A summary of some applications of power spectra to airplane turbulence problems.
Power spectral density /PSD/ methods applied to prediction of aircraft responses to continuous turbulence
TURBULENCE MEASURING APPARATUS↗
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Some applications of power spectra to airplane turbulence problems.
Power spectral density /PSD/ methods applied to prediction of aircraft responses to continuous turbulence
WIND TUNNEL STABILITY TEST↗
Factorization of spectra by discrete Fourier transforms
Discrete Fourier transform method for factoring spectral density functions, calculating absolute error
Rino, C. L.↗
Elimination of cloud effects in sensing ozone from 9.6 micron band.
Description of an objective method for extracting the spectral information from the 9.6 micron region pertaining to atmospheric ozone. This method has been developed by examining a large number of Nimbus 4 infrared interferometer-spectrometer spectra. The method is capable of eliminating, not only the effects of clouds, but also those of interference from the reststrahlen bands of desert sands.
Prabhakara, C.↗
Study to investigate and evaluate means of optimizing the Ku-band communication function for the space shuttle
The forward link of the overall Ku-band communication system consists of the ground- TDRS-orbiter communication path. Because the last segment of the link is directed towards a relatively low orbiting shuttle, a PN code is used to reduce the spectral density. A method is presented for incorporating code acquisition and tracking functions into the orbiter's Ku-band receiver. Optimization of a three channel multiplexing technique is described. The importance of Costas loop parameters to provide false lock immunity for the receiver, and the advantage of using a sinusoidal subcarrier waveform, rather than square wave, are discussed.
Simon, M. K.↗
A Fourier approach to cloud motion estimation
A Fourier technique is described for estimating cloud motion from pairs of pictures using the phase of the cross spectral density. The method allows motion estimates to be made for individual spatial frequencies, which are related to cloud pattern dimensions. Results obtained are presented and compared with the results of a Fourier domain cross correlation scheme. Using both artificial and real cloud data show that the technique is relatively sensitive to the presence of mixtures of motions, changes in cloud shape, and edge effects.
Arking, A.↗
Variability in the determination of total atmospheric ozone using remote sensing spectroscopic techniques
A spectroscopic method for remote sensing of total ozone has been applied to airborne observations of solar near-UV radiation in the 3100 to 3600 A wavelength region. The method involves detailed spectral matching of the solar observations with synthetic profiles containing various amounts of ozone absorption. For the 3100-3200 A region, measurements above the tropopause agree well with Broadfoot's (1972) extra-terrestrial solar irradiance values. Discrepancies between the observed spectra and the synthetic profiles at other wavelength regions may be due to distorted ozone absorption coefficients or the presence of other UV-absorbing species in the stratosphere.
Sivjee, G. G.↗
Energy spectrum of corona impulses generated from insulated wires under high a.c. voltages
This paper suggests methods for calculating spectral energy densities of corona impulses generated from insulated conductors. The calculation is based on the data obtained from the measurement of corona pulse waveforms, repetition rates and relevant statistical properties of corona impulses.
Doreswamy, C. V.↗
Simulation of meteorological satellite (METSAT) data using LANDSAT data
The information content which can be expected from the advanced very high resolution radiometer system, AVHRR, on the NOAA-6 satellite was assessed, and systematic techniques of data interpretation for use with meteorological satellite data were defined. In-house data from LANDSAT 2 and 3 were used to simulate the spatial, spectral, and sampling methods of the NOAA-6 satellite data.
Austin, W. W.↗
An optimal control approach to the design of moving flight simulators
An abstract flight simulator design problem is formulated in the form of an optimal control problem, which is solved for the linear-quadratic-Gaussian special case using a mathematical model of the vestibular organs. The optimization criterion used is the mean-square difference between the physiological outputs of the vestibular organs of the pilot in the aircraft and the pilot in the simulator. The dynamical equations are linearized, and the output signal is modeled as a random process with rational power spectral density. The method described yields the optimal structure of the simulator's motion generator, or 'washout filter'. A two-degree-of-freedom flight simulator design, including single output simulations, is presented.
Sivan, R.↗
Study of the system of middle atmosphere-ionosphere using remote-sensing data
In the present investigation, the methods of statistical spectral analysis are employed for a study of the quasi-periodic changes of state parameters of the middle atmosphere and the ionosphere, taking into account oscillations with periods of several days. The considered oscillations are typical for planetary waves. The theory and empirical findings regarding transient planetary waves are utilized as a basis for the concepts employed in the data analysis and for the interpretation of the results. The results of the investigation show a presence of coherent variations in the time series of radiation density measurements and other state parameters for the middle atmosphere and the ionosphere. The existence of presumably dynamic coupling processes can be recognized in oscillations with periods of about 16 or 5 days.
Hass, H.↗
Navier-Stokes solution on the CYBER-203 by a pseudospectral technique
A three-level, time-split, mixed spectral/finite difference method for the numerical solution of the three-dimensional, compressible Navier-Stokes equations has been developed and implemented on the Control Data Corporation (CDC) CYBER-203. This method uses a spectral representation for the flow variables in the streamwise and spanwise coordinates, and central differences in the normal direction. The five dependent variables are interleaved one horizontal plane at a time and the array of their values at the grid points of each horizontal plane is a typical vector in the computation. The code is organized so as to require, per time step, a single forward-backward pass through the entire data base. The one-and two-dimensional Fast Fourier Transforms are performed using software especially developed for the CYBER-203.
Lambiotte, J. J.↗
Dispersion characteristics for wide slotlines on low-permittivity substrates
A spectral-domain Galerkin method is used to calculate the dispersion characteristics of wide slotlines on low-permittivity substrates that are electrically thin. The range of parameters covered are d/lambda sub 0 = 0.006-0.06, W/lambda sub 0 = 0.005-2.0, and epsilon sub r = 2.22, 3.0, 3.8, and 9.8. The choice of expansion and testing functions makes possible the extraction of the asymptotic form of the infinite integrals, resulting in a computationally efficient solution. The agreement between calculated and measured slot wavelengths on narrow and wide slots is generally within 2.0 percent over 2-6 GHz.
Janaswamy, R.↗
Sun-view angle effects on reflectance factors of corn canopies
The effects of sun and view angles on reflectance factors of corn (Zea mays L.) canopies ranging from the six leaf stage to harvest maturity were studied on the Purdue University Agronomy Farm by a multiband radiometer. The two methods of acquiring spectral data, the truck system and the tower systrem, are described. The analysis of the spectral data is presented in three parts: solar angle effects on reflectance factors viewed at nadir; solar angle effects on reflectance factors viewed at a fixed sun angle; and both sun and view angles effect on reflectance factors. The analysis revealed that for nadir-viewed reflectance factors there is a strong solar angle dependence in all spectral bands for canopies with low leaf area index. Reflectance factors observed from the sun angle at different view azimuth angles showed that the position of the sensor relative to the sun is important in determining angular reflectance characteristics. For both sun and view angles, reflectance factors are maximized when the sensor view direction is towards the sun.
Ranson, K. J.↗
Quantitative abundance estimates from bidirectional reflectance measurements
A simplified approach for estimating mineral abundances in mineral mixtures from bidirectional reflectance measurements is presented. Fundamental to this approach is a priori information concerning reflectance spectra of the individual minerals and an estimate of the particle sizes of the components. Simplified equations for bidirectional reflectance are used to linearize the systematics of spectral mixing. The method was used to determine the relative proportions of olivine, magnetite, enstatite, and anorthite in a mixture; the mass fractions of mixture components were calculated on the basis of known particle diameters. The results indicate that for materials without strongly adsorbing components, the accuracy of abundance determinations is better than 5 percent.
Mustard, John F.↗
A preliminary investigation of large-scale organized motions in a supersonic turbulent boundary layer on a curved surface
An experimental investigation concentrating on the change in the large-scale organized motions of a supersonic turbulent boundary layer subjected to a short region of concave surface curvature is presented. Two flows were studied, a relatively weak and a relatively strong perturbation. In both flows the freestream Mach number was 2.89 and the Reynolds number based on momentum thickness was 81,900. Hot-wire anemometry and schlieren photography provided the principle tools for this investigation. Hot-wire data were analyzed using spectral and correlation methods and conditional sampling techniques. Changes in structure angle and results of conditionally sampled velocity signals are discussed. The strong perturbation is found to increase the structure angle, and in both flows the length scales of the organized motions are altered.
Donovan, J. F.↗
Radiometric calibrations of portable sources in the vacuum ultraviolet
The primary UV radiometric calibration standards of the Atomic and Plasma Radiation Division of the NBS are the hydrogen arc and the blackbody line arc. The secondary standards are the argon mini- and maxiarcs, and the deuterium arc lamp. Calibration methods involving both spectral radiance and irradiance, as well as the evaluation of their uncertainties, are discussed. Attention is given to the establishment of an irradiance scale, and the absolute spectral irradiance, measured as a function of wavelength, at a 50-cm distance from the field aperture for five different continuum sources.
Klose, Jules Z.↗
Some spectral approximation of one-dimensional fourth-order problems
Some spectral type collocation method well suited for the approximation of fourth-order systems are proposed. The model problem is the biharmonic equation, in one and two dimensions when the boundary conditions are periodic in one direction. It is proved that the standard Gauss-Lobatto nodes are not the best choice for the collocation points. Then, a new set of nodes related to some generalized Gauss type quadrature formulas is proposed. Also provided is a complete analysis of these formulas including some new issues about the asymptotic behavior of the weights and we apply these results to the analysis of the collocation method.
Bernardi, Christine↗