| Instrument: | Aircraft Laser Infrared Absorption Spectrometer (ALIAS) |
| Principal Investigator: | Christopher R. Webster |
| Co-Investigator: | Randy D. May |
| Organization: | Mail Stop 183-401 Jet Propulsion Laboratory National Aeronautics and Space Administration 4800 Oak Grove Drive Pasadena, CA 91109-8099 |
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Measurement Description: The Aircraft Laser Infrared Absorption Spectrometer (ALIAS) instrument is a very high resolution scanning tunable diode laser spectrometer which makes direct, simultaneous measurements of HCl, NO2, CO, CH4, and N2O (including vertical profiles) at sub-part-per-billion level sensitivities over a 3-30 second integration time. The measurement technique is based upon using tunable lead-salt diode lasers operating from 3.4 to 8 microns wavelength scanning over absorption lines recorded using second harmonic absorption spectroscopy. The 80-meter optical path is defined by two spherical mirrors separated by 1 meter in a multipass Herriott cell. Unique features include a sample inlet/throttle system designed to achieve near-isokinetic sampling in PSC events, an in-flight wavelength reference cell rack, a mechanical fringe-spoiler, and a four-laser/four-detector dewar with 48-hour hold- time. Sample cell flush time is 1-2 seconds. The instrument weighs about 160 lbs. and uses a Pentium-based flight computer with a 2-Gbyte sealed hard-disk. ALIAS has flown over 250 times in 5 major NASA missions.
| Accuracy: | Typically 2-10%, depending upon calibration gases and IR spectral parameters |
| Precision: | Typically 0.2-4%, depending upon SNR for observed atmospheric concentration |
| Detection Limits: | HCl and NO2 (0.03 ppbv); N2O, CH4, and CO (0.1 ppbv) |
| Response Time: | 3 second data collection for tracer gases; 30 seconds for HCl and NO2 |
| Location on ER-2: | Super pod on right wing |
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