt tunable diode laser sources. It is designed to make in situ measurements in the lower and middle stratosphere on either a balloon platform or high-altitude remotely piloted aircraft. Chemical species that can be measured precisely include long-lived tracers N2O and CH4, the shorter-lived tracer CO, and chemically active species HCl and NO2. Advances in electronic instrumentation developed for ALIAS-I, with the experience of more than 250 flights on board NASA's ER-2 aircraft., have been implemented in ALIAS-II. The two-channel spectrometer features an open cradle, multipass absorption cell to ensure minimal contamination from inlet and surfaces. Time resolution of the instrument is less than or equal to 3 s, allowing rapid in situ measurements with excellent spatial resolution. ALIAS-II has completed successful balloon flights from New Mexico, Alaska, and Brazil providing CH4 and N2O vertical profiles in the tropics, mid-latitudes, and high northern latitudes up to altitudes of 32 km. (C) 1999 Optical Society of America.