Azimuthal Difference Research Articles

Measurement of Ocean Surface Currents by the CRL HF Ocean Surface Radar of FMCW Type. Part 2. Current Vector

The Communications Research Laboratory (CRL) has been developing high-frequency ocean surface radars (HFOSRs). The CRL dual-site HFOSR system can clarify the distribution of surface currents with a nominal range of 50 km. This paper presents a theoretical and experimental analysis of the measurement error of the current vector obtained by the CRL HFOSR system, using a comparison of instantaneous current vectors acquired by the HFOSR system and current meters moored at a depth of 2 m, taking account of the vertical current shear. The theoretical analysis shows that the probability distribution of the measurement error of the current vector forms concentric ellipses at a spatial scale that depends on the RMS measurement error of radial current velocity and with an aspect ratio that depends only on the azimuthal difference of the radar beams. When the azimuthal difference is a right angle, the measurement error of the current vector is at a minimum. A comparison between instantaneous current vectors measured by the CRL HFOSR system and moored current meters shows that the distribution of the difference vector between the radar current and the meter current agrees well with the theoretical measurement error of the current vector and that the RMS of difference vector length is about 10 cm s−1 while the azimuthal difference between two radar beams is between 45 and 135 degrees. The accuracy of current measurement by the dual-site HFOSR system is therefore considered to be less than 10 cm s−1 in this range of azimuthal difference. The theoretical analysis will be applicable for a wider range of the azimuthal difference of the radar beams.

Abstract :Detection of Naturally Fractured Tight Gas Reservoirs: Case Histories from the Uinta and Wind River Basins Using 2-D and 3-D Seismic Data 

The goal of two U.S. DOE research projects directed by Blackhawk Geometries, contract no. DE-AC21-92MC28135 and DE-AC21-94MC31224, is the detection of gas-filled fractures using seismic methods. If highly fractured areas can be located using seismic techniques prior to drilling, it can greatly benefit field development. Shear wave seismic detects fractures, but it is expensive to acquire. If P-wave data can also detect fractures, the costs of finding fractured areas will be significantly reduced. In the Uinta Basin, 2 multi-component seismic lines and a multicomponent VSP were used to define fractures in the Upper Green River formation. The azimuthal difference of the P-wave AVO gradients showed open fracture directions consistent with the shear and VSP data. The dominant fracture direction at the Wind River Basin study area is East-West, and this information was used to design a processing sequence which splits the 3-D dataset into two subsets. Compressional waves which travel parallel to the dominant fracture direction will not sense the fractures, while compressional waves which travel perpendicular to the dominant fracture direction will sense the maximum influence of the fractures. The two data subsets were processed independently, and the azimuthally variant seismic attributes were compared to production from wells to calibrate the seismic attributes to production.

Origin of optical anisotropy in strained InxGa1−xAs/InP and InyAl1−yAs/InP heterostructures

Optical anisotropy in mismatched InxGa1−xAs/InP and InyAl1−yAs/InP heterostructures has been investigated by variable azimuthal angle ellipsometry and reflectance difference spectroscopy. The two approaches are shown to yield strongly correlated results. A comparison to high resolution x-ray diffraction, transmission electron microscopy, and atomic force microscopy studies indicates that large optical anisotropies are associated with surface roughening that results from three-dimensional growth. Our findings demonstrate that fast and nondestructive measurements of optical anisotropy can provide important information about the growth mode and crystalline quality of strained epitaxial layers.

Possible shallow crustal shear wave anisotropy off Lofoten, Norway, inferred from three-component ocean-bottom seismographs

Summary P- and S-wave velocity models along two perpendicular profiles 145 and 175 km long on the undrilled continental shelf off Lofoten, northern Norway, have been obtained from the study of nine three-component ocean bottom seismographs. A VP/VS ratio of 1.96–2.15 is found in the sedimentary layers along a NE-SW profile. These high values are consistent with shaly sediments, which are identified in dredged bedrock samples. Along a NW-SE profile the S-wave velocities in the sedimentary layers are 5-10 per cent higher than along a NE-SW profile. The most likely explanation for this velocity difference is seismic anisotropy, which might be caused by liquid-filled microfractures alligned along the direction of the present-day maximum horizontal compressive stress. The Vp/Vs ratio in the upper crystalline crust is found to be 1.75 along both profiles. If the inferred anisotropy described above is caused by aligned microcracks, the lack of anisotropy in the crystalline basement indicates that these cracks are restricted to the sedimentary layers. It must be emphasized, however, that the observed azimuthal difference in S-wave velocities could be caused by lateral velocity variations in the sediments, although the anisotropy hypothesis is considered more likely.

Evolution of the caldera‐forming eruption at Crater Lake, Oregon, indicated by component analysis of lithic fragments

Crater Lake caldera (8 × 10 km), formed 6845 years B. P. (14C age) during the climactic eruption of the volcanic edifice known as Mount Mazama, is intermediate in size between small calderas associated with central vent eruptions and large calderas that have ring fracture vent systems. Our quantitative study of lithic fragments in the ejecta confirms the existing model of changes in vent configuration during the climactic eruption of Mount Mazama. Initial activity was from a single vent that produced a rhyodacite pumice fall from a Plinian column. Altered preexisting volcanic rocks are the predominant lithic type in the Plinian deposit, and their extensive hydrothermal alteration is considered as evidence of their relatively deep origin. The Wineglass Welded Tuff lies atop the Plinian deposit and contains a higher proportion of fresh volcanic rocks, suggesting enlargement of the single vent by slumping of its walls. This same vent enlargement caused the Plinian eruption column to collapse and feed valley‐hugging pyroclastic flows that deposited the Wineglass Welded Tuff. When enough material was erupted from the shallow magma chamber that its roof was no longer adequately supported, Mount Mazama collapsed to form the caldera, while highly energetic pyroclastic flows produced the climactic ignimbrite. A lag breccia that represents the proximal facies of the compositionally zoned climactic ignimbrite lies atop the Wineglass Welded Tuff and contains predominantly altered volcanic rocks of deeper origin, accompanied by minor granitoids from the magma chamber walls. Azimuthal differences in lithic component proportions in the lag breccia correlate well with the geology of the caldera walls, indicating that the climactic ignimbrite was ejected by multiple vents along a ring fracture system. Systematic lithic component changes within the lag breccia suggest different quarrying levels that reflect waxing and waning of the discharge rate during the caldera collapse phase of the climactic eruption. Our lithic component analysis demonstrates that calderas that may be too small to experience structural resurgence, such as Crater Lake, nevertheless may form by syneruptive subsidence along ring fractures.

Localization and recall of the spatial position of sounds

Memory for the location of auditory stimuli was tested after delays of 1 min, 30 min, or 24 h. Eleven environmental sounds were presented to 22 subjects in each of 11 different free-field positions, spaced evenly in a semicircle around the subject in the horizontal plane. Initial localization acuity was recorded upon presentation of each stimulus. To test memory for location, target stimuli were presented over headphones, and subjects attempted to recall the original position. Memory for location was significantly less accurate than initial localization, even after 1 min. Male subjects’ accuracy decreased over time, but there was no effect of delay for female subjects. A large effect of stimulus position was also noted, with stimuli coming from central locations remembered better than those coming from the extremes, an effect not accounted for by azimuthal differences in localization accuracy. Analysis of the error distributions indicated that this pattern was largely due to the presence of right–left reversals. These reversals suggest the existence of two separate components to auditory spatial memory: side and azimuth, and that these two parts can be dissociated.

Adaptation to transformed auditory localization cues in a hybrid real/virtual environment.

The ability of humans to adapt to intermodal discrepancies is an important factor in the design of virtual environments. In the present study, azimuthal localization cues were altered (to magnify azimuthal differences near zero degrees) relative to real proprioceptive, visual, and vestibular cues. Subjects were alternately tested and trained in hybrid real/virtual environments where auditory stimuli were synthesized (using a PC, Convolvotron, and electromagnetic head tracker) to be at one of 13 discrete positions marked by real lights. Testing consisted of identifying the azimuth of virtual sound sources without relevant visual feedback or significant head motion. During training, a virtual sound from one of the positions was gated on with the light at that position, and subjects turned their heads to face the composite stimulus. Further identification experiments involving modified experimental procedures, as well as minimum-audible-angle discrimination experiments, were performed to help clarify the results. Preliminary findings on resolution, bias, and identification will be briefly overviewed. [Work supported by AFOSR, Grant 90-200.]

Widespread Cenozoic (?) remagnetization in Thailand and its implications for the India-Asia collision

Paleomagnetic study of 13 sites from the Khorat plateau in Thailand spanning ages from the Devonian to the Jurassic, and reappraisal of published results from the Triassic to the Cretaceous show that most of the Indochina block suffered complete remagnetization after the Triassic and possibly after the Cretaceous, most likely at the time of the collision of India and Eurasia. The paleodirection associated with this remagnetization is consistent with the contention that Thailand was a part of Eurasia at that time and that it has suffered some 20° of clockwise rotation subsequently. Also consistent is the observed azimuthal difference of Mesozoic fold axes on either side of the Red River fault, as is the early geometry of and sense of motion on this fault. Re-interpretation of late Neogene data suggests that rotation may have continued into the Neogene. The remagnetization event prevents the determination of paleopositions of Thailand prior to the Cenozoic, but carries great interest in the frame of the extrusion tectonics concept.

Measuring and modeling spectral characteristics of a tallgrass prairie

This study was conducted to evaluate the diurnal and seasonal, spectral reflectance characteristics of barned and unburned areas of a tallgrass prairie, based on field measurements and models of radiation transport in plant canopies. Burning of the senescent vegetation, resulting from the previous years' growth, is a common management practice, which results in improved productivity and affects the succession of grass species. The burned and unburned grass canopies showed distinctly different, diurnal and seasonal, spectral reflectance characteristics in the visible and infrared regions of the spectrum. These were attributed to the differences in development of the two plant canopies and the azimuthal differences in sensor - sun - canopy positions during field measurements of spectral reflectance. The radiation transper model properly simulated the diurnal spectral behavior of the two canopies. The simulated, seasonal, spectral reflectance values for the unburned grass canopy were greater than the measured ones, because of limitations in proper representation of the layer of senescent vegetation in the model.

Pn velocity study using a temporary seismographic network in the Shillong Plateau, Northeast India

Abstract Seismic P -wave velocity ( Pn ) of the uppermost mantle beneath the Shillong Plateau has been studied using a temporary seismographic network. Refracted Pn arrivals of shallow distant earthquakes ( M > 3.0) recorded at pairs of stations, lying within 2° azimuthal differences with respect to a given epicenter, are used in this study. Since the method is based on relative travel-time differences, the measurement is independent of origin time and location errors. The average Pn velocity is found to be 8.57 ± 0.02 km/sec, which is higher than the average mantle velocity 8.13 km/sec under other areas of the Indian subcontinent. The observed high Pn velocity beneath the plateau may be attributed to the presence of high density material.

Rupture characteristics and tomographic source imaging of ML ∼ 3 earthquakes near Anza, southern California

The rupture characteristics of several ML ∼ 3 earthquakes near Anza, California, are determined from time domain analysis of path‐corrected, displacement pulses. These pulses are corrected for propagation effects (apparent attenuation, scattering, site resonance) using the waveforms of adjacent small events (ML ≤ 2.1) as empirical Green's functions. The earthquakes studied occurred during two swarm sequences near Cahuilla, in an area characterized by swarm activity at shallow depth (< 5 km). The data consist of seismograms recorded by the Anza seismic network, a high dynamic range local array with digital telemetry. The waveforms of adjacent small events (ML ≤ 2.1) are deconvolved from those of the ML ∼ 3 events to yield the source time functions of the larger earthquakes. The ML ∼ 3 earthquakes display a variety of rupture modes, similar to those reported for large shocks but over much shorter time scales and distances. Events with single and multiple ruptures are observed. Relative locations of the subevents are obtained from azimuthal differences in the time separation of pulses in the deconvolved displacement waveforms. Some events (as small as ML 2.4) display unilateral rupture propagation, as manifested by azimuthal variations in the pulse widths of the deconvolved displacement pulses. A tomographic back projection technique is applied to the deconvolved displacement pulses to image the slip velocity on the fault as a function of time after nucleation and distance along the fault, using a one‐dimensional fault model. The tomographic inversion for one of the events (ML 2.4) reveals a unilateral rupture with rupture velocity about equal to the shear wave velocity (Vs) and fault length of 300 m. A similar inversion for an ML 3.7 event resolves two subevents separated by about 200 m and yields an average rupture velocity of 0.8Vs. These rupture velocities are similar to those reported for large earthquakes, indicating that rupture velocity is independent of seismic moment down to 3.1 × 1019 dyn cm, the smallest event studied. There are clear variations in pulse width for neighboring events with similar seismic moments, implying significant differences in static stress drops. Factor of five variations in stress drop (11–61 bars) are calculated for events within 200 m of each other. Thus the stress and/or strength along this fault zone varies considerably over distances of hundreds of meters.

Cross measurements in magnetic recording: A new way of determining head performance

A description is given of how to separately the recording and playback performance of an inductive head relative to that of a "reference" head. The resulting relative recording and relative playback figures are completely insensitive to azimuthal differences between recording and playback head and are independent of errors in track adjustment. Second order effects can now be measured. In addition, when the measuring system carries out the simple calculations necessary for obtaining these figures, a considerable amount of time and effort for interpretation is saved.

Anisotropic plate thickening model.

A model which combines the plate thickening model and the preferred orientation olivine model is proposed to interpret P-wave velocity azimuthal anisotropy in the lithosphere. Two layers of anisotropy are used to interpret the low velocity zone structure introduced by Asada and Shimamura in the Northwestern Pacific as a result of the azimuthal difference of the maximum P-wave velocity axes. We also suggested that the rate of anisotropy changes with depth.

The shrinking cone limit and quark spin effects in muon-induced dimuon events

In the context of a high momentum approximation we predict azimuthal asymmetries and differences between like and opposite sign dimuon events in μN scattering. These result from the transference of spin information between production and decay processes when the incident beam is polarized. The analysis is geared towards the E.M.C. data, against which we also examine the consequences of our kinematic approximation.

Correlations in multiparticle production

The correlations among the charged particles, produced in interactions o$\stackrel{\mathrm{\ifmmode \dot{}\else \.{}\fi{}}}{\mathrm{f}}$ 200, 300, and 400 GeV protons and 200 GeV pions with emulsion nuclei are investigated. An asymmetry between the projectile and the target hemispheres is observed. For two-particle distributions, short-range pseudorapidity correlation is found. The correlation between the azimuthal difference $\ensuremath{\Delta}\ensuremath{\varphi}=|{\ensuremath{\varphi}}_{1}\ensuremath{-}{\ensuremath{\varphi}}_{2}|$ and the pseudorapidity difference $\ensuremath{\Delta}\ensuremath{\eta}=|{\ensuremath{\eta}}_{1}\ensuremath{-}{\ensuremath{\eta}}_{2}|$ indicates that the short-range rapidity correlation persists over the full $\ensuremath{\Delta}\ensuremath{\varphi}$ range.

Coding of directional information by single neurones in the S-segment of the FM bat, Myotis lucifugus.

1. Response parameters of S-segment neurones of the FM bat Myotis lucifugus were measured as a sound was delivered from different azimuthal angles around the animal's head. 2. The response parameters investigated were the amplitude and threshold of the evoked potential (N3) of the S-segment, together with the threshold, latency and number of impulses (per stimulus pulse) of single units. 3. All the neurones studied had their lowest thresholds either at 20-40 degrees contralateral, or 20-40 degrees ipsilateral or at the front (0 degrees). 4. The amplitude of the sound affected the relationship between stimulus direction and the amplitude of a non-monotonic N3, and the relationship between stimulus direction and the number of impulses of a non-monotonic single unit. It had so such effects with a monotonic N3 and a monotonic single unit. 5. From a study of N3 amplitudes and numbers of impulses of single neurones, it appeared that an azimuthal difference as small as 3 degrees could be easily coded at a 95% correct level with stimuli presented at around 20 degrees ipsilateral, 20 degrees contralateral, and at the front. 6. The inter-aural pressure difference (IPD), which is considered an essential cue for echolocation in Myotis (Shimozawa et al. 1974), changed linearly with angle from 0 to 40 degrees lateral at a rate of 0.4 dB/degree for sounds between 33.5 and 49.0 kHz. 7. Assuming the just-detectable IPD to be 0.5 dB (as in man), the minimum detectable azimuthal difference of Myotis around the median plane would be 1.25 degrees.

Azimuthal Correlations of High-Transverse-Momentumπ0Pairs

We have studied correlations between two ${\ensuremath{\pi}}^{0}'\mathrm{s}$ produced at the CERN intersecting storage rings, utilizing detectors with large azimuthal acceptance. We find that the previously observed enhancement of two ${\ensuremath{\pi}}^{0}'\mathrm{s}$ produced at azimuthal difference near 180\ifmmode^\circ\else\textdegree\fi{} can be made to vanish when certain kinematic effects are removed. However, we observe aligned configurations above 8 GeV of transverse energy unexplained by such kinematic effects.

Spectral Content of Teleseismic P-Waves Recorded at the Hagfors Observatory

Summary Bandpass spectra of short period P-waves recorded at the Hagfors Observatory in Sweden from some 200 seismic events at distances from 20 to 100 degrees have been analysed. Attempts at estimating significant differences between spectra of signals originating from the same epicentre region show that an increase of the focal depth from 40 km to 80 km can shift the spectral content substantially towards higher frequencies. The size effect within a range of one magnitude unit, however, is not very strongly shown. An outline of the large-scale regional variations of the spectral characteristics for shallow focus events shows a systematic azimuthal difference. Events in geographical regions such as the Northeast Pacific, the North Atlantic Ridge and South America appear to radiate less high frequency energy than North-west Pacific and Central Asian events.

Studies on the Protection against Cold Damage to Citrus Trees. II

In order to study the cause of the azimuthal difference in frost injuries influenced the crown of citrus trees, the distribution of leaf and air-temperature, the Strength of air-current and the direction of it were measured, and also photo-hours and osmotic concentration of the leaves were surveyed.1. Frost injuries are found remarkable in the surface part of tree-crown extending south to north-east side, but in the south-west to north-west side of tree crown, no or very little injury is seen.2. The leaf-temperature at night in winter is lower in the south to north-east side of tree-crown than that in the south-west to north-west side, This distribution of leaf-temperature above fact and the azimuthal distribution of frost injury are in agreement. The leaf-temperature in the down-stream of air-current, where which leaves were damaged badly, was lower by 1.5 to 2.0°C than that of the up-stream of air-current. The central part of the tree-crown was the highest in temperature.3. The direction of air-current at night was south-west to west. The strength of air-current was weak at the south-east to north-east side down-stream but it was strong up-stream air-current of the tree-crown, especially at the top part of it.4. The cause of the azimuthal difference in frost injury was lowering of the temperature of leaves in the south to north-east side.

浅発地震の走時より出された日本の表層構造

The travel time curve of shallow earthquake gives information about the structure of the earth's crust. But, in usual the observed travel times are plotted against epicentral distances without any consideration on azimuthal differences of observatories with respect to the epicentre. Therefore, by the analysis of the travel time curve made by the above procedure, only vertical irregularities of structure of the earth are obtained in assumption of no lateral irregular structures of the crust. Plots of the observed travel time have some deviations from mean curve in Japan. These deviations seem to contain systematic tendencies which exceed the amount of observation errors. The systematic deviations may be caused by the lateral ununiformness of crustal structure. From this view point, the author attempted a new method of analysis of travel time curves. That is, vertical sections are taken in Japan as in Fig. 1 and the travel time curves of the sections are made from the date of earthquakes and observatories in the belt near the sections. Thus we can easily determined the local characteristics of the structure which derived from analysis of several travel time curves of another section at intersection.Epicenters of the earthquakes and sections are illustrated in Fig. 1. The crustal structure derived by this method are illustrated in Fig. 2, Fig. 3 and Fig. 4. The present report is a preliminary one satisfying the observed travel times of shallow earthquakes. The more accurate data from the observations of artificial explosions and local earthquakes will give some modification to this structures.