265 research outputs found
A review of remote sensing and grasslands literature
Studies between 1971 and 1980 dealing with remote sensing of rangelands/grasslands in the multispectral band are summarized and evaluated. Vegetation and soil reflectance properties are described. In the majority of the studies, the effect of the reflectance of green rangelands vegetation on the reflectance from the total scene is the primary concern. Developments in technique are summarized and recommendations for further research are presented
Composition and assembly of a spectral data base for corn and soybean multicrop segments
There are no author-identified significant results in this report
Composition and assembly of a spectral data base for transition year spring wheat blind sites
There are no author-identified significant results in this report
Large Area Crop Inventory Experiment (LACIE). Phase 3 direct wheat study of North Dakota
The author has identified the following significant results. The green number and brightness scatter plots, channel plots of radiance values, and visual study of the imagery indicate separability between barley and spring wheat/oats during the wheat mid-heading to mid-ripe stages. In the LACIE Phase 3 North Dakota data set, the separation time is more specifically the wheat soft dough stage. At this time, the barley is ripening, and is therefore, less green and brighter than the wheat. Only 4 of the 18 segments studied indicate separation of barley/other spring small grain, even though 11 of the segments have acquisitions covering the wheat soft dough stage. The remaining seven segments had less than 5 percent barley based on ground truth data
Large Area Crop Inventory Experiment (LACIE). LACIE transition year plan for the direct estimation of wheat from LANDSAT imagery
There are no author-identified significant results in this report
Preliminary evaluation of spectral, normal and meteorological crop stage estimation approaches
Several of the projects in the AgRISTARS program require crop phenology information, including classification, acreage and yield estimation, and detection of episodal events. This study evaluates several crop calendar estimation techniques for their potential use in the program. The techniques, although generic in approach, were developed and tested on spring wheat data collected in 1978. There are three basic approaches to crop stage estimation: historical averages for an area (normal crop calendars), agrometeorological modeling of known crop-weather relationships agrometeorological (agromet) crop calendars, and interpretation of spectral signatures (spectral crop calendars). In all, 10 combinations of planting and biostage estimation models were evaluated. Dates of stage occurrence are estimated with biases between -4 and +4 days while root mean square errors range from 10 to 15 days. Results are inconclusive as to the superiority of any of the models and further evaluation of the models with the 1979 data set is recommended
Few-cycle soliton propagation
Soliton propagation is usually described in the ``slowly varying envelope
approximation'' (SVEA) regime, which is not applicable for ultrashort pulses.
We present theoretical results and numerical simulations for both NLS and
parametric () ultrashort solitons in the ``generalised few-cycle
envelope approximation'' (GFEA) regime, demonstrating their altered
propagation.Comment: 4 pages, 4 figure
Large Area Crop Inventory Experiment (LACIE). Composition and assembly of a spectral-met data base for spring and winter wheat, volume 2
There are no author-identified significant results in this report
Dynamics of soap bubble bursting and its implications to volcano acoustics
In order to assess the physical mechanisms at stake when giant gas bubbles
burst at the top of a magma conduit, laboratory experiments have been
performed. An overpressurized gas cavity is initially closed by a thin liquid
film, which suddenly bursts. The acoustic signal produced by the bursting is
investigated. The key result is that the amplitude and energy of the acoustic
signal strongly depend on the film rupture time. As the rupture time is
uncontrolled in the experiments and in the field, the measurement of the
acoustic excess pressure in the atmosphere, alone, cannot provide any
information on the overpressure inside the bubble before explosion. This could
explain the low energy partitioning between infrasound, seismic and explosive
dynamics often observed on volcanoes
How to be causal: time, spacetime, and spectra
I explain a simple definition of causality in widespread use, and indicate
how it links to the Kramers Kronig relations. The specification of causality in
terms of temporal differential eqations then shows us the way to write down
dynamical models so that their causal nature /in the sense used here/ should be
obvious to all. To extend existing treatments of causality that work only in
the frequency domain, I derive a reformulation of the long-standing Kramers
Kronig relations applicable not only to just temporal causality, but also to
spacetime "light-cone" causality based on signals carried by waves. I also
apply this causal reasoning to Maxwell's equations, which is an instructive
example since their casual properties are sometimes debated.Comment: v4 - add Appdx A, "discrete" picture (not in EJP); v5 - add Appdx B,
cause classification/frames (not in EJP); v7 - unusual model case; v8 add
reference
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