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NASA NTRS2002

Retrievals of Profiles of Fine And Coarse Aerosols Using Lidar And Radiometric Space Measurements

In couple of years we expect the launch of the CALIPSO lidar spaceborne mission designed to observe aerosols and clouds. CALIPSO will collect profiles of the lidar attenuated backscattering coefficients in two spectral wavelengths (0.53 and 1.06 microns). Observations are provided along the track of the satellite around the globe from pole to pole. The attenuated backscattering coefficients are sensitive to the vertical distribution of aerosol particles, their shape and size. However the information is insufficient to be mapped into unique aerosol physical properties and vertical distribution. Infinite number of physical solutions can reconstruct the same two wavelength backscattered profile measured from space. CALIPSO will fly in formation with the Aqua satellite and the MODIS spectro-radiometer on board. Spectral radiances measured by MODIS in six channels between 0.55 and 2.13 microns simultaneously with the CALIPSO observations can constrain the solutions and resolve this ambiguity, albeit under some assumptions. In this paper we describe the inversion method and apply it to aircraft lidar and MODIS data collected over a dust storm off the coast of West Africa during the SHADE experiment. It is shown that the product of the single scattering albedo, omega, and the phase function, P, for backscattering can be retrieved from the synergism between measurements avoiding a priori hypotheses required for inverting lidar measurements alone. The resultant value of (omega)P(180 deg.) = 0.016/sr are significantly different from what is expected using Mie theory, but are in good agreement with recent results obtained from lidar observations of dust episodes. The inversion is robust in the presence of noise of 10% and 20% in the lidar signal in the 0.53 and 1.06 pm channels respectively. Calibration errors of the lidar of 5 to 10% can cause an error in optical thickness of 20 to 40% respectively in the tested cases. The lidar calibration errors cause degradation in the ability to fit the MODIS data. Therefore the MODIS measurements can be used to identify the calibration problem and correct for it. The CALIPSO-MODIS measurements of the profiles of fine and coarse aerosols, together with CALIPSO measurements of clouds vertical distribution, is expected to be critically important in understanding aerosol transport across continents and political boundaries, and to study aerosol-cloud interaction and its effect on precipitation and global forcing of climate.

Kaufman, Yoram↗

NASA NTRS1980

Recent assessment of the performance and accuracy of a chemiluminescent rocket sonde for upper atmospheric ozone measurements

The chemiluminescent rocket ozonesonde utilizing rhodamine-B as a detector and self-pumping for air sampling has been improved. The instrument employs standard meteorological sounding systems and is the only technique available for routine nighttime ozone measurements above balloon altitudes. The chemiluminescent detector, when properly calibrated, is shown to be specific to ozone, stable, and of sufficient sensitivity for accurate measurements of ozone from about 65-20 km. An error analysis indicates that the measured ozone profiles have an absolute accuracy of about + or - 12% and a precision of about + or - 6%. Approximately 20 flights have been conducted for geophysical investigations, while additional flights were conducted with other rocket and satellite ozone soundings for comparisons. In general, these comparisons showed good agreement.

Hilsenrath, E.↗

NASA NTRS1981

Preliminary design for a Zero Gravity Test Facility (ZGTF). Volume 1: Technical

The functional requirements and best conceptual design of a test facility that simulates weightless operating conditions for a high gain antenna systems (HGAS), that will broadcast to the Tracking Data Relay Satellites were defined. The typical HGAS defined is mounted on a low Earth orbiting satellite, and consists of an antenna with a double gimbal pointing system mounted on a 13 foot long mast. Typically, the gimbals are driven by pulse modulated dc motors or stepper motors. These drivers produce torques on the mast, with jitter that excites the satellite and may cause disturbances to sensitive experiments. The dynamic properties of the antenna support structure (mast), including flexible mode characteristics were defined. The torque profile induced on the spacecraft by motion of the high gain antenna was estimated. Gain and phase margins of the servo control loop of the gimbal drive electronics was also verified.

Germain, A.↗

NASA NTRS1983

Factors influencing the marine boundary layer during a cold-air outbreak

The model for the cloud-topped marine boundary layer during a cold air outbreak developed by Stage and Businger (1981a) is used in conjunction with a test profile based on a fall outbreak episode over Lake Ontario to study factors influencing marine boundary-layer evolution. Sensitivity tests are done which show changes in layer evolution resulting from variation of wind speed, radiative sky temperature, water surface temperature, humidity of the shoreline sounding and divergence. The behavior of the layer in the presence of a region of cold-water upwelling near the shore is also investigated. It is found that the main effect of the upwelling region is to delay modification of the boundary-layer air.

Stage, S. A.↗

NASA NTRS1984

Ultraviolet spectral morphology of the O stars - The remarkable luminosity dependence of the Si IV stellar wind effect

An extensive survey of ultraviolet O type spectra, by means of high-resolution data from the International Ultraviolet Explorer archives, shows a strong correlation between both the photospheric and stellar wind features, and the optical spectral types. In particular, the stellar wind effect in the Si IV resonance doublet displays a strong luminosity dependence which has not been completely described before: there is no effect anywhere on the main sequence, but it develops gradually through the intermediate luminosity classes into a full P Cygni profile in the supergiants. This behavior is in sharp contrast to that of the C IV and N V, which have strong P Cygni profiles throughout most of the O type domain, including the main sequence. The Si IV effect simultaneously provides a sensitive classification criterion and poses an outstanding problem for detailed astrophysical interpretation. In addition, a new emission feature at 1574 A, possibly due to N III or to N IV forbidden line, is reported.

Walborn, N. R.↗

NASA NTRS1989

Diurnal variations of mesospheric ozone obtained by ground-based microwave radiometry

From December 1986 until April 1987 ground-based microwave observations of the diurnal variation of mesospheric ozone were made over Bern, Switzerland. These data were of sufficient quality to define the characteristics diurnal behavior of the ozone mixing ratio during winter and equinoctial conditions. The observed diurnal variation of ozone peaks at about 74 km, where its amplitude is about a factor of 6. At 65 km the observed diurnal variation is a factor of 3, whereas at 55 km it is only a factor of 1.4. One-dimensional model calculations accurately reproduce the relative diurnal variation of ozone at equinox, suggesting that the model value of the ozone photolysis rate coefficient is accurate to better that 10 percent. For winter conditions, however, the model underpredicts the observed relative diurnal variation by a factor of 2; a major part of this discrepancy is due to an observed postmidnight increase in ozone. Various suggested changes in model parameters to better produce the ozone abundance vertical profile result in only small differences in the relative diurnal variation, indicating that these observations do not provide a sensitive test of the mesospheric chemistry controlling the abundance of odd oxygen.

Zommerfelds, W. C.↗

NASA NTRS1992

Aerodynamic design of turbomachinery blading in three-dimensional flow - An application to radial inflow turbines

A computational method, based on a theory for turbomachinery blading design in three-dimensional inviscid flow, is applied to a parametric design study of a radial inflow turbine wheel. As the method requires the specification of swirl distribution, a technique for its smooth generation within the blade region is proposed. Excellent agreements have been obtained between the computed results from this design method and those from direct Euler computations, demonstrating the correspondence and consistency between the two. The computed results indicate the sensitivity of the pressure distribution to a lean in the stacking axis and a minor alteration in the hub/shroud profiles. Analysis based on Navier-Stokes solver shows no breakdown of flow within the designed blade passage and agreement with that from design calculation; thus the flow in the designed turbine rotor closely approximates that of an inviscid one. These calculations illustrate the use of a design method coupled to an analysis tool for establishing guidelines and criteria for designing turbomachinery blading.

Yang, Y. L.↗

NASA NTRS2001

UIT Observations of Early-Type Galaxies and Analysis of the FUSE Spectrum of a Subdwarf B Star

This work covers Ultraviolet Imaging Telescope (UIT) observations of early-type galaxies (155 nm) and Far Ultraviolet Spectroscopic Explorer (FUSE) spectra of a Galactic subdwarf B star (sdB). Early UV space astronomy missions revealed that early-type galaxies harbor a population of stars with effective temperatures greater than that of the main sequence turn-off (about 6,000 K) and UV emission that is very sensitive to characteristics of the stellar population. We present UV (155 nm) surface photometry and UV-B color profiles for 8 E and SO galaxies observed by UIT. Some objects have de Vaucouleurs surface brightness profiles, while others have disk-like profiles, but we find no other evidence for the presence of a disk or young, massive stars. There is a wide range of UV-B color gradients, but there is no correlation with metallicity gradients. SdB stars are the leading candidate UV emitters in old, high metallicity stellar populations (e.g., early-type galaxies). We observed the Galactic sdB star PG0749+658 with FUSE and derived abundances with the aim of constraining models of the heavy element distribution in sdB atmospheres. All of the elements measured are depleted with respect to solar, except for Cr and Mn, which are about solar, and Ni, which is enhanced. This work was supported in part by NASA grants NAG5-700 and NAG5-6403 to the University of Virginia and NAS5-32985 to Johns Hopkins University.

Ohl, Raymond G.↗

NASA NTRS2001

Spectral Diagnostics for Early-Type Stars in Support of High-Resolution Satellite Observation

High-resolution X-ray spectra have recently been obtained using the Chandra X-ray Satellite Observatory for the two hot supergiant stars zeta Pup and delta Ori. The spectra show the presence of strong K-shell line emission from O, Ne, Mg, Si, and S, as well as strong L-shell line emission from Fe. Initial examination of the spectra indicates that the lines are significantly broader than what would be expected for a stationary plasma, and appear to be consistent with Doppler-broadened emission from hot plasma forming in shock-heated regions embedded in the wind (see Figure 1). Chandra has sufficient spectral resolution to study the velocity structure of isolated X-ray line profiles. Our analysis for zeta Pup has shown blue-shifted and skewed line profiles, providing the most direct evidence that the X-ray source is embedded in the stellar wind. The sensitivity of the He-like fir (forbidden-intercombination-resonance) lines to a strong UV radiation field is used to estimate the radial distances at which lines of O VII, Ne IX, Mg XI, Si XIII, and S XV originate.

MacFarlane, Joseph J.↗

NASA NTRS2003

Remote Sensing of Vertical Distributions of Smoke Aerosol Off the Coast of Africa

In 2004 NASA plans to launch the Cloud-Aerosol Lidar and Infrared Pathfinder Satellite Observations- CALIPSO mission, with a two-wavelength lidar aboard. CALIPSO will fly in formation with the Moderate Resolution Imaging Spectro-Radiometer (MODIS) on the Aqua satellite. Here we present inversions of combined aircraft lidar and MODIS data to study the properties of smoke off the southwest coast of Southern Africa. The inversion derives profiles of the aerosol extinction due to fine and coarse particles. Comparisons with three sets of airborne in situ measurements show excellent agreement of the aerosol extinction profiles; however the inversion derives smaller spectral dependence of the extinction than the in situ measurements. The inversion is sensitive to the aerosol backscattering-to-extinction ratio (BER). Due to nonsphericity of the coarse aerosols, the range of BERs of the smoke aerosol is 0.014 to 0.021 sr(sup -l) for the fine and coarse particles at 0.53 and 1.06 pm wavelengths, which do not differ much from the value for dust (0.016 sr(sup -1)) at these wavelengths.

Kaufman, Y. J.↗

NASA NTRS1999

New Generation Lidar Technology and Applications

Lidar has been a tool for atmospheric research for several decades. Until recently routine operational use of lidar was not known. Problems have involved a lack of appropriate technology rather than a lack of applications. Within the last few years, lidar based on a new generation of solid state lasers and detectors have changed the situation. Operational applications for cloud and aerosol research applications are now well established. In these research applications, the direct height profiling capability of lidar is typically an adjunct to other types of sensing, both passive and active. Compact eye safe lidar with the sensitivity for ground based monitoring of all significant cloud and aerosol structure and the reliability to operate full time for several years is now in routine use. The approach is known as micro pulse lidar (MPL). For MPL the laser pulse repetition rate is in the kilohertz range and the pulse energies are in the micro-Joule range. The low pulse energy permits the systems to be eye safe and reliable with solid state lasers. A number of MPL systems have been deployed since 1992 at atmospheric research sites at a variety of global locations. Accurate monitoring of cloud and aerosol vertical distribution is a critical measurement for atmospheric radiation. An airborne application of lidar cloud and aerosol profiling is retrievals of parameters from combined lidar and passive sensing involving visible, infrared and microwave frequencies. A lidar based on a large pulse, solid state diode pumped ND:YAG laser has been deployed on the NASA ER-2 high altitude research aircraft along with multi-spectral visible/IR and microwave imaging radiometers since 1993. The system has shown high reliability in an extensive series of experimental projects for cloud remote sensing. The retrieval of cirrus radiation parameters is an effective application for combined lidar and passive sensing. An approved NASA mission will soon begin long term lidar observation of atmospheric structure from space. The Geoscience Laser Altimeter System (GLAS) of the Earth Observing System is scheduled for deployment in the 2001 time frame. GLAS is both a cloud and aerosol lidar and a surface altimeter, principally for monitoring of polar ice sheets. The GLAS instrument is based on all solid state lasers operating at 40 Hz and high efficiency, solid state detectors. The design lifetime is three to five years. Data from the GLAS mission is expected to revolutionize some aspects of our understanding of the global distribution of cloud and aerosols for global climate prediction.

Spinhirne, James D.↗

NASA NTRS1980

An experiment concept to measure stratospheric trace constituents by Laser Heterodyne Spectroscopy

The concept and techniques of a Laser Heterodyne Spectrometer experiment for measuring the vertical profiles of several stratospheric trace gases are discussed. The goal of the experiment is to develop a laser heterodyne receiver capable of measuring 2-4 gases simultaneously from Spacelab and, ultimately, from free-flying platforms. Sensitivity analyses are currently being performed for tenuous molecules such as ClO, ClONO2, NOCl, HO2, H2O2, and N2O5, although the capability exists for measuring more abundant gases, such as O3, HNO3, N2O, NO2, and CH4. Results indicate that O3 and ClO vertical profiles can be measured with an accuracy equal to or better than 95% and 80%, respectively, over the total profile. Laboratory measurements of the performance characteristics of the local oscillator and heterodyne detector are discussed with reference to 'excess-noise' and Doppler-shift effects.

Allario, F.↗

NASA NTRS1984

Simulation Experiments on the Relative Accuracy of Inferred Atmospheric States from Idealized Wind and Temperature Profiling Systems

The First GARP Global Experiment (FGGE) led to the planning, design and implementation of a global observing system. Technologies as coherent CO2 LIDAR systems and highly sensitive IR detectors offer the potential of more accurate global spaceborne observation systems. The advent of super computers allows general circulation modeling and more sophisticated data analysis schemes. The consideration of advanced spaceborne systems better suited to meet the new emerging requirements are suggested. The Global Weather Experiment provides us with a new baseline to assess data accuracy and forecasting capabilities which is used for study of the incremental performance.

Halem, M.↗

NASA NTRS1980

Experimental investigation of a three dimensional turbulent boundary layer with a non disappearing pressure gradient

The results of measuring profiles of temporally determined velocities and Reynolds tension, wall shear stresses and pressure distribution in a three dimensional, turbulent boundary layer with pressure gradients in both tangential directions are reported. For determining the velocities X wire probes were used whose cooling was gauged according to magnitude and direction of the flow and was described with an effective cooling speed. In the evaluation consideration is given to the directional sensitivity of the hot wire. The ratio of the turbulence viscosities is calculated for both tangential directions and is found to be approximately N equals 1.2. Further, the profiles of the mixing path lengths for the flow direction are found to vary only slightly with increasing X-coordinates, while the boundary layer thickness increases substantially. The relationships of turbulent shear stress to turbulent, kinetic fluctuation energy is approximately constant over a large part of the boundary layer.

Mueller, U.↗

NASA NTRS1993

Numerical and experimental investigation of the bending response of thin-walled composite cylinders

A numerical and experimental investigation of the bending behavior of six eight-ply graphite-epoxy circular cylinders is presented. Bending is induced by applying a known end-rotation to each end of the cylinders, analogous to a beam in bending. The cylinders have a nominal radius of 6 inches, a length-to-radius ratio of 2 and 5, and a radius-to-thickness ratio of approximately 160. A (+/- 45/0/90)S quasi-isotropic layup and two orthotropic layups, (+/- 45/0 sub 2)S and (+/- 45/90 sub 2)S, are studied. A geometrically nonlinear special-purpose analysis, based on Donnell's nonlinear shell equations, is developed to study the prebuckling responses and gain insight into the effects of non-ideal boundary conditions and initial geometric imperfections. A geometrically nonlinear finite element analysis is utilized to compare with the prebuckling solutions of the special-purpose analysis and to study the buckling and post buckling responses of both geometrically perfect and imperfect cylinders. The imperfect cylinder geometries are represented by an analytical approximation of the measured shape imperfections. Extensive experimental data are obtained from quasi-static tests of the cylinders using a test fixture specifically designed for the present investigation. A description of the test fixture is included. The experimental data are compared to predictions for both perfect and imperfect cylinder geometries. Prebuckling results are presented in the form of displacement and strain profiles. Buckling end-rotations, moments, and strains are reported, and predicted mode shapes are presented. Observed and predicted moment vs. end-rotation relations, deflection patterns, and strain profiles are illustrated for the post buckling responses. It is found that a geometrically nonlinear boundary layer behavior characterizes the prebuckling responses. The boundary layer behavior is sensitive to laminate orthotropy, cylinder geometry, initial geometric imperfections, applied end-rotation, and non-ideal boundary conditions. Buckling end-rotations, strains, and moments are influenced by laminate orthotropy and initial geometric imperfections. Measured buckling results correlate well with predictions for the geometrically imperfect specimens. The postbuckling analyses predict equilibrium paths with a number of scallop-shaped branches that correspond to unique deflection patterns. The observed postbuckling deflection patterns and measured strain profiles show striking similarities to the predictions in some cases. Ultimate failure of the cylinders is attributed to an interlaminar shear failure mode along the nodal lines of the postbuckling deflection patterns.

Fuchs, J. P.↗

NASA NTRS2005

Sensitivity of Stratospheric Retrievals from Radio Occultations on Upper Boundary Conditions

The main uncertainty in the stratospheric retrievals from GPS radio occultation (RO) measurements comes from the lack of reliable measurements in the upper stratosphere and above where the bending due to the neutral atmosphere is weak and residual ionospheric effects are strong. In this work, we quantify the bias and uncertainty of the refractivity and temperature retrievals due to different upper boundary strategies using a simulation study. We use lidar refractivity and temperature profiles as the input states in generating the synthetic occultations. Random noise levels commensurate with the CHAMP RO measurements are then added to the simulated data. Through this study, the sensitivity of stratospheric retrievals to upper boundary methods and parameters are examined. Such error characterizations are important prerequisites towards the effective use of GPS RO data in climate monitoring.

GPS↗

NASA NTRS1975

Error analysis of Dobson spectrophotometer measurements of the total ozone content

A study of techniques for measuring atmospheric ozone is reported. This study represents the second phase of a program designed to improve techniques for the measurement of atmospheric ozone. This phase of the program studied the sensitivity of Dobson direct sun measurements and the ozone amounts inferred from those measurements to variation in the atmospheric temperature profile. The study used the plane - parallel Monte-Carlo model developed and tested under the initial phase of this program, and a series of standard model atmospheres.

Holland, A. C.↗

NASA NTRS1991

Hypersonic cone flow predictions using an implicit upwind space-marching code

Solutions have been computed and results are presented for Problem 1, the case of Mach 9 transitional flow past a 7 deg half-angle cone at zero incidence. The solutions were computed using a code developed for the integration of the parabolized Navier-Stokes equations. The algorithm employed in the code is based on a Roe-type flux-difference-splitting scheme applied following a finite-volume approach. The basic algorithm has been modified to make it implicit and second-order accurate in the crossflow directions. Results are presented in terms of surface pressure and heat transfer as well as boundary layer profiles of pitot pressure, Mach number, and tangential velocity. The case was recalculated several times in an effort to determine sensitivities to such parameters as grid density, wall temperature, turbulence model parameters, as well as freestream expansion. Comparisons with the experimental data are presented and discussed.

Lawrence, Scott L.↗