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Results for “Model transferability”

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 163 records · Page 9
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Heat transfer model for predicting squib ignition times

A squib ignition model based on transient heat condition from the hot bridgewire to the pyrotechnic is described. No Arrhenius-type chemical reaction is included. Instead, a thermal contact resistance is postulated to exist between the hot bridgewire and the pyrotechnic. Ignition is assumed to occur when a 2.5 micron layer of pyrotechnic next to the bridgewire reaches a characteristic ignition temperature for that pyrotechnic. This model was applied to the JPL squib, which uses a 50 micron (0.002-in.) diameter Tophet A bridgewire to ignite a boron, potassium perchlorate mix. A computer program was utilized that solves the transient heat condition problem with the boundary conditions stipulated by the model. The thermal contact conductance at the interface was determined by trial and error so that the experimentally determined ignition time for one firing condition would be properly predicted by the model. The agreement was quite good for tests run between -129 C and +93.3 C at current levels of 3.5 and 5 A. Axial heat conduction along the bridgewire is shown to be negligible.

Sernas, V.↗
NASA NTRS1979

Application of a coupled aerosol formation: Radiative transfer model to climatic studies of aerosols

A sophisticated one dimensional physical-chemical model of the formation and evolution of stratospheric aerosols was used to predict the size and number concentration of the stratospheric aerosols as functions of time and altitude following: a large volcanic eruption; increased addition of carbonyl sulfide (OCS) or sulfur dioxide (SO2) to the troposphere; increased supersonic aircraft (SST) flights in the stratosphere; and, large numbers of space shuttle (SS) flights through the stratosphere. A radiative-convective one dimensional climate sensitivity study, using the results of the aerosol formation model, was performed to assess the ground level climatic significance of these perturbations to the stratospheric aerosol layer. Volcanic eruptions and large OCS or SO2 increases could cause significant climatic changes. Currently projected SS launches and moderate fleets of SST's are unlikely to upset the stratospheric aerosol layer enough to significantly impact climate.

Toon, O. B.↗
NASA NTRS1979

A comparative study of microwave radiometer observations over snowfields with radiative transfer model calculations

Truck mounted microwave instrumentation was used to study the microwave emission characteristics of the Colorado Rocky Mountain snowpack in the vicinity of Fraser, Colorado during the winter of 1978. The spectral signatures of 5.0, 10.7, 18, and 37 GHz radiometers with dual polarization were used to measure the snowpack density and temperature profiles, rain profile, and free water content. These data were compared with calculated results based on microscopic scattering models for dry, surface melting, and very wet snowpacks.

Chang, A. T. C.↗
NASA NTRS1980

A comparison of radiative transfer models for predicting the microwave emission from soils

Two general types of numerical models for predicting microwave emission from soils are compared-coherent and noncoherent. In the former, radiation in the soil is treated coherently, and the boundary conditions on the electric fields across the layer boundaries are used to calculate the radiation intensity. In the latter, the radiation is assumed to be noncoherent, and the intensities of the radiation are considered directly. The results of the two approaches may be different because of the effects of interference, which can cause the transmitted intensity at the surface (i.e., emissivity) to be sometimes higher and sometimes lower for the coherent case than for the noncoherent case, depending on the relative phases of reflected fields from the lower layers. This coupling between soil layers in the coherent models leads to greater soil moisture sampling depths observed with this type of model, and is the major difference that is found between the two types of models. In noncoherent models, the emissivity is determined by the dielectric constraint at the air/soil interface. The subsequent differences in the results are functions of both the frequency of the radiation being considered and the steepness of the moisture gradient near the surface. The calculations were performed at frequencies of 1.4 and 19.4 GHz and for two sets of soil profiles. Little difference was observed between the models at 19.4 GHz; and only at the lower frequency were differences apparent because of the greater soil moisture sampling depth at this frequency.

Schmugge, T. J.↗
NASA NTRS1981

A comparison of radiative transfer models for predicting the microwave emission from soils

Noncoherent and coherent numerical models for predicting emission from soils are compared. Coherent models use the boundary conditions on the electric fields across the layer boundaries to calculate the radiation intensity, and noncoherent models consider radiation intensities directly. Interference may cause different results in the two approaches when coupling between soil layers in coherent models causes greater soil moisture sampling depths. Calculations performed at frequencies of 1.4 and 19.4 GHz show little difference between the models at 19.4 GHz, although differences are apparent at the lower frequency. A definition for an effective emissivity is also given for when a nonuniform temperature profile is present, and measurements made from a tower show good agreement with calculations from the coherent model.

Schmugge, T. J.↗
NASA NTRS1982

Simple radiative transfer model for relationships between canopy biomass and reflectance

A modified Kubelka-Munk model has been utilized to derive useful equations for the analysis of apparent canopy reflectance. Based on the solution to the model simple working equations were formulated by employing reflectance characteristic parameters. The relationships derived show the asymptotic nature of reflectance data that is typically observed in remote sensing studies of plant biomass. They also establish the range of expected apparent canopy reflectance values for specific plant canopy types. The usefulness of the simplified equations was demonstrated by the exceptionally close fit of the theoretical curves to two separately acquired data sets for alfalfa and shortgrass prairie canopies.

Park, J. K.↗
NASA NTRS1983

The O(+) 834-A dayglow - Satellite observations and interpretation with a radiation transfer model

The observations were made with the EUV spectrometer on the Air Force satellite STP-78-1. The dayglow intensity was observed at an altitude of 600 km to vary with magnetic latitude from 30 R to 300 R in the near zenith direction (theta - 40 deg) and from 400 R to 500 R in the near nadir direction (theta = 140 deg). The correspondingly large near zenith to near nadir intensity ratio of 0.3-0.65 over much of the dayside is seen as suggesting that the O(+) ions in the topside ionosphere constitute an optically thick medium for resonance scattering of 834-A airglow emission even at this high altitude. The STP 78-1 airglow data are normalized by means of simultaneous measurements of the O(+) density from the Explorer AE-E spacecraft at 460-km altitude near the equator. It is noted that for the ionization excitation of atomic oxygen leading to the production of O(+) atoms in 4P state, a g value of 1.1 x 10 to the -8th/s at zero optical depth is required. The latitudinal distribution of O(+) density derived from the 834-A airglow data reveals a double peak surrounding an equatorial trough (characteristic of the equatorial anomaly) at altitudes below 1000 km and a single peak at the magnetic equator above 1000 km.

Kumar, S.↗
NASA NTRS1988

Identification and recovery of discontinuous synoptic features in satellite-retrieved brightness temperatures using a radiative transfer model

An attempt is made to recover and identify discontinuous synoptic features from satellite-retrieved brightness temperatures, with attention to near-discontinuities in temperature and moisture that are typically found in fronts and inversions. Efforts are made to ascertain whether the vectors of satellite channel brightness temperatures can be classified according to synoptic source, and whether those sources are amenable to quantification.

White, G. A., III↗
NASA NTRS1989

Radiative transfer modeling of Saturn's outer B ring

The present investigation of Voyager images of the Saturn outer B ring's light-scattering behavior gives attention to the four radial regions formed by brighter and darker areas within and outside the 'spokes'. The B-ring particles are found to have a strongly backscattering phase function and a large-particle scattering albedo of 0.54 in the dark regions and 0.58 in the bright ones; these albedos are interpretable as due to multiple scattering among very pure ice grains covering the ring particle surfaces. It is shown that dark micrometeoroid impacts into the B ring would have darkened the particles to their current spherical albedo in as little as 100 to 200 million years.

Doyle, Laurance R.↗
NASA NTRS1990

Radiative transfer modeling constraints on the size of the spoke particles in Saturn's rings

The spoke particle sizes of Saturn's outer B ring constitute an important parameter for spoke formation and evolution theories, prompting the present effort to find constraining observations. The spokes' apparent optical depths are found to increase with wavelength. A relationship is derived for the contribution of the spokes' small particle optical depth, taking multiple-scatter and flatter spoke-region large-particle phase functions into account; the spokes' optical depths still generally appear to increase or remain constant with increasing wavelength.

Doyle, Laurance R.↗
NASA NTRS1992

Radiative transfer models

The purpose of this work was to assist with the development of analytical techniques for the interpretation of infrared observations. We have done the following: (1) helped to develop models for continuum absorption calculations for water vapor in the far infrared spectral region; (2) worked on models for pressure-induced absorption for O2 and N2 and their comparison with available observations; and (3) developed preliminary studies of non-local thermal equilibrium effects in the upper stratosphere and mesosphere for infrared gases. These new techniques were employed for analysis of balloon-borne far infrared data by a group at the Harvard-Smithsonian Center for Astrophysics. The empirical continuum absorption model for water vapor in the far infrared spectral region and the pressure-induced N2 absorption model were found to give satisfactory results in the retrieval of the mixing ratios of a number of stratospheric trace constituents from balloon-borne far infrared observations.

Horwitz, James L.↗