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The Aircraft Laser Infrared Absorption Spectrometer (ALIAS) instrument is a high-resolution (0.0003 cm-(1)) scanning tunable-diode-laser spectrometer designed, tested, and flown more than 30 times on the National Aeronautics and Space Administration's high-altitude ER-2 aircraft in the Airborne Arctic Stratospheric Expedition of 1991-1992. Using long-path infrared laser absorption spectroscopy to detect optical absorptions as small as 10-(5), ALIAS provides fast, continuous in-situ measurements of key atmospheric gases, with gas detection sensitivities of tens of parts in 10(12). With four lasers and detectors in a single liquid-nitrogen Dewar, simultaneous measurements of HCI, NO(2), HNO(3), CH(4), and N(2)O are made using laser sources at 3.4-8 µm, injected into a 1-m-long, 80-pass Herriott cell.

An experimental study of the interaction of a turbulent boundary layer with a wavy wall was conducted in a wind tunnel. A smooth neoprene rubber sheet comprising a portion of the floor of the tunnel was mechanically deformed into 12 sinusoidal waves which progressed upwind or down at controlled speed. The turbulent layer thickness was a little less than the wavelength. The mean velocity profile was linear on a semi-log plot over a substantial range of vertical height.The wall pressure was observed to be asymmetrical about the wave profile, resulting in a pressure drag. Flow separation was not the cause of the drag. The drag was found to be larger than that predicted by the inviscid wave generation theory. The measurements indicate that the waves strongly modulate the turbulent structure. The phase of the turbulent stresses with respect to the waves varies with wave speed, indicating that the dynamical reaction time of the turbulence is not negligible in comparison with the wave period.

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