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Search indexed NASA NTRS and DOE OSTI research on propulsion, heat transfer, battery materials and energy systems. Follow report and document links to the original sources.

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At least 451 records · Page 25
All sourcesNASA NTRSDOE OSTI
NASA NTRS1989

Scattering of light by crystals - A modified Kirchhoff approximation

A modified Kirchhoff approximation (MKA) is developed for the scattering of light by randomly oriented crystals. The reflected and transmitted near fields are calculated from ray tracing; the corresponding far fields are then obtained via the vector Kirchhoff integral. On the shadow side of the particle, an additional near field exactly cancels the incident field and causes the forward diffraction. MKA contains a particle size dependence, which is not included in ray optics treatments, and satisfactory results can be obtained for size parameters larger than ten. The scattering phase functions and degrees of linear polarization are calculated for some hexagonal and cubic water ice crystals using MKA. The Kirchhoff approximation for particles other than crystals is discussed, and attention is paid to the backscattering enhancement due to the cyclic passage of internally or multiply externally reflected electromagnetic waves.

Muinonen, Karri↗
NASA NTRS1974

Application of holography to flow visualization within rotating compressor blade row

Two holographic interblade row flow visualization systems were designed to determine the three-dimensional shock patterns and velocity distributions within the rotating blade row of a transonic fan rotor, utilizing the techniques of pulsed laser transmission holography. Both single- and double-exposure bright field holograms and dark field scattered-light holograms were successfully recorded. Two plastic windows were installed in the rotor tip casing and outer casing forward of the rotor to view the rotor blade passage. The viewing angle allowed detailed investigation of the leading edge shocks and shocks in the midspan damper area; limited details of the trailing edge shocks also were visible. A technique was devised for interpreting the reconstructed holograms by constructing three dimensional models that allowed identification of the major shock systems. The models compared favorably with theoretical predictions and results of the overall and blade element data. Most of the holograms were made using the rapid double-pulse technique.

Wuerker, R. F.↗
NASA NTRS1991

Forward looking wind shear detection program

Delco Systems' Forward Looking Windshear Detection program is reviewed in viewgraph form. Topics covered include extinction of radiance by absorbing and scattering media, atmospheric absorption in the far infrared region, an inframetrics imaging radiometer, a basic radiance signal equation, and tower and flight test plans.

Gallagher, Brian↗
NASA NTRS1986

Ultrasonic characterization of microstructure in powder metal alloy

The ultrasonic wave propagation characteristics were measured for IN-100, a powder metallurgy alloy used for aircraft engine components. This material was as a model system for testing the feasibility of characterizing the microstructure of a variety of inhomogeneous media including powder metals, ceramics, castings and components. The data were obtained for a frequency range from about 2 to 20 MHz and were statistically averaged over numerous volume elements of the samples. Micrographical examination provided size and number distributions for grain and pore structure. The results showed that the predominant source for the ultrasonic attenuation and backscatter was a dense (approx. 100/cubic mm) distribution of small micropores (approx. 10 micron radius). Two samples with different micropore densities were studied in detail to test the feasibility of calculating from observed microstructural parameters the frequency dependence of the microstructural backscatter in the regime for which the wavelength is much larger than the size of the individual scattering centers. Excellent agreement was found between predicted and observed values so as to demonstrate the feasibility of solving the forward problem. The results suggest a way towards the nondestructive detection and characterization of anomalous distributions of micropores when conventional ultrasonic imaging is difficult. The findings are potentially significant toward the application of the early detection of porosity during the materials fabrication process and after manufacturing of potential sites for stress induced void coalescence leading to crack initiation and subsequent failure.

Tittmann, B. R.↗
NASA NTRS1988

Analysis of the light scattering interferometry for spheres larger than the light wavelength

A theoretical model, based on the geometrical optics approach, has been developed to simulate various aspects of the phase Doppler particle analyzer (PDPA). The model has taken into consideration the non-uniform (Gaussian) illumination of the particles as they pass through the probe volume. Instrument response curves have been generated for various scattering angles by performing spatial and temporal integration of the scattered intensity distribution over the receiver surface. Experimental and theoretical investigations have established the applicability of this instrument to both forward and backscatter angles.

Bachalo, W. D.↗
NASA NTRSDate not supplied

A Comprehensive Forward Model for Spaceborne Radar Instruments

We present the development and validation of a comprehensive forward model designed to enhance remote sensing capabilities of spaceborne radar instruments. To overcome limitations in existing models, we integrated a Discrete Dipole Approximation (DDA) cloud scattering database into our Radiative Transfer Model (RTM), focusing on microwave frequencies. By simulating the optical properties of non-spherical frozen hydrometeors, the DDA technique effectively reduced discrepancies between simulated and observed values, surpassing traditional Mie tables. The evaluation of DDA lookup tables involved comparisons with a collocated dataset comprising short-term forecasts and satellite microwave data, providing evidence of their superiority. Additionally, we address the challenges of assimilating active radar measurements, which offer vertically resolved insights into clouds and precipitation. We explored the assimilation of spaceborne radar measurements in Numerical Weather Prediction (NWP) models by integrating a forward radar model, along with its adjoint and tangent linear, into the data assimilation system. Evaluation using CloudSat measurements demonstrated promising agreement between simulations and observations, particularly when the input hydrometeor profiles aligned with the measured reflectivity profiles, showcasing the potential of the developed forward radar model. Moreover, we discuss other challenges in radar measurement assimilation within NWP models, including potential observation errors and biases.

Isaac Moradi↗
NASA NTRS1995

Sizing of colloidal particle and protein molecules in a hanging fluid drop

We report non-invasive particle size measurements of polystyrene latex colloidal particles and bovine serum albumin (BSA) protein molecules suspended in tiny hanging fluid drops of 30 micro-Liter volume using a newly designed fiber optic probe. The probe is based upon the principles of the technique of dynamic light scattering (DLS). The motivation for this work comes from growing protein crystals in outer space. Protein crystals have been grown previously in hanging drops in microgravity experiments on-board the space shuttle orbiter. However, obtaining quantitative information on nucleation and growth of the protein crystals in real time has always been a desired goal, but hitherto not achieved. Several protein researchers have shown interest in using DLS to monitor crystal growth process in a droplet, but elaborate instrumentation and optical alignment problems have made in-situ applications difficult. We demonstrate that such an experiment is now possible. Our system offers fast (5 seconds) determination of particle size, utilize safe levels of very low laser power (less than or equal to 0.2 mW), a small scattering volume (approximately 2 x 10(exp -5) cu mm) and high spatial coherence (Beta) values. This is a major step forward when compared to currently available DLS systems.

Ansari, Rafat R.↗
NASA NTRS1992

Spectropolarimetry of V854 Centauri at minimum light - Clues to the geometry of the dust and emission-line region

The RCB star V854 Cen is observed during a very deep decline (Delta m = 8.2) at the AAT. The continuum polarization is very high, ranging from 14 percent at 4200 A to about 4 percent at 6500 A. The polarization decreases across the emission lines, but the polarized flux remains constant. This indicates that the emission lines are unpolarized, so the emission probably arises in a region unobscured by dust. In such a deep minimum, the visible continuum flux is probably almost entirely scattered light, which explains its high polarization. The scattered flux may arise in the same clouds contributing to the observed IR flux if the albedo is low and the grains forward throwing. The emission-line spectrum itself is very unusual for an RCB star in decline, with strong C2 bands and Balmer lines.

Whitney, Barbara A.↗
NASA NTRS2001

Satellite Remote Sensing of Tropical Precipitation and Ice Clouds for GCM Verification

This project, supported by the NASA New Investigator Program, has primarily been funding a graduate student, Darren McKague. Since August 1999 Darren has been working part time at Raytheon, while continuing his PhD research. Darren is planning to finish his thesis work in May 2001, thus some of the work described here is ongoing. The proposed research was to use GOES visible and infrared imager data and SSM/I microwave data to obtain joint distributions of cirrus cloud ice mass and precipitation for a study region in the Eastern Tropical Pacific. These joint distributions of cirrus cloud and rainfall were to be compared to those from the CSU general circulation model to evaluate the cloud microphysical amd cumulus parameterizations in the GCM. Existing algorithms were to be used for the retrieval of cloud ice water path from GOES (Minnis) and rainfall from SSM/I (Wilheit). A theoretical study using radiative transfer models and realistic variations in cloud and precipitation profiles was to be used to estimate the retrieval errors. Due to the unavailability of the GOES satellite cloud retrieval algorithm from Dr. Minnis (a co-PI), there was a change in the approach and emphasis of the project. The new approach was to develop a completely new type of remote sensing algorithm - one to directly retrieve joint probability density functions (pdf's) of cloud properties from multi-dimensional histograms of satellite radiances. The usual approach is to retrieve individual pixels of variables (i.e. cloud optical depth), and then aggregate the information. Only statistical information is actually needed, however, and so a more direct method is desirable. We developed forward radiative transfer models for the SSM/I and GOES channels, originally for testing the retrieval algorithms. The visible and near infrared ice scattering information is obtained from geometric ray tracing of fractal ice crystals (Andreas Macke), while the mid-infrared and microwave scattering is computed with Mie scattering. The radiative transfer is performed with the Spherical Harmonic Discrete Ordinate Method (developed by the PI), and infrared molecular absorption is included with the correlated k-distribution method. The SHDOM radiances have been validated by comparison to version 2 of DISORT (the community "standard" discrete-ordinates radiative transfer model), however we use SHDOM since it is computationally more efficient.

Evans, K. Franklin↗
NASA NTRS2009

Method for Measuring the Volume-Scattering Function of Water

The volume scattering function (VSF) of seawater affects visibility, remote sensing properties, in-water light propagation, lidar performance, and the like. Currently, it s possible to measure only small forward angles of VSF, or to use cumbersome, large, and non-autonomous systems. This innovation is a method of measuring the full range of VSF using a portable instrument. A single rapid-sensing photosensor is used to scan a green laser beam, which delivers the desired measurement. By using a single sensor, inter-calibration is avoided. A compact design is achieved by using drift-free detector electronics, fiber optics, and a new type of photomultiplier. This provides a high angular resolution of 1 or better, as well as the ability to focus in on a VSF region of particular interest. Currently, the total scattering of light is measured as a difference from the other two parts of the light budget equation. This innovation will allow the direct calculation of the total scattering of light by taking an integral of the VSF over all angles. This directly provides one of the three components of the light budget equation, allowing greater versatility in its calculation.

Agrawal, Yogesh C.↗
NASA NTRS1979

Radiation of an acoustic source near the trailing edge of a wing in forward motion

The acoustic sources simulating engine or jet noise are located near the trailing edge. During landing or take-off operations the flap angle is not small. Solutions for the scattering of the acoustic sources, monopoles, dipoles or quadrupoles, by the wing with the flap at finite angle are constructed for the case that the acoustic wave length is much larger than the length of the flap but may be of the same order as the chord. For each given geometry of the flap and the position of the singularities, critical orientations of the dipoles and the quadrupoles are defined along which the noise becomes 'suppressed', i.e., the far field pressure becomes one order smaller.

Ting, L.↗
NASA NTRS2021

3D Cloud Tomography and Droplet Size Retrieval from Multi-Angle Polarimetric Imaging of Scattered Sunlight from Above

Tomography aims to recover a three-dimensional (3D) density map of a medium or an object. In medical imaging,it is extensively used for diagnostics via X-ray computed tomography (CT). We define and derive a tomographyof cloud droplet distributions via passive remote sensing. We use multi-view polarimetric images to fit a 3Dpolarized radiative transfer (RT) forward model. Our motivation is 3D volumetric probing of vertically-developedconvectively-driven clouds that are ill-served by current methods in operational passive remote sensing. Currenttechniques are indeed based on strictly 1D RT modeling and applied to a single cloudy pixel, where cloud geometrydefaults to that of a plane-parallel slab. Incident unpolarized sunlight, once scattered by cloud droplets, changesits polarization state according to droplet size. Therefore, polarimetric measurements in the rainbow and gloryangular regions can be used to infer the droplet size distribution. This work defines and derives a framework for afull 3D tomography of cloud droplets for both their mass concentration in space and their distribution across arange of sizes. This gridded 3D retrieval of key microphysical properties is made tractable by our novel approachthat involves a restructuring and partial linearization of an open-source polarized 3D RT code to accommodate aspecial two-step iterative optimization technique. Physically-realistic synthetic clouds are used to demonstrate themethodology with rigorous uncertainty quantification, while a real-world cloud imaged by AirMSPI is processedto illustrate the new remote sensing capability

Schechner, Yoav Y.↗
NASA NTRS2019

Modeling Atmosphere-Ocean Radiative Transfer: A PACE Mission Perspective

The research frontiers of radiative transfer (RT) in coupled atmosphere-ocean systems are explored to enable new science and specifically to support the upcoming Plankton, Aerosol, Cloud ocean Ecosystem (PACE) satellite mission. Given (i) the multitude of atmospheric and oceanic constituents at any given moment that each exhibits a large variety of physical and chemical properties and (ii) the diversity of light-matter interactions (scattering, absorption, and emission), tackling all outstanding RT aspects related to interpreting and/or simulating light reflected by atmosphere-ocean systems becomes impossible. Instead, we focus on both theoretical and experimental studies of RT topics important to the science threshold and goal questions of the PACE mission and the measurement capabilities of its instruments. We differentiate between (a) forward (FWD) RT studies that focus mainly on sensitivity to influencing variables and/or simulating data sets, and (b) inverse (INV) RT studies that also involve the retrieval of atmosphere and ocean parameters. Our topics cover (1) the ocean (i.e., water body): absorption and elastic/inelastic scattering by pure water (FWD RT) and models for scattering and absorption by particulates (FWD RT and INV RT); (2) the air-water interface: variations in ocean surface refractive index (INV RT) and in whitecap reflectance (INV RT); (3) the atmosphere: polarimetric and/or hyperspectral remote sensing of aerosols (INV RT) and of gases (FWD RT); and (4) atmosphere-ocean systems: benchmark comparisons, impact of the Earth's sphericity and adjacency effects on space-borne observations, and scattering in the ultraviolet regime (FWD RT). We provide for each topic a summary of past relevant (heritage) work, followed by a discussion (for unresolved questions) and RT updates.

Chowdhary, Jacek↗
NASA NTRS1993

Airborne synthetic aperture radar observations and simulations for waves in ice

The Canada Centre for Remote Sensing CV-580 aircraft collected C-band SAR data over the marginal ice zone off the east coast of Newfoundland during the Labrador Ice Margin Experiment (LIMEX) in March 1989. One component of the LIMEX '89 program was the study of ocean waves penetrating the marginal ice zone. We consider nearly coincidental observations of waves in ice by airborne SAR and wave-induced ice motion measurements. We explain the wave patterns observed in the SAR imagery, and the corresponding SAR image spectra, in terms of SAR wave imaging models. These include the well-known tilt cross-section modulation, linear, quasi-linear, and nonlinear velocity bunching forward mapping models (FMMs), and the assertion that the concept of coherence time limitation applies differently to the cases of waves in ice and open water. We modify the concept of the scene coherence time to include two parts: first, a decorrelation time deduced from the inherent azimuth cutoff in the nonlinear velocity bunching FMM; and second, the intrinsic scene coherence time which is a measure of the time scale over which an open water Bragg scattering patch retains its phase structure. Either of these coherence time scales could dominate the SAR image formation process, depending upon the environmental conditions (the wave spectrum and the wind speed, for example). Observed SAR image spectra and forward mapped ice motion package spectra are favorably compared.

Vachon, Paris W.↗
NASA NTRS1985

QCD-motivated description of very high energy particle interactions

Cross sections for the production of secondaries with large transverse momentum can become comparable to the total cross section in the TeV energy range. It is argued that the onset of this effect is observed at sub TeV energies via an increase of the rapidity distribution near y = 0, an increase of p sub T with energy and, most directly, via a correlation between p sub T and multiplicity. If indeed scaling violations are associated with the hard scattering of partons, then scaling violations are largely confined to the central region and have little effect on cosmic ray data which are sensitive to the forward fragmentation region.

Gaisser, T. K.↗
NASA NTRS2012

Impacts of Spatial Fidelity Violations in the Forward Signal Model on DOAS-based Greenhouse Gas Retrievals: a Preliminary Analysis for OCO-2 (and Other Missions)

Success in three aspects of OCO‐2 mission is threatened by unaccounted spa,al variability effects, all involving atmospheric scattering: 1. Low/moderately opaque clouds can escape the prescreening by mimicking a brighter surface. 2. Prescreening does not account for long‐range radia,ve impact (adjacency effect) of nearby clouds. Need for extended cloud masking? 3. Oblique looks in target mode are highly exposed to surface adjacency and aerosol variability effects.We'll be covering all three bases!

aerosols↗
NASA NTRS2002

Investigation of Venus Surface Properties

Strong localized radar echoes have been observed at decimeter wavelengths from the highlands of Venus since the earliest radar maps were obtained over 30 years ago. These echoes are some five to ten times stronger than those from the presumably basaltic rocks seen at lower altitudes elsewhere on Venus. Observations of thermal emission from the visible disk of Venus at wavelengths corresponding to those used in the radar mapping confirm that the regions of high reflectivity also exhibit low emissivity, as expected from considerations of detailed thermodynamic balance. Two possibilities have been put forward to explain this unexpected aspect of the Venus highlands: 1) surface materials of high effective dielectric constant, probably associated with finite electrical conductivity, and 2) volume scattering associated with multiple scattering from a layer of very-low-loss material containing voids and extending down a few hundred wavelengths beneath the surface. Analogs to these two mechanisms are found elsewhere in the solar system, and each is capable of explaining the basic observations. as of the early 1990's. In 1993, however, it became possible to carry out a bistatic observation of the anomalous highland regions using the Magellan spacecraft, then in orbit about Venus. In this experiment the on-board telemetry transmitter was aimed at the planet's surface with its linear S-band polarization vector oriented at 45 deg to the spacecraft-Venus-Earth scattering plane. The pointing of the transmitting antenna was adjusted so that the spacecraft-to-illuminated-surface incidence angle equalled the Earth-to-Venus-surface incidence angle. In this way, the experiment emphasized the specular scattering component. A full Stokes-Vector analysis of the reflected signal as received on Earth was carried out as the illuminated region scanned across the highland regions of Venus. From the observed position angle of the echo, it was possible to calculate the Fresnel reflectivity of a number of regions on Venus, including the high-altitude Maxwell Montes, and to show unequivocally that the complex dielectric constant of that anomalous area was 100 +/- 50i, as compared to 4.0 (real) for the typical lowland area. Thus this experiment was able to rule out definitively an hypothesis of volume scattering as the explanation for the anomalous scattering in the Venus highlands.

Ford, Peter G.↗
NASA NTRS2016

Polarized View of Supercooled Liquid Water Clouds

Supercooled liquid water (SLW) clouds, where liquid droplets exist at temperatures below 0 C present a well known aviation hazard through aircraft icing, in which SLW accretes on the airframe. SLW clouds are common over the Southern Ocean, and climate-induced changes in their occurrence is thought to constitute a strong cloud feedback on global climate. The two recent NASA field campaigns POlarimeter Definition EXperiment (PODEX, based in Palmdale, California, January-February 2013) and Studies of Emissions and Atmospheric Composition, Clouds and Climate Coupling by Regional Surveys (SEAC4RS, based in Houston, Texas in August- September 2013) provided a unique opportunity to observe SLW clouds from the high-altitude airborne platform of NASA's ER-2 aircraft. We present an analysis of measurements made by the Research Scanning Polarimeter (RSP) during these experiments accompanied by correlative retrievals from other sensors. The RSP measures both polarized and total reflectance in 9 spectral channels with wavelengths ranging from 410 to 2250 nm. It is a scanning sensor taking samples at 0.8deg intervals within 60deg from nadir in both forward and backward directions. This unique angular resolution allows for characterization of liquid water droplet size using the rainbow structure observed in the polarized reflectances in the scattering angle range between 135deg and 165deg. Simple parametric fitting algorithms applied to the polarized reflectance provide retrievals of the droplet effective radius and variance assuming a prescribed size distribution shape (gamma distribution). In addition to this, we use a non-parametric method, Rainbow Fourier Transform (RFT),which allows retrieval of the droplet size distribution without assuming a size distribution shape. We present an overview of the RSP campaign datasets available from the NASA GISS website, as well as two detailed examples of the retrievals. In these case studies we focus on cloud fields with spatial features varying between glaciated and liquid phases at altitudes as high as 10 km, which correspond to temperatures close to the homogeneous freezing temperature of pure water drops (about -35 C or colder). The multimodal droplet size distributions retrieved from RSP data in these cases are consistent with the multi-layer cloud structure observed by correlative Cloud Physics Lidar (CPL) measurements.

Clouds↗