Langley Research Center

About: Langley Research Center is a facility organization based out in Hampton, Virginia, United States. It is known for research contribution in the topics: Mach number & Wind tunnel. The organization has 15945 authors who have published 37602 publications receiving 821623 citations. The organization is also known as: NASA Langley & NASA Langley Research Center.

Nondestructive defect identification with terahertz time-of-flight tomography

Abstract: We demonstrate the application of terahertz (THz) time-of-flight tomographic imaging to identify the distribution of defects in foam materials. Based on THz time-domain spectroscopy technology, THz imaging probes targets with picosecond pulses of broad-band radiation in the frequency range from 100 GHz to 3 THz. The reflected THz wave from the target is measured using electrooptic sampling, which provides two-dimensional images with phase and amplitude information, as well as the spectroscopic properties of the object. The depth information is recorded in the THz time-domain waveform. Several reconstruction models are developed for tomographic imaging of defects inside foam. Foam insulation of space shuttle fuel tanks, with prebuilt defects, are investigated with THz tomographic imaging. Most prebuilt defects are pinpointed and models used to identify different kinds of defects are discussed.

Temporal variations of atomic oxygen in the upper mesosphere from SABER

Abstract: [1] One of the atmospheric constituents that can be retrieved from observations by the Sounding of the Atmosphere using Broadband Emission Radiometry (SABER) instrument on the Thermosphere-Ionosphere-Mesosphere Energetics and Dynamics (TIMED) satellite is atomic oxygen in the upper mesosphere. Atomic oxygen can be determined during both day and night using two different techniques that both rely on ozone chemistry. The O concentrations retrieved from SABER data are higher by a factor of 2–5 compared to concentrations determined from other measurements and techniques and compiled in current empirical models. This paper presents variability of atomic oxygen with a focus on the diurnal cycle in low latitudes and the seasonal cycle of daily mean atomic oxygen globally. The results show a large diurnal variation, ranging from a factor of 2 to more than a factor of 10, of atomic oxygen near the equator. The relative magnitude varies with season (larger near the equinoxes) and with altitude (largest near 85 km). Vertical transport by the migrating diurnal tide explains the observed variation. The semiannual variation in tidal amplitude affects the seasonal variation of daily average atomic oxygen, which likely indicates that there is irreversible transport by the tides. At high latitudes, the atomic oxygen variation is characterized by wintertime maxima over the altitude range 80–95 km and summertime maxima above. The wintertime peaks are associated with the downwelling from the mean circulation and are particularly strong in late winter of 2004, 2006, and 2009, responding to the unusual dynamical situations in those years.

Airborne and spaceborne lidar measurements of water vapor profiles: a sensitivity analysis

Abstract: This paper presents an evaluation of the random and systematic error sources associated with differential absorption lidar (DIAL) measurements of tropospheric water vapor profiles from airborne and spaceborne platforms. The results of this analysis are used in the development and performance evaluation of the Lidar Atmospheric Sensing Experiment (LASE) H2O DIAL system presently under development at the NASA Langley Research Center for operation on a high altitude ER-2 aircraft. The analysis shows that a less than 10-percent H2O profile measurement accuracy is possible for the LASE system with a vertical and horizontal resolution of 200 m and 10 km, respectively, at night and 300 m and 20 km during the day. Global measurements of H2O profiles from spaceborne DIAL systems can be made to a similar accuracy with a vertical resolution of 500 m and a horizontal resolution of 100 km.

CGILS: Results from the first phase of an international project to understand the physical mechanisms of low cloud feedbacks in single column models

Abstract: CGILS—the CFMIP-GASS Intercomparison of Large Eddy Models (LESs) and single column models (SCMs)—investigates the mechanisms of cloud feedback in SCMs and LESs under idealized climate change perturbation. This paper describes the CGILS results from 15 SCMs and 8 LES models. Three cloud regimes over the subtropical oceans are studied: shallow cumulus, cumulus under stratocumulus, and well-mixed coastal stratus/stratocumulus. In the stratocumulus and coastal stratus regimes, SCMs without activated shallow convection generally simulated negative cloud feedbacks, while models with active shallow convection generally simulated positive cloud feedbacks. In the shallow cumulus alone regime, this relationship is less clear, likely due to the changes in cloud depth, lateral mixing, and precipitation or a combination of them. The majority of LES models simulated negative cloud feedback in the well-mixed coastal stratus/stratocumulus regime, and positive feedback in the shallow cumulus and stratocumulus regime. A general framework is provided to interpret SCM results: in a warmer climate, the moistening rate of the cloudy layer associated with the surface-based turbulence parameterization is enhanced; together with weaker large-scale subsidence, it causes negative cloud feedback. In contrast, in the warmer climate, the drying rate associated with the shallow convection scheme is enhanced. This causes positive cloud feedback. These mechanisms are summarized as the “NESTS” negative cloud feedback and the “SCOPE” positive cloud feedback (Negative feedback from Surface Turbulence under weaker Subsidence—Shallow Convection PositivE feedback) with the net cloud feedback depending on how the two opposing effects counteract each other. The LES results are consistent with these interpretations.

Validation of ozone measurements from the Atmospheric Chemistry Experiment (ACE)

Abstract: This paper presents extensive {bias determination} analyses of ozone observations from the Atmospheric Chemistry Experiment (ACE) satellite instruments: the ACE Fourier Transform Spectrometer (ACE-FTS) and the Measurement of Aerosol Extinction in the Stratosphere and Troposphere Retrieved by Occultation (ACE-MAESTRO) instrument. Here we compare the latest ozone data products from ACE-FTS and ACE-MAESTRO with coincident observations from nearly 20 satellite-borne, airborne, balloon-borne and ground-based instruments, by analysing volume mixing ratio profiles and partial column densities. The ACE-FTS version 2.2 Ozone Update product reports more ozone than most correlative measurements from the upper troposphere to the lower mesosphere. At altitude levels from 16 to 44 km, the average values of the mean relative differences are nearly all within +1 to +8%. At higher altitudes (45–60 km), the ACE-FTS ozone amounts are significantly larger than those of the comparison instruments, with mean relative differences of up to +40% (about +20% on average). For the ACE-MAESTRO version 1.2 ozone data product, mean relative differences are within ±10% (average values within ±6%) between 18 and 40 km for both the sunrise and sunset measurements. At higher altitudes (~35–55 km), systematic biases of opposite sign are found between the ACE-MAESTRO sunrise and sunset observations. While ozone amounts derived from the ACE-MAESTRO sunrise occultation data are often smaller than the coincident observations (with mean relative differences down to −10%), the sunset occultation profiles for ACE-MAESTRO show results that are qualitatively similar to ACE-FTS, indicating a large positive bias (mean relative differences within +10 to +30%) in the 45–55 km altitude range. In contrast, there is no significant systematic difference in bias found for the ACE-FTS sunrise and sunset measurements.