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Results for “ELECTROMAGNETIC MEASUREMENT”

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 343 records · Page 19

Mobile Instruments Measure Atmospheric Pollutants

As a part of NASA's active research of the Earth s atmosphere, which has included missions such as the Atmospheric Laboratory of Applications and Science (ATLAS, launched in 1992) and the Total Ozone Mapping Spectrometer (TOMS, launched on the Earth Probe satellite in 1996), the Agency also performs ground-based air pollution research. The ability to measure trace amounts of airborne pollutants precisely and quickly is important for determining natural patterns and human effects on global warming and air pollution, but until recent advances in field-grade spectroscopic instrumentation, this rapid, accurate data collection was limited and extremely difficult. In order to understand causes of climate change and airborne pollution, NASA has supported the development of compact, low power, rapid response instruments operating in the mid-infrared "molecular fingerprint" portion of the electromagnetic spectrum. These instruments, which measure atmospheric trace gases and airborne particles, can be deployed in mobile laboratories - customized ground vehicles, typically - to map distributions of pollutants in real time. The instruments must be rugged enough to operate rapidly and accurately, despite frequent jostling that can misalign, damage, or disconnect sensitive components. By measuring quickly while moving through an environment, a mobile laboratory can correlate data and geographic points, revealing patterns in the environment s pollutants. Rapid pollutant measurements also enable direct determination of pollutant sources and sinks (mechanisms that remove greenhouse gases and pollutants), providing information critical to understanding and managing atmospheric greenhouse gas and air pollutant concentrations.

Source record↗

Experimental measurement and theoretical modeling of microwave scattering and the structure of the sea surface influencing radar observations from space

The electromagnetic bias is an error present in radar altimetry of the ocean due to the non-uniform reflection from wave troughs and crests. A study of the electromagnetic bias became necessary to permit error reduction in mean sea level measurements of satellite radar altimeters. Satellite radar altimeters have been used to find the upper and lower bounds for the electromagnetic bias. This report will present a theory using physical optics scattering and an empirical model of the short wave modulation to predict the electromagnetic bias. The predicted electromagnetic bias will be compared to measurements at C and Ku bands.

Arnold, David↗

Current driven instabilities of an electromagnetically accelerated plasma

A plasma instability that strongly influences the efficiency and lifetime of electromagnetic plasma accelerators was quantitatively measured. Experimental measurements of dispersion relations (wave phase velocities), spatial growth rates, and stability boundaries are reported. The measured critical wave parameters are in excellent agreement with theoretical instability boundary predictions. The instability is current driven and affects a wide spectrum of longitudinal (electrostatic) oscillations. Current driven instabilities, which are intrinsic to the high-current-carrying magnetized plasma of the magnetoplasmadynmic (MPD) accelerator, were investigated with a kinetic theoretical model based on first principles. Analytical limits of the appropriate dispersion relation yield unstable ion acoustic waves for T(i)/T(e) much less than 1 and electron acoustic waves for T(i)/T(e) much greater than 1. The resulting set of nonlinear equations for the case of T(i)/T(e) = 1, of most interest to the MPD thruster Plasma Wave Experiment, was numerically solved to yield a multiparameter set of stability boundaries. Under certain conditions, marginally stable waves traveling almost perpendicular to the magnetic field would travel at a velocity equal to that of the electron current. Such waves were termed current waves. Unstable current waves near the upper stability boundary were observed experimentally and are in accordance with theoretical predictions. This provides unambiguous proof of the existence of such instabilites in electromagnetic plasma accelerators.

Chouetri, E. Y.↗

Hoop/column and tetrahedral truss electromagnetic tests

The distortion of antennas was measured with a metric camera system at discrete target locations on the surface. Given are surface distortion for hoop column reflector antennas, for tetrahedral truss reflector antennas, and distortion contours for the tetrahedral truss reflector. Radiation patterns at 2.27-GHz, 4.26-GHz, 7.73-GHz and 11.6-GHz are given for the hoop column antenna. Also given are radiation patterns at 4.26-GHz and 7.73-GHz for the tetrahedral truss antenna.

Bailey, M. C.↗

Spacecraft charging at high altitudes - The SCATHA satellite program

Satellites at synchronous altitude exhibit unexplained behavior in the operation of electronic circuits and in the performance of thermal controls. A possible explanation for this behavior is the fact that satellites can be charged to large negative voltages by energetic electrons in the space environment. A space measurements program entitled SCATHA has been formulated to determine the characteristics of the charging process, to measure the response of the satellite when charging occurs, and to evaluate the utility of various corrective techniques which can minimize differential charging on the satellite. The instrumentation will measure charging levels and rates of twenty samples of satellite materials, some of which will be modified to prevent buildup of electrostatic charge. The electromagnetic interference background on the satellite will be measured for comparison with MIL STD 461, Electromagnetic Interference Characteristics Requirements for Equipment.

Mcpherson, D. A.↗

The Inner Structure of Collisionless Magnetic Reconnection: The Electron-Frame Dissipation Measure and Hall Fields

It was recently proposed that the electron-frame dissipation measure, the energy transfer from the electromagnetic field to plasmas in the electron s rest frame, identifies the dissipation region of collisionless magnetic reconnection [Zenitani et al., Phys. Rev. Lett. 106, 195003 (2011)]. The measure is further applied to the electron-scale structures of antiparallel reconnection, by using two-dimensional particle-in-cell simulations. The size of the central dissipation region is controlled by the electron-ion mass ratio, suggesting that electron physics is essential. A narrow electron jet extends along the outflow direction until it reaches an electron shock. The jet region appears to be anti-dissipative. At the shock, electron heating is relevant to a magnetic cavity signature. The results are summarized to a unified picture of the single dissipation region in a Hall magnetic geometry.

Zenitani, Seiji↗

Ionizing radiation

The penetrating ionizing space radiations are found to be extremely diverse in the energy range of both their particulate and their electromagnetic components. Radiation terms and measures and ionizing radiation classes and sources are presented. Whole body radiation effects are examined, including radiation intensity and rate effectiveness factors. Radiation effects on specific body systems, such as blood, skin, visual, and reproductive systems are also discussed.

Warren, S.↗

Remote sensing of the atmosphere from environmental satellites

The paper outlines the basis of remote sensing in satellite meteorology, the evolution of remote sensors, examples of practical applications, and a prospectus of future developments. The meteorological satellites use instrumentation sensitive to different regions of the electromagnetic spectrum to observe and measure atmospheric and surface properties. In the ultraviolet, solar variability is measured and total atmospheric ozone determined. In the visible, imagery of cloud systems provides better location of storms in data-sparse areas, observes ice and snow boundaries, and monitors floods. Capabilities of microwave imagery are discussed along with successful uses of geosynchronous satellites. Future environmental satellite programs are discussed in some detail, including GARP, TIROS-N and CLIMSAT.

Allison, L. J.↗

A Recoverable Plasma Diagnostics Package (RPDP) for Spacelab

The RPDP is a fully instrumented, ejectable and recoverable unit with flight and ground support systems so that it can be utilized attached to the orbiter remote manipulator system, tethered from the orbiter, or as an orbiter subsatellite. Core instruments on the RPDP are flight proven hardware which provide diagnostics measurements of energetic particles, AC electromagnetic and electrostatic waves, vector magnetic field signatures of current systems, vector electric field signatures associated with plasma flow and particle acceleration, thermal plasma ion composition and density, thermal plasma electron density and temperature, and images of optical emissions regions in UV or visible wavelengths.

Shawhan, S. D.↗

Some aspects of the identification of continuous vibrating systems

This paper deals with the identification of systems described by the one-dimensional, second order wave equation. Such equations arise commonly in various areas of mathematical physics, such as, acoustics, elastic wave propagation, and electromagnetic theory. Assuming that suitable measurements are made at only one point in the spatial domain, sufficient conditions for unique identification of the system eigenvalues and system coefficients are presented.

Udwadia, F. E.↗

Microwave Radiometric Studies of Composition and Structure

In the past decade the use of ground-based microwave radiometry has grown as a useful measurement technique. Microwave radiometry is the precise measurement of small amounts of electromagnetic radiation at quite short wavelengths (submillimeter to centimeter). Growth in this field was carefully nutured by the radio astronomy community. Future growth was also discussed.

Olivero, J. J.↗

Noncontacting Measurement of Shaft Angle

Fiber-optic transducer offers several advantages over mechanical linkages. Angular position of rotary valve measured by pair of optical-fiber deflectometers. Measurement device sensitive, immune to electromagnetic interference, and does not wear out since fibers do not make contact with valve. Device more rugged than linear or rotary variable-differential transformers it replaces.

Barkhoudarian, S.↗

Phoretic and Radiometric Force Measurements on Microparticles in Microgravity Conditions

Thermophoretic, diffusiophoretic and radiometric forces on microparticles are being measured over a wide range of gas phase and particle conditions using electrodynamic levitation of single particles to simulate microgravity conditions. The thermophoretic force, which arises when a particle exists in a gas having a temperature gradient, is measured by levitating an electrically charged particle between heated and cooled plates mounted in a vacuum chamber. The diffusiophoretic force arising from a concentration gradient in the gas phase is measured in a similar manner except that the heat exchangers are coated with liquids to establish a vapor concentration gradient. These phoretic forces and the radiation pressure force acting on a particle are measured directly in terms of the change in the dc field required to levitate the particle with and without the force applied. The apparatus developed for the research and the experimental techniques are discussed, and results obtained by thermophoresis experiments are presented. The determination of the momentum and energy accommodation coefficients associated with molecular collisions between gases molecules and particles and the measurement of the interaction between electromagnetic radiation and small particles are of particular interest.

Davis, E. James↗