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At least 145 records · Page 8

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NASA NTRS1980

The SPS interference problem-electronic system effects and mitigation techniques

The potential for interference between solar power satellites (SPS) and other Earth satellite operations was examined along with interference problems involving specific electronic devices. Conclusions indicate that interference is likely in the 2500 MHz to 2690 MHz direct broadcast satellite band adjacent to SPS. Estimates of the adjacent channel noise from SPS in this band are as high as -124 dBc/4 kHz and -100 dBc/MHz, where dBc represents decibels relative to the total power in the fundamental. A second potential problem is the 7350 MHz, 3d harmonic from SPS that falls within the 7300 MHz to 7450 MHz space to Earth, government, satellite assignment. Catastrophic failures can be produced in integrated circuits when the microwave power levels coupled into inputs and power leads reach 1 to 100 watts. The failures are typically due to bonding wire melting, metallization failures, and junction shorting. Nondestructive interaction or interference, however, generally occurs with coupled power levels of the order of 10 milliwatts. This integration is due to the rectification of microwave energy by the numerous pn junctions within these circuits.

Juroshek, J. R.↗

NASA NTRS1984

Flight test results for the Digital Integrated Automatic Landing Systems (DIALS): A modern control full-state feedback design

The Digital Integrated Automatic Landing System (DIALS) is discussed. The DIALS is a modern control theory design performing all the maneuver modes associated with current autoland systems: localizer capture and track, glideslope capture and track, decrab, and flare. The DIALS is an integrated full-state feedback system which was designed using direct-digital methods. The DIALS uses standard aircraft sensors and the digital Microwave Landing System (MLS) signals as measurements. It consists of separately designed longitudinal and lateral channels although some cross-coupling variables are fed between channels for improved state estimates and trajectory commands. The DIALS was implemented within the 16-bit fixed-point flight computers of the ATOPS research aircraft, a small twin jet commercial transport outfitted with a second research cockpit and a fly-by-wire system. The DIALS became the first modern control theory design to be successfully flight tested on a commercial-type aircraft. Flight tests were conducted in late 1981 using a wide coverage MLS on Runway 22 at Wallops Flight Center. All the modes were exercised including the capture and track of steep glidescopes up to 5 degrees.

Hueschen, R. M.↗

NASA NTRS1987

Polarized fluorescence spectroscopy of O2(+)

Polarized fluorescence measurements involving the A 2Pi(u) - X 2Pi(g) and b 4Sigma(g)(-) - a 4Pi(u) transitions in O2(+) following narrow-band photoexcitation of O2/X 3Sigma(g)(-)/ are reported. The analysis, based on the conventional high-J limit, involves deducing the quadrupole alignment factor from which the relative strengths of degenerate photoexcitation channels responsible for the population distribution in the A 2Pi(u) and b 4Sigma(g)(-) states of O2(+) can be estimated. The measured A-channel polarization exhibits pronounced structure which correlates well with the known positions of Rydberg states, whereas the polarization signal in the b channel has broad and less prominent features. Discrepancies between theoretical and measured results can largely be accounted for by additional configuration mixing and autoionization considerations.

Keller, J. W.↗

NASA NTRS1991

Fade-durations derived from land-mobile-satellite measurements in Australia

Transmissions from the Japanese ETS-V geostationary satellite were measured at L band (1.5 GHz) in a vehicle driving on roads of southeastern Australia. The measurements were part of a program designed to characterize propagation effects due to roadside trees and terrain for mobile satellite service. It is shown that the cumulative distributions of fade and nonfade durations follow a lognormal and power law, respectively. At 1 percent probability, fades last 2-8 m, and nonfades 10-100 m, depending on the degree of shadowing. Phase fluctuations are generally small, allowing the channel characteristics to be estimated from levels only.

Hase, Yoshihiro↗

NASA NTRS1990

Thermal behavior of the SHOOT gallery arm

The planned Superfluid Helium On-Orbit Transfer (SHOOT) experiment will show the feasibility of resupplying orbiting facilities with liquid helium. The SHOOT experiment, designed for transfer rates of 300 to 800 liters/hr, will use a thermomechanical pump and four screen covered flow channels for fluid acquisition. Cavitation and thermal behavior was examined in ground based tests of the pump and of a full sized channel. A model for estimating the temperature profile at the pump inlet is presented. Large temperature increases in this region can significantly degrade the performance of the fountain pump.

Nissen, J. A.↗

NASA NTRS1991

Thermal behavior of the SHOOT gallery arm

Nissen, J. A.↗

NASA NTRS1995

A New Potential Energy Surface for N+O2: Is There an NOO Minimum?

We report a new calculation of the N+02 potential energy surface using complete active space self-consistent field internally contracted configuration interaction with the Dunning correlation consistent basis sets. The peroxy isomer of N02 is found to be a very shallow minimum separated from NO+O by a barrier of only 0.3 kcal/mol (excluding zero-point effects). The entrance channel barrier height is estimated to be 8.6 kcal/mol for ICCI+Q calculations correlating all but the Ols and N1s electrons with a cc-p VQZ basis set.

Walch, Stephen P.↗

NASA NTRS1997

Airborne Millimeter-Wave Radiometric Observations of Cirrus Clouds

This paper reports the first radiometric measurements of cirrus clouds in the frequency range of 89-325 GHz from a high-altitude aircraft flight. The measurements are conducted with a Millimeter-wave Imaging Radiometer (MIR) on board the NASA ER-2 aircraft over a region in northern Oklahoma. Aboard the same aircraft are a cloud lidar system and a multichannel radiometer operating at the visible and infrared wavelengths. The instrument ensemble is well suited for identifying cirrus clouds. It is shown that the depressions in brightness temperatures associated with a few intense cirrus clouds occur at all frequency channels of the MIR. Estimates of total ice water path of the cirrus clouds are derived from comparisons of radiative transfer calculations and observed brightness depressions.

Wang, J. R.↗

NASA NTRS2005

The High Temperature Response of the TRACE 171 Angstrom and 195 Angstrom Channels

The CHIANTI spectral code is used to estimate line and continuum intensity contributions to the TRACE 171 Angstrom and 195 Angstrom channels, widely used for imaging a variety of solar features and phenomena, including quiet Sun and active region loops and solar flares. It is shown that the 171 Angstrom channel has a high-temperature response, so high-temperature (approx. 10 MK) features in flares, prominent in TRACE 195 approx.\AA\ images as well as X-ray images from Yohkoh and RHESSI, are sometimes visible in images made in the 171 Angstrom channel. Such features consist of hot loop-top emission, either confined spots or 'spine' structures in loop arcades. This is illustrated with TRACE and X-ray flare images.

Phillips, K. J. H.↗

NASA NTRS2012

The Kinematic and Microphysical Control of Storm Integrated Lightning Flash Extent

Objective: To investigate the kinematic and microphysical control of lightning properties, particularly those that may govern the production of nitrogen oxides (NOx) in thunderstorms, such as flash rate, type (intracloud [IC] vs. cloud-to-ground [CG] ) and extent. Data and Methodology: a) NASA MSFC Lightning Nitrogen Oxides Model (LNOM) is applied to North Alabama Lightning Mapping Array (NALMA) and Vaisala National Lightning Detection Network(TradeMark) (NLDN) observations following ordinary convective cells through their lifecycle. b) LNOM provides estimates of flash type, channel length distributions, lightning segment altitude distributions (SADs) and lightning NOx production profiles (Koshak et al. 2012). c) LNOM lightning characteristics are compared to the evolution of updraft and precipitation properties inferred from dual-Doppler (DD) and polarimetric radar analyses of UAHuntsville Advanced Radar for Meteorological and Operational Research (ARMOR, Cband, polarimetric) and KHTX (S-band, Doppler).

Carey, Lawrence D.↗

NASA NTRS2012

Gravity Wave Variances and Propagation Derived from AIRS Radiances

As the first gravity wave (GW) climatology study using nadir-viewing infrared sounders, 50 Atmospheric Infrared Sounder (AIRS) radiance channels are selected to estimate GW variances at pressure levels between 2-100 hPa. The GW variance for each scan in the cross-track direction is derived from radiance perturbations in the scan, independently of adjacent scans along the orbit. Since the scanning swaths are perpendicular to the satellite orbits, which are inclined meridionally at most latitudes, the zonal component of GW propagation can be inferred by differencing the variances derived between the westmost and the eastmost viewing angles. Consistent with previous GW studies using various satellite instruments, monthly mean AIRS variance shows large enhancements over meridionally oriented mountain ranges as well as some islands at winter hemisphere high latitudes. Enhanced wave activities are also found above tropical deep convective regions. GWs prefer to propagate westward above mountain ranges, and eastward above deep convection. AIRS 90 field-of-views (FOVs), ranging from +48 deg. to −48 deg. off nadir, can detect large-amplitude GWs with a phase velocity propagating preferentially at steep angles (e.g., those from orographic and convective sources). The annual cycle dominates the GW variances and the preferred propagation directions for all latitudes. Indication of a weak two-year variation in the tropics is found, which is presumably related to the Quasi-biennial oscillation (QBO). AIRS geometry makes its out-tracks capable of detecting GWs with vertical wavelengths substantially shorter than the thickness of instrument weighting functions. The novel discovery of AIRS capability of observing shallow inertia GWs will expand the potential of satellite GW remote sensing and provide further constraints on the GW drag parameterization schemes in the general circulation models (GCMs).

AIRS↗

NASA NTRS1982

Laser Doppler anemometer measurements using nonorthogonal velocity components - Error estimates

Laser Doppler anemometers (LDAs) that are arranged to measure nonorthogonal velocity components (from which orthogonal components are computed through transformation equations) are more susceptible to calibration and sampling errors than are systems with uncoupled channels. In this paper uncertainty methods and estimation theory are used to evaluate, respectively, the systematic and statistical errors that are present when such devices are applied to the measurement of mean velocities in turbulent flows. Statistical errors are estimated for two-channel LDA data that are either correlated or uncorrelated. For uncorrelated data the directional uncertainty of the measured velocity vector is considered for applications where mean streamline patterns are desired.

Orloff, K. L.↗

NASA NTRS1981

Parametric analysis of closed cycle magnetohydrodynamic (MHD) power plants

A parametric analysis of closed cycle MHD power plants was performed which studied the technical feasibility, associated capital cost, and cost of electricity for the direct combustion of coal or coal derived fuel. Three reference plants, differing primarily in the method of coal conversion utilized, were defined. Reference Plant 1 used direct coal fired combustion while Reference Plants 2 and 3 employed on site integrated gasifiers. Reference Plant 2 used a pressurized gasifier while Reference Plant 3 used a ""state of the art' atmospheric gasifier. Thirty plant configurations were considered by using parametric variations from the Reference Plants. Parametric variations include the type of coal (Montana Rosebud or Illinois No. 6), clean up systems (hot or cold gas clean up), on or two stage atmospheric or pressurized direct fired coal combustors, and six different gasifier systems. Plant sizes ranged from 100 to 1000 MWe. Overall plant performance was calculated using two methodologies. In one task, the channel performance was assumed and the MHD topping cycle efficiencies were based on the assumed values. A second task involved rigorous calculations of channel performance (enthalpy extraction, isentropic efficiency and generator output) that verified the original (task one) assumptions. Closed cycle MHD capital costs were estimated for the task one plants; task two cost estimates were made for the channel and magnet only.

Owens, W.↗

NASA NTRS1993

Predicting LANDSAT MSS endmember signatures from corresponding higher resolution TM fraction images

The approach to predicting Landsat Multispectral Scanner System (MSS) endmember signatures from fraction images derived from high resolution Landsat Thematic Mapper (TM) data is presented. The purpose, conducted in the Mogi-Guacu study site located in Sao Paulo State, Brazil, was to determine if information derived from a mixture model applied to higher resolution TM data could serve as ground truth for the lower resolution MSS sensor. The Constrained Least Squares (CLS) method was used to generate vegetation, soil, and shade fraction images from the TM data. The resulting images were then used to estimate the endmember spectral response for MSS data by regressing each MSS spectral channel against the corresponding proportion values estimated for the same resolution cells from the TM mixture model. The evaluation of the predicted signatures was performed by comparing the corresponding fraction images derived from both the MSS and TM data acquired on 14 Sep. 1986. The techniques serves as a potential tool for integrating information in global studies where remote sensors with different spectral and spatial resolutions were used.

Shimabukuro, Yosio E.↗

NASA NTRS1985

Sea surface temperature - Observations from geostationary satellites

Multispectral image data acquired from the VISSR atmospheric sounder (VAS) on the geostationary GOES satellites were used to estimate sea surface temperatures (SST). A procedure was developed to screen VAS visible and infrared data for cloud-free regions for estimation of SST from the clear infrared radiances. A data set of matches between the VAS radiances and high quality buoy estimates of SST was produced. A linear regression analysis of these matches was performed to generate an empirical algorithm relating the VAS window channel brightness temperatures to the estimates of SST recorded by NOAA fixed environment buoys. Daily maps of SST during Hurricanes Alicia (1983) and Debbie (1982) demonstrated the ability of VAS to monitor air-sea interactions at high temporal and spatial scales.

Bates, J. J.↗

NASA NTRS2008

Spectrally Resolved Flux Derived from Collocated AIRS and CERES Observations and its Application in Model Validation: Clear-Sky Over the Tropic Oceans - Part I

Spectrally resolved outgoing IR flux, the integrand of the outgoing longwave radiation (OLR), has its unique value in evaluating model simulations. Here we describe an algorithm of deriving such clear-sky outgoing spectral flux through the whole IR region from the collocated Atmospheric Infrared Sounder (AIRS) and the Clouds & the Earth's Radiant Energy System (CERES) measurements over the tropical oceans. Based on the scene types and corresponding angular distribution models (ADMs) used in the CERES Single Satellite Footprint (SSF) dataset, spectrally-dependent ADMs are developed and used to estimate the spectral flux at each AIRS channel. A multivariate linear prediction scheme is then used to estimate spectral fluxes at frequencies not covered by the AIRS instrument. The whole algorithm is validated using synthetic spectra as well as the CERES OLR measurements. Using the GFDL AM2 model simulation as a case study, the application of the derived clear-sky outgoing spectral flux in model evaluation is illustrated. By comparing the observed and simulated spectral flux in 2004, compensating errors in the simulated OLR from different absorption bands can be revealed, so does the errors from frequencies within a given absorption band. Discrepancies between the simulated and observed spatial distributions and seasonal evolutions of the spectral fluxes at different spectral ranges are further discussed. The methodology described in this study can be applied to other surface types as well as cloudy-sky observations and corresponding model evaluations.

Huang, Xianglei↗

NASA NTRS2012

Mars Atmospheric CO2 Condensation Above the North and South Poles as Revealed by Radio Occultation, Climate Sounder, and Laser Ranging Observations

We study the condensation of CO2 in Mars atmosphere using temperature profilesretrieved from radio occultation measurements from Mars Global Surveyor (MGS) as wellas the climate sounding instrument onboard the Mars Reconnaissance Orbiter (MRO),and detection of reflective clouds by the MGS Mars Orbiter Laser Altimeter (MOLA). Wefind 11 events in 1999 where MGS temperature profiles indicate CO2 condensation andMOLA simultaneously detects reflective clouds. We thus provide causal evidence thatMOLA non-ground returns are associated with CO2 condensation, which strongly indicatestheir nature being CO2 clouds. The MGS and MRO temperature profiles together revealthe seasonal expansion and shrinking of the area and the vertical extent of atmosphericsaturation. The occurrence rate of atmospheric saturation is maximized at high latitudes inthe middle of winter. The atmospheric saturation in the northern polar region exhibits moreintense seasonal variation than in the southern polar region. In particular, a shrinking ofsaturation area and thickness from LS 270 to 300 in 2007 is found; this is probablyrelated to a planet-encircling dust storm. Furthermore, we integrate the condensation areaand the condensation occurrence rate to estimate cumulative masses of CO2 condensatesdeposited onto the northern and southern seasonal polar caps. The precipitation flux isapproximated by the particle settling flux which is estimated using the impulse responses ofMOLA filter channels. With our approach, the total atmospheric condensation mass canbe estimated from these observational data sets with average particle size as the onlyfree parameter. By comparison with the seasonal polar cap masses inferred from thetime-varying gravity of Mars, our estimates indicate that the average condensate particleradius is 822 mm in the northern hemisphere and 413 mm in the southern hemisphere.Our multi-instrument data analysis provides new constraints on modeling the global climateof Mars.

MOLA↗

NASA NTRS2012

Sensitivity Analysis for Atmospheric Infrared Sounder (AIRS) CO2 Retrieval

The Atmospheric Infrared Sounder (AIRS) is a thermal infrared sensor able to retrieve the daily atmospheric state globally for clear as well as partially cloudy field-of-views. The AIRS spectrometer has 2378 channels sensing from 15.4 micrometers to 3.7 micrometers, of which a small subset in the 15 micrometers region has been selected, to date, for CO2 retrieval. To improve upon the current retrieval method, we extended the retrieval calculations to include a prior estimate component and developed a channel ranking system to optimize the channels and number of channels used. The channel ranking system uses a mathematical formalism to rapidly process and assess the retrieval potential of large numbers of channels. Implementing this system, we identifed a larger optimized subset of AIRS channels that can decrease retrieval errors and minimize the overall sensitivity to other iridescent contributors, such as water vapor, ozone, and atmospheric temperature. This methodology selects channels globally by accounting for the latitudinal, longitudinal, and seasonal dependencies of the subset. The new methodology increases accuracy in AIRS CO2 as well as other retrievals and enables the extension of retrieved CO2 vertical profiles to altitudes ranging from the lower troposphere to upper stratosphere. The extended retrieval method for CO2 vertical profile estimation using a maximum-likelihood estimation method. We use model data to demonstrate the beneficial impact of the extended retrieval method using the new channel ranking system on CO2 retrieval.

sensitivity analysis↗