Textural Ordination Based on Fourier Spectral Decomposition: A Method to Analyze and Compare Landscape Patterns

We propose an approach to texture characterization and comparison that directly uses the information of digital images of the earth surface without requesting a prior distinction of structural ‘patches'. Digital images are partitioned into square ‘windows' that define the scale of the analysis and which are submitted to the two-dimensional Fourier transform for extraction of a simplified textural characterization (in terms of coarseness) via the computation of a ‘radial' power spectrum. Spectra computed from many images of the same size are systematically compared by means of a principal component analysis (PCA), which provides an ordination along a limited number of coarseness vs. fineness gradients. As an illustration, we applied this approach to digitized panchromatic air photos depicting various types of land cover in a semiarid landscape of northern Cameroon. We performed ‘textural ordinations' at several scales by using square windows with sides ranging from 120 m to 1 km. At all scales, we found two coarseness gradients (PCA axes) based on the relative importance in the spectrum of large (> 50 km−1), intermediate (30–50 km−1), small (10–25 km−1) and very small (<10 km−1) spatial frequencies. Textural ordination based on Fourier spectra provides a powerful and consistent framework to identifying prominent scales of landscape patterns and to compare scaling properties across landscapes

Impact de la perturbation par les interventions sylvicoles et le feu sur la dynamique d’un peuplement forestier en zone semi-décidue de Côte d’Ivoire

Le dispositif permanent de la Téné (Côte d’Ivoire) est un peuplement forestier aménagé depuis 1978 afin d’étudier, à long terme, la dynamique des essences à potentiel commercial. En 1983, le dispositif a été parcouru à plus de 65% par un feu de forêt. L’objectif de la présente étude est de décrire l’effet de la perturbation occasionnée par les interventions sylvicoles et le passage du feu sur la dynamique du peuplement. Les résultats obtenus et les tests statistiques appliqués ont montré une homogénéité entre les parcelles avant les modalités sylvicoles tandis qu’après celle-ci une différence significative est observée entre les parcelles témoins et traitées. L’évolution de la surface terrière, au cours du temps, montre deux grandes périodes dont la première située entre 1978 à 1982 correspond à l’effet traitement et la seconde traduit par l’effet du feu après 1986. L’impact de la perturbation s’est fait aussi sentir en 1978 sur la surface terrière des essences commerciales tandis qu’au delà de 1994, cet effet s’est fait au profit des essences secondaires. Ces résultats montrent que les interventions sylvicoles supposées favoriser l’accroissement, en volume, des essences commerciales peuvent être vulnérables au feu et entraîner à long terme des effets majeurs sur la dynamique du peuplement.Mots clés : exploitation forestière, éclaircie, feu de forêt, traitements sylvicoles, composition floristique

Water vapor radiometry research and development phase

This report describes the research and development phase for eight dual-channel water vapor radiometers constructed for the Crustal Dynamics Project at the Goddard Space Flight Center, Greenbelt, Maryland, and for the NASA Deep Space Network. These instruments were developed to demonstrate that the variable path delay imposed on microwave radio transmissions by atmospheric water vapor can be calibrated, particularly as this phenomenon affects very long baseline interferometry measurement systems. Water vapor radiometry technology can also be used in systems that involve moist air meteorology and propagation studies

Clustering of Bi-Dimensional and Heterogeneous Times Series: Application to Social Sciences Data

We present an application of bi-dimensional and heterogeneous time series clustering in order to resolve a Social Sciences study issue. The dataset is the result of a survey involving more than eight thousand handicapped persons. Sociologists need to know if there are in this dataset some homogeneous classes of people according to two attributes: the idea that handicapped people have about the quality of their life and their couple status (i.e. if they have a partner or not). These two attributes are time series so we had to adapt the k-Means clustering algorithm in order to be efficient with this kind of data. For this purpose, we use the Longest Common Subsequence time series distance for its efficiency to manage time stretching and we extend it to the bidimensional and heterogeneous case. The results of our unsupervised process give some pertinent and surprising clusters that can be easily analyzed by sociologists.Présentation d'une application d'un "bi-dimensional and heterogeneous time series clustering" pour résoudre un problème en sciences sociales. Les données concernent plus de huit mille personnes en situation de handicap. Le problème est de savoir s'il existe de groupes homogènes vis-à-vis de la qualité de vie ressentie et de la vie de couple déclarée. A ces deux séries temporelles, un algorithme de k-Means clustering a été adapté. Nous avons utilisé the Longest Common Subsequence time series distance et nous l'avons étendue au cas bi-dimensionnel et hétérogène. Le résultat a été pertinent et surprenant, utile à l'analyse sociologique

Surface composition of BaTiO3/SrTiO3(001) films grown by atomic oxygen plasma assisted molecular beam epitaxy

We have investigated the growth of BaTiO3 thin films deposited on pure and 1% Nb-doped SrTiO3(001) single crystals using atomic oxygen assisted molecular beam epitaxy (AO-MBE) and dedicated Ba and Ti Knudsen cells. Thicknesses up to 30 nm were investigated for various layer compositions. We demonstrate 2D growth and epitaxial single crystalline BaTiO3 layers up to 10 nm before additional 3D features appear; lattice parameter relaxation occurs during the first few nanometers and is completed at {\guillemotright}10 nm. The presence of a Ba oxide rich top layer that probably favors 2D growth is evidenced for well crystallized layers. We show that the Ba oxide rich top layer can be removed by chemical etching. The present work stresses the importance of stoichiometry and surface composition of BaTiO3 layers, especially in view of their integration in devices.Comment: In press in J. Appl. Phy

Coupling potential of ICESat/GLAS and SRTM for the discrimination of forest landscape types in French Guiana

The Shuttle Radar Topography Mission (SRTM) has produced the most accurate nearly global elevation dataset to date. Over vegetated areas, the measured SRTM elevations are the result of a complex interaction between radar waves and tree crowns. In this study, waveforms acquired by the Geoscience Laser Altimeter System (GLAS) were combined with SRTM elevations to discriminate the five forest landscape types (LTs) in French Guiana. Two differences were calculated: (1) penetration depth, defined as the GLAS highest elevations minus the SRTM elevations, and (2) the GLAS centroid elevations minus the SRTM elevations. The results show that these differences were similar for the five LTs, and they increased as a function of the GLAS canopy height and of the SRTM roughness index. Next, a Random Forest (RF) classifier was used to analyze the coupling potential of GLAS and SRTM in the discrimination of forest landscape types in French Guiana. The parameters used in the RF classification were the GLAS canopy height, the SRTM roughness index, the difference between the GLAS highest elevations and the SRTM elevations and the difference between the GLAS centroid elevations and the SRTM elevations. Discrimination of the five forest landscape types in French Guiana was possible, with an overall classification accuracy of 81.3% and a kappa coefficient of 0.75. All forest LTs were well classified with an accuracy varying from 78.4% to 97.5%. Finally, differences of near coincident GLAS waveforms, one from the wet season and one from the dry season, were analyzed. The results showed that the open forest LT (LT12), in some locations, contains trees that lose leaves during the dry season. These trees allow LT12 to be easily discriminated from the other LTs that retain their leaves using the following three criteria: (1) difference between the GLAS centroid elevations and the SRTM elevations, (2) ratio of top energy in the wet season to top energy in the dry season, or (3) ratio of ground energy in the wet season to ground energy in the dry season

Low grade waste heat recovery in an intercooled recuperated closed cycle gas turbine

The context of the work is the study of a 180 bar nitrogen recuperated and intercooled turbo-compressor of 300 MWe. The net efficiency of this closed cycle gas turbine is assessed between 37 and 37.5%, but which could be increased by considering waste heat recovery techniques. Among waste heat recovery technologies which are currently used in conventional gas turbines we find organic Rankine cycles (ORC). This kind of machine is similar to a conventional steam cycle energy conversion system, but uses an organic fluid instead of water. A main challenge is the low level of temperature of waste (90°C). Preliminary studies are carried out on the design of ORC using three different fluids: traditional and mature R245fa technology, innovative R125 cycle and high pressure low temperature transcritical CO2 machine. Different architectures are compared and advantages of using transcritical cycles have been underlined. From a thermodynamic point of view the best solution would be to use R125 cycle at a supercritical pressure at precooler secondary side and at a subcritical pressure at intercooler secondary side. A supplementary power of more than 15 MWe could be achieved. The resulting combined cycle could reach a net efficiency of 39%.Papers presented to the 12th International Conference on Heat Transfer, Fluid Mechanics and Thermodynamics, Costa de Sol, Spain on 11-13 July 2016

Photon detection with CMOS sensors for fast imaging

International audiencePixel detectors employed in high energy physics aim to detect single minimum ionizing particle with micrometric positioning resolution. Monolithic CMOS sensors succeed in this task thanks to a low equivalent noise charge per pixel of around 10 to 15 e-, and a pixel pitch varying from 10 to a few 10 s of microns. Additionally, due to the possibility for integration of some data treatment in the sensor itself, readout times of have been reached for 100 kilo-pixels sensors. These aspects of CMOS sensors are attractive for applications in photon imaging. For X-rays of a few keV, the efficiency is limited to a few % due to the thin sensitive volume. For visible photons, the back-thinned version of CMOS sensor is sensitive to low intensity sources, of a few hundred photons. When a back-thinned CMOS sensor is combined with a photo-cathode, a new hybrid detector results (EBCMOS) and operates as a fast single photon imager. The first EBCMOS was produced in 2007 and demonstrated single photon counting with low dark current capability in laboratory conditions. It has been compared, in two different biological laboratories, with existing CCD-based 2D cameras for fluorescence microscopy. The current EBCMOS sensitivity and frame rate is comparable to existing EMCCDs. On-going developments aim at increasing this frame rate by, at least, an order of magnitude. We report in conclusion, the first test of a new CMOS sensor, LUCY, which reaches 1000 frames per seco

The First Swift BAT Gamma-Ray Burst Catalog

We present the first Swift Burst Alert Telescope (BAT) catalog of gamma-ray bursts (GRBs), which contains bursts detected by the BAT between 2004 December 19 and 2007 June 16. This catalog (hereafter BAT1 catalog) contains burst trigger time, location, 90% error radius, duration, fluence, peak flux, and time averaged spectral parameters for each of 237 GRBs, as measured by the BAT. The BAT-determined position reported here is within 1.75' of the Swift X-ray Telescope (XRT)-determined position for 90% of these GRBs. The BAT T_90 and T_50 durations peak at 80 and 20 seconds, respectively. From the fluence-fluence correlation, we conclude that about 60% of the observed peak energies, Epeak, of BAT GRBs could be less than 100 keV. We confirm that GRB fluence to hardness and GRB peak flux to hardness are correlated for BAT bursts in analogous ways to previous missions' results. The correlation between the photon index in a simple power-law model and Epeak is also confirmed. We also report the current status for the on-orbit BAT calibrations based on observations of the Crab Nebula.Comment: 63 pages, 23 figures, Accepted in ApJS, Corrected for the BAT ground position, the image significance, and the error radius of GRB 051105, Five machine-readable tables are available at http://swift.gsfc.nasa.gov/docs/swift/results/bat1_catalog