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At least 397 records · Page 22
All sourcesNASA NTRSDOE OSTI
NASA NTRS1994

An Algorithm to Generate Deep-Layer Temperatures from Microwave Satellite Observations for the Purpose of Monitoring Climate Change

An algorithm for generating deep-layer mean temperatures from satellite-observed microwave observations is presented. Unlike traditional temperature retrieval methods, this algorithm does not require a first guess temperature of the ambient atmosphere. By eliminating the first guess a potentially systematic source of error has been removed. The algorithm is expected to yield long-term records that are suitable for detecting small changes in climate. The atmospheric contribution to the deep-layer mean temperature is given by the averaging kernel. The algorithm computes the coefficients that will best approximate a desired averaging kernel from a linear combination of the satellite radiometer's weighting functions. The coefficients are then applied to the measurements to yield the deep-layer mean temperature. Three constraints were used in deriving the algorithm: (1) the sum of the coefficients must be one, (2) the noise of the product is minimized, and (3) the shape of the approximated averaging kernel is well-behaved. Note that a trade-off between constraints 2 and 3 is unavoidable. The algorithm can also be used to combine measurements from a future sensor (i.e., the 20-channel Advanced Microwave Sounding Unit (AMSU)) to yield the same averaging kernel as that based on an earlier sensor (i.e., the 4-channel Microwave Sounding Unit (MSU)). This will allow a time series of deep-layer mean temperatures based on MSU measurements to be continued with AMSU measurements. The AMSU is expected to replace the MSU in 1996.

Goldberg, Mitchell D.↗
NASA NTRS2004

Development of a Computationally Efficient, High Fidelity, Finite Element Based Hall Thruster Model

This report documents the development of a two dimensional finite element based numerical model for efficient characterization of the Hall thruster plasma dynamics in the framework of multi-fluid model. Effect of the ionization and the recombination has been included in the present model. Based on the experimental data, a third order polynomial in electron temperature is used to calculate the ionization rate. The neutral dynamics is included only through the neutral continuity equation in the presence of a uniform neutral flow. The electrons are modeled as magnetized and hot, whereas ions are assumed magnetized and cold. The dynamics of Hall thruster is also investigated in the presence of plasma-wall interaction. The plasma-wall interaction is a function of wall potential, which in turn is determined by the secondary electron emission and sputtering yield. The effect of secondary electron emission and sputter yield has been considered simultaneously, Simulation results are interpreted in the light of experimental observations and available numerical solutions in the literature.

Jacobson, David↗
NASA NTRS2001

Sensitive Technique Developed Using Atomic Force Microscopy to Measure the Low-Earth-Orbit Atomic Oxygen Erosion of Polymers

A recession measurement technique has been developed at the NASA Glenn Research Center to determine the atomic oxygen durability of polymers exposed to the space environment for short durations. Polymers such as polyimide Kapton and Teflon FEP (fluorinated ethylene propylene, DuPont) are commonly used in spacecraft because of their desirable properties, such as flexibility, low density, and in the case of FEP, low solar absorptance and high thermal emittance. Polymers on the exterior of spacecraft in the low- Earth-orbit environment are exposed to energetic atomic oxygen, resulting in erosion and potential structural loss. It is, therefore, important to understand the atomic oxygen erosion yield (E, the volume loss per incident oxygen atom) of polymers being considered in spacecraft design. Because long-term space exposure data are rare and very costly, short-term exposures, such as on the space shuttles, are often relied on for atomic oxygen erosion determination. The most common technique for determining E is through mass-loss measurements. For limited-duration exposure experiments, such as shuttle flight experiments, the atomic oxygen fluence is often so small that mass-loss measurements are not sensitive enough. Therefore, a recession measurement technique has been developed at Glenn to obtain accurate erosion yields of polymers exposed to low atomic oxygen fluences.

deGroh, Kim D.↗
NASA NTRS2019

Joint 3D-Wind Retrievals with Stereoscopic Views from MODIS and GOES

Atmospheric motion vectors (AMVs), derived by tracking patterns, represent the winds in a layer characteristic of the pattern. AMV height (or pressure), important for applications in atmospheric research and operational meteorology, is usually assigned using observed IR brightness temperatures with a modeled atmosphere and can be inaccurate. Stereoscopic tracking provides a direct geometric height measurement of the pattern that an AMV represents. We extend our previous work with multi-angle imaging spectroradiometer (MISR) and GOES to moderate resolution imaging spectroradiometer (MODIS) and the GOES-R series advanced baseline imager (ABI). MISR is a unique satellite instrument for stereoscopy with nine angular views along track, but its images have a narrow (380 km) swath and no thermal IR channels. MODIS provides a much wider (2330 km) swath and eight thermal IR channels that pair well with all but two ABI channels, o e ring a rich set of potential applications. Given the similarities between MODIS and VIIRS, our methods should also yield similar performance with VIIRS. Our methods, as enabled by advanced sensors like MODIS and ABI, require high-accuracy geographic registration in both systems but no synchronization of observations. AMVs are retrieved jointly with their heights from the disparities between triplets of ABI scenes and the paired MODIS granule. We validate our retrievals against MISR-GOES retrievals, operational GOES wind products, and by tracking clear-sky terrain. We demonstrate that the 3D-wind algorithm can produce high-quality AMV and height measurements for applications from the planetary boundary layer (PBL) to the upper troposphere, including cold-air outbreaks, wildfire smoke plumes, and hurricanes.

Carr, James L.↗
NASA NTRS2018

Enhancements to the Open Access Spectral Band Adjustment Factor Online Calculation Tool for Visible Channels

With close to 40 years of satellite observations, from which, cloud, land-use, and aerosol parameters can be measured, inter-consistent calibrations are needed to normalize retrievals across satellite records. Various visible-sensor inter-calibration techniques have been developed that utilize radiometrically stable Earth targets, e.g., deep convective clouds and desert/polar ice pseudo-invariant calibration sites. Other equally effective, direct techniques for intercalibration between satellite imagers are simultaneous nadir overpass comparisons and ray-matched radiance pairs. Combining independent calibration results from such varied techniques yields robust calibration coefficients, and is a form of self-validation. One potential source of significant error when cross-calibrating satellite sensors, however, are the often small but substantial spectral discrepancies between comparable bands, which must be accounted for. As such, visible calibration methods rely on a Spectral Band Adjustment Factor (SBAF) to account for the spectral-response function- induced radiance differences between analogous imagers. The SBAF is unique to each calibration method as it is a function of the Earth-reflected spectra. In recent years, NASA Langley pioneered the use of SCIAMACHY-, GOME-2-, and Hyperion-retrieved Earth spectra to compute SBAFs. By carefully selecting hyperspectral footprints that best represent the conditions inherent to an inter-calibration technique, the uncertainty in the SBAF is greatly reduced. NASA Langley initially provided the Global Space-based Inter-calibration System processing and research centers with online SBAF tools, with which users select conditions to best match their calibration criteria. This article highlights expanded SBAF tool capabilities for visible wavelengths, with emphasis on the use of the spectral range filtering for the purpose of separating scene conditions for the channel that the SBAF is needed based on the reflectance values of other bands. In other words, spectral filtering will enable better scene-type selection for bands where scene determination is difficult without information from other channels, which should prove valuable to users in the calibration community.

Scarino, Benjamin↗
NASA NTRSDate not supplied

Latest Progress and Results in LEO-GEO and GEO-GEO Stereo AMVs

Atmospheric motion vectors (AMVs), derived by tracking patterns, represent the winds in a layer characteristic of the pattern. AMV height (or pressure), important for applications in atmospheric research and operational meteorology, is usually assigned using observed IR brightness temperatures with a modeled atmosphere and can be inaccurate. Stereoscopic tracking provides a direct geometric height measurement of the pattern that an AMV represents. We extend our previous work with multi-angle imaging spectro–radiometer (MISR) and GOES to moderate resolution imaging spectroradiometer (MODIS) and the GOES-R series advanced baseline imager (ABI). MISR is a unique satellite instrument for stereoscopy with nine angular views along track, but its images have a narrow (380 km) swath and no thermal IR channels. MODIS provides a much wider (2330 km) swath and eight thermal IR channels that pair well with all but two ABI channels, offering a rich set of potential applications. Given the similarities between MODIS and VIIRS, our methods should also yield similar performance with VIIRS. Our methods, as enabled by advanced sensors like MODIS and ABI, require high-accuracy geographic registration in both systems but no synchronization of observations. AMVs are retrieved jointly with their heights from the disparities between triplets of ABI scenes and the paired MODIS granule. We validate our retrievals against MISR-GOES retrievals, operational GOES wind products, and by tracking clear-sky terrain. We demonstrate that the 3D-wind algorithm can produce high-quality AMV and height measurements for applications from the planetary boundary layer (PBL) to the upper troposphere, including cold-air outbreaks, wildfire smoke plumes, and hurricanes.

Atmospheric motion vectors↗
NASA NTRS1988

Mixing rates calculated from potential vorticity

Horizontal mixing coefficients K(yy) and K(yz) were computed using potential vorticity and gradients calculated from NMC data for geopotential heights and temperatures. It was found that the mid-latitude to polar mixing coefficients depend on the use of nongeostrophic winds, which yield K(yy) values which are mostly positive, whereas geostophic winds yield K(yy) values which were largely negative near the polar region. A comparison of the K(yy) values calculated from the potential vorticity fluxes and gradients with the K(yy) values calculated using the momentum balance between the flux of potential vorticity and the residual circulation has shown that the residual-circulation-balanced K(yy) values in the upper stratosphere were much larger than the values calculated by the present method. It is suggested that this difference is the result of breaking gravity waves in the upper stratosphere and lower mesosphere.

Newman, Paul A.↗
NASA NTRS2021

Exploring uncertainties in global crop yield projections in a large ensemble of crop models and CMIP5 and CMIP6 climate scenarios

Concerns over climate change are motivated in large part because of their impact on human society. Assessing the effect of that uncertainty on specific potential impacts is demanding, since it requires a systematic survey over both climate and impacts models. We provide a comprehensive evaluation of uncertainty in projected crop yields for maize, spring and winter wheat, rice, and soybean, using a suite of nine crop models and up to 45 CMIP5 and 34 CMIP6 climate projections for three different forcing scenarios. To make this task computationally tractable, we use a new set of statistical crop model emulators. We find that climate and crop models contribute about equally to overall uncertainty. While the ranges of yield uncertainties under CMIP5 and CMIP6 projections are similar, median impact in aggregate total caloric production is typically more negative for the CMIP6 projections (+1% to −19%) than for CMIP5 (+5% to −13%). In the first half of the 21st century and for individual crops is the spread across crop models typically wider than that across climate models, but we find distinct differences between crops: globally, wheat and maize uncertainties are dominated by the crop models, but soybean and rice are more sensitive to the climate projections. Climate models with very similar global mean warming can lead to very different aggregate impacts so that climate model uncertainties remain a significant contributor to agricultural impacts uncertainty. These results show the utility of large-ensemble methods that allow comprehensively evaluating factors affecting crop yields or other impacts under climate change. The crop model ensemble used here is unbalanced and pulls the assumption that all projections are equally plausible into question. Better methods for consistent model testing, also at the level of individual processes, will have to be developed and applied by the crop modeling community.

crop yield projections↗
NASA NTRS1985

Numerical simulation of positive-potential conductors in the presence of a plasma and a secondary-emitting dielectric

A 2 1/2-dimensional, cylindrically symmetric particle in cell program is used to simulate the interaction of a plasma with a positively biased disk covered by a dielectric material (Kapton). Several runs using different combinations of bias voltages and secondary electron yields are discussed. Special attention is paid to the role of the secondaries as the dielectric surface changes from a negative potential to become increasingly positive. This is termed the 'snapover' process. The contribution due to secondaries is examined by plotting the distribution (number versus position) of the particles emitted by the impacting on the dielectric. These plots show that secondaries are drawn back into the dielectric as well as the conductor in the case of snapover. Mechanisms and experimental implications for these particular distributions are discussed.

Kessel, R. L.↗
NASA NTRS2013

Automatic Data Filter Customization Using a Genetic Algorithm

This work predicts whether a retrieval algorithm will usefully determine CO2 concentration from an input spectrum of GOSAT (Greenhouse Gases Observing Satellite). This was done to eliminate needless runtime on atmospheric soundings that would never yield useful results. A space of 50 dimensions was examined for predictive power on the final CO2 results. Retrieval algorithms are frequently expensive to run, and wasted effort defeats requirements and expends needless resources. This algorithm could be used to help predict and filter unneeded runs in any computationally expensive regime. Traditional methods such as the Fischer discriminant analysis and decision trees can attempt to predict whether a sounding will be properly processed. However, this work sought to detect a subsection of the dimensional space that can be simply filtered out to eliminate unwanted runs. LDAs (linear discriminant analyses) and other systems examine the entire data and judge a "best fit," giving equal weight to complex and problematic regions as well as simple, clear-cut regions. In this implementation, a genetic space of "left" and "right" thresholds outside of which all data are rejected was defined. These left/right pairs are created for each of the 50 input dimensions. A genetic algorithm then runs through countless potential filter settings using a JPL computer cluster, optimizing the tossed-out data s yield (proper vs. improper run removal) and number of points tossed. This solution is robust to an arbitrary decision boundary within the data and avoids the global optimization problem of whole-dataset fitting using LDA or decision trees. It filters out runs that would not have produced useful CO2 values to save needless computation. This would be an algorithmic preprocessing improvement to any computationally expensive system.

Mandrake, Lukas↗
NASA NTRS1972

High-Q toroidal cavities for high frequency klystrons.

A toroidal cavity developed for a 4-KW 12 GHz satellite-borne television transmitter klystron is described. The cavity has an internal Q 40% higher than that of a conventional cylindrical doubly reentrant cavity, thus yielding higher circuit efficiency and conserving energy which cannot be recovered in multistage depressed potential beam collectors. As a result of optimization studies with a digital computer program for obtaining cavity field distributions by a relaxation method and for computing the intrinsic cavity parameters, a particular cavity configuration with conical reentrant tunnel tips and toroidal walls is shown to provide good thermal characteristics and mechanical rigidity as well as low internal losses.

Branch, G. M.↗
NASA NTRS1974

Formation of O3/+/ by the reaction of metastable O2/+/ ions with O2

The high resolution of the photoionization mass spectrophotometer was utilized to resolve some doubts about the participating species in the reaction of metastable oxygen molecular ions with oxygen molecules to yield ozone ions and oxygen radicals. It is found from inspection of the appearance potential of the ozone ion that an a4 Pi-excited state is responsible for the formation of ozone near the appearance potential of these lines.

Ajello, J. M.↗
NASA NTRS1977

The multiple applications of electrons in space

An electron source such as a simple cathode is a cheap and light device which can serve several technological and scientific purposes in space: (1) electrostatic charging of a spacecraft can be limited by releasing electrons accumulated on the conductive elements of their surface; (2) the erosion of conductive coatings and the ability of conductive paints to withstand the space environment can be evaluated by monitoring the flow of charged particles impinging on their surface; (3) measuring the current collected by the spacecraft surface as a function of its potential with respect to an emitter is a very sensitive diagnostic technique which can yield a number of plasma parameters, such as density and temperature; (4) it is possible to convert the thermal motion of space plasmas into electrical energy by collecting energetic electrons and returning them to the medium as cold particles; (5) a wave in a plasma is characterized by a conduction current density which gives rise to fluctuations of the current flowing to the surface.

Grard, R. J. L.↗
NASA NTRS1982

Application of future remote sensing systems to irrigation

Area estimates of irrigated crops and knowledge of crop type are required for modeling water consumption to assist farmers, rangers, and agricultural consultants in scheduling irrigation for distributed management of crop yields. Information on canopy physiology and soil moisture status on a spatial basis is potentially available from remote sensors, so the questions to be addressed relate to: (1) timing (data frequency, instantaneous and integrated measurement); and scheduling (widely distributed spatial demands); (2) spatial resolution; (3) radiometric and geometric accuracy and geoencoding; and (4) information/data distribution. This latter should be overnight, with no central storage, onsite capture, and low cost.

Miller, L. D.↗
NASA NTRS1983

An ab initio study of core-valence correlation

Especially in the cases of the first two columns of the periodic table, the inclusion of core-valence correlation in ab initio CI calculations yields a contraction of the atomic valence shell and improves both calculated atomic ionization potentials and atomic energy separations. For the alkali dimers Na2, K2, and Rb2, the presently calculated bond lengths are in excellent agreement with experiments when core-valence is included. In addition, the valence dissociation energies are accurate.

Partridge, H.↗
NASA NTRS1987

Electrical potential measurements in the lower atmosphere

Lower-atmospheric potential measurements obtained in 1983 through 1985 using the Hy-wire technique are summarized in this paper. Observed values of the potential were in the range of 50-100 kV in Fairbanks, AK, compared with 100-200 kV at Wallops Island, VA. When one-hour averages are formed from the entire data set the result is a unitary variation very reminiscent of both the Carnegie curve and more recent stratospheric electric field data. A comparison with an aircraft potential measurement in the same vicinity during April 1983 demonstrates that the two techniques yield roughly similar results, except that the Hy-wire measurements were 20-30 percent lower in absolute value.

Woosley, J. D.↗
NASA NTRS1990

Multipole radiation in charged-particle scattering

This paper formulates the general problem of photon emission in particle scattering using a classical and quantum mechanical approach. The connection between the classical short collision time (SCT) and Born results is examined for various special classifications of problems. In the dipole case the two formulations yield results that can be expressed in the same form and for arbitrary scattering potential. For quadrupole emission the SCT and Born results are the same only for a short-range potential, however. The quadrupole problem is more sensitive to details in the process because the calculation requires an expansion of the total amplitude for the process to lowest order in the photon wave number or momentum. The special case of photon emission associated with spin-flip transitions during scattering is considered for spin-1/2 particles. Like classical magnetic dipole radiation, there is no infrared divergence feature for this type of emission.

Gould, Robert J.↗
NASA NTRS1994

On the effects of filtering on convective-core statistics

Analysis of convective events north of Australia during the equatorial Monsoon Experiment (EMEX) reinforces accumulating evidence that convective cores over the tropical ocean are weak, with small diameters and vertical velocities. Superposition of smaller-scale turbulence on the convective core signal could yield artificially small cores, and thus produce sampling bias by aircraft. To investigate this potential source of bias, a side-by-side analysis of filtered and unfiltered vertical velocity data was performed while investigating the EMEX convective cores. Data were collected by the NOAA P3 and NCAR Electra using filtered (Graham filter) and non-filtered cores. The effects of filtering vertical velocity data to identify updraft and downdraft cores were noticeable but smaller than expected. Updraft cores had a vertical velocity greater than 1 m/sec for at least 500 m, and downdraft cores were defined analogously so that the filter eliminated events with less than a 500 m apparent diameter. Median and 10 percent core diameters were increased by 20-25 percent at most, with larger increases at higher levels (fewer small events). The maximum vertical velocity was changed only by changing the individual events in the distribution, but changes were detectable. At the lower levels, where many small, weak cores are introduced by filtering, average vertical velocity for the updraft cores was lowered by up to around 10 percent. Mass flux was changed the least, since diameter and mean vertical velocity respond to filtering in opposite ways. The filtering procedure increased total mass flux slightly due to inclusion of more upward moving air into the sample.

Lemone, Margaret A.↗