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At least 19 records
All sourcesNASA NTRSDOE OSTI
NASA NTRS1972

Differential phase measurements of D-region partial reflections

Differential phase partial reflection measurements were used to deduce D region electron density profiles. The phase difference was measured by taking sums and differences of amplitudes received on an array of crossed dipoles. The reflection model used was derived from Fresnel reflection theory. Seven profiles obtained over the period from 13 October 1971 to 5 November 1971 are presented, along with the results from simultaneous measurements of differential absorption. Some possible sources of error and error propagation are discussed. A collision frequency profile was deduced from the electron concentration calculated from differential phase and differential absorption.

Wiersma, D. J.↗
NASA NTRS1982

New advances in the partial-reflection-drifts experiment using microprocessors

Improvements to the partial reflection drifts experiment are completed. The results of the improvements include real time processing and simultaneous measurements of the D region with coherent scatter. Preliminary results indicate a positive correlation between drift velocities calculated by both methods during a two day interval. The possibility now exists for extended observations between partial reflection and coherent scatter. In addition, preliminary measurements could be performed between partial reflection and meteor radar to complete a comparison of methods used to determine velocities in the D region.

Ruggerio, R. L.↗
NASA NTRS1973

Analysis of partial-reflection data from the solar eclipse of 10 Jul. 1972

Partial-reflection data collected for the eclipse of July 10, 1972 as well as for July 9 and 11, 1972, are analyzed to determine eclipse effects on D-region electron densities. The partial-reflection experiment was set up to collect data using an on-line PDP-15 computer and DECtape storage. The electron-density profiles show good agreement with results from other eclipses. The partial-reflection programs were changed after the eclipse data collection to improve the operation of the partial-reflection system. These changes were mainly due to expanded computer hardware and have simplified the operations of the system considerably.

Bean, T. A.↗
NASA NTRS1974

An evaluation of the partial reflection technique and results from the winter 1971 - 1972 D region

Fundamental physical and chemical processes, and measurement techniques on the D region are reviewed. Design considerations about a partial-reflection system are made, and the main characteristics of the partial-reflection system at the University of Illinois are presented. The nature of the partial reflections is discussed, particularly reflections produced by gradients in electron density and by random fluctuations in a locally homogeneous random medium. Possible reasons for disagreement between partial reflections and rocket measurements are discussed. Some suggestions are made to improve partial-reflection data reduction, including the use of only maximums of the reflections and deconvolution of the data. The results of partial-reflection measurements at Wallops Island, Virginia during the 1971-1972 winter are presented and compared to rocket measurements.

Dasilva, L. C.↗
DOE OSTI2024

Modeling Partial Reflection Paths for Infrasound Analysis

Numerical methods enabling simulation of scattered and partially reflected infrasonic propagation paths produced by interaction with fine-scale structure in the middle atmosphere have been implemented in the infraGA ray tracing software. This capability enables simulation of ensonification in the classical stratospheric “shadow zone” that has been observed during the Humming Roadrunner and LSECE surface explosion campaigns as well as in other data sets. In the case of LSECE, a pair of stations roughly 140 kilometers east of the source location observed arrivals with celerities (horizontal group velocities) slightly slower than observed stratospheric paths at similar azimuths. The arrivals exhibited increasing trace velocity later in the wavetrain indicating a steepening of the arrival path for longer or slower propagation paths. Simulation of partially reflected paths using the updated infraGA software methods finds good agreement between observed and predicted infrasonic ensonification at these locations within the stratospheric shadow zone. Further development of the partial reflection physics and comparison with other data sets is needed to more robustly understand how such anomalous infrasonic signals can be predicted; however, the demonstration of this capability is a promising first step in such analyses.

97 MATHEMATICS AND COMPUTING↗
NASA NTRS1973

Partial-reflection studies of D-region winter variability

D-region electron densities were measured from December, 1972, to July, 1973, at Urbana, Illinois (latitude 40.2N) using the partial-reflection technique. During the winter, electron densities at altitudes of 72, 76.5, and 81 km show cyclical changes with a period of about 5 days that are highly correlated between these altitudes, suggesting that the mechanism responsible for the winter anomaly in D-region ionization applies throughout this height region. From January 13 to February 3, a pronounced wave-like variation occurred in the partial-reflection measurements, apparently associated with a major stratospheric warming that developed in that period. During the same time period, a traveling periodic variation is observed in the 10-mb height; it is highly correlated with the partial-reflection measurements. Electron density enhancements occur approximately at the same time as increases in the 10-mb height. Comparison of AL and A3 absorption measurements with electron density measurements below 82 km indicates that the winter anomaly in D-region ionization is divided into two types. Type 1, above about 82 km, extends horizontally for about 200 km while type 2, below about 82 km, extends for a horizontal scale of at least 1000 km.

Denny, B. W.↗
NASA NTRS1972

Partial reflections of radio waves from the lower ionosphere

The addition of phase difference measurements to partial reflection experiments is discussed, and some advantages of measuring electron density this way are pointed out. The additional information obtained reduces the requirement for an accurate predetermination of collision frequency. Calculations are also made to estimate the errors expected in partial-reflection experiments due to the assumption of Fresnel reflection and to the neglect of coupling between modes. In both cases, the errors are found to be of the same order as known errors in the measurements due to current instrumental limitations.

Connolly, D. J.↗
NASA NTRS1972

Mode coupling in partial reflections from the ionosphere at vertical incidence.

The effect of mode coupling has been calculated for radio waves partially reflected from the lower ionosphere at vertical incidence. Calculations were made for parameters appropriate to the partial reflection experiments (Belrose, 1970). The four reflection coefficients (two direct and two coupled) are calculated for a plane discontinuity using a matrix perturbation analysis. The ratios of coupled to direct reflection coefficients are calculated for a general one-dimensional reflecting layer using the coupled equations of Clemmow and Heading (1954). At the highest electron density considered, 10,000 per cu cm, about 10% of the reflected extraordinary wave amplitude might be due to coupling from the incident ordinary wave. The effect is smaller at lower electron density.

Connolly, D. J.↗
NASA NTRS1984

Partial Reflection Spaced Antenna Wind Measurements

The nature of partially reflecting (PR) irregularities is briefly reviewed and the techniques used in the PR spaced antenna method are discussed. The radars addressed use frequencies in the 2 to 6 MHz range operate in a pulse mode at vertical incidence. Radar system parameters including receiver dynamic range, coherent and incoherent detection, and post detection filtering are examined. Finally, data system parameters and real time analysis techniques are discussed.

Fraser, G. J.↗
NASA NTRS1976

Simultaneous partial reflection and meteor radar wind observations at Urbana, Illinois, during the winter of 1974-1975

A program of observation was undertaken during the winter of 1974-1975 utilizing the meteor winds radar and partial reflection system at Urbana, Illinois. The north-south component of the prevailing wind representative of 80-100 km altitude was deduced for four 24-h observational periods during which partial reflection measurements of D-region electron density were made. These observations indicate southward mean motion during periods of higher electron density and northward mean motion during periods of lower electron density. This is consistent with the idea that increases in the transport of nitric oxide from the auroral zone is a cause of winter increases in D-region electron density at midlatitudes.

Geller, M. A.↗
NASA NTRS1986

Hardware requirements: A new generation partial reflection radar for studies of the equatorial mesosphere

A new partial reflection (PR) radar is being developed for operation at the proposed Equatorial Observatory. The system is being designed to make maximum use of recent advances in solid-state technology in order to minimize the power requirements. In particular, it is planned to use a solid-state transmitter in place of the tube transmitters previously used in PR systems. Solid-state transmitters have the advantages that they do not need high voltage supplies, they do not require cathode heaters with a corresponding saving in power consumption and parts are readily available and inexpensive. It should be possible to achieve 15 kW peak powers with recently announced fast switching transistors. Since high mean powers are desirable for obtaining good signal-to-noise ratios, it is also planned to phase code the transmitted pulses and decode after coherent integration. All decoding and signal processing will be carried out in dedicated microprocessors before the signals are passed to a microcomputer for on-line analysis. Recent tests have shown that an Olivetti M24 micro (an IBM compatible) running an 8-MHz clock with a 8087 coprocessor can analyze data at least as fast as the minicomputers presently being used with the Adelaide PR rad ar and at a significantly lower cost. The processed winds data will be stored in nonvolatile CMOS RAM modules; about 0.5 to 1 Mbyte is required to store one week's information.

Vincent, R. A.↗
NASA NTRS1981

Investigation of the winds and electron concentration variability in the D region of the ionosphere by the partial-reflection radar technique

The development and first observations of the partial-reflection drifts experiment at Urbana, Illinois (40 N) are described. The winds data from the drifts experiment are compared with electron concentration data obtained by the differential-absorption technique to study the possible meteorological causes of the winter anomaly in the mesosphere at midlatitudes. winds data obtained by the meteor-radar experiment at Urbana are also compared with electron concentration data measured at Urban. A significant correlation is shown is both cases between southward winds and increasing electron concentration measured at the same location during winter. The possibility of stratospheric/mesospheric coupling is investigated by comparing satellite-measured 0.4 mbar geopotential data with mesospheric electron concentration data. No significant coupling was observed. The winds measured at Saskatoon, Saskatchewan (52 N) are compared with the electron concentrations measured at Urban, yielding constant fixed relationship, but significant correlations for short segments of the winter. A significant coherence is observed at discrete frequencies during segments of the winter.

Weiland, R. M.↗
NASA NTRS1986

The Adelaide MF partial-reflection radar and VHF ST radar

The microwave frequency (MF) partial-reflection radar ran continuously since November 1983, with data being analyzed in real time. The spaced antenna technique was used routinely to produce a climatology of the mean circulation, atmospheric tides, and gravity waves. Since the beginning of 1985, the system was also used as a Doppler radar to measure the spectral widths of the mesospheric echoes. This has enabled the turbulence dissipation rates to be determined. The Stratosphere-Troposphere (ST) radar was operated in the spaced antenna mode to measure winds in November 1984, in conjunction with a cooperative campaign to study the propagation of cold fronts across SE Australia. Observations were also performed to study the structure of the more intense and deeper cold fronts, which occur in late winter.

Vincent, R. A.↗
NASA NTRS1992

First observations of mesospheric dynamics with a partial reflection radar in Hawaii (22 deg N, 160 deg W)

A partial-reflection MF radar was installed at the Pacific Missile Range Facility on Kanai, Hawaii in September 1990. The wind measurements obtained with this radar system in Hawaii during the first year of operation are reviewed. The data reveal a broad spectrum of motions ranging from a mix of the equatorial mesopause semiannual oscillation (MSAO) and the annual mean cycle at middle and high latitudes in the zonal mean structure to low-frequency, tidal, and gravity wave motions at higher frequencies. The zonal mean wind structure is characterized by a downward progression of strong eastward and westward phases of the MSAO from approximately January to July. An eastward maximum of about 60/ms near 80 km during January and February is found, which descends rapidly, and a westward maximum of about 50 ms near 85 km during March and April is found, which descends much more slowly. The second MSAO cycle is greatly suppressed relative to the first due to the reversal of the correlation between this and the annual cycle at higher latitudes from July to December.

Fritts, David C.↗
NASA NTRS1984

Measurements of Partial Reflections at 3.18 Mhz Using the CW Radar Technique

An equipment for measuring partial reflections using the FM-CW-radar principle at 3.18 MHz, installed at the Ionospheric Observatory Juliusruh of the CISTP (HHI), is described. The linear FM-chirp of 325 kHz bandwidth is Gaussian-weighted in amplitude and gives a height resolution of 1.5 km (chirp length is 0.6 sec). Preliminary results are presented for the first observation period in winter 1982/83.

Priese, J.↗