1,543 research outputs found
Discrimination of growth and water stress in wheat by various vegetation indices through a clear a turbid atmosphere
Reflectance data were obtained over a drought-stressed and a well-watered wheat plot with a hand-held radiometer having bands similar to the MSS bands of the LANDSAT satellites. Data for 48 clear days were interpolated to yield reflectance values for each day of the growing season, from planting until harvest. With an atmospheric path radiance model and LANDSAT-2 calibration data, the reflectance were used to simulate LANDSAT digital counts (not quantized) for the four LANDSAT bands for each day of the growing season, through a clear (approximately 100 km meteorological range) and a turbid (approximately 10 km meteorological range) atmosphere. Several ratios and linear combinations of bands were calculated using the simulated data, then assessed for their relative ability to discriminate vegetative growth and plant stress through the two atmospheres. The results show that water stress was not detected by any of the indices until after growth was retarded, and the sensitivity of the various indices to vegetation depended on plant growth stage and atmospheric path radiance
Diurnal patterns of wheat spectral reflectances and their importance in the assessment of canopy parameters from remotely sensed observations
Spectral reflectances of Produra wheat were measured at 13 different times of the day at Phoenix, Arizona, during April 1979 using a nadir-oriented hand-held 4-band radiometer which had bandpass characteristics similar to those on LANDSAT satellites. Different Sun altitude and azimuth angles caused significant diurnal changes in radiant return in both visible and near-IR regions of the spectrum and in several vegetation indices derived from them. The magnitude of these changes were related to different canopy architecture, percent cover and green leaf area conditions. Spectral measurements taken at each time period were well correlated with green leaf area index but the nature of the relationship changed significantly with time of day. Thus, a significant bias in the estimation of the green leaf area index from remotely sensed spectral data could occur if sun angles are not properly accounted for
The use of multilayer network analysis in animal behaviour
Network analysis has driven key developments in research on animal behaviour
by providing quantitative methods to study the social structures of animal
groups and populations. A recent formalism, known as \emph{multilayer network
analysis}, has advanced the study of multifaceted networked systems in many
disciplines. It offers novel ways to study and quantify animal behaviour as
connected 'layers' of interactions. In this article, we review common questions
in animal behaviour that can be studied using a multilayer approach, and we
link these questions to specific analyses. We outline the types of behavioural
data and questions that may be suitable to study using multilayer network
analysis. We detail several multilayer methods, which can provide new insights
into questions about animal sociality at individual, group, population, and
evolutionary levels of organisation. We give examples for how to implement
multilayer methods to demonstrate how taking a multilayer approach can alter
inferences about social structure and the positions of individuals within such
a structure. Finally, we discuss caveats to undertaking multilayer network
analysis in the study of animal social networks, and we call attention to
methodological challenges for the application of these approaches. Our aim is
to instigate the study of new questions about animal sociality using the new
toolbox of multilayer network analysis.Comment: Thoroughly revised; title changed slightl
Hand-held radiometry: A set of notes developed for use at the Workshop of Hand-held radiometry
A set of notes was developed to aid the beginner in hand-held radiometry. The electromagnetic spectrum is reviewed, and pertinent terms are defined. View areas of multiband radiometers are developed to show the areas of coincidence of adjacent bands. The amounts of plant cover seen by radiometers having different fields of view are described. Vegetation indices are derived and discussed. Response functions of several radiometers are shown and applied to spectrometer data taken over 12 wheat plots, to provide a comparison of instruments and bands within and among instruments. The calculation of solar time is reviewed and applied to the calculation of the local time of LANDSAT satellite overpasses for any particular location in the Northern Hemisphere. The use and misuse of hand-held infrared thermometers are discussed, and a procedure for photographic determination of plant cover is described. Some suggestions are offered concerning procedures to be followed when collecting hand-held spectral and thermal data. A list of references pertinent to hand-held radiometry is included
A Model for Understanding Positive Intergroup Relations Using the In-Group-Favoring Norm
We present a model of intergroup relations focused on the role of the in-group-favoring norm as capable of facilitating positive intergroup relations. We begin by defining the in-group-favoring norm and describing how it affects self-evaluations and evaluations of out-group members. We then outline how positive intergroup relations may result via the implementation of specific techniques fundamental to the in-group-favoring norm, including emphasizing the value of interactions with the out-group, establishing cooperative intergroup norms, and establishing superordinate goals. In so doing, we discuss how classic moderators of intergroup relations, including leadership, guilt, and in-group norms are facilitators of positive intergroup relations once in-group interests are considered
Competition between Traveling Fluid Waves of Left and Right Spiral Vortices and Their Different Amplitude Combinations
Stability, bifurcation properties, and the spatiotemporal behavior of
different nonlinear combination structures of spiral vortices in the counter
rotating Taylor-Couette system are investigated by full numerical simulations
and by coupled amplitude equation approximations. Stable cross-spiral
structures with continuously varying content of left and right spiral modes are
found. They provide a stability transferring connection between the initially
stable, axially counter propagating wave states of pure spirals and the axially
standing waves of so-called ribbons that become stable slightly further away
from onset of vortex flow.Comment: 4 pages, 5 figure
Controlling the stability transfer between oppositely traveling waves and standing waves by inversion-symmetry-breaking perturbations
The effect of an externally applied flow on symmetry degenerated waves
propagating into opposite directions and standing waves that exchange stability
with the traveling waves via mixed states is analyzed. Wave structures that
consist of spiral vortices in the counter rotating Taylor-Couette system are
investigated by full numerical simulations and explained quantitatively by
amplitude equations containing quintic coupling terms. The latter are
appropriate to describe the influence of inversion symmetry breaking
perturbations on many oscillatory instabilities with O(2) symmetry.Comment: 4 pages, 4 figure
Dissipative instability in a partially ionised prominence plasma slab
We investigate the nature of dissipative instability appearing in a
prominence planar thread filled with partially ionised plasma in the
incompressible limit. The importance of partial ionisation is investigated in
terms of the ionisation factor and wavelength of waves propagating in the slab.
To highlight the role of partial ionisation, we have constructed models
describing various situations we can meet in solar prominence fine structure.
Matching the solutions for the transversal component of the velocity and total
pressure at the interfaces between the prominence slab and surrounding plasmas,
we derived a dispersion relation whose imaginary part describes the evolution
of the instability. Results are obtained in the limit of weak dissipation. We
have investigated the appearance of instabilities in prominence dark plumes
using single and two-fluid approximations. We show that dissipative
instabilities appear for flow speeds that are less than the Kelvin-Helmholtz
instability threshold. The onset of instability is determined by the
equilibrium flow strength, the ionisation factor of the plasma, the wavelength
of waves and the ion-neutral collisional rate. For a given wavelength and for
ionisation degrees closer to a neutral gas, the propagating waves become
unstable for a narrow band of flow speeds, meaning that neutrals have a
stabilising effect. Our results show that the partially ionised plasma
describing prominence dark plumes becomes unstable only in a two-fluid (charged
particles-neutrals) model, that is for periods that are smaller than the
ion-neutral collision time. The present study improves our understanding of
stability of solar prominences and the role of partial ionisation in
destabilising the plasma. We show the necessity of two-fluid approximation when
discussing the nature of instabilities: waves in a single fluid approximation
show a great deal of stability.Comment: 12 pages, 11 figure
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