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At least 1,495 records · Page 83
All sourcesNASA NTRSDOE OSTI
NASA NTRS1975

X-ray reflection and scatter measurements on selected optical samples

The results from an experimental program to determine the reflection efficiency and scatter parameters of selected optical samples are presented. The measurements were made using 8.34A X-rays at various angles of incidence. Selected samples were contaminated after being measured and then remeasured to determine the effects of contamination. The instrumentation involved in taking the data, including the X-ray reflectometer and data processing equipment, is discussed in detail. The condition of the optical surfaces, the total reflection measurements, the scatter measurements, and the analysis are discussed.

Fields, S. A.↗
NASA NTRS1976

Spectral reflectance and radiance characteristics of water pollutants

Spectral reflectance characteristics of water pollutants and water bodies were compiled using the existing literature. Radiance calculations were performed at satellite altitude for selected illumination angles and atmospheric conditions. The work described in this report was limited to the reflective portion of the spectrum between 0.40 micrometer to 1.0 micrometer.

Wezernak, C. T.↗
NASA NTRS1975

Plant, soil, and shadow reflectance components of row crops

Data from the first Earth Resource Technology Satellite (LANDSAT-1) multispectral scanner (MSS) were used to develop three plant canopy models (Kubelka-Munk (K-M), regression, and combined K-M and regression models) for extracting plant, soil, and shadow reflectance components of cropped fields. The combined model gave the best correlation between MSS data and ground truth, by accounting for essentially all of the reflectance of plants, soil, and shadow between crop rows. The principles presented can be used to better forecast crop yield and to estimate acreage.

Richardson, A. J.↗
NASA NTRS1976

Electromagnetic reflection and transmission at interfaces involving graded dielectrics with applications to planetary radar astronomy

Reflection and transmission of electromagnetic waves at an interface between two homogeneous materials is modified when a transition zone of linearly increasing permittivity is inserted between the half spaces. Mathematical expressions for reflection and transmission coefficients are derived for waves at arbitrary incidence angles and polarized either in or perpendicular to the plane of incidence. Discontinuities in permittivity at the transition-zone boundaries are allowed. There is efficient transmission between the two half-spaces for transition-zone thicknesses of a wavelength or greater. For sharper changes, the matching layer has diminishing effect and the wave-interface interaction is characterized by the difference in properties between the two half-spaces. Examples applicable to lunar radar astronomy and airborne terrestrial remote sensing are used to illustrate the relationship between wavelength and thickness of the transition layer.

Simpson, R. A.↗
NASA NTRS1975

Comparison between reflectivity statistics at heights of 3 and 6 km and rain rate statistics at ground level

An experiment was conducted to study the relations between the empirical distribution functions of reflectivity at specified locations above the surface and the corresponding functions at the surface. A bistatic radar system was used to measure continuously the scattering cross section per unit volume at heights of 3 and 6 km. A frequency of 3.7 GHz was used in the tests. It was found that the distribution functions for reflectivity may significantly change with height at heights below the level of the melting layer.

Crane, R. K.↗
NASA NTRS1976

Simultaneous partial reflection and meteor radar wind observations at Urbana, Illinois, during the winter of 1974-1975

A program of observation was undertaken during the winter of 1974-1975 utilizing the meteor winds radar and partial reflection system at Urbana, Illinois. The north-south component of the prevailing wind representative of 80-100 km altitude was deduced for four 24-h observational periods during which partial reflection measurements of D-region electron density were made. These observations indicate southward mean motion during periods of higher electron density and northward mean motion during periods of lower electron density. This is consistent with the idea that increases in the transport of nitric oxide from the auroral zone is a cause of winter increases in D-region electron density at midlatitudes.

Geller, M. A.↗
NASA NTRS1975

Analysis and correction of ground reflection effects in measured narrowband sound spectra using cepstral techniques

Ground reflections generate undesirable effects on acoustic measurements such as those conducted outdoors for jet noise research, aircraft certification, and motor vehicle regulation. This paper shows how cepstral techniques developed in speech processing can be adapted to identify the echo delay time and to correct for ground reflection effects. A sample result is presented using an actual narrowband sound pressure level spectrum. The technique can readily be adapted to existing fast Fourier transform type spectrum measurement instrumentation to provide field measurement of echo time delays.

Miles, J. H.↗
NASA NTRS1975

Solar and atmospheric effects on satellite imagery derived from aircraft reflectance measurements

Solar and atmospheric effects on satellite imagery were investigated by measuring terrain reflectance from low-flying aircraft. Radiometric data were recorded over three test sites in California, Georgia, and South Dakota. Radiance from Skylab (EREP) S190A and ERTS-1 (Landsat-1) sensors was linearly correlated with wide-band terrain reflectance. The results support the proposition that the coefficients of the regression equation are the path radiance and a quantity representing the product of total irradiance and beam transmittance at the time of satellite overflight. These coefficients should be useful as linear conversion coefficients for extending spectral signatures in computer-aided classification work on satellite imagery.

Dana, R. W.↗
NASA NTRS1977

Low-reflection silicon solar cells

Alteration of surface of silicon solar cell with chemical etchant prior to application of antireflection (AR) coating and encapsulant FEP Teflon, reduces surface reflectivity to 2%. Reduced reflection achieved occurs at all wavelengths resulting in improved short circuit current and spectral response. Improved collection efficiency is also expected.

Baraona, C. R.↗
NASA NTRS1976

Impulsive solar X-ray bursts. 4: Polarization, directivity and spectrum of the reflected and total bremsstrahlung radiation from a beam of electrons directed toward the photosphere

A Monte Carlo method is described for evaluation of the spectrum, directivity and polarization of X-rays diffusely reflected from stellar photospheres. the accuracy of the technique is evaluated through comparison with analytic results. Using the characteristics of the incident X-rays of the model for solar X-ray flares, the spectrum, directivity and polarization of the reflected and the total X-ray fluxes are evaluated. The results are compared with observations.

Langer, S. H.↗
NASA NTRS1977

Measurements of the reflection factor of flat ground surfaces

Measurements are made of the reflection factors of asphalt, concrete, and sod at oblique angles of incidence. Initial measurements were carried out in an anechoic chamber to eliminate the effects of wind and temperature gradients. These were followed by measurements made outdoors over a wider frequency range. Data are presented for the magnitudes of the reflection factors of asphalt, concrete, and sod at angles of incidence of 38 deg and 45 deg.

Ventres, C. S.↗
NASA NTRS1976

Investigation of the effect of atmospheric dust on the determination of total ozone from the earth's ultraviolet reflectivity measurements, 2

Results of a detailed analysis of the simulated measurements for the BUV (Nimbus-4) configuration are described by using a total-ozone estimation procedure. A set of recommendations are discussed for increasing the accuracy and confidence level of the total ozone values estimated from the measurements of the earth's ultraviolet reflectivity at five different wavelengths (BUV configuration). A tentative procedure is also considered for the estimation of total ozone from measurements of reflectivity at six different wavelengths specified in the SBUV/TOMS (Nimbus-G) configuration.

Dave, J. V.↗
NASA NTRS1976

High purity silica reflective heat shield development

A hyperpure vitreous silica material is being developed for use as a reflective and ablative heat shield for planetary entry. Various purity grades and forms of raw materials were evaluated along with various processing methods. Slip casting of high purity grain was selected as the best processing method, resulting in a highly reflective material in the wavelength bands of interest (the visible and ultraviolet regions). The selected material was characterized with respect to optical, mechanical and physical properties using a limited number of specimens. The process has been scaled up to produce a one-half scale heat shield (18 in. dia.) (45.72 cm) for a Jupiter entry vehicle. This work is now being extended to improve the structural safety factor of the heat shield by making hyperpure silica material tougher through the addition of silica fibers.

Nachtscheim, P. R.↗
NASA NTRS1977

Diffraction of a shock wave by a compression corner. II - Single Mach reflection

The two-dimensional time-dependent Euler equations which govern the flow field resulting from the interaction of a planar shock with a compression corner are solved for initial conditions which result in single Mach reflection of the incident planar shock. The Euler equations are first transformed to include the self-similarity of the flow field. A second transformation is employed to normalize the distances between the ramp and the reflected shock and between the wall and the Mach stem. The resulting equations in strong conservation-law form are solved using a second-order discontinuity-fitting finite-difference approach. The results are compared with experimental interferograms and existing first-order shock-capturing numerical solutions.

Shankar, V.↗
NASA NTRS1976

Lunar surface remanent magnetic fields detected by the electron reflection method

We present maps of the lunar surface remanent magnetic fields detected by the electron reflection method. These maps provide substantial coverage of the latitude band from 30 N southward to 30 S with a resolution of about 40 km and a sensitivity of about 0.2 gamma at the lunar surface. Regions of remanent magnetization are observed ranging in size from the resolution limit of 1.25 deg to above approximately 60 deg. The largest contiguous region fills the Big Backside Basin where it is intersected by the spacecraft orbital tracks. Preliminary analyses of the maps show that the source regions of lunar limb compressions correspond to regions of strong surface magnetism, and that there does not appear to be sharply discontinuous magnetization at the edges of maria. We also analyze the electron reflection observations to obtain information on the direction and distribution of magnetization in the Van de Graaff anomaly region.

Lin, R. P.↗
NASA NTRS1977

Impulsive solar X-ray bursts. III - Polarization, directivity, and spectrum of the reflected and total bremsstrahlung radiation from a beam of electrons directed toward the photosphere

The paper presents the spectrum, directivity, and state of polarization of the bremsstrahlung radiation expected from a beam of high-energy electrons spiraling along radial magnetic field lines toward the photosphere. A Monte Carlo method is then described for evaluation of the spectrum, directivity, and polarization of X-rays diffusely reflected from stellar photospheres. The accuracy of the technique is evaluated through comparison with analytic results. The calculated characteristics of the incident X-rays are used to evaluate the spectrum, directivity, and polarization of the reflected and total X-ray fluxes. The results are compared with observations.

Langer, S. H.↗
NASA NTRS1977

The reflection coefficient in stimulated parametric backscattering

The step-function approximation of the anomalous reflection coefficient in laser-induced parametric backscattering currently used in the theory of nonlinear laser plasma interactions is improved using a simple exponential derived from elliptic functions. The validity of the single-reflection analysis is reaffirmed.

Yu, C.↗