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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 181 records · Page 10
All sourcesNASA NTRSDOE OSTI
NASA NTRS1977

The evaluation of satellite-borne weather radar system designs using real ground-based radar data

The paper presents method of evaluating proposed satellite radar systems using real radar data, and discusses methods of displaying the results which will hopefully facilitate easy comparison of systems. A single pencil beam pulsed radar system is considered while the precipitation data base comes from six rain days observed by SPANDAR. The many additional factors that must be considered in the radar equation such as attenuation and scattering (Mie and Rayleigh) are discussed along with some indication where possible errors lie.

Dobson, E. B.↗
NASA NTRS1978

Direct evaluation of aerosol-mass loadings from multispectral extinction data

A formula is derived for the evaluation of the total volume of aerosol in a column, and hence for the aerosol columnar mass loading, from multispectral extinction data. This formula is exact in the 'anomalous diffraction' approximation, and reasonably accurate for Mie scattering, over a fairly wide range of refractive indices typical of real aerosols.

Box, M. A.↗
NASA NTRS1979

Determination of the ground albedo and the index of absorption of atmospheric particulates by remote sensing. II - Application

A hemispherical radiometer has been used to obtain spectrally narrow-band measurements of the downward hemispheric diffuse and total (global) flux densities at varying solar zenith angles on 14 days over Tucson. Data are presented which illustrate the effects of temporally varying atmospheric conditions as well as clear stable conditions on the ratio of the diffuse to direct solar radiation at the earth's surface. The ground albedo and the effective imaginary term of the complex refractive index of atmospheric particulates are derived from the diffuse-direct ratio measurements on seven clear stable days at two wavelengths using the statistical procedure described by King and Herman (1979). Results indicate that the downwelling diffuse radiation field in the midvisible region in Tucson can be adequately described by Mie scattering theory if the ground albedo is 0.279 + or - 0.100 and the index of absorption is 0.0306 + or - 0.0082.

King, M. D.↗
NASA NTRS1980

DIAL with heterodyne detection including speckle noise: Aircraft/shuttle measurements of O3, H2O, and NH3 with pulsed tunable CO2 lasers

Atmospheric trace constituent measurements with higher vertical resolution than attainable with passive radiometers are discussed. Infrared differential absorption lidar (DIAL), which depends on Mie scattering from aerosols, has special advantages for tropospheric and lower stratospheric applications and has great potential importance for measurements from shuttle and aircraft. Differential absorption lidar data reduction involves comparing large amplitude signals which have small differences. The accuracy of the trace constituent concentration inferred from DIAL measurements depends strongly on the errors in determining the amplitude of the signals. Thus, the commonly used SNR expression (signal divided by noise in the absence of signal) is not adequate to describe DIAL measurement accuracy and must be replaced by an expression which includes the random coherent (speckle) noise within the signal. A comprehensive DIAL computer algorithm is modified to include heterodyne detection and speckle noise. Examples for monitoring vertical distributions of O3, H2O, and NH3 using a ground-, aircraft-, or shuttle-based pulsed tunable CO2 laser DIAL system are given.

Brockman, P.↗
NASA NTRS1981

Radiative properties of the background stratospheric aerosols and implications for perturbed conditions

A series of Mie scattering calculations has been performed to define the wavelength-dependent, single scattering properties of aerosols present in the stratosphere during July 1979. Additional radiative transfer computations were conducted to assess the impact of aerosols on the earth's radiation budget. For these purposes, an extensive set of measurements of aerosol characteristics that were obtained in Alaska from aircraft and satellite platforms was used. At that time, the optical depth was too small for aerosols to significantly impact earth's climate. But the optical depth of the stratospheric aerosol layer has been large enough during some volcanically perturbed periods for the aerosols to have caused a noticeable warming of the stratosphere and cooling of the troposphere.

Pollack, J. R.↗
NASA NTRS1982

Rain measurements from space using a modified Seasat-type radar altimeter

The incorporation in the 13.5 GHz Seasat-type radar altimeter of a mode to measure rain rate is investigated. Specifically, an algorithm is developed relating the echo power at the various range bins, to the rain rate taking into consideration Mie scattering and path attenuation. The dependence of the algorithm on rain drop size distribution and nonuniform rain structure are examined and associated uncertainties defined. A technique for obtaining drop size distribution through the measurements of power at the top of the raincell and power difference through the cell also is investigated together with an associated error analysis. A description of the minor hardware modifications to the basic Seasat design is given for implementing the rain measurements.

Goldhirsh, J.↗
NASA NTRS1981

Potential of dual-measurement techniques for accurate determination of instantaneous rainfall rate from space

The incorporation in the 13.5 GHz SEASAT type radar altimeter of a mode to measure rain rate is investigated. Specifically, an algorithm is developed relating the echo power at the various range bins to the rain rate, taking into consideration Mie scattering and path attenuation. The dependence of the algorithm on rain drop size distribution, and non-uniform rain structure are examined and associated uncertainties defined. A technique for obtaining drop size distribution through the measurements of power at the top of the raincell and power difference through the cell is also investigated together with an associated error analysis. A description of the minor hardware modifications to the basic SEASAT design is given for implementing the rain measurements.

Ulbrich, C. W.↗
NASA NTRS1983

Laboratory analysis of techniques for remote sensing of estuarine parameters using laser excitation

The theoretical concepts underlying remote sensing of estuarine parameters using laser excitation are examined. The concepts are extended to include Mie scattering as a measure of the total suspended solids and to develop the water Raman signal as an internal standard. Experimental validation of the theory was performed using backscattered laser light from a laboratory tank to simulate a remote-sensing geometry. Artificially prepared sediments and biological cultures were employed to check specific aspects of the theory under controlled conditions. Natural samples gathered from a variety of water types were also analyzed in the tank to further enhance the simulation. The results indicate that it should be possible to remotely quantify total suspended solids, dissolved organics, attenuation coefficient, chlorophyll a, and phycoerythrin in estuarine water using laser excitation.

Exton, R. J.↗
NASA NTRS1983

Lidar remote measurements of Space Shuttle ground cloud emissions

The application of lidar remote sensing techniques to the measurement of spacecraft-booster-exhaust-cloud parameters is illustrated, using data obtained from the launch of STS-3. Mie-scatter measurements of plume and cloud particulates were made by a mobile unit with computer controlled elevation and azimuth coverage. Scattergraphs of typical STS-3 lidar data are presented and discussed. The potential use of DIAL techniques to measure the concentrations of HCl, N2H4, and NO2 is evaluated in terms of EPA overall-standard-deviation guidelines. It is shown that currently operational lidar systems can be modified to determine contamination or air pollution by these molecular species resulting from spacecraft launches.

Caputo, B.↗
NASA NTRS1983

Passive and active remote sensing of atmospheric precipitation

Both passive and active remote sensing of atmospheric precipitation are studied with the vector radiative transfer equations by making use of the Mie scattering phase functions and incorporating the raindrop-size distributions. For passive remote sensing, the Gaussian quadrature method is employed to solve for the brightness temperatures. For active remote sensing, an iterative approach carrying out to the second order in albedo is used to calculate for the bistatic coefficients, the backscattering cross sections/unit volume, and the interchannel cross talks. The calculated results are plotted as a function of rainfall rates and compared to various available experimental data. The theoretical model is easily applied to the remote sensing of aerosol particles, smoke, fog, and haze at infrared and visible frequencies.

Jin, Y. Q.↗
NASA NTRS1984

Velocity visualization in gaseous flows

Techniques yielding simultaneous, multiple-point measurements of velocity in reacting or nonreacting flow fields have the potential to significantly impact basic and applied studies of fluid mechanics. This research program is aimed at investigating several candidate schemes which could provide such measurement capability. The concepts under study have in common the use of a laser source (to illuminate a column, a grid, a plane or a volume in the flow) and the collection of light at right angles (from Mie scattering, fluorescence, phosphorescence or chemiluminescence) using a multi-element solid-state camera (100 x 100 array of photodiodes). The work will include an overview and a status report of work in progress with particular emphasis on the method of Doppler-modulated absorption.

Hanson, R. K.↗
NASA NTRS1984

Saturated laser fluorescence in turbulent sooting flames at high pressure

The primary objective was to develop a quantitative, single pulse, laser-saturated fluorescence (LSF) technique for measurement of radical species concentrations in practical flames. The species of immediate interest was the hydroxyl radical. Measurements were made in both turbulent premixed diffusion flames at pressures between 1 and 20 atm. Interferences from Mie scattering were assessed by doping with particles or by controlling soot loading through variation of equivalence ratio and fuel type. The efficacy of the LSF method at high pressure was addressed by comparing fluorescence and adsorption measurements in a premixed, laminar flat flame at 1-20 atm. Signal-averaging over many laser shots is sufficient to determine the local concentration of radical species in laminar flames. However, for turbulent flames, single pulse measurements are more appropriate since a statistically significant number of laser pulses is needed to determine the probability function (PDF). PDFs can be analyzed to give true average properties and true local kinetics in turbulent, chemically reactive flows.

King, G. B.↗
NASA NTRS1984

Characterization of Surface Reflectance Variation Effects on Remote Sensing

The use of Monte Carlo radiative transfer codes to simulate the effects on remote sensing in visible and infrared wavelengths of variables which affect classification is examined. These variables include detector viewing angle, atmospheric aerosol size distribution, aerosol vertical and horizontal distribution (e.g., finite clouds), the form of the bidirectional ground reflectance function, and horizontal variability of reflectance type and reflectivity (albedo). These simulations are used to characterize the sensitivity of observables (intensity and polarization) to variations in the underlying physical parameters both to improve algorithms for the removal of atmospheric effects and to identify techniques which can improve classification accuracy. It was necessary to revise and validate the simulation codes (CTRANS, ARTRAN, and the Mie scattering code) to improve efficiency and accommodate a new operational environment, and to build the basic software tools for acquisition and off-line manipulation of simulation results. Initial calculations compare cases in which increasing amounts of aerosol are shifted into the stratosphere, maintaining a constant optical depth. In the case of moderate aerosol optical depth, the effect on the spread function is to scale it linearly as would be expected from a single scattering model. Varying the viewing angle appears to provide the same qualitative effect as modifying the vertical optical depth (for Lambertian ground reflectance).

Pearce, W. A.↗
NASA NTRS1984

Optimization of fringe-type laser anemometers for turbine engine component testing

The fringe type laser anemometer is analyzed using the Cramer-Rao bound for the variance of the estimate of the Doppler frequency as a figure of merit. Mie scattering theory is used to calculate the Doppler signal wherein both the amplitude and phase of the scattered light are taken into account. The noise from wall scatter is calculated using the wall bidirectional reflectivity and the irradiance of the incident beams. A procedure is described to determine the optimum aperture mask for the probe volume located a given distance from a wall. The expected performance of counter type processors is also discussed in relation to the Cramer-Rao bound. Numerical examples are presented for a coaxial backscatter anemometer.

Seasholtz, R. G.↗
NASA NTRS1983

The formation of polar stratospheric clouds

Measurements of the stratospheric aerosol by SAM II during the northern and southern winters of 1979 showed a pronounced increase in extinction on occasions when the temperature fell to a low value (below 200 K). The correlation between extinction and temperature is evaluated on the basis of thermodynamic considerations. As the temperature falls, the hygroscopic aerosols absorb water vapor from the atmosphere, growing as they do so. The effect of the temperature on the size distribution and composition of the aerosol is determined, and the optical extinction at 1 micron wavelength is calculated using Mie scattering theory. The theoretical predictions of the change in extinction with temperature and humidity are compared with the SAM II results at 100 mb, and the water vapor mixing ratio and aerosol number density are inferred from these results. A best fit of the theoretical curves to the SAM II data gives a water vapor content of 5-6 ppmv, and a total particle number density of 6-7 particles/cu cm.

Steele, H. M.↗
NASA NTRS1983

Microwave emission from an irregular snow layer

Emission from an irregular snow layer is modeled by a layer of Mie scatterers using the radiative transfer method. Comparisons are made with measurements showing snow wetness effects and rough air-snow boundary effects. For convenience of reference, theoretical model behavior is also illustrated.

Eom, H. J.↗
NASA NTRS1984

Optical properties of NH3 ice from the far infrared to the near ultraviolet

The optical constants (n(r), n(i)) for solid ammonia in the cubic phase from 0.14 to 200 microns are displayed in both graphical and tabular form. The refractive indices n(r) were obtained from previously published spectra of the absorption index n(i) by means of the Kramers-Kronig dispersion relation. Mie scattering parameters in the same spectral range are graphically illustrated for particle sizes from 1 to 100 microns. An application of these results to the atmosphere of the planet Jupiter is also presented.

Martonchik, J. V.↗