Surface radiation properties from electromagnetic theory.
Electromagnetic theory of surface radiation properties, analyzing specular reflectance of optically smooth surfaces
Hering, R. G.↗
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Light Scattering By Nonspherical Particles: Current Status and Challenging Issues
Quantitative analyses of remote sensing measurements of aerosols, clouds, precipitation, and particulate surfaces as well as computations of the Earth's radiation balance require detailed understanding of the interaction of small particles with light and other electromagnetic radiation. The convenient availability of the Lorenz-Mie theory has led to a widespread practice of treating all particles as if they were spheres. However, many natural and anthropogenic particles have nonspherical shapes, and the accumulated knowledge suggests that their scattering and radiative properties can be dramatically different from those of equivalent spheres. This presentation will summarize the recent significant progress achieved in the area of electromagnetic scattering by nonspherical particles and outline major problems that still await solution. The talk will cover the following specific topics: (1) comparison of most widely used exact and approximate theoretical techniques; (2) outline of laboratory and field measurement techniques; (3) compare theory and experiment; (4) need for a statistical approach in dealing with natural particles; (5) remote sensing and radiative transfer applications; and (6) major unsolved problems.
Mishchenko, Michael↗
Dielectric properties of battery electrolytes
An effort was made to determine the effects of electromagnetic radiation on the terminal properties of electrochemical cells. Various constituents of the battery were measured to determine basic electromagnetic properties. These properties were used to predict how much radiation would be absorbed by a battery in a particular field configuration. The frequency range covered from 0 to 40 GHz with the greatest emphasis on the microwave range from 2.6 to 40 GHz. The measurements were made on NiCd, AgZn, and Pb acid cells. Results from observation show nothing which suggested any interaction between radiation and cells, and no incidence of any peaks of energy absorption was observed.
Source record↗
Review of measurements of the RF spectrum of radiation from lightning
A review is presented of the measurements reported in the literature of the spectrum of electromagnetic radiation from lightning in the frequency range from 1 kHz to 1 GHz. Measurements have been made either by monitoring the power received at individual frequencies using a narrow bandwidth recording device tuned to the frequencies under investigation or by recording the transient (time dependent) radiation with a wide bandwidth device and then Fourier transforming the waveform to obtain a spectrum. Measurements of the first type were made extensively in the 1950’s and 1960’s and several composite spectra have been deduced by normalizing the data of different investigators to common units of bandwidth and distance. The composite spectra tend to peak near 5 kHz and then decrease roughly as (frequency).’ upto nearly 100 MHz where scatter in the data make the behaviour uncertain. Measurements of the second type have been reported for return strokes, the stepped leader and for some intracloud processes. The spectrum of first return strokes obtained in this manner is very similar to the composite spectra obtained from the narrowband measurements.
Lightning Spectrum↗
Review of measurements of the RF spectrum of radiation from lightning
A review is presented of the measurements reported in the literature of the spectrum of electromagnetic radiation from lightning in the frequency range from 1 kHz to 1 GHz. Measurements have been made either by monitoring the power received at individual frequencies using a narrow bandwidth recording device or by recording the transient (time dependent) radiation with a wide bandwidth device and then Fourier transforming the waveform to obtain a spectrum. Measurements of the first type were made extensively in the 1950's and 1960's and several composite spectra have been deduced by normalizing the data of different investigators to common units of bandwidth and distance. The composite spectra tend to peak near 5 kHz and then decrease roughly as 1/(frequency) up to nearly 100 MHz where scatter in the data make the behaviour uncertain. The spectrum obtained with measurements of the second type is similar. Recent experiments have extended the frequency range covered to several 10's of MHz and include spectra for return strokes, the stepped leader and for some intracloud processes. The spectrum of first return strokes obtained in this manner is very similar to the spectrum of the composite flash obtained from the narrowband measurements.
Radiation↗
Development of a proposed international standard for certification of aircraft to High Intensity Radiated Fields (HIRF)
Avionic systems performing critical functions in modern aircraft are potentially susceptible to the hazards of electromagnetic radiation from ground and airborne transmitters. The Federal Aviation Administration (FAA) requested that the Society of Automotive Engineers (SAE) coordinate the development of procedures and guidance material which can be used during the aircraft certification process to ensure adequate protection against high intensity radiated fields (HIRF). This paper addresses both the technical challenge of drafting a certification procedure and guidance standard as well as the management process used by the SAE subcommittee AE4R to converge a diverse range of opinions by its international membership in the shortest possible time.
Sargent, Noel B.↗
Indium Tin Oxide-Magnesium Fluoride Co-Deposited Films for Spacecraft Applications
Highly transparent coatings with a maximum sheet resistivity between 10(exp 8) and 10(exp 9) ohms/square are desired to prevent charging of solar arrays for low Earth polar orbit and geosynchronous orbit missions. Indium tin oxide (ITO) and magnesium fluoride (MgF2) were ion beam sputter co-deposited onto fused silica substrates and were evaluated for transmittance, sheet resistivity and the effects of simulated space environments including atomic oxygen (AO) and vacuum ultraviolet (VUV) radiation. Optical properties and sheet resistivity as a function of MgF2 content in the films will be presented. Films containing 8.4 wt.% MgF2 were found to be highly transparent and provided sheet resistivity in the required range. These films maintained a high transmittance upon exposure to AO and to VUV radiation, although exposure to AO in the presence of charged species and intense electromagnetic radiation caused significant degradation in film transmittance. Sheet resistivity of the as-fabricated films increased with time in ambient conditions. Vacuum beat treatment following film deposition caused a reduction in sheet resistivity. However, following vacuum heat treatment, sheet resistivity values remained stable during storage in ambient conditions.
Dever, Joycer A.↗
Terrestrial Sources of X-Ray Radiation and Their Effects on NASA Flight Hardware
X-rays are an energetic and penetrating form of ionizing electromagnetic radiation, which can degrade NASA flight hardware. The main concern posed by such radiation is degradation of active electronic devices and, in some cases, diodes. Non-electronic components are only damaged at doses that far exceed the point where any electronic device would be destroyed. For the purposes of this document, flight hardware can be taken to mean an entire instrument, the flight electronics within the instrument or the individual microelectronic devices in the flight electronics. This document will discuss and describe the ways in which NASA flight hardware might be exposed to x-rays, what is and isn't a concern, and how to tell the difference. First, we must understand what components in flight hardware may be vulnerable to degradation or failure as a result of being exposed to ionizing radiation, such as x-rays. As stated above, bulk materials (structural metals, plastics, etc.) are generally only affected by ionizing radiation at very high dose levels. Likewise, passive electronic components (e.g. resistors, capacitors, most diodes) are strongly resistant to exposure to x-rays, except at very high doses. The main concerns arise when active components, that is, components like discrete transistors and microelectronic devices, are exposed to ionizing radiation. Active components are designed to respond to minute changes in currents and voltages in the circuit. As such, it is not surprising that exposure to ionizing radiation, which creates ionized and therefore electrically active particles, may degrade the way the hardware performs. For the most part, the mechanism for this degradation is trapping of the charges generated by ionizing radiation by defects in dielectric materials in the hardware. As such, the degree of damage is a function of both the quantity of ionizing radiation exposure and the physical characteristics of the hardware itself. The metric that describes the level of exposure to ionizing radiation is total ionizing dose (TID). The unit of TID is the rad, which is defined as 100 ergs absorbed per gram of material. Dose can be expressed in other units, for example grays (gy), where 1 gy = 100 rads. The actual fluence of radiation needed to deliver a rad depends on the absorbing material, so units of dose are usually stated in reference to the material of interest. That is, for microelectronic devices, the unit of dose is generally rad (Si) or rad (SiO2). However, the definition of absorbed dose in this fashion has the advantage that the type of radiation causing the ionization can be normalized so that a realistic and adequate comparison can be made. The sensitivity of microelectronic parts to TID varies over many orders of magnitude. (Note: Doses to humans are typically expressed in rems-or roentgen-equivalent-man-which measures tissue damage, and depends on the type of radiation, as well as the dose in rads.) Thus far, the "softest" parts tested at NASA showed damage at 500 rads (Si), while parts that are radiation-hardened by design can remain functional to doses on the order of 107 rads (Si). This broad range of sensitivity highlights one of the most important considerations when considering the effects of radiation on electronic parts: In order to determine whether a radiation exposure is a concern for a particular part, one must understand the technologies used in the part and their vulnerabilities to TID damage. A NASA radiation expert should be consulted to obtain such information.
X-ray↗
Primordial gravitational waves and the blackbody radiation anisotropy
If relict gravitational waves deriving from a chaotic initial singularity contain a nonisotropic component, then this radiation can produce a frame dragging; effect which will induce a dipole anisotropy in the observed temperature distribution of the 3 K electromagnetic radiation background. The measured dipole and quadrupole distributions of the electromagnetic background can thus be used to bound the effective wave parameters of the nonisotropic part of the gravitational background. Using available data, the dimensionless amplitude of this nonisotropic part is found to be less than 0.0005 for wavelengths less than the Hubble radius. The effective energy density of this nonisotropic component of the gravitational radiation background is less than 2 x 10 to the -8th times the critical density.
Adams, P. J.↗
Observed beaming of terrestrial myriametric radiation
Observations by the Dynamics Explorer 1 satellite are discussed which validate the theory that terrestrial myriametric radiation (TMR) is produced by the linear conversion of electrostatic upper hybrid waves to electromagnetic radiation via a radio window. A remote sensing technique based on the theory is used to investigate the location and characteristics of the source region. Finally, the location of the TMR source region is demonstrated by direct measurement.
Jones, Dyfrig↗
The interaction with the lower ionosphere of electromagnetic pulses from lightning: Excitation of optical emissions
A self consistent and fully kinetic simulation of the interaction of lightning radiated electromagnetic (EM) pulses with the nighttime lower ionosphere indicates that optical emissions observable with conventional instruments would be excited. For example, emissions of the 1st and 2nd positive bands of N2 occur at rates reaching 7 x 10(exp 7) and 10(exp 7) cu cm/s respectively at 92 km altitude for a lightning discharge with an electric field E(sub 100) = 20 V/m (normalized to a 100 km distance). The maximum height integrated intensities of these emissions are 4 x 10(exp 7) and 6 x 10(exp 6) R respectively, lasting for approx. 50 micrometers.
Taranenko, Y. N.↗
Cyclotron maser radiation from a source structure localized perpendicular to the ambient magnetic field
Particle simulations were used to investigate the properties of electromagnetic radiation produced by the cyclotron maser instability in a source region which is localized in the direction perpendicular to the uniform magnetic field. In the procedure used, the simulation model of Pritchett and Strangeway (1985) for the generation of auroral kilometric radiation (AKR) along an auroral field line was modified to include inhomogeneities perpendicular to the magnetic field. The results are compared with the previous homogeneous simulations with regard to efficiency and saturation mechanism and with expectations based on the feedback model. The implications for the generation and propagation of AKR are discussed.
Pritchett, P. L.↗
An investigation of the thermal shock resistance of lunar regolith and the recovery of hydrogen from lunar soil heated using microwave radiation
The objective is to develop a better understanding of the thermal shock properties of lunar regolith sintered using 2.45 GHz electromagnetic radiation and to do a preliminary study into the recovery of bound hydrogen in lunar soil heated using 2.45 GHz radiation. During the first phase of this work, lunar simulant material was used to test whether or not microhardness data could be used to infer thermal shock resistance and later actual lunar regolith was used. Results are included on the lunar regolith since this is of primary concern and not the simulant results. They were similar, however. The second phase investigated the recovery of hydrogen from lunar regolith and results indicate that microwave heating of lunar regolith may be a good method for recovery of bound gases in the regolith.
Meek, T. T.↗
A computer program to evaluate optical systems
A computer program is used to evaluate a 25.4 cm X-ray telescope at a field angle of 20 minutes of arc by geometrical analysis. The object is regarded as a point source of electromagnetic radiation, and the optical surfaces are treated as boundary conditions in the solution of the electromagnetic wave propagation equation. The electric field distribution is then determined in the region of the image and the intensity distribution inferred. A comparison of wave analysis results and photographs taken through the telescope shows excellent agreement.
Innes, D.↗
Non-equilibrium radiation nuclear reactor
An externally moderated thermal nuclear reactor is disclosed which is designed to provide output power in the form of electromagnetic radiation. The reactor is a gaseous fueled nuclear cavity reactor device which can operate over wide ranges of temperature and pressure, and which includes the capability of processing and recycling waste products such as long-lived transuranium actinides. The primary output of the device may be in the form of coherent radiation, so that the reactor may be utilized as a self-critical nuclear pumped laser.
Thom, K.↗
Synchrotron radiation with radiation reaction
A rigorous discussion is presented of the classical motion of a relativistic electron in a magnetic field and the resulting electromagnetic radiation when radiation reaction is important. In particular, for an electron injected with initial energy gamma(0), a systematic perturbative solution to the Lorentz-Dirac equation of motion is developed for field strengths satisfying gamma(0) B much less than 6 x 10 to the 15th G. A particularly accurate solution to the electron orbital motion in this regime is found and it is demonstrated how lowest-order corrections can be calculated. It is shown that the total energy-loss rate corresponds to what would be found using the exact Larmor power formula without including radiation reaction. Provided that the particle energy and field strength satisfy the same contraint, it is explicitly demonstrated that the intuitive prescription for calculating the time-integrated radiation spectrum described above is correct.
Nelson, Robert W.↗
Leaf light reflectance, transmittance, absorptance, and optical and geometrical parameters for eleven plant genera with different leaf mesophyll arrangements.
Review of research on radiation interactions within plant canopies and communities and interactions of various leaf structures (mesophyll arrangements) with electromagnetic radiation involved in the interpretation of data sensed from air or spacecraft. The hypothesis underlying the research reported is that leaf mesophyll arrangements influence spectral energy measurements of leaves.
Gausman, H. W.↗
An analysis of space environment effects on performance and missions of a Solar Electric Propulsion Stage (SEPS)
The development of an analysis which addresses the problems of degrading space environmental effects on the performance and missions of a Solar Electric Propulsion Stage (SEPS) is reported. A detailed study concerning the degrading effects of the Van Allen Belt charged-particle radiation on specific spacecraft subsystems is included, along with some of the thermal problems caused by electromagnetic radiation from the sun. The analytical methods used require the integration of two distinct analyses. The first, is a low-thrust trajectory analysis which uses analytical approximations to optimum steering for orbit raising, including three-dimensional plane change cases. The second is the conversion of the Vette time-averaged differential energy spectra for protons and electrons into a 1-MeV electron equivalent environment as a function of spatial position and thickness of various shielding materials and solar-cell cover slides.
Mcglathery, D. M.↗