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NASA NTRS1978

Regional variations in upper mantle compressional velocities beneath southern California 1. Post-shock temperatures: Their experimental determination, calculation, and implications, 2.

The compressional velocity within the upper mantle beneath Southern California is investigated through observations of the dependence of teleseismic P-delays at all stations of the array on the distance and azimuth to the event. The variation of residuals with azimuth was found to be as large as 1.3 sec at a single station; the delays were stable as a function of time, and no evidence was found for temporal velocity variations related to seismic activity in the area. These delays were used in the construction of models for the upper mantle P-velocity structure to depths of 150 km, both by ray tracing and inversion techniques. The models exhibit considerable lateral heterogeneity including a region of low velocity beneath the Imperial Valley, and regions of increased velocity beneath the Sierra Nevada and much of the Transverse Ranges. The development is described of a technique for the experimental determination of post-shock temperatures, and its application to several metals and silicates shocked to pressures in the range 5 to 30 GPa. The technique utilizes an infra-red radiation detector to determine the brightness temperature of the free surface of the sample after the shock wave has passed through it.

Raikes, S. A.↗

NASA NTRS1977

Comparisons of some scattering theories with recent scatterometer measurements

The paper compares the predictions of two different types of sea scatter theories with recent scatterometer measurements which indicate the variations of the backscattering coefficient with polarization, incident angle, wind speed, and azimuth angle. Wright's theory (1968) differs from that of Chan and Fung (1977) in two major aspects: (1) Wright uses Phillips' sea spectrum (1966) while Chan and Fung use that of Mitsuyasu and Honda, and (2) Wright uses a modified slick sea slope distribution by Cox and Munk (1954) while Chan and Fung use the slick sea slope distribution of Cox and Munk defined with respect to the plane perpendicular to the look direction. Satisfactory agreements between theory and experimental data are obtained when Chan and Fung's model is used to explain the wind and azimuthal dependence of the scattering coefficient.

Fung, A. K.↗

NASA NTRS1978

Heliocentric distance dependence of the interplanetary magnetic field

Numerous spacecraft measurements bearing on the heliocentric distance dependencies of both large- and small-scale properties of the interplanetary magnetic field (IMF) are assembled and compared. These data tend to indicate that the average of the radial field component varies as the inverse square of distance. However, the azimuthal component is rather strongly a function of time, being influenced by both the time-dependent solar wind speed and the evolution of the source field at the sun. Thus, unless the solar wind speed dependence is taken into account, individual sets of measurements by a single spacecraft give an azimuthal component gradient which is steeper than the inverse distance dependence predicted from the Parker spiral model. A least squares fit to the composite (five spacecraft) solar rotation average data set gives a result close to the inverse distance dependence. Preliminary Helios results suggest general consistency with the spiral model.

Behannon, K. W.↗

NASA NTRS1978

Rigidity-independent coronal propagation and escape of solar protons and alpha particles

In a study of rigidity-independent coronal propagation processes, data on the azimuthal variation of the solar proton/alpha-particle ratio were obtained. Sources for the data included a statistical analysis of events observed by Heos-2, a comparative study of events recorded by both Heos-2 and Pioneer-10 and -11, and a multiday survey of individual events observed by Heos-2 and Pioneer-10. The statistical investigation of Heos-2 events reveals an increase of the lower value of the proton/alpha-particle ratio away from the well-connected region. The data from one or two spacecraft connected at different heliolongitudes indicates no azimuthal dependence of the proton/alpha-particle ratio. All the data appear to suggest rigidity-independent propagation or escape processes.

Perron, C.↗

NASA NTRS1979

Evaluation and modeling of the topographic effect on the spectral response from NADIR pointing sensors

A field experiment, using a hand-held radiometer, was designed and conducted to assess a simple theoretical incidence model for simulating the topographic effect of a uniform sand surface. Seven data sets were taken to compare effects of solar elevation and azimuth encountered at different times of year. Analysis of these data showed considerable variation in radiance values for different slope angles and aspects and that these values varied considerably with changes in solar elevation and azimuth. The field measured variations in spectral response were found to have generally strong correlations with the theoretical model. The reason for the occurrence of lower correlations are given and methods for improving the model are suggested. A model to simulate LANDSAT sensor response was applied to two subsets of the field data to establish the magnitude of the topographic effect on satellite data.

Holben, B. N.↗

NASA NTRS1979

HCMM: Soil moisture in relation to geologic structure and lithology, northern California

The author has identified the following significant results. First-look qualitative geologic evaluation of day- and night-IR images discloses several en echelon linear features extending throughout the central part of the northern coast range in California, across the Mendocino triple junction and into southern Oregon. Preliminary examination of these features with respect to topographic expression, vegetation, sun angle and azimuth, and atmospheric conditions suggests that they may be related to the intracontinental plate boundary (Lake Mountain Fault zone of Herd) of the Humbolt Plate. The linear features, which cut across several climatic zones and differently vegetated regions are not confined to topographic valleys, but cross the ridges and valleys at varying angles. Lithology within the Great Valley Sequence can be detected on a few of the images; however, preliminary evaluation suggests that the thermal banding observed may be a function of sun azimuth or late-day sun angle. Soil moisture, related to lithologic composition cannot be ruled out at this time.

Rich, E. I.↗

NASA NTRS1978

Present-day plate motions

An instantaneous plate-motion model, Relative Motion 2 (RM2), is obtained by inverting a data set comprising 110 spreading rates, 78 transform fault azimuths, and 142 earthquake slip vectors. RM2 is compared with angular velocity vectors which best fit the data along individual plate boundaries and, while the model performs close to optimally in most regions, attention is directed to those regions which are not suitably described by the model. Reasons for the discrepancies between RM2 and observations for the India-Antarctica plate boundary, the Pacific-India plate boundary, and the east-west trending transform fault azimuths observed in the French-American Mid-Ocean Undersea Study area are discussed.

Minster, J. B.↗

NASA NTRS1978

Real-time synthetic aperture radar data processing for space applications

Range and azimuth correlation in the time domain using current state-of-the-art CCD LSI technology provides a potentially practical means of achieving real-time pipeline processing of SAR images for future space missions. The proposed range correlator approach, using already demonstrated CCD transversal filtering techniques, will require very little power: less than 10 watts per Seasat-type 20-km processing module. The azimuth correlator architecture is considerably more demanding since it requires a large number of parallel chips (1020 for a Seasat-type 20-km module) to achieve a real-time processing capability.

Arens, W. E.↗

NASA NTRS1979

The Jovian magnetodisk

Magnetic field measurements made by the vector helium magnetometers on board Pioneers-10 and 11 reveal the existence of a current sheet (thickness of about 2 Jupiter radii) carrying an eastward current. Self-consistent studies of the current sheet show that the magnitude of the current is of the order of 0.01/Am and that the current is carried by a hot (T greater than 1 keV) plasma, the density of which varies between 1 cu cm at 30 Jupiter radii to 100 cu cm at 80 Jupiter radii. The current sheet is warped azimuthally and parallel to the magnetic dipole equator. The existence of an azimuthal field component indicates a poloidal plasma flow transporting some 10 to the 29th ions per second from Jupiter into the outer magnetosphere. It is shown that, if the outer magnetosphere is in a steady state, this plasma must be transported outward within the current sheet by a diffusion process which is faster than the one responsible for particle transport in the inner magnetosphere but slower than Bohm diffusion.

Goertz, C. K.↗

NASA NTRS1979

Pc 3 magnetic pulsations and precipitation of energetic electrons

The synchronous altitude satellite ATS 1 data and near-conjugate measurements of bremsstrahlung X-rays and ground magnetic variations were used to analyze an event of modulated auroral zone electron precipitation and magnetic pulsations in the Pc range. Transverse, azimuthal, nearly linearly polarized waves observed at ATS 1, ground magnetic pulsations at College, Alaska, and intervals of modulated electron precipitation centered on local magnetic moon, and noted in the X-ray data from Fort Yukon, Alaska, are discussed, noting that the origin of the Pc 3 waves is attributed to local field line resonances induced by Kelvin-Helmholtz instability at the magnetopause. The wave resonance model can explain observed differences in the pulsation activity at the ground, balloon, and satellite if account is taken of the spatial sensitivities of the techniques and the location of observing sites with respect to the probable location of resonant field lines. The data suggest that electron precipitation pulsations will correlate with Pc 3 magnetic pulsations when substorm injections coupled with azimuthal drift provide enhanced energetic particle fluxes with dayside resonance regions.

Arthur, C. W.↗

NASA NTRS1979

A rocket-borne energy spectrometer using multiple solid-state detectors for particle identification

A rocket-borne experiment using energy spectrometers that allows particle identification by the use of multiple solid-state detectors is described. The instrumentation provides information regarding the energy spectrum, pitch-angle distribution, and the type of energetic particles present in the ionosphere. Particle identification was accomplished by considering detector loss mechanisms and their effects on various types of particles. Solid state detectors with gold and aluminum surfaces of several thicknesses were used. The ratios of measured energies for the various detectors were compared against known relationships during ground-based analysis. Pitch-angle information was obtained by using detectors with small geometrical factors mounted with several look angles. Particle flux was recorded as a function of rocket azimuth angle. By considering the rocket azimuth, the rocket precession, and the location of the detectors on the rocket, the pitched angle of the incident particles was derived.

Fries, K. L.↗

NASA NTRS1980

Unsteady density and velocity measurements in the 6 foot x 6 foot wind tunnel

The methods used and the results obtained in four aero-optic tests are summarized. It is concluded that the rather large values of density fluctuation appear to be the result of much higher Mach number than freestream and the violent turbulence in the flow as it separates from the turret. A representative comparison of fairing on-fairing off rms density fluctuation indicates essentially no effect at M = 0.62 and a small effect at M = 0.95. These data indicate that some slight improvement in optical quality can be expected with the addition of a fairing, although at M = 0.62 its effect would be nil. Fairings are very useful in controlling pressure loads on turrets, but will not have first order effects on optical quality. Scale sizes increase dramatically with increasing azimuth angle for a reprensentative condition. Since both scale sizes and fluctuation levels increase (total turbulence path length also increases) with azimuth angle, substantial optical degradation might be expected. For shorter wave lengths, large degradations occur.

Rose, W. C.↗

NASA NTRS1979

Pioneer-Venus solar flux radiometer

The paper presents the design and performance characteristics of the Solar Flux Radiometer flown on the Large Probe of the Pioneer-Venus Multiprobe spacecraft. Radiance measurements of the Venusian atmosphere in spectral channels between 400 and 1800 nm as a function of altitude were made, along with elevation and azimuthal measurements of the radiation field performed with five optical channels. Filtered Si and Ge photovoltaic detector output currents were processed with logarithmic transimpedance converters prior to being multiplexed and digitized. Atmospheric sampling in elevation and azimuth was done according to a Gaussian integration scheme; the received data were used to determine the deposition of solar energy in the Venus atmosphere along with upward and downward fluxes and radiances with an altitude resolution of several hundred meters between 67 km and the surface.

Palmer, J. M.↗

NASA NTRS1980

Pioneer Venus Sounder Probe Solar Flux Radiometer

The Solar Flux Radiometer aboard the Pioneer Venus Sounder Probe operated successfully during its descent through the atmosphere of Venus. The instrument measured atmospheric radiance over the spectral range from 400 to 1800 nm as a function of altitude. Elevation and azimuthal measurements on the radiation field were made with five optical channels. Twelve filtered Si and Ge photovoltaic detectors were maintained near 30 C with a phase-change material. The detector output currents were processed with logarithmic transimpedance converters and digitized with an 11-bit A/D converter. Atmospheric sampling in both elevation and azimuth was done according to a Gaussian integration scheme. The serial output data averaged 20 bits/sec, including housekeeping (sync, spin period, sample timing and mode). The data were used to determine the deposition of solar energy in the atmosphere of Venus between 67 km and the surface along with upward and downward fluxes and radiances with an altitude resolution of several hundred meters. The results allow for more accurate modeling of the radiation balance of the atmosphere than previously possible.

Tomasko, M. G.↗

NASA NTRS1979

Investigations of coherent structures in free turbulent shear flows

The dynamics of large-scale coherent structures in general, and studies based on flow-visualization and phase-locked hot-wire measurements of the structures in the near fields of circular jets are considered. A study involving the nature of coherent structures under conditions of stable vortex pairing induced by controlled axisymmetric acoustic excitation reveals that azimuthal coherence initially enhanced by the excitation is lost before the end of the potential core through evolution of azimuthal lobe structures and turbulent breakdown. The evolution of a spark-induced spot in an axisymmetric turbulent mixing layer is also investigated, and the coherent Reynolds stress associated with the spot is found to be much higher than the background turbulence Reynolds stress. In addition, the state of organization in a high Reynolds number unperturbed axisymmetric mixing layer is examined, and it is shown that the shear layer is infrequently organized and the motions are intensely three-dimensional, while tearing and fractional pairing occur as frequently as complete pairing.

Hussain, A. K. M. F.↗

NASA NTRS1979

Calibration of the Space Shuttle Microwave Scanning Beam Landing System using a laser tracker

Verification tests of the Space Shuttle Microwave Scanning Beam Landing System (MSBLS) performed with respect to the Precision Laser Tracking System are reported. MSBLS ground station measurements of the azimuth, elevation and range of a NASA Jetstar aircraft equipped with a laser retroreflector, a MSBLS antenna and commissioning instruments including a MSBLS navigation set of the type installed in the Orbiter, during the performance of radial, orbital and glideslope runs with respect to the ground station were compared with laser ground station measurements of aircraft position. Data obtained from flight testing at Shuttle landing sites reveal MSBLS distance measuring equipment performance to be very good, with elevation errors found at very low elevation angles and azimuth errors as a function of aircraft attitude. The Precision Laser Tracking System has thus proven to be a satisfactory instrument for determining MSBLS performance, and an ideal instrument for its calibration.

Ford, K.↗

NASA NTRS1981

The statistical character of Pc 4 magnetic pulsations at synchronous orbit

A statistical study of 215 magnetic pulsation events identified on the basis of waveform and period as Pc 4 (45- to 150-s period) observed at synchronous orbit by ATS 6 is reported. The study was designed to be similar to that done with Pc 3 (10- to 45-s period) by Arthur et al. (1977). These Pc 4 are found to occur most often near 1800 local time but are observed at all local times. The dominant period is approximately 100 s, but a secondary peak in the distribution occurred at approximately 53 s. They tend to be nearly linearly polarized, principally transverse to the ambient magnetic field. The Pc 4 are found to divide naturally into two classes (radial and azimuthal) on the basis of the azimuth of the major axis of polarization. These classes divide further into low-frequency (less than or equal to 0.015 Hz) and high-frequency (greater than or equal to 0.015 Hz) classes. These four classes organize the remaining wave characteristics quite well. Division of the Pc 4 events into these classes does not lead to identification of a single source mechanism as it did with Pc 3. However, some correspondence between the classes and various proposed mechanisms does exist.

Arthur, C. W.↗

NASA NTRS1980

The topographic effect on spectral response from nadir-pointing sensors

It is difficult to interpret multispectral Landsat earth resources data in areas of rugged and mountainous terrain because of the topographic effect on the sensor response. The objectives of this study were to examine and quantify the topographic effect on the sensor response from a uniform sand surface, to assess a simple theoretical incidence model for modeling the radiance from the surface, and to simulate Landsat sensor response due to the topographic effect. A field experiment was designed to collect data from a large range of slope angles and aspects at a range of solar elevations, using a hand-held radiometer. Analysis of these data showed that the magnitude of the topographic effect varied as a function of the solar elevation, the azimuthal orientation of the slope, and the slope inclination. The field measured variations in spectral response were found to have generally strong correlations with the theoretical model, and it was shown that the applicability of the Lambertian assumption varied within and between data sets. It is concluded that if slope angle, aspect, and solar zenith angle and azimuth are known, a technique incorporating a model to reduce the topographic effect prior to multispectral classification may be developed.

Holben, B. N.↗