1,523 research outputs found
A Study of the Breakup Characteristics of the Chena River Basin Using ERTS Imagery: Completion Report
ERTS Project 110-5Snowmelt and rainfall floodinq is a major water resource problem in
Alaska. At the present time, forecastinq of these floods is based on a
sparse hydrological and climatological network. Numerous basins with
drainage areas of 5,000 km2 and less remain completely ungaged. The lack
of data causes uncertainty in the design of transportation schemes such as
tile Trans-Alaska oil pipeline. This project studied the utility of using
ERTS-l imagery as a source of additional data for the prediction of snowmelt
runoff, the most dynamic hydroloqic event in arctic and subarctic
basins. Snow distribution as determined from the satellite imagery was
compared with values determined from the conventional snow course stations
and with the results of a snowmelt energy model. The Chena River Basin
was selected because of the availability of ground truth data for comparison.
Very good agreement for snow distribution and rates of ablation was
found between the ERTS-l imagery, the snowmelt model, and field measurements.
Monitoring snowmelt rates for relatively small basins appears to be practical.
The main limitation of the ERTS-l imagery is the interval of coverage.
More frequent overflights providing coverage are needed for the study of
transient hydrologic events. ERTS-l data is most useful when used in conjunction
with snowmelt prediction models and existing snow course data.
These results should prove very useful in preliminary assessment of hydrologic
conditions in ungaged watersheds and will provide a tool for month-to-month
volume forecasting.This work was supported by National Aeronautics and Space Administration,
Grant NAS 5-21833
A study of the break-up characteristics of Chena River Basin using ERTS imagery
The author has identified the following significant results. The Chena River Basin was selected because of the availability of ground truth data for comparison. Very good agreement for snow distribution and rates of ablation was found between the ERTS-1 imagery, the snowmelt model, and field measurements. Monitoring snowmelt rates for relatively small basins appears to be practical. The main limitation of the ERTS-1 imagery is the interval of coverage. More frequent overflights providing coverage are needed for the study of transient hydrologic events. ERTS-1 data is most useful when used in conjunction with snowmelt prediction models and existing snow course data. These results should prove very useful in preliminary assessment of hydrologic conditions in ungaged watersheds and will provide a tool for month-to-month volume forecasting
Break-up characteristics of the Chena River watershed, central Alaska
The author has identified the following significant results. The snow melt for a small watershed (5130 sq km) in Central Alaska was successfully monitored with ERTS-1 imagery. Aerial photography was used as supporting data for periods without satellite coverage. Comparison both with actual measurements and with a computer model showed good agreement
Jahn-Teller stabilization of a "polar" metal oxide surface: Fe3O4(001)
Using ab initio thermodynamics we compile a phase diagram for the surface of
Fe3O4(001) as a function of temperature and oxygen pressures. A hitherto
ignored polar termination with octahedral iron and oxygen forming a wave-like
structure along the [110]-direction is identified as the lowest energy
configuration over a broad range of oxygen gas-phase conditions. This novel
geometry is confirmed in a x-ray diffraction analysis. The stabilization of the
Fe3O4(001)-surface goes together with dramatic changes in the electronic and
magnetic properties, e.g., a halfmetal-to-metal transition.Comment: 4 pages, 4 figure
Localized magnetoplasmon modes arising from broken translational symmetry in semiconductor superlattices
The electromagnetic propagator associated with the localized collective
magnetoplasmon excitations in a semiconductor superlattice with broken
translational symmetry, is calculated analytically within linear response
theory. We discuss the properties of these collective excitations in both
radiative and non-radiative regimes of the electromagnetic spectra. We find
that low frequency retarded modes arise when the surface density of carriers at
the symmetry breaking layer is lower than the density at the remaining layers.
Otherwise a doublet of localized, high-frequency magnetoplasmon-like modes
occurs.Comment: Revtex file + separate pdf figure
Electron locking in semiconductor superlattices
We describe a novel state of electrons and phonons arising in semiconductor
superlattices (SSL) due to strong electron-phonon interactions. These states
are characterized by a localization of phonons and a self-trapping or locking
of electrons in one or several quantum wells due to an additional,
deformational potential arising around these locking wells in SSL. The effect
is enhanced in a longitudinal magnetic field.
Using the tight-binding and adiabatic approximations the whole energy
spectrum of the self-trapped states is found and accurate, analytic expressions
are included for strong electron-phonon coupling. Finally, we discuss possible
experiments which may detect these predicted self-trapped states.Comment: 8 pages, 2 figures. Please note that the published article has the
title 'Electron locking in layered structures by a longitudinal magnetic
field
Cross spectral analysis of Swabian Jura (SW Germany) three-component microearthquake recordings
Similar three-component microearthquake records have been observed in the Swabian Jura (SW Germany) seismic zone for different source-receiver geometries. This data set is used to study the resolution power of cross spectral analysis techniques for the estimation of relative differential times as well as the applicability to velocity monitoring. The differential times are estimated in the frequency domain by assuming a linear-phase cross spectrum with the slope indicating the individual time difference. All earthquakes have been relocated with respect to a master event, using the relative P and S delay times from the cross spectral analysis as a measure of source mislocation. The overall location error is strongly dependent on the inital distance between master and studied event. For earthquakes initially located farther apart than approximately 1.5 km, the relocalization result in terms of total location error was poorer, whereas for events initially located closer than 1 km the precision of the relocalization was improved. The remaining residuals are of the order of 10 ms, which is approximately 3 times the digitization interval. In order to test the applicability of cross spectral analysis to velocity monitoring, synthetic data were used to model the influences of noise and source time function differences. The effect of additive white noise seems to be acceptable in cases where the S/N ratio is sufficiently high. Small changes in the shape of the source time function, however, were found to be of great influence to the differential time estimates. Variation of rise, sustain and decay times, which were negligible in the coherence spectrum, spuriously introduced phase differences which, in terms of delay times, easily reach the magnitude of the digitization interval. Thus, velocity monitoring using cross spectral analysis techniques seems to depend strongly on the equality - in contrast to similarity - of the source time functions of the events which are compared. The coherence spectrum is not a sufficient measure to detect all the significant differences.
ARK: https://n2t.net/ark:/88439/y035103
Permalink: https://geophysicsjournal.com/article/213
 
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