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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 325 records · Page 18
All sourcesNASA NTRSDOE OSTI
NASA NTRS1984

Effects of atmosphere and view and illumination geometry on visible and near infrared radiance data from the advanced very high resolution radiometer (AVHR)

The use of Dave's models to evaluate satellite off-nadir remote sensing of green vegetation cover types by simulating the visible and near-infrared advanced very high resolution radiometer (AVHRR) NOAA-6 and NOAA-7 radiances for three green-leaf biomass levels and bare soil. Ground measurements of surface reflectances were used. The simulations were done along a scan line at 30 deg latitude during the summer solstice, equinox, and winter solstice. The simulation models are described and the effect of atmosphere over moderately vegetated surfaces is discussed. The results show that sensor response to atmospheric path length can be substantial for the AVHRR visible and near-infrared channels and normalized difference values, but they can be minimized by high sun and clear atmospheric viewing. The results indicate that AVHRR data would be most useful for monitoring low green leaf biomas canopies.

Holben, B. N.↗
NASA NTRS1983

Evaluation of procedures to correct for variable viewing and illumination geometry when observing a non-Lambertian surface through the atmosphere

Data from the Advanced Very High Resolution Radiometer aboard the NOAA polar orbiting satellite are being operationally applied to provide estimates of vegetation cover and/or condition over a large part of the earth by the USDA. The wide scan angle (+ or - 54 deg) of this system permits daily views of the earth when used to its limits. Five-day repetitive coverage is acquired, assuming cloud-free conditions, in current operations which limit the use of the scan to the center + or - 14 deg of swath. While use of the full scan width would provide clear acquisitions frequent enough to monitor crop development and condition even with normal cloudiness, these off-nadir data are made difficult to interpret due to the non-Lambertian nature of the surface, enhanced effect of the atmosphere, inclusion of subpixel and thin invisible clouds in the scene, and differences in illumination across the scene; all of which contribute to variations in observed reflected radiation. Some approaches to provide corrections for these effects are discussed here.

Whitehead, V. S.↗
NASA NTRS1985

Convergence of Chahine's nonlinear relaxation inversion method used for limb viewing remote sensing

The application of Chahine's (1970) inversion technique to remote sensing problems utilizing the limb viewing geometry is discussed. The problem considered here involves occultation-type measurements and limb radiance-type measurements from either spacecraft or balloon platforms. The kernel matrix of the inversion problem is either an upper or lower triangular matrix. It is demonstrated that the Chahine inversion technique always converges, provided the diagonal elements of the kernel matrix are nonzero.

Chu, W. P.↗
NASA NTRS1985

Finite field of view effects on inversion of limb thermal emission observations

It is pointed out that the technique of thermal emission spectroscopy provides an effective means for remote sounding of stratospheric temperature structure and constituent distributions. One procedure for measuring the stratospheric infrared spectrum involves the conduction of observations along ray paths tangent to the stratospheric limb. Thermal emission limb tangent observations have certain advantages compared to other types of observations. The techniques for determining temperature and trace gas distributions from limb thermal emission radiances are based on the assumption that the bulk of opacity lies near the tangent point. Ideally, the field of view (FOV) of the observing instrument should be very small. The effect of a finite FOV is to reduce the spatial resolution of the retrieved temperature and constituent profiles. The present investigation is concerned with the effects of the FOV on the inversion of infrared thermal emission measurements for balloon platforms. Attention is given to a convenient method for determining the weighting functions.

Abbas, M. M.↗
NASA NTRS1983

Effect of limb darkening functions variations on deconvolution of wide-field-of-view measurements of earth emitted radiation

A solution is presented to the problem of deconvolving wide field of view measurements of earth-emitted radiation for the case of limb-darkening functions which are geographically dependent. The method of linear perturbations is used and the effects of limb-darkening function variations at various scales are evaluated. A simple model for the geographical variation of the limb-darkening function based on the radiant exitance is introduced. It is shown that the effect of these variations on the global average radiant exitance vanishes identically, and is insignificant for large spatial scales. For wave numbers six through twelve, the limb-darkening effects are small but possibly significant. At wave numbers greater than twelve, the noise due to meteorological variability dominates for an orbit altitude of 1100 km. The smallness of these effects is due to the smoothness of the monthly averaged radiant exitance field.

Smith, G. L.↗
NASA NTRS1984

External view construction for database uniformization

Database uniformization refers to the building of a common user interface facility to support uniform access to any or all of a collection of distributed heterogeneous databases. A proposed solution for database uniformization includes a global data manager which accepts a user's query on the user's global view and returns the results by consulting the various databases. In this paper the external-to-conceptual mapping component of the global data manager is described and the design using portions of sample NASA GSFC databases is illustrated with typical applications.

Grant, J.↗
NASA NTRS1986

Shuttle imaging radar views the Earth from Challenger: The SIR-B experiment

In October 1984, SIR-B obtained digital image data of about 6.5 million km2 of the Earth's surface. The coverage is mostly of selected experimental test sites located between latitudes 60 deg north and 60 deg south. Programmed adjustments made to the look angle of the steerable radar antenna and to the flight attitude of the shuttle during the mission permitted collection of multiple-incidence-angle coverage or extended mapping coverage as required for the experiments. The SIR-B images included here are representative of the coverage obtained for scientific studies in geology, cartography, hydrology, vegetation cover, and oceanography. The relations between radar backscatter and incidence angle for discriminating various types of surfaces, and the use of multiple-incidence-angle SIR-B images for stereo measurement and viewing, are illustrated with examples. Interpretation of the images is facilitated by corresponding images or photographs obtained by different sensors or by sketch maps or diagrams.

Ford, J. P.↗
NASA NTRS1985

Atmospheric transmittance from spacecraft using multiple view angle imagery

A procedure for determining atmospheric transmittance using surface images acquired at several view angles from space is presented. Fourier filtering of the image data is used to mitigate the effects of atmospheric path radiance and instrument noise. Although it is essential for some contrast to be present in the images, knowledge of the atmospheric scattering phase function or the surface bidirectional reflectance function is not required. The method appears to provide absolute transmittances with an accuracy of better than 10 percent, which is useful in some applications.

Diner, D. J.↗
NASA NTRS1986

Theory of homogeneous nucleation - A chemical kinetic view

A simple function with two undetermined parameters has been used in place of the Thomson-Gibbs relation to relate the activation energy of the vaporization reaction to cluster size. The parameters are iterated to assume optimum values in numerical computation so experimental data may be correlated. Calculations show this approach closely predicts and correlates available data for water, benzene, and ethanol. The nucleation formulism is redeveloped with an emphasis on the chemical kinetic view. Surface tension of the liquid and free energy of droplet formation are not used in its derivation.

Yang, C. H.↗
NASA NTRS1986

Sun angle, view angle, and background effects on spectral response of simulated balsam fir canopies

An experiment is described that examines the effects of solar zenith angle and background reflectance on the composite scene reflectance of small balsam fir (Abies balsamea (L.) Mill.) arranged in different densities. In this study, the shape, density, and, consequently, the needle area index and phytomass of the canopies, as well as the background reflectance, were controlled. The effects of sun angle, view angle, and background reflectance on the multispectral response of small balsam fir trees were significant. Regression models relating spectral vegetation indices (i.e., normalized difference (ND) and greenness (GR) to phytomass) showed very poor relationships for balsam fir canopies with a grass background. However, strong linear relationships were found for ND and GR with phytomass for a background that simulated the reflectance of snow. Changing solar zenith angle significantly affected the models relating ND to phytomass for the snow background, but was not significant in the model relating GR to phytomass for the snow background

Ranson, K. J.↗
NASA NTRS1986

Double window viewing chamber assembly

A viewing chamber which permits observation of a sample retained therein includes a pair of double window assemblies mounted in opposed openings in the walls thereof so that a light beam can directly enter and exit from the chamber. A flexible mounting arrangement for the outer windows of the window assemblies enables the windows to be brought into proper alignment. An electrical heating arrangement prevents fogging of the outer windows whereas desiccated air in the volume between the outer and inner windows prevents fogging of the latter.

Keller, V. W.↗
NASA NTRS1987

Atlas of wide-field-of-view outgoing longwave radiation derived from Nimbus 6 Earth radiation budget data set, July 1975 to June 1978

An atlas of monthly mean outgoing longwave radiation global contour maps and associated spherical harmonic coefficients is presented. The atlas contains 36 months of continuous data from July 1975 to June 1978. The data were derived from the first Earth radiation budget experiment, which was flown on the Nimbus-6 Sun-synchronous satellite in 1975. Only the wide-field-of-view longwave measurements are cataloged in this atlas. The contour maps along with the associated sets of spherical harmonic coefficients form a valuable data set for studying different aspects of our changing climate over monthly, annual, and interannual scales in the time domain, and over regional, zonal, and global scales in the spatial domain.

Bess, T. Dale↗
NASA NTRS1985

Computerized data reduction techniques for nadir viewing remote sensors

Computer resources have been developed for the analysis and reduction of MAPS experimental data from the OSTA-1 payload. The MAPS Research Project is concerned with the measurement of the global distribution of mid-tropospheric carbon monoxide. The measurement technique for the MAPS instrument is based on non-dispersive gas filter radiometer operating in the nadir viewing mode. The MAPS experiment has two passive remote sensing instruments, the prototype instrument which is used to measure tropospheric air pollution from aircraft platforms and the third generation (OSTA) instrument which is used to measure carbon monoxide in the mid and upper troposphere from space platforms. Extensive effort was also expended in support of the MAPS/OSTA-3 shuttle flight. Specific capabilities and resources developed are discussed.

Tiwari, S. N.↗
NASA NTRS1986

Field-of-view effects in estimating precipitation from satellite microwave radiances

A one-dimensional cloud model for predicting precipitation is examined. The relation between the averaged brightness temperature and the rainfall rate for various microwave frequencies and field-of-view (FOVs) is studied. The model is utilized to simulate the rainfall rate and brightness temperature data for 19 GHz, a 30 km FOV, 37 GHz, and a combination of IR and microwave data. The data produced by the simulations are described and analyzed.

Adler, Robert F.↗
NASA NTRS1987

Nimbus 7 earth radiation budget wide field of view climate data set improvement. II - Deconvolution of earth radiation budget products and consideration of 1982-1983 El Nino event

A deconvolution technique is employed that permits recovery of daily averaged earth radiation budget (ERB) parameters at the top of the atmosphere from a set of the Nimbus 7 ERB wide field of view (WFOV) measurements. Improvements in both the spatial resolution of the resultant fields and in the fidelity of the time averages is obtained. The algorithm is evaluated on a set of months during the period 1980-1983. The albedo, outgoing long-wave radiation, and net radiation parameters are analyzed. The amplitude and phase of the quasi-stationary patterns that appear in the spatially deconvolved fields describe the radiation budget components for 'normal' as well as the El Nino/Southern Oscillation (ENSO) episode years. They delineate the seasonal development of large-scale features inherent in the earth's radiation budget as well as the natural variability of interannual differences. These features are underscored by the powerful emergence of the 1982-1983 ENSO event in the fields displayed. The conclusion is that with this type of resolution enhancement, WFOV radiometers provide a useful tool for the observation of the contemporary climate and its variability.

Ardanuy, Phillip E.↗
NASA NTRS1988

Periscope For Viewing Weld Penetration

Periscope enables viewing of weld joint from inside cylindrical duct to determine when weld penetration occurs. Supplies steady stream of inert gas to shield joint. Device used to calibrate and evaluate techniques for sensing weld penetration.

Gordon, Stephen S.↗
NASA NTRS1987

Surface composition of Mars: A Viking multispectral view

A new method of analyzing multispectral images takes advantage of the spectral variation from pixel to pixel that is typical for natural planetary surfaces, and treats all pixels as potential mixtures of spectrally distinct materials. For Viking Lander images, mixtures of only three spectral end members (rock, soil, and shade) are sufficient to explain the observed spectral variation to the level of instrumental noise. It was concluded that a large portion of the Martian surface consists of only two spectrally distinct materials, basalt and palgonitic soil. It is emphasized, however, that as viewed through the three broad bandpasses of Viking Orbiter, other materials cannot be distinguished from the mixtures.

Adams, John B.↗
NASA NTRS1988

Deconvolution results for wide field-of-view radiometer measurements of reflected solar radiation

The measurement of reflected solar radiation by spacecraft wide-field-of-view radiometers is considered analytically, and the method proposed by Smith (1987) for the solution of the discretized governing equations is described and demonstrated. The theoretical basis of the singular-value decomposition method (partitioning the albedo field into observable and unobservable components) is outlined; its application to Nimbus 7 ERB data is explained in detail; and numerical results are presented in graphs and maps and briefly characterized.

Smith, G. Louis↗