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Results for “RADIATION FIELD”

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 145 records · Page 8
All sourcesNASA NTRSDOE OSTI
NASA NTRS1974

Means for mapping radiated fields and for measuring differential movement of antenna elements

Null seeking system uses two transponders located at selected points on dish to detect phase-front of received signal. One signal line has continuously variable phase shifter driven by reversible stepmotor. Each of two transponders on dish is a dipole with mixer crystal between elements. Crystal is driven, in turn, by 181.6MHz signal carried by miniature coaxial cable.

Lundy, C. C.↗
NASA NTRS1973

On the dependence of the two-level source function on its radiation field.

The consequences of the universally made assumption that the stimulated emission profile is identical to the absorption profile are quantitatively investigated for a two-level atom with Doppler redistribution. The nonlinear terms arising in the source function are evaluated iteratively. We find that the magnitude of the effects is probably completely negligible for visible and UV solar lines.

Steinitz, R.↗
NASA NTRS1975

Radiation field wave forms produced by lightning stepped leaders

Broadband electric field data are presented which show stepped leader wave forms preceding records of distant lightning return strokes. The majority of leader pulses are characterized by a large initial peak with a small and slow opposite overshoot. Total pulse durations range from 15-40 microsec several milliseconds before the return stroke to 2-10 microsec immediately preceding the return stroke. Close to the ground the stepped leader pulses occur at regular 10- to 20-microsec intervals and are almost unipolar with rise times of about 1 microsec and full widths at half maximum in the range from 1 to 3 microsec. The ratio of the peak of the last leader pulse to the subsequent return stroke peak is typically 0.1, which suggests a peak step current near the ground of about 10% of the return stroke peak current.

Krider, E. P.↗
NASA NTRS1975

Regular radiation field pulses produced by intracloud lightning discharges

Sequences or bursts of uniform pulses have been recorded during a large fraction of intracloud lightning discharges in Florida and Arizona. The wave form of a typical pulse begins with a fast large-amplitude portion followed by a small and slowly varying overshoot. The full width and half maximum of the large amplitude peak is typically 0.75 microsec, and the time intervals between pulses are typically 5 microsec in both maritime and continental storms. The pulse shapes and interval times suggest that the source of these pulses in an intracloud dart-stepped leader process similar to that which has been photographed in discharges to ground.

Krider, E. P.↗
NASA NTRS1976

Efficient detection, analysis and classification of lightning radiation fields

Modeling the large scale lightning flash structure is considered. Large scale flash data has been measured from strip charts of storms of August 5, August 26, and September 12, 1975. The data is being processed by a computer program called SASEV to estimate the large scale flash statistics. The program, experimental results, and conclusions for the large scale flash structure are described. The progress made in examining the internal flash structure consists mainly of developing the software required to process the NASA digital tape data. A FORTRAN program has been written for the statistical analysis of series of events. The statistics computed and tests performed are found to be particularly useful in the analysis of lightning data.

Harger, R. O.↗
NASA NTRS1978

Far-field radiation patterns of aperture antennas by the Winograd Fourier transform algorithm

A more time-efficient algorithm for computing the discrete Fourier transform, the Winograd Fourier transform (WFT), is described. The WFT algorithm is compared with other transform algorithms. Results indicate that the WFT algorithm in antenna analysis appears to be a very successful application. Significant savings in cpu time will improve the computer turn around time and circumvent the need to resort to weekend runs.

Heisler, R.↗
NASA NTRS1979

The 63 micron radiation field in the earth's thermosphere and its influence on the atomic hydrogen temperature

The thermal escape of hydrogen from the earth's atmosphere is strongly affected by its temperature at the exobase. It has been suggested recently that the hydrogen temperature might be significantly lower than the thermospheric temperature as a result of a collisional exchange of energy with atomic oxygen. The tendency is to cool the hydrogen since the energy of the excited 3P1 level of oxygen can be lost from the atmosphere via magnetic dipole emission of the micron line (3P2-3P1). A detailed calculation of the net cooling effect as a function of altitude throughout the thermosphere is presented. The calculations have been performed for both day and night conditions and for periods of maximum and minimum solar activity conditions. It is found that its effect on Delta T/T varies from a very small value to a maximum of about 3%. The theoretical framework for describing deviations of the 63 micron emission from local thermodynamic equilibrium is given and it is shown that these effects can cause the emission to be reduced by as much as 40% near 500 km.

Durrance, S. T.↗
NASA NTRS1980

Submicrosecond risetimes in lightning radiation fields

Measurements of lightning electric fields, E, and dE/dt signatures were made near Tampa Bay, Florida, under conditions where the field propagation from the source to the detector was entirely over sea water. The fast transitions found on the initial portion of return stroke E waveforms have 10 to 90 percent risetimes ranging from 40 to 200 nsec, with a mean of 90 nsec. The maximum dE/dt values during these transitions range from 5 to 80 (V/m)microsec, with a mean of about 30 (V/m)microsec when normalized to a distance of 100 km. The initial risetimes of stepped-leader impulses that occur just prior to the first return stroke in cloud-to-ground flashes are very similar to the fast transitions in return strokes. The dE/dt values during leader steps range from 10 to 40 (V/m)/microsec with a mean of 20 (V/m)/microsec when normalized to 100 km. The fast impulses superimposed on large-amplitude intracloud waveforms have E risetimes and dE/dt values similar to those of the leader steps.

Weidman, C. D.↗