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NASA NTRS2004

Space Shuttle UHF Communications Performance Evaluation

An extension boom is to be installed on the starboard side of the Space Shuttle Orbiter (SSO) payload bay for thermal tile inspection and repairing. As a result, the Space Shuttle payload bay Ultra High Frequency (UHF) antenna will be under the boom. This study is to evaluate the Space Shuttle UHF communication performance for antenna at a suitable new location. To insure the RF coverage performance at proposed new locations, the link margin between the UHF payload bay antenna and Extravehicular Activity (EVA) Astronauts at a range distance of 160 meters from the payload bay antenna was analyzed. The communication performance between Space Shuttle Orbiter and International Space Station (SSO-ISS) during rendezvous was also investigated. The multipath effects from payload bay structures surrounding the payload bay antenna were analyzed. The computer simulation tool based on the Geometrical Theory of Diffraction method (GTD) was used to compute the signal strengths. The total field strength was obtained by summing the direct fields from the antennas and the reflected and diffracted fields from the surrounding structures. The computed signal strengths were compared to the signal strength corresponding to the 0 dB link margin. Based on the results obtained in this study, RF coverage for SSO-EVA and SSO- ISS communication links was determined for the proposed payload bay antenna UHF locations. The RF radiation to the Orbiter Docking System (ODS) pyros, the payload bay avionics, and the Shuttle Remote Manipulator System (SRMS) from the new proposed UHF antenna location was also investigated to ensure the EMC/EMI compliances.

Hwu, Shian U.↗

NASA NTRS1986

Calculated occultation profiles of Io and the hot spots

Occultations of Io by other Galilean satellites in 1985 provide a means to locate volcanic hot spots and to model their temperatures. The expected time variations in the integral reflected and emitted radiation of the occultations are computed as a function of wavelength (visual to 8.7 microns). The best current ephemerides were used to calculate the geometry of each event as viewed from earth. Visual reflectances were modeled from global mosaics of Io. Thermal emission from the hot spots was calculated from Voyager 1 IRIS observations and, for regions unobserved by IRIS, from a model based on the distribution of low-albedo features. The occultations may help determine (1) the location and temperature distribution of Loki; (2) the source(s) of excess emission in the region from long 50 deg to 200 deg and (3) the distribution of small, high-temperature sources.

Mcewen, A. S.↗

NASA NTRS1975

Usefulness of LANDSAT data for monitoring plant development and range conditions in California's annual grassland

A network of sampling sites throughout the annual grassland region of California was established to correlate plant growth stages and forage production to climatic and other environmental factors. Plant growth and range conditions were further related to geographic location and seasonal variations. A sequence of LANDSAT data was obtained covering critical periods in the growth cycle. This was analyzed by both photointerpretation and computer aided techniques. Image characteristics and spectral reflectance data were then related to forage production, range condition, range site and changing growth conditions. It was determined that repeat sequences with LANDSAT color composite images do provide a means for monitoring changes in range condition. Spectral radiance data obtained from magnetic tape can be used to determine quantitatively the critical stages in the forage growth cycle. A computer ratioing technique provided a sensitive indicator of changes in growth stages and an indication of the relative differences in forage production between range sites.

Carneggie, D. M.↗

NASA NTRS1992

Directional and temporal variability of the APAR/VI relationships - The case of a sunflower canopy

Detailed biomass and structure measurements as well as photosynthetically active radiation (PAR) balance and bidirectional and polarized reflectances in various wavebands from 450 nm to 1750 nm have been conducted over a sunflower canopy in France. Preliminary results show that the vegetation indices (NDVI or TSAVI) computed from the red and near-infrared reflectances exhibit strong directional and temporal (variation with the sun zenith angle) features. The relationship between the vegetation indices and the PAR fraction absorbed or intercepted by the canopy is likely to vary greatly with these factors.

Baret, F.↗

NASA NTRS1993

Performance of the X-/Ka/KABLE-band dichroic plate in the DSS-13 beam waveguide antenna

The first Ka-band downlink demonstration was recently carried out by the Ka-Band Link Experiment (KABLE) in association with the Mars Observer spacecraft. In order to support the mission, a dichroic plate was required in the DSS-13 beam waveguide antenna to allow simultaneous X- and Ka-band operation. An X-/ Ka-/ KABLE-band dichroic plate was designed to transmit Ka-band downlink (31.8-32.3 GHz), Ka-band uplink (34.2-34.7 GHz), and KABLE (33.6-33.8 GHz) frequencies, while reflecting X-band (8.4-8.5 GHz). A computer program was developed for the analysis of a dichroic plate with rectangular apertures by using the mode-matching method. The plate was then fabricated and tested. The reflection, group delay, and noise temperature in the antenna system due to the dichroic plate were measured. The experimental results show good agreement with theoretical prediction.

Chen, J. C.↗

NASA NTRS1982

Satellite measurements of cloud reflectance and optical thickness

The cloud reflectance and the optical thickness have been computed with the aid of atmospheric models from the first eleven months (April 1970-February 1971) of backscattered ultraviolet (BUV) data over the Pacific Ocean. Both the cloud and the optical thickness are derived from the 380 nm channel by assuming that the entire IFOV (200 km) is filled by stratiform clouds. The analysis shows a large variability in the cloud reflectance in both the intertropic conversion zone (ITCZ) and the high latitudes. It is also found that for 90 percent of the time in the tropics, the clouds have an optical thickness of less than 10. An analysis of clouds with optical thickness between 10 and 20 shows that in the tropics the minimum frequency coincides with the dry zone at 2.5 deg S and the maximum frequency for clouds of optical thickness 10-20 is greater in summer than in winter and irrespective of the season; 50 percent of the time the clouds have an optical thickness less than 13.

Ahmad, Z.↗

NASA NTRS1987

Evaluation of surface energy and radiation balance systems on the Konza Prairie

Four Surface Energy and Radiation Balance Systems (SERBS) were installed and operated for two weeks in Kansas during July of 1986. Surface energy and radiation balances were investigated on six sites on the Konza Prairie about 3 km south of Manhattan, Kansas. Measurements were made to allow the computation of these radiation components: total solar and diffuse radiation, reflected solar radiation, net radiation, and longwave radiation upward and downward. Measurements were made to allow the computation of the sensible and latent heat fluxes by the Bowen ratio method using differential psychrometers on automatic exchange mechanisms. The report includes a description of the experimental sites, data acquisition systems and sensors, data acquisitions system operating instructions, and software used for data acquisition and analysis. In addition, data listings and plots of the energy balance components for all days and systems are given.

Fritschen, Leo J.↗

NASA NTRS1969

Research and education in management of large- scale technical programs. Appendix A - Uses and misuses of computers in urban affairs. Appendix B - Build, a community development simulation game. Appendix C - Urban simulation and gaming, preliminary experience and perspectives. Appendix D - Public attitudes toward programs of large- scale technological change, some reflections and policy prescriptions Semiannual progress report

Research and education in management of large scale technical programs - computers in urban affairs

Orlando, J. A.↗

NASA NTRS2006

Loci-STREAM Version 0.9

Loci-STREAM is an evolving computational fluid dynamics (CFD) software tool for simulating possibly chemically reacting, possibly unsteady flows in diverse settings, including rocket engines, turbomachines, oil refineries, etc. Loci-STREAM implements a pressure- based flow-solving algorithm that utilizes unstructured grids. (The benefit of low memory usage by pressure-based algorithms is well recognized by experts in the field.) The algorithm is robust for flows at all speeds from zero to hypersonic. The flexibility of arbitrary polyhedral grids enables accurate, efficient simulation of flows in complex geometries, including those of plume-impingement problems. The present version - Loci-STREAM version 0.9 - includes an interface with the Portable, Extensible Toolkit for Scientific Computation (PETSc) library for access to enhanced linear-equation-solving programs therein that accelerate convergence toward a solution. The name "Loci" reflects the creation of this software within the Loci computational framework, which was developed at Mississippi State University for the primary purpose of simplifying the writing of complex multidisciplinary application programs to run in distributed-memory computing environments including clusters of personal computers. Loci has been designed to relieve application programmers of the details of programming for distributed-memory computers.

Wright, Jeffrey↗

NASA NTRS1991

A computer graphics based model for scattering from objects of arbitrary shapes in the optical region

A computer-graphics-based model, named DIANA, is presented for generation of objects of arbitrary shape and for calculating bidirectional reflectances and scattering from them, in the visible and infrared region. The computer generation is based on a modified Lindenmayer system approach which makes it possible to generate objects of arbitrary shapes and to simulate their growth, dynamics, and movement. Rendering techniques are used to display an object on a computer screen with appropriate shading and shadowing and to calculate the scattering and reflectance from the object. The technique is illustrated with scattering from canopies of simulated corn plants.

Goel, Narendra S.↗

NASA NTRS1980

Measuring coal deposits by radar

Front-surface, local-oscillator radar directly compares frequency of signals reflected from front and back surfaces of coal deposits. Thickness is measured directly as frequency difference. Transmitter is frequency modulated, so thickness is computed directly from frequency difference. Because front and back reflections are detected in combination rather than separately, masking of comparatively weak back signal is less problem. Also system is not sensitive to extraneous reflections from targets between transmitting antenna and coal surface.

Barr, T. A.↗

NASA NTRS1979

Evaluation of SLAR and thematic mapper MSS data for forest cover mapping using computer-aided analysis techniques

The spatial characteristics of the data were evaluated. A program was developed to reduce the spatial distortions resulting from variable viewing distance, and geometrically adjusted data sets were generated. The potential need for some level of radiometric adjustment was evidenced by an along track band of high reflectance across different cover types in the Varian imagery. A multiple regression analysis was employed to explore the viewing angle effect on measured reflectance. Areas in the data set which appeared to have no across track stratification of cover type were identified. A program was developed which computed the average reflectance by column for each channel, over all of the scan lines in the designated areas. A regression analysis was then run using the first, second, and third degree polynomials, for each channel. An atmospheric effect as a component of the viewing angle source of variance is discussed. Cover type maps were completed and training and test field selection was initiated.

Hoffer, R. M.↗

NASA NTRS1976

Table and Charts of Equilibrium Normal-shock Properties for Pure Hydrogen with Velocities to 70 km/sec. Revised.

Errors found in the original edition are corrected. Refinement was made in procedures for solving the conservation relations for an incident (moving), standing, and reflected normal shock, as well as in computational methods for determining thermochemical-equilibrium hydrogen properties. A six-species hydrogen model replaces the original four-species model, and the heat of formation and spectroscopic constants used in this six-species model are listed in appendix A. In appendix B, comparisons are made between a number of methods for determining equilibrium thermodynamic properties for hydrogen for several values of pressure and temperatures to 50000 K. A comparison is also performed between the present method and a second method for determining thermodynamic properties and flow velocity behind an incident shock into pure hydrogen and behind a reflected shock.

Miller, C. G., III↗

NASA NTRS1974

Light scattering in planetary atmospheres

This paper reviews scattering theory required for analysis of light reflected by planetary atmospheres. Section 1 defines the radiative quantities which are observed. Section 2 demonstrates the dependence of single-scattered radiation on the physical properties of the scatterers. Section 3 describes several methods to compute the effects of multiple scattering on the reflected light.

Hansen, J. E.↗

NASA NTRS2001

Computational Aeroacoustics by the Space-time CE/SE Method

In recent years, a new numerical methodology for conservation laws-the Space-Time Conservation Element and Solution Element Method (CE/SE), was developed by Dr. Chang of NASA Glenn Research Center and collaborators. In nature, the new method may be categorized as a finite volume method, where the conservation element (CE) is equivalent to a finite control volume (or cell) and the solution element (SE) can be understood as the cell interface. However, due to its rigorous treatment of the fluxes and geometry, it is different from the existing schemes. The CE/SE scheme features: (1) space and time treated on the same footing, the integral equations of conservation laws are solve( for with second order accuracy, (2) high resolution, low dispersion and low dissipation, (3) novel, truly multi-dimensional, simple but effective non-reflecting boundary condition, (4) effortless implementation of computation, no numerical fix or parameter choice is needed, an( (5) robust enough to cover a wide spectrum of compressible flow: from weak linear acoustic waves to strong, discontinuous waves (shocks) appropriate for linear and nonlinear aeroacoustics. Currently, the CE/SE scheme has been developed to such a stage that a 3-13 unstructured CE/SE Navier-Stokes solver is already available. However, in the present paper, as a general introduction to the CE/SE method, only the 2-D unstructured Euler CE/SE solver is chosen as a prototype and is sketched in Section 2. Then applications of the CE/SE scheme to linear, nonlinear aeroacoustics and airframe noise are depicted in Sections 3, 4, and 5 respectively to demonstrate its robustness and capability.

Loh, Ching Y.↗

NASA NTRS1986

Calibration of NOAA-7 AVHRR, GOES-5 and GOES-6 VISSR/VAS solar channels

The NOAA-7, GOES-5 and GOES-6 Visible Infrared Spin Scan Radiometer/Vertical Atmospheric Sounder (VISSR/VAS) solar channels were calibrated. The White Sands Monument area in New Mexico, whose reflectance properties are well known, and space are used as calibration targets. The shortwave reflected terrestrial irradiance that is measured at satellite altitude is computed using a fairly accurate radiative transfer model which accounts for multiple scattering and bidirectional effects. The ground target reflectance and relevant characteristics of the overlying atmosphere are estimated from climatological data and observation at the nearest meteorological sites. The approach is believed to produce accuracies of 8 to 13% depending on the channel considered.

Frouin, R.↗

NASA NTRS1987

Calibration of NOAA-7 AVHRR, GOES-5, and GOES-6 VISSR/VAS solar channels

Frouin, Robert↗

NASA NTRS2004

Numerical Simulation of the Oscillations in a Mixer: An Internal Aeroacoustic Feedback System

The space-time conservation element and solution element method is employed to numerically study the acoustic feedback system in a high temperature, high speed wind tunnel mixer. The computation captures the self-sustained feedback loop between reflecting Mach waves and the shear layer. This feedback loop results in violent instabilities that are suspected of causing damage to some tunnel components. The computed frequency is in good agreement with the available experimental data. The physical phenomena are explained based on the numerical results.

Jorgenson, Philip C. E.↗