Spatial Coherence Research Papers - Academia.edu (original) (raw)

Climate change is already altering the magnitude and/or frequency of extreme events which will in turn affect plant fitness more than any change in the average. Although the fingerprint of anthropogenic warming in recent phenological records is well understood, the impacts of extreme events have been largely neglected. Thus, the temperature response of European phenological records to warm and cold spells was studied using the COST725 database. We restricted our analysis to the period 1951-2004 due to better spatial coverage. Warm and cold spells were identified using monthly mean ENSEMBLES temperature data on a 0.5°grid for Europe. Their phenological impact was assessed as anomalies from maps displaying mean onsets for 1930-1939. Our results clearly exhibit continental cold spells predominating in the period 1951-1988, especially during the growing season, whereas the period from 1989 onwards was mainly characterised by warm spells in all seasons. The impacts of these warm/cold spells on the onset of phenological seasons differed strongly depending on species, phase and timing. "False" phases such as the sowing of winter cereals hardly reacted to summer warm/cold spells; only the sowing of summer cereals mirrored spring temperature warm/cold spells. The heading dates of winter cereals did not reveal any consistent results probably due to fewer warm/cold spells identified in the relevant late spring months. Apple flowering and the harvest of winter cereals were the best indicators of warm/ cold spells in early spring and summer, also being spatially coherent with the patterns of warm/cold spells.

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- Climate Change, Environmental Monitoring, Biometeorology, Seasonality

In standard near-field scanning optical microscopy (NSOM), a subwavelength probe acts as an optical 'stethoscope' to map the near field produced at the sample surface by external illumination 1 . This technique has been applied using visible 1,2 , infrared 3 , terahertz 4 and gigahertz 5,6 radiation to illuminate the sample, providing a resolution well beyond the diffraction limit. NSOM is well suited to study surface waves such as surface plasmons 7 or surfacephonon polaritons 8 . Using an aperture NSOM with visible laser illumination, a near-field interference pattern around a corral structure has been observed 9 , whose features were similar to the scanning tunnelling microscope image of the electronic waves in a quantum corral 10 . Here we describe an infrared NSOM that operates without any external illumination: it is a near-field analogue of a night-vision camera, making use of the thermal infrared evanescent fields emitted by the surface, and behaves as an optical scanning tunnelling microscope 11,12 . We therefore term this instrument a 'thermal radiation scanning tunnelling microscope' (TRSTM). We show the first TRSTM images of thermally excited surface plasmons, and demonstrate spatial coherence effects in near-field thermal emission.

- by Jean-jacques Greffet
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- Multidisciplinary, Near-field scanning optical microscopy, Nature, Terahertz

In this paper we show the latest achievements of HgCdTe-based infrared bispectral focal plane arrays (FPAs) at LETI infrared laboratory. We present and compare the two different pixel architectures that are studied now in our laboratory, named ''NPN'' and ''pseudo-planar''. With these two technologies, a wide range of system applications in dual-band detection can be covered. Advantages of both architectures will be pointed out. We also review performances obtained with these different architectures. The first one has been studied for several years in our laboratory, and we review results obtained on FPAs of size 256 · 256 pixels on a 25 lm pitch, in the MWIR/MWIR (3 lm/5 lm) range. Very high noise equivalent temperature difference (NETD) operability is obtained, at 99.8% for the k c = 3 lm band and 98.7% for the k c = 5 lm band. The second one has been developed more recently, to address other applications that need temporal coherence as well as spatial coherence. We show detailed performances measured on pseudo-planar type FPAs of size 256 · 256 pixels on a 30 lm pitch, in the MWIR/LWIR (5 lm/9 lm) range. The results are also very promising for these prototypes, with NETD as low as 15 mK for an integration time as short as 1 ms, and good operability. The main manufacturing issues are also presented and discussed for both pixel architectures. Challenging process steps are, firstly, molecular beam epitaxy (MBE) HgCdTe heterostructure growth, on large substrates (cadmium zinc telluride) and heterosubstrates (germanium), and, secondly, detector array fabrication on a nonplanar surface. In particular, trenches or hole etching steps, photolithography and hybridization are crucial to improve uniformity, number of defects and performances. Some results of surface, structural and electrical characterizations are shown to illustrate these issues. On the basis of these results, the short-term and longterm objectives and trends for our research and development are presented, in terms of pixel pitch reduction, wavelengths, and dual-band FPA size.

- by Pierre Castelein and +1
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- Electronic Materials, Molecular beam epitaxy, Temporal coherence, Research and Development

Collision detection between moving objects is an open question which raises major problems concerning its algorithmic complexity. In this paper we present a polygon collision detection algorithm which uses polygon decomposition through triangle coverings and polygon influence areas (implemented by signs of barycentric coordinates). By using influence areas and the temporal and spatial coherence property, the amount of time needed to detect a collision between objects is reduced. By means of these techniques, a valid representation for any kind of polygon is obtained, whether concave or convex, manifold or non-manifold, with or without holes, as well as a collision detection algorithm for this type of figures. This detection algorithm has been compared with the well-known PIVOT2D [Hof01] one and better results have been achieved in most situations. This improvement together with its possible extension to 3D makes it an attractive method because pre-processing of the polygons is no longer necessary. Besides, since this method uses sign operations, it proves to be a simple, more efficient and robust method.

In the southwestern part of the Ashanti Belt, the results of fractal and Fry analyses of the spatial pattern of 51 known mines/prospects of (mostly lode) gold deposits and the results of analysis of their spatial associations with faults and fault intersections suggest different predominant structural controls on lode gold mineralisation at local and district scales. Intersections of NNE-and NW-trending faults were likely predominantly involved in local-scale structural controls on lode gold mineralisation, whilst NNEtrending faults were likely predominantly involved in district-scale structural controls on lode gold mineralisation. The results of the spatial analyses facilitate the conceptualisation and selection of spatial evidence layers for lode gold prospectivity mapping in the study area. The applications of the derived map of lode gold prospectivity and a map of radial density of spatially coherent lode gold mines/ prospects results in a one-level prediction of 37 undiscovered lode gold prospects. The applications of quantified radial density fractal dimensions of the spatial pattern of spatially coherent lode gold mines/prospects result in an estimate of 40 undiscovered lode gold prospects. The study concludes finally that analysis of the spatial pattern of discovered mineral deposits is the key to a strong link between mineral prospectivity mapping and assessment of undiscovered mineral deposits.

- by John Carranza
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- Geology, Geochemistry, Structural Control, Fractal Analysis

Cold electrons bunches can be created by near-threshold photoionisation of a cloud of cold atoms in a magneto-optical trap (MOT). The electrons can be extracted with temperatures less than 15 K and, due to their low momentum spread, an electron bunch created from cold atoms has high spatial coherence. Coupled with the potential of high brightness, a cold atom electron source (CAES) is a promising prospect for single-shot diffractive imaging of nanoscale objects.
This thesis describes the construction and characterisation of a cold atom electron source. A CAES relies on laser cooling and trapping techniques which require stable, high precision external cavity diode lasers (ECDLs) with narrow linewidth, minimal frequency noise and reproducible day-to-day operation.
The research presented here begins by extending the current understanding of this crucial component of the apparatus, specifically to detail a new model of laser frequency mode selection that shows the critical role played by the external cavity in determining the frequency stability. A geometric relationship is introduced, defining in a straightforward way how the mode-hop-free tuning range of an ECDL can be optimised. It is also shown that the frequency linewidth of an ECDL varies with the focus of the collimation lens used. This previously unidentified effect is described with a Gaussian optics model, and shown theoretically and experimentally to have a significant effect on the laser linewidth. A new monolithic block ECDL design based on these results was constructed for the CAES apparatus and performed favourably in comparison to previous designs, proving to be robust and reliable.
A CAES is a new type of electron source whose quantitatively different properties are under intense study. A model describing the spatial coherence properties of a CAES using a statistical optics framework was developed to better understand the capabilities of the source in diffractive imaging applications. The extracted electron bunches are shown to have properties analogous to quasi-monochromatic paraxial optical wavefields. Based on the theoretical model, I have developed and implemented a novel technique to measure the transverse spatial coherence of the source using electron bunches arbitrarily shaped in two dimensions. The coherence length measurement indicates a lower limit of 10 nm for cold electron bunches, an order of magnitude larger than conventional photoemission electron sources.
Such a large coherence length required the development of a diffractive imaging model for assessing the viability of current and future experiments. An analytic expression describing the electrostatic potential of a single biomolecule was derived for use in a diffraction simulation algorithm. Simulated diffraction patterns of a biomolecule were produced indicating single shot imaging of nanoscale objects using a CAES will be achievable.
Compared with conventional electron sources, the CAES thus has several advantages for diffractive imaging applications: the demonstrated substantial increase in source coherence; the novel ability to create low emittance, arbitrarily shaped electron bunches; and the high brightness potential desirable for single-shot imaging. The simulations and experiments characterising the CAES source described here demonstrate the viability of diffractive imaging experiments anticipated in the near future.

- by Sebastian Saliba
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- Electron Diffraction, Partial Coherence, Spatial Coherence, Electron Sources

Multispectral thermal infrared remote sensing of surface emissivities can detect and monitor long term land vegetation cover changes over arid regions. The technique is based on the link between spectral emissivities within the 8.5-9.5 μm interval and density of sparsely covered terrains. The link exists regardless of plant color, which means that it is often possible to distinguish bare soils from senescent and non-green vegetation. This capability is typically not feasible with vegetation indices. The method is demonstrated and verified using ASTER remote sensing observations between 2001 and 2003 over the Jornada Experimental Range, a semi-arid site in southern New Mexico, USA. A compilation of 27 nearly cloud-free, multispectral thermal infrared scenes revealed spatially coherent patterns of spectral emissivities decreasing at rates on the order of 3% per year with R 2 values of ∼ 0.82. These patterns are interpreted as regions of decreased vegetation densities, a view supported by groundbased leaf area index transect data. The multi-year trend revealed by ASTER's 90-m resolution data are independently confirmed by 1-km data from Terra MODIS. Comparable NDVI images do not detect the long-term spatially coherent changes in vegetation. These results show that multispectral thermal infrared data, used in conjunction with visible and near infrared data, could be particularly valuable for monitoring land cover changes.

- by Frédéric Jacob
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- Remote Sensing, Near Infrared, Geomatic Engineering, New Mexico

The simulation of remote sensing images is a useful tool for a variety of tasks, such as the definition of future Earth Observation systems, the optimization of instrument specifications, and the development and validation of data processing algorithms. A scene simulator for optical hyperspectral and multispectral data has been implemented in the frame of the Environmental Mapping and Analysis Program (EnMAP) mission. EnMAP is a German built hyperspectral space sensor scheduled for launch in 2012. EnMAP will measure in the 420-2450 nm spectral range at a varying spectral sampling of 6.5-10 nm. Images will cover 30 km×30 km areas at an approximate ground sampling distance of 30 m. The EnMAP scene simulator presented in this paper is able to generate realistic EnMAP-like data in an automatic way under a set of user-driven instrumental and scene parameters. Radiance and digital numbers data are generated by 5 sequential processing modules which are able to produce data over a range of natural environments, acquisition and illumination geometries, cloud covers and instrument configurations. The latter include the simulation of data non-uniformity in the spatial and spectral domains, spatially coherent and non-coherent instrumental noise and instrument's modulation transfer function. Realistic surface patterns for the simulated data are provided by existing remote sensing data in different environments, from dry geological sites to green vegetation areas. A flexible radiative transfer simulation scheme enables the generation of different illumination, observation and atmospheric conditions. The methodology applied to the complete scene simulation and some sample results are presented and analyzed in this paper.

- by Karl Segl
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- Geophysics, Imaging spectroscopy, Geomatic Engineering, Natural Environment

This work is devoted to a presentation of the ECOCLIMAP-II database for Western Africa, which is an upgrade for this region of the former initiative, ECOCLIMAP-I, implemented at global scale. ECOCLIMAP-II is a dual database at 1-km resolution that comprises an ecosystem classification and a coherent set of land surface parameters. This new physiographic information (e.g. leaf area index, fractional vegetation cover, albedo and land cover classification), was especially developed in the framework of the African Monsoon Multidisciplinary Analysis (AMMA) programme in order to support the modelling of land-atmosphere interactions, which stresses the importance of the present study. Criteria for coherence between prevalent land cover classifications and the analysis of time series of the satellite leaf area index (LAI) between 2000 and 2007 constitute the analysis tools for setting up ECOCLIMAP-II. The LAI and inferred fraction of vegetation cover are spatially distributed per land cover unit. The fraction of vegetation cover is handled to split the land surface albedo into vegetation and bare soil albedo components, as is required for a large number of applications. The new ECOCLIMAP-II land cover product is improved with regard to the spatial coherence compared to former version. The reliability of the physiographic details is also confirmed through verification with land cover products at higher resolution.

- by Armel Kaptue
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- Remote Sensing, Time Series, Land Cover, Geomatic Engineering

Holographic Displays (HDs) provide 3D images with all natural depth cues via computer generated holograms (CGHs) implemented on spatial light modulators (SLMs). HDs are coherent light processing systems based on interference and diffraction, thus they generally use laser light. However, laser sources are relatively expensive, available only at some particular wavelengths and difficult to miniaturize. In addition, highly coherent nature of laser light makes some undesired visual effects quite evident, such as speckle noise, interference due to stray light or defects of optical components. On the other hand, LED sources are available in variety of wavelengths, has small die size, and no speckle artifact. However, their finite spatial size introduce some degree of spatial incoherence in an HD system and degrade image resolution, which is the subject of the study in this paper. Our theoretical analysis indicates that the amount of resolution loss depends on the distance between hologram and SLM image planes. For some special configurations, the source size has no effect at all. We also performed experiments with different configurations using lasers and LEDs with different emission areas that vary from 50 µm to 200 µm, and determined Contrast Transfer Function (CTF) curves which agree well with our theoretical model. The results show that it is possible to find configurations where LEDs combined with pinholes almost preserve natural resolution limit of human eye while keeping the loss in light efficiency within tolerable limits.

- by vahid pourreza ghoushchi and +1
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- Digital Holography, LED Lighting, Coherence, Spatial Coherence

Wayfinding, or the ability to plan and navigate a course over the landscape, is a subject of investigation in geography, neurophysiology, psychology, urban planning, and landscape design. 1–4 With the prevalence of GPS-assisted navigation systems, or " wayfinders, " computer scientists are also increasingly interested in understanding how people plan their movements and guide others. However, the importance of wayfinding as a process that regulates human mobility has only recently been incorporated into archeological research design. 5,6 Hominin groups were able to disperse widely during the course of prehistory. The scope of these dispersals speaks to the innate navigation abilities of hominins. Their long-term success must have depended on an ability to communicate spatial information effectively. Here, we consider the extent to which some landscapes may have been more conducive to wayfinding than others. We also describe a tool we have created for quantifying landscape legibility (sensu Gollege 2), a complex and under-explored concept in archeology, with a view to investigating the impact of landscape structure on human way-finding and thus, patterns of dispersal during prehistory. To this end, we have developed a method for quantifying legibility using a Geographic Information System (GIS) and apply it to a test case in prehistoric Iberia.

- by Dario Guiducci
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- Landscape Archaeology, Wayfinding, Visual Saliency, Spatial Coherence

1] We propose a multimodel ensemble forecast framework for streamflow forecasts at multiple locations that incorporates large-scale climate information. It has four broad steps: (1) Principal component analysis is performed on the spatial streamflows to identify the dominant modes of variability. (2) Potential predictors of the dominant streamflow modes are identified from several large-scale climate features and snow water equivalent information.

We describe the spatial coherence properties of a cold atom electron source in the framework of a quasihomogeneous waveﬁeld. The model is used as the basis for direct measurements of the transverse spatial coherence length of electron bunches extracted from a cold atom electron source. The coherence length is determined from the measured visibility of a propagated electron distribution with a sinusoidal proﬁle of variable spatial frequency. The electron distribution was controlled via the intensity proﬁle of an atomic excitation laser beam patterned with a spatial light modulator. We measure a lower limit to the coherence length at the source of lc=7.8±0.9 nm.

- by Sebastian Saliba
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- Partial Coherence, Laser beam shaping, Coherent electrons, Phase Space Methods

1] Long-term observational data reveal that both the frequency and amount of light rain have decreased in eastern China (EC) for 1956-2005 with high spatial coherency. This is different from the trend of total rainfall observed in EC, which decreases in northern EC and increases in southern EC. To examine the cause of the light rain trends, we analyzed the long-term variability of atmospheric water vapor and its correlation with light rain events. Results show very weak relationships between large-scale moisture transport and light rain in EC. Because of human activities, pollutant emission has increased dramatically in China for the last few decades, leading to a significant reduction in visibility between 1960 and 2000. Cloud-resolving model simulations over EC show that aerosols corresponding to polluted conditions can significantly increase the cloud droplet number concentration (CDNC) and reduce droplet sizes compared to pristine conditions. This can lead to a significant decline in raindrop concentration and delay raindrop formation because smaller cloud droplets are less efficient in the collision and coalescence processes. Together with weaker convection, the precipitation frequency and amount are significantly reduced in the polluted case in EC. Satellite data also reveal higher CDNC and smaller droplet size over polluted land in EC relative to pristine regions, which is consistent with the model results. Observational evidences and simulations results suggest that the significantly increased aerosol concentrations produced by air pollution are at least partly responsible for the decreased light rain events observed in China over the past 50 years.

- by Jiwen Fan and +1
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- Air pollution, Multidisciplinary, Water Cycle, Global change

In this paper we show the latest achievements of HgCdTe-based infrared bispectral focal plane arrays (FPAs) at LETI infrared laboratory. We present and compare the two different pixel architectures that are studied now in our laboratory, named “NPN” and “pseudo-planar”. With these two technologies, a wide range of system applications in dual-band detection can be covered. Advantages of both architectures will be pointed out. We also review performances obtained with these different architectures. The first one has been studied for several years in our laboratory, and we review results obtained on FPAs of size 256 × 256 pixels on a 25 μm pitch, in the MWIR/MWIR (3 μm/5 μm) range. Very high noise equivalent temperature difference (NETD) operability is obtained, at 99.8% for the λc = 3 μm band and 98.7% for the λc = 5 μm band. The second one has been developed more recently, to address other applications that need temporal coherence as well as spatial coherence. We show detailed performances measured on pseudo-planar type FPAs of size 256 × 256 pixels on a 30 μm pitch, in the MWIR/LWIR (5 μm/9 μm) range. The results are also very promising for these prototypes, with NETD as low as 15 mK for an integration time as short as 1 ms, and good operability. The main manufacturing issues are also presented and discussed for both pixel architectures. Challenging process steps are, firstly, molecular beam epitaxy (MBE) HgCdTe heterostructure growth, on large substrates (cadmium zinc telluride) and heterosubstrates (germanium), and, secondly, detector array fabrication on a nonplanar surface. In particular, trenches or hole etching steps, photolithography and hybridization are crucial to improve uniformity, number of defects and performances. Some results of surface, structural and electrical characterizations are shown to illustrate these issues. On the basis of these results, the short-term and long-term objectives and trends for our research and development are presented, in terms of pixel pitch reduction, wavelengths, and dual-band FPA size.

The impact of grazing by herbivorous fishes (Acanthuridae, Scaridae, and Pomacentridae) on low coral-cover reefs was assessed by measuring rates of benthic algal production and consumption on inshore and offshore reefs in the upper Florida Keys. Algal production rates, determined in situ with caged and uncaged experimental plates, were low (mean 1.05 g C m À2 day À1 ) and similar among reef types. Algal consumption rates were estimated using two different models, a detailed model incorporating fish bite rates and algal yield-per-bite for one species extrapolated to a guild-wide value, and a general regression relating fish biomass to algal consumption. Algal consumption differed among reef types: a majority of algal production was consumed on offshore reefs (55-100%), whereas consumption on inshore patch reefs was 31-51%. Spatial variation in algal consumption was driven by differences in herbivorous fish species composition, density, and size-structure among reef types. Algal consumption rates also varied temporally due to seasonal declines in bite rates and intermittent presence of large-bodied, vagile, schooling species. Spatial coherence of benthic community structure and temporal stability of algal turf over 3 years suggests that grazing intensity is currently sufficient to limit further spread of macroalgal cover on these low coral-cover reefs, but not to exclude it from the system.

- by Michelle Paddack
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- Earth Sciences, Coral Reefs, Biological Sciences, Seasonality

Microphone arrays have been used in various applications to capture conversations, such as in meetings and teleconferences. In many cases, the microphone and likely source locations are known a priori, and calculating beamforming filters is therefore straightforward. In ad-hoc situations, however, when the microphones have not been systematically positioned, this information is not available and beamforming must be achieved blindly. In achieving this, a commonly neglected issue is whether it is optimal to use all of the available microphones, or only an advantageous subset of these. This paper commences by reviewing different approaches to blind beamforming, characterising them by the way they estimate the signal propagation vector and the spatial coherence of noise in the absence of prior knowledge of microphone and speaker locations. Following this, a novel clustered approach to blind beamforming is motivated and developed. Without using any prior geometrical information, microphones are first grouped into localised clusters, which are then ranked according to their relative distance from a speaker.

- by Iman Himawan
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- Engineering, Signal Processing, Statistical Analysis, Speech Recognition

To carry out a realistic simulation of earthquake strong ground motion for applied studies, one needs an earthquake fault/source simulator that can integrate most relevant features of observed earthquake ruptures. A procedure of this kind is proposed that creates a broadband kinematic source model. At lower frequencies, the source is described as propagating slip pulse with locally variable velocity. The final slip is assumed to be a 2D random function. At higher frequencies, radiation from the same running strip is assumed to be random and incoherent in space. The model is discretized in space as a grid of point subsources with certain time histories. At lower frequencies, a realistic shape of source spectrum is generated implicitly by simulated kinematics of slip pulse propagation. At higher frequencies, the original approach is used to generate signals with spectra that plausibly approximate the prescribed smooth far-field source spectrum. This spectrum is set on the basis of the assumedly known regional empirical spectral scaling law, and subsource moment rate time histories are conditioned so as to fit this expected spectrum. For the random function that describes final slip over the fault area, probability distribution of amplitudes is assumed lognormal, on the basis of exploratory analysis of inverted slip distributions. Similarly, random functions that describe local slip rate time histories are assumed to have the lognormal distribution of envelope amplitudes. In this way one can effectively emulate expressed "asperities" of final slip and occasional occurrence of large spikes on near-source accelerograms. A special procedure is proposed to simulate the spatial coherence of high-frequency fault motion. This approach permits to simulate fault motion plausibly at high spatial resolution, creating the prerequisite for the simulation of strong motion in the vicinity of a fault. A particular realization (sample) of a source created in a simulation run depends on several random seeds, and also on a considerable number of parameters. Their values can be selected so as to take into account expected source features; they can also be perturbed, to examine the source-related component of uncertainty of strong motion. The proposed approach to earthquake source specification is well adapted to the study of deterministic seismic hazard: it may be used for simulation of individual scenario events, or suites of such events, as well as for the analysis of uncertainty for expected ground motion parameters from a particular class of events. Examples are given of application of the proposed approach to strong motion simulations and related uncertainty estimation.

- by Alexander Gusev
- •
- Geophysics, Probability Distribution & Applications, Spectrum, Spatial Coherence

The spatio-temporal variability of boreal summer monsoon onset over the Philippines is studied through the analysis of daily rainfall data across a network of 76 gauges for the period 1977 to 2004 and the pentad Merged Analysis of Precipitation from the US Climate Prediction Center from 1979 to 2006. The onset date is defined using a local agronomic definition, namely the first wet day of a 5-day period receiving at least 40 mm without any 15-day dry spell receiving less than 5 mm in the 30 days following the start of that period. The onset is found to occur rather abruptly across the western Philippines around mid-May on average and is associated with the set-up of a "classical" monsoonal circulation with low-level easterlies subsequently veering to southerly, and then southwesterly. The onset manifests itself merely as a seasonal increase of rainfall over the eastern Philippines, where rainfall occurs throughout most of the year.

- by Vincent Moron
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- Oceanography, Climate, Sea surface temperature, Indian Ocean

Keywords: chacma baboon coordination group behaviour Papio ursinus sociality synchrony For group-living individuals to remain spatially coherent, coordinated behaviour across group members is essential. We investigated what factors can promote or constrain the achievement of such behavioural synchronization (measured as diversity in activities among group members) in a social primate. Two wild groups of chacma baboons, Papio ursinus, were studied in the field by instantaneous scan sampling during full-day follows to test the hypotheses that individual activity budgets, habitat constraints and group properties can all affect patterns of behavioural synchrony. Observed synchrony across individuals was variable, and analysed using a generalized linear mixed model. We found support for each of our three hypotheses. First, the probability of a group being synchronized increased with the number of pregnant females, but decreased with the number of sexually swollen females in a group. Synchrony also declined throughout the day. We interpret these two results in terms of variations in the activity budgets of both sexes related to their reproductive strategies, and changing levels of satiation among individual group members, respectively. Second, synchrony was highest in a 'closed' woodland habitat, and lowest in 'open' desert habitat. This is interpreted as a consequence of habitat differences in food patch configuration and/or predation risk. Third, we found a nonlinear relationship with increasing group cohesion, suggesting that where opportunities for information transfer are limited, behavioural synchrony may be constrained. Overall, our simple approach to quantifying behavioural synchrony highlights the role of both individual variation and the (social and ecological) environment in determining group-level patterns of behaviour. Ó

- by Andrew King
- •
- Social Interaction, Group Behavior, Animal Behaviour, Biological Sciences

We measure the spatial coherence function of a quasi-monochromatic 1.1 keV X-ray beam from an undulator at a third-generation synchrotron. We use a Young's slit apparatus to measure the coherence function and ®nd that the coherence measured is poorer than expected. We show that this dierence may be attributed to the eects of speckle due to the beamline optics. The conditions for successful coherence transport are considered. Ó

- by Christopher Chantler
- •
- Optics, X Rays, Optical physics, Spatial Coherence

We experimentally demonstrate that violations of Bell's inequalities for two-photon polarization-entangled states with colored noise are extremely robust, whereas this is not the case for states with white noise. Controlling the amount of noise by using the timing compensation scheme introduced by Kim et al. ͓Phys. Rev. A 67, 010301͑R͒ ͑2003͔͒, we have observed violations even for states with very high noise, in excellent agrement with the predictions of Cabello et al. ͓Phys. Rev. A 72, 052112 ͑2005͔͒.

- by Gerard Collins
- •
- Measure Theory, Thermodynamics, Data Mining, Quantum Information

- by Wim Ubachs
- •
- Measure Theory, Thermodynamics, Data Mining, Quantum Information

Mostly, the typical light distribution of a light source, as a LED or an excimer laser, is not suitable for the application. The excimer laser beam for example shows a distinct elliptical Gaussian profile. As another example the layout of the light emitting chip and the reflector of a LED form an extremely inhomogeneous luminescent area. To achieve a better adapted beam profile a homogenizing setup with beam shaping qualities can be used. In this talk two setups for homogenization with the help of refractive micro lens arrays are shown and compared. The main attention is turned on the influence of the numerical aperture of the micro lenses, the limitations due to the spatial coherence degree and the difficulties of the alignment of the systems. In addition, a diffractive solution of homogenization for spatial partially coherence is presented.

- by Irina Harder
- •
- Beam shaping, Spatial Coherence, Excimer Laser, Numerical Aperture

We present results on development and experimental implementation of a 1−kHz, coherent extreme ultraviolet (XUV) radia− tion source based on high−order harmonic generation of the femtosecond, near−infrared laser pulses produced by the tita− nium−doped sapphire laser system (35 fs, 1.2 mJ, 810 nm) at the Institute of Physics AS CR / PALS Centre. The source com− prises a low−density static gas cell filled with a conversion medium, typically argon. The comprehensive optimization of the XUV harmonic source has been performed with respect to major parameters such as gas pressure in the cell, cell length, po− sition of the focus of the driving laser field with respect to the gas cell position, size of the driving near−infrared laser beam, chirp of the femtosecond pulse, and the focal length of the lens deployed in the experimental setup. Harmonic spectra were recorded using an XUV transmission grating spectrometer developed specifically for this purpose. Detailed characterization of the XUV source has been performed including measurement of the XUV beam profile, M 2 parameter of the beam, absolute energy, and spatial coherence.

- by Ladislav Pina and +1
- •
- Ultrafast Optics, Titanium, Near Infrared, Optical physics

1] Latitudinal and diurnal distributions of spectral power and spatial coherency parameters of the geomagnetic variations in the Pc5-6 (1-6 mHz) frequency range are analyzed using data of magnetometer stations in Antarctica. The available stations give the possibility to form a latitude chain along the geomagnetic meridian 40°E stretching from magnetic latitude 69°S to 86°S. Long-period ULF activity at polar cap latitudes is characterized by lower amplitudes and wider spectra with lower central frequencies as compared with typical auroral Pc5 pulsations. The meridional distribution of average Pc5-6 spectral power is nonmonotonic and has a minimum near 80°. In general, the low-frequency broadband ULF activities in the polar cap and at auroral latitudes seem to be decoupled. This long-period ULF activity in the polar cap could be an image of wave activity in the tail lobes or the manifestation of turbulent component of the ionospheric convection at very high latitudes, but this requires further investigation.

- by Viacheslav Pilipenko and +2
- •
- Multidisciplinary, Low Frequency, Ionosphere, Magnetospheric Physics

The SELF (SEa Level Fluctuations: geophysical interpretation and environmental impact) project has been developed and realized in the framework of the Environment Programme designed by the Commission of the European Communities. The SELF project was aimed at providing a reliable base for the determination, in the Mediterranean area, of sea-level variations which could then be used as a possible indicator of climate changes and to study the interactions taking place among the ocean, the atmosphere., and the solid Earth. The project has made it possible to define a consistent network of well-established tide gauges encompassing the Mediterranean Basin as far as the Black Sea and to determine to centimeter accuracy the tide gauge benchmark heights in a global well-defined reference system such as the one provided by the SLR/VLBI space techniques. The SELF network constitutes, for the Mediterranean, the necessary prerequisite towards achieving the actual capability to separate vertical crustal movements from true sea-level variations. This has been accomplished through the use of space techniques namely SLR, VLBI and GPS in conjunction with Water Vapor Radiometer observations and absolute gravity measurements. The analysis of the available tide gauge records has shown a high spatial coherence of the annual to multidecadal sea-level variability. Sea-level fluctuations at periods longer than two months were found to be strongly correlated with air pressure. The seasonal cycle was found to be variable in time. Relative sea-level trends determined from records longer than 30 years are less than 1.5 mm/yr. Crustal movement rates as * Corresponding author.

- by Marzenna Sztobryn
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- Earth Sciences, Climate Change, Sea Level, Spatial Scale

It is current practice to take tiny samples from a painting to mount and examine in cross-section under a microscope. However, since conservation practice and ethics limit sampling to a minimum and to areas along cracks and edges of paintings, which are often unrepresentative of the whole painting, results from such analyses cannot be taken as representative of a painting as a whole. Recently in a preliminary study, we have demonstrated that near-infrared Optical Coherence Tomography (OCT) can be used directly on paintings to examine the cross-section of paint and varnish layers without contact and the need to take samples. OCT is an optical interferometric technique developed for in vivo imaging of the eye and biological tissues; it is essentially a scanning Michelson's interferometer with a 'broadband' source that has the spatial coherence of a laser. The low temporal coherence and high spatial concentration of the source are the keys to high depth resolution and high sensitivity 3D imaging. The technique is non-invasive and noncontact with a typical working distance of 2 cm. This non-invasive technique enables cross-sections to be examined anywhere on a painting. In this paper, we will report new results on applying near-infrared en-face OCT to paintings conservation and extend the application to the examination of underdrawings, drying processes, and quantitative measurements of optical properties of paint and varnish layers.

- by Justin Pedro
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- Optical coherence tomography, Confocal Microscopy, Near Infrared, Temporal coherence

We report on the generation and rapid characterization of structured beams of arbitrary spatial coherence. An experimental setup is introduced capable of generating partially coherent fields by incoherently superposing fully coherent fields. The characterization is performed using the spectral information in the interferogram produced when using a two-dimensional nonredundant array of pinholes. An example of a partially coherent "doughnut" beam is given and proved to be partially coherent.

By measuring the fringe visibility in a Young's double pinhole experiment, we demonstrate that quasiphase-matched high-harmonic generation produces beams with very high spatial coherence at wavelengths around 13 nm. To our knowledge these are the highest spatial coherence values ever measured at such short wavelengths from any source without spatial filtering. This results in a practical, small-scale, coherent, extreme-ultraviolet source that is useful for applications in metrology, imaging, and microscopy.

- by Ariel Paul
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- Optics, Quantum Physics, Nonlinear Optics, Quantum Mechanics

The presence of speckle noise in the reconstruction process of digital hologram reduces the signal to noise ratio (SNR) in the reconstructed images. In this paper we present wavelet filtering to improve SNR in the reconstructed images.... more

Satellite-based hyperspectral imaging became a reality in November 2000 with the successful launch and operation of the Hyperion system on board the EO-1 platform. Hyperion is a pushbroom imager with 220 spectral bands in the 400-2500 nm... more

- by Jonathan Huntington
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- Geology, South Australia, Hyperspectral Imaging, Infrared

One main process in Computer Vision is image segmentation as a tool to other visual tasks. Although there are many approaches to grey scale image segmentation, nowadays most of the digital images are colour images. This paper introduces a new method for colour image segmentation. We focus our work on a topological study of colour distribution, e.g., image histogram. We argue that this point of view bring us the possibility to find dominant colours by preserving the spatial coherence of the histogram. To achieve it, we find and extract ridges of the colour distribution and assign a unique colour at every ridge as a representative colour of an interest region. This method seems to be not affected by shadows in a wide range of tested images.

The paper presents a qualitative and quantitative analysis of flood variability and forcing of major European rivers since AD 1500. We compile and investigate flood reconstructions which are based on documentary evidence for twelve Central European rivers and for eight Mediterranean rivers. Flood variability and underlying climatological causes are reconstructed by using hermeneutic approaches including critical source analysis and by applying a semi-quantitative classification scheme. The paper describes the driving climatic causes, seasonality and variability of observed flood events within the different river catchments covering the European mainland. Historical flood data are presented and recent research in the field of historical flood reconstructions is highlighted. Additionally, the character of the different flood series is discussed. A comparison of the historical flood seasonality in relation to modern distribution is given and aspects of the spatial coherence are present...

- by Rüdiger Glaser
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- Multidisciplinary, Seasonality, Source Code Analysis, Comparative Analysis

A frequency-wavenumber tidal analysis for deriving internal-tide harmonic constants from TOPEX/ Poseidon (T/P) measurements of sea-surface height (SSH) has been developed, taking advantage of the evident temporal and spatial coherence and the weak dissipation of internal tides. Previous analyses consisted of simple tidal analysis at individual points, which gave inconsistent harmonic constants at altimeter track crossover points. Such analyses have difficulty in distinguishing between the effects of interference, incoherence, and dissipation. The frequency-wavenumber analysis provides an objective way to interpolate the internal tides measured along altimetry tracks to any arbitrary point, while leveraging all available data for optimal tidal estimates. Tidal analysis of T/P data from 2000 to 2007 is used to predict in situ time series measured during the 2001-2002 Hawaiian Ocean mixing experiment (HOME), the 1987 reciprocal tomography experiment (RTE87), and the 1991 acoustic mid-ocean dynamics experiment (AMODE), demonstrating both the temporal coherence and the lack of incoherent elements to this wave propagation. It has been conjectured that significant energy would be lost from mode-1 internal tides as they cross the 28.91N critical latitude of parametric subharmonic instability (PSI). No apparent change in amplitude at 28.91N was detected by this analysis, however. Further, after correcting for changes in background stratification, the amplitude of the mode-1 internal tide was found to decrease by less than 20% over the 2000 km between the Hawaiian Ridge and 401N. A significant fraction of the variability of internal waves, that component associated with mode-1 internal tides, appears to be predictable over most of the world's oceans, using harmonic constants derived from satellite altimetry.

- by Matthew Dzieciuch
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- Geochemistry, Oceanography, Time Series, Temporal coherence

This paper is dedicated to Prof. Hannes Lichte on the occasion of his 65th birthday.

- by Axel Lubk
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- Phase Retrieval, Ultramicroscopy, Optical physics, Spatial Coherence

Real time rendering of atmospheric light scattering is one of the most difficult lighting effect to achieve in computer graphics. This paper presents a new real time method which renders these effects including volumetric shadows, which provides a great performance improvement over previous methods. Using an analytical expression of the light transport equation we are able to render directly the contribution of the participating medium on any surface. The rendering of shadow planes, sorted with a spatial coherence technique, and in the same philosophy than the shadow volume algorithm will add the volumetric shadows. Realistic images can be produced in real time for usual graphic scenes and at a high level framerate for complex scenes, allowing animation of lights, objects or even participating media. The method proposed in this paper use neither precomputation depending on light positions, nor texture memory. Figure 1: The same scene lit a. (left) classically, b. (center) with single scattering and c. (right) with single scattering and volumetric shadows (right) .

Obtaining satisfactory visibility of undersea objects has been historically difficult due to the absorptive and scattering properties of seawater. Mitigating these effects has been a long term research focus, but recent advancements in hardware, software, and algorithmic methods have led to noticeable improvement in system operational range. This paper is intended to provide a summary of recently reported research in the area of Underwater Optics and Vision and briefly covers advances in the following areas: 1) Image formation and image processing methods; 2) Extended range imaging techniques; 3) Imaging using spatial coherency (e.g. holography); and 4) Multiple-dimensional image acquisition and image processing.

- by Frank M Caimi
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- Image Processing, Remote Sensing, Imaging, Optical Imaging

We present a hardware architecture and processing unit for point sampled data. Our design is focused on fundamental and computationally expensive operations on point sets including k-nearest neighbors search, moving least squares approximation, and others. Our architecture includes a configurable processing module allowing users to implement custom operators and to run them directly on the chip. A key component of our design is the spatial search unit based on a kd-tree performing both kNN and εN searches. It utilizes stack recursions and features a novel advanced caching mechanism allowing direct reuse of previously computed neighborhoods for spatially coherent queries. In our FPGA prototype, both modules are multi-threaded, exploit full hardware parallelism, and utilize a fixed-function data path and control logic for maximum throughput and minimum chip surface. A detailed analysis demonstrates the performance and versatility of our design.

- by Gael Guennebaud
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- Configural Processing, Kd Tree, Spatial Coherence, Hardware architecture

We review in this article the influence of surface waves on the thermally excited electromagnetic field. We study in particular the field emitted at subwalength distances of material surfaces. After reviewing the main properties of surface waves, we introduce the fluctuation-dissipation theorem that allows to model the fluctuating electromagnetic fields. We then analyse the contribution of these waves in a variety of phenomena. They give a leading contribution to the density of electromagnetic states, they produce both temporal coherence and spatial coherence in the near field of planar thermal sources. They can be used to modify radiative properties of surfaces and to design partially spatially coherent sources. Finally, we discuss the role of surface waves in the radiative heat transfer and the theory of dispersion forces at the subwavelength scale.

- by Jean-jacques Greffet
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- Condensed Matter Physics, Surface Science, Heat Transfer, Temporal coherence

A portable matched-field processing (MFP) system for tracking marine mammals is presented, constructed by attaching a set of autonomous flash-memory acoustic recorders to a rope to form a four-element vertical array, or "insta-array." The acoustic data are initially time-synchronized by performing a matched-field global inversion using acoustic data from an opportunistic source, and then by exploiting the spatial coherence of the ocean ambient noise background to measure and correct for the relative clock drift between the autonomous recorders. The technique is illustrated by using humpback whale song collected off the eastern Australian coast to synchronize the array, which is then used to track the dive profile of the whale using MFP methods. The ability to deploy autonomous instruments into arbitrary "insta-array" geometries with conventional fishing gear may permit nonintrusive array measurements in regions currently too isolated, expensive, or environmentally hostile for standard acoustic equipment.

- by Melania Guerra and +1
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- Underwater Acoustics, Time Synchronization, IEEE, Flash memory

We present results from 1078 high resolution spectra of 990 stars in the young open cluster NGC 2264, obtained with the Hectochelle multiobject echelle spectrograph on the 6.5m MMT. We confirm 471 stars as members, based on their radial velocity and/or Hα emission. The radial velocity distribution of cluster members is non-Gaussian with a dispersion of σ ≈ 3.5km s -1 . We find a substantial north-south velocity gradient and spatially coherent structure in the radial velocity distribution, similar to that seen in the molecular gas in the region. Our results suggest that there are at least three distinguishable subclusters in NGC 2264, correlated with similar structure seen in 13 CO emission, which is likely to be a remnant of initial structure in this very young cluster. We propose that this substructure is the result of gravitational amplification of initial inhomogeneities during overall collapse to a filamentary distribution of gas and stars, as found in simulations by .

- by John Stauffer
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- Physics, Organic Chemistry, Astrophysical Plasma, Star Formation

MJ MANTONa,*, PM DELLA-MARTAb, MR HAYLOCKa, KJ HENNESSYc, N. NICHOLLSa, LE CHAMBERSa, DA COLLINSb, G. DAWd, A. FINETe, D. GUNAWANf, K. INAPEg, H. ISOBEh, TS KESTINi, P. LEFALEj, CH LEYUk, T. LWINl, L. MAITREPIERREm, N. ...

- by Paul Della-marta
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- Environmental Engineering, Civil Engineering, Climate Change, Climatology

yield map represent grain mixed from a certain area, and some uncertainty is associated with the exact size Crop yield maps reflect stable yield patterns and annual random and geographical location of this area as well as meayield variation. Procedures for classifying a sequence of yield maps surement error. For the same location, this uncertainty to delineate yield zones were evaluated in two irrigated maize (Zea mays L.) fields. Yield classes were created using empirically defined is likely to vary from year to year because of different yield categories or through hierarchical or nonhierarchical cluster combine travel paths. Therefore, a single-year yield map analysis techniques. Cluster analysis was conducted using average is useful for interpretation of possible causes of yield yield (MY), average yield and its standard deviation (MS), or all variation but may be of limited value for more strategic individual years (AY) as input variables. All methods were compared SSCM decisions over medium-to long-term periods. based on the average yield variability accounted for (RVc). Methods Procedures must be developed to correct or eliminate in which yield was empirically classified into three or four classes recognizable errors of yield monitor measurement and accounted for less than 54% of the yield variability observed and integrate multiyear sequences of yield maps. Here, we failed to delineate high-yielding areas. Six to seven yield classes established by cluster analysis of MY accounted for 60 to 66% of the yield assume that a sequence of corrected and interpolated variability. Differences among cluster analysis methods were small yield maps, which need to be classified to delineate areas for MY as data source. However, fuzzy-k-means clustering had lower with different yield expectation within a field, has been RVc than other methods if used with the MS or AY data. The spatial obtained. Such classification will result in a map of past fragmentation of yield class maps increased in the order MY Ͻ MS Ͻ yield performance. With multiple years of georefer-AY. Univariate cluster analysis of mean relative yield measured for enced yield data, repeating patterns and their more staat least 5 yr should be used for yield classification in irrigated fields ble natural causes may be separated from random variawhere six to seven classes appear to provide sufficient resolution of the yield variability observed. More research should be conducted to tion in each year, providing a basis for spatially varying develop methods that result in spatially coherent yield zones and to yield goals and other SSCM decisions. understand differences between rainfed and irrigated environments Interpretation and classification of multiple-year in the importance of mapping yield goals for crop management.

- by Viacheslav Adamchuk
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- Agronomy, Standard Deviation, Maize, Cluster Analysis
- by Chandrasekhar Roychoudhuri
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- Optics, Wavelets, Oscillations, Spatial Coherence

A fundamental problem in optical and digital holography is the presence of speckle noise in the reconstruction process. Many approaches have been carried out in order to overcome such a problem ranging from modifying the spatial coherence of the illumination (optical techniques) to image processing techniques (digital techniques). This work shows the merged use of digital image processing techniques in order to reduce the speckle noise in digital reconstruction of optically recorded Fresnel's holograms. The proposed filtering techniques are illustrated with experimental results.

We investigate a digital holographic microscope that permits us to modify the spatial coherence state of the sample illumination by changing the spot size of a laser beam on a rotating ground glass. Out-offocus planes are refocused by digital holographic reconstruction with numerical implementation of the Kirchhoff-Fresnel integral. The partial coherence nature of the illumination reduces the coherent artifact noise with respect to fully coherent illumination. The investigated configuration allows the spatial coherence state to be changed without modifying the illumination level of the sample. The effect of the coherence state on the digital holographic reconstruction is theoretically and experimentally evaluated. We also show how multiple reflection interferences are limited by the use of reduced spatial coherent illumination.

- by Christophe Minetti and +1
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- Mechanical Engineering, Image Reconstruction, Holography, Applied

1] A suite of climate change indices derived from daily temperature and precipitation data, with a primary focus on extreme events, were computed and analyzed. By setting an exact formula for each index and using specially designed software, analyses done in different countries have been combined seamlessly. This has enabled the presentation of the most up-to-date and comprehensive global picture of trends in extreme temperature and precipitation indices using results from a number of workshops held in data-sparse regions and high-quality station data supplied by numerous scientists world wide. Seasonal and annual indices for the period 1951-2003 were gridded. Trends in the gridded fields were computed and tested for statistical significance. Results showed widespread significant changes in temperature extremes associated with warming, especially for those indices derived from daily minimum temperature. Over 70% of the global land area sampled showed a significant decrease in the annual occurrence of cold nights and a significant increase in the annual occurrence of warm nights. Some regions experienced a more than doubling of these indices. This implies a positive shift in the distribution of daily minimum temperature throughout the globe. Daily maximum temperature indices showed similar changes but with smaller magnitudes. Precipitation changes showed a widespread and significant increase, but the changes are much less spatially coherent compared with temperature change. Probability distributions of indices derived from approximately 200 temperature and 600 precipitation stations, with nearcomplete data for 1901-2003 and covering a very large region of the Northern Hemisphere midlatitudes (and parts of Australia for precipitation) were analyzed for the periods 1901-1950, 1951-1978 and 1979-2003. Results indicate a significant warming throughout the 20th century. Differences in temperature indices distributions are particularly pronounced between the most recent two periods and for those indices related to minimum temperature. An analysis of those indices for which seasonal time series are available shows that these changes occur for all seasons although they are generally least pronounced for September to November. Precipitation indices show a tendency toward wetter conditions throughout the 20th century.

- by Little Caesar
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- Climate Change, Time Series, Climate variability, Multidisciplinary