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Imhof, W. L.

Publications and source records attributed to Imhof, W. L..

At least 37 records · Page 2
All sourcesNASA NTRSDOE OSTI
NASA NTRS1981

Effects of the August 1972 solar particle events on stratospheric ozone

High-energy proton data obtained by polar-orbiting satellite and several balloon flights are used to derive the spatial extent and ionization profiles of regions irradiated by the intense solar particle events (SPE) of August 1972. Backscattered ultraviolet ozone sensors on the Nimbus 4 satellite identified and tracked the polar ozone cavity created by particle ionization during the intense, ten-hour period of August 4, which persisted and rotated as a semirigid mass in an east-to-west direction during 53 days of continuous tracking. Time-dependent chemistry calculations have been performed to show the cause, magnitude, and temporal features of the ozone reduction. Attempts to verify the predicted temperature changes have been unsuccessful due to limitations in the temperature measurement techniques used.

Reagan, J. B.↗
NASA NTRS1979

Prediction of energetic particle disturbances

The prediction of fluxes of energetic particles of solar or magnetospheric origin is addressed. Topics include the prediction of the properties of the particle populations generated by magnetospheric storms and substorms, and the prediction of long term variations in the populations of magnetospheric particles.

Paulikas, G. A.↗
NASA NTRS1979

Short term magnetospheric particle variations (1 minute T 1 day), appendix 1

A schematic representation of the generation and propagation processes for energetic particles of concern in solar terrestrial predictions is given. Particle precipitation at low, mid, and high altitudes is discussed with emphasis on prediction techniques. Methods given for testing of such techniques include traditional collaborations, enhanced collaborations, simulated prediction schemes, and field tests.

Higbie, P. R.↗
NASA NTRS1978

High resolution spectroscopy from low altitude satellites

The P 78 1 satellite to be placed in a synchronous polar orbit at an altitude of 550-660 km will carry two identical high resolution spectrometers each consisting of a single (approximately 85 cc) intrinsic germanium IGE detector. The payload also includes a pair of phoswitch scintillators, an array of CdTe detectors and several particle detectors, all of which are mounted on the wheel of the satellite. The intrinsic high purity IGE detectors receive cooling from two Stirling cycle refrigerators and facilitate the assembly of large and complex detector arrays planned for the next generation of high sensitivity instruments such as those planned for the gamma ray observatory. The major subsystems of the spectrometer are discussed as well as its capabilities.

Nakano, G. H.↗
NASA NTRS1977

Fine energy resolution survey of the sky with a germanium gamma-ray spectrometer

A fine-energy-resolution survey (38 to 2700 keV) of the sky has been performed from a spinning polar-orbiting satellite with a cooled germanium spectrometer. The measurements, performed with a fast time resolution (32 ms), permit one to analyze the energy spectra from repeated noon-midnight orbits in selected portions of the local daytime or nighttime sky. During the initial period of the experiment, the sky was surveyed in two broad intervals spanning the galactic plane at longitudes of approximately 255 to 328 deg and 99 to 168 deg, respectively. In the former interval a significant increase in counting rate was observed when the spectrometer viewed the galactic plane. Locally generated backgrounds were removed from the galactic-plane spectrum by subtracting, on a spin-for-spin basis, the contribution measured at a viewing direction with a comparable declination north of the celestial equator. The net spectra from the galactic plane have been examined for evidence of gamma-ray lines. The possible presence of lines near 1121 and 1369 keV emitted from the galactic plane over the galactic longitudinal interval approximately 255 deg to approximately 328 deg is suggested by the data, but better statistics are needed to establish their existence firmly. Comparisons are made with previously reported extraterrestrial lines with assumed normalizations made for the different viewing directions in the two experiments.

Imhof, W. L.↗
NASA NTRS1977

The effects of the geosynchronous energetic particle radiation environment on spacecraft charging phenomena

The energetic electron environment at the geosynchronous orbit is responsible for a variety of adverse charging effects on spacecraft components. The most serious of these is the degradation and failure of a complementary-metal-oxide-semiconductor (CMOS) electronic components as a result of internal charge-buildup induced by the energetic electrons. Efforts to accurately determine the expected lifetime of these components in this orbit are hampered by the lack of detailed knowledge of the electron spectrum and intensity, particularly of the more penetrating energies greater than 1.5 MeV. This problem is illustrated through the calculation of the dose received by a CMOS device from the energetic electrons and associated bremsstrahlung as a function of aluminum shielding thickness using the NASA AE-6 and the Aerospace measured electron environments. Two computational codes which were found to be in good agreement were used to perform the calculations. For a given shielding thickness the dose received with the two radiation environments differ by as much as a factor of seven with a corresponding variation in lifetime of the CMOS.

Reagan, J. B.↗
NASA NTRS1977

Narrow spikes in the selective precipitation of relativistic electrons in mid-latitudes

Relativistic electron precipitation spikes were observed in the quasi-trapped population at midlatitudes by an array of electron detectors aboard the low-altitude polar-orbiting satellite 1972-076B. The fluxes of electrons of energies not less than 4 MeV may undergo pronounced enhancements, while the intensities of electrons in the few hundred keV range may not be significantly affected. Energy spectra and pitch angle distributions were measured over the energy range 160 keV to 2.4 MeV with a combination of three spectrometers. Fluxes of energetic electrons (greater than 4 MeV) were measured with high sensitivity in each of two large plastic scintillator anticoincidence counters surrounding a germanium spectrometer.

Imhof, W. L.↗
NASA NTRS1976

Analysis of high resolution satellite data for cosmic gamma ray bursts

Cosmic gamma ray bursts detected a germanium spectrometer on the low altitude satellite 1972-076B were surveyed. Several bursts with durations ranging from approximately 0.032 to 15 seconds were found and are tabulated. The frequency of occurrence/intensity distribution of these events was compared with the S to the -3/2 power curve of confirmed events. The longer duration events fall above the S to the -3/2 power curve of confirmed events, suggesting they are perhaps not all true cosmic gamma-ray bursts. The narrow duration events fall closely on the S to the -3/2 power curve. The survey also revealed several counting rate spikes, with durations comparable to confirmed gamma-ray bursts, which were shown to be of magnetospheric origin. Confirmation that energetic electrons were responsible for these bursts was achieved from analysis of all data from the complete payload of gamma-ray and energetic particle detectors on board the satellite. The analyses also revealed that the narrowness of the spikes was primarily spatial rather than temporal in character.

Imhof, W. L.↗
NASA NTRS1975

Direct satellite observations on bremsstrahlung radiation as a technique to investigate its role in meteorological processes

It was suggested that bremsstrahlung radiation associated with strong auroras (in turn associated with geomagnetic disturbances) may cause increased ionization near the 300-millibar level, which, in turn, leads to the formation of cirrus clouds. These clouds could modify the outgoing black body radiation rates and influence weather patterns. The first satellite observations on bremsstrahlung radiation produced in the atmosphere by precipitating energetic electrons are discussed. This type of observation affords the possibility of directly monitoring the bremsstrahlung energy input to the lower atmosphere over large segments of earth and at frequent intervals. Detailed measurements on the spatial and energy distributions of the bremsstrahlung radiation are feasible with present techniques, and satellite data on widespread bremsstrahlung events are presented and discussed. From comparison of the ion production rates from cosmic rays with those calculated from bremsstrahlung from precipitating energetic electrons, it is concluded that bremsstrahlung radiation is a negligible contributor to the ionization near the 300-millibar level.

Johnson, R. G.↗
NASA NTRS1974

Direct satellite observations on bremsstrahlung radiation as a technique to investigate its role in meteorological processes

Satellite observations on bremsstrahlung produced in the atmosphere by precipitating energetic electrons are reported. This type of observation affords the possibility of directly monitoring the bremsstrahlung energy input to the lower atmosphere over large segments of the earth and at frequent intervals. From comparison of the ion production rates from cosmic rays with those calculated for bremsstrahlung from precipitating energetic electrons, it is concluded that bremsstrahlung is a negligible contributor to the ionization near the 300-mb level.

Johnson, R. G.↗
NASA NTRS1973

Preliminary results from the first satellite of a high-resolution germanium gamma-ray spectrometer: Description of instrument, some activation lines encountered, and studies of the diffuse spectra

Gamma radiation from terrestrial and extraterrestrial sources were investigated with a high resolution Ge(Li) spectrometer-cryogen system flown onboard a low altitude, spin stabilized, polar orbiting satellite. A brief description is given of the instrument and preliminary results obtained from earth orbit are discussed. Attempts were made to use angular distributions and geomagnetic latitude spectral variations to determine diffuse background spectrum, detect gamma ray line emissions from solar flares, and search for positron annihilation radiation coming from the direction of the galactic center.

Nakano, G. H.↗
NASA NTRS1973

Preliminary results from the first satellite of a high-resolution germanium gamma-ray spectrometer: Backgrounds from electron bremsstrahlung and from electron-positron annihilation

Detailed data are presented on the bremsstrahlung backgrounds measured by a satellite-borne high resolution Ge(Li) gamma ray spectrometer. Two bremsstrahlung classes were discussed: (1) those arising from radiation belt electrons stopping in the vicinity of the spectrometer, and (2) bremsstrahlung produced by electrons precipitating into the earth's atmosphere.

Imhof, W. L.↗
NASA NTRS1969

Penetrating radiations

High energy electromagnetic radiation and energetic particles from sun, galaxies, and nuclear explosions in spacecraft environment

Gaines, E. E.↗