Automated detection and mapping of crown discolouration caused by jack pine budworm with 2.5 m resolution multispectral imagery     

《International Journal of Applied Earth Observation and Geoinformation》2005,7(1):61-77

Jack pine budworm (Choristoneura pinus pinus (Free.)) is a native insect defoliator of mainly jack pine (Pinus banksiana Lamb.) in North America east of the Rocky Mountains. Periodic outbreaks of this insect, which generally last two to three years, can cause growth loss and mortality and have an important impact ecologically and economically in terms of timber production and harvest. The jack pine budworm prefers to feed on current year needles. Their characteristic feeding habits cause discolouration or reddening of the canopy. This red colouration is used to map the distribution and intensity of defoliation that has taken place that year (current defoliation). An accurate and consistent map of the distribution and intensity of budworm defoliation (as represented by the red discolouration) at the stand and within stand level is desirable.Automated classification of multispectral imagery, such as is available from airborne and new high resolution satellite systems, was explored as a viable tool for objectively classifying current discolouration. Airborne multispectral imagery was acquired at a 2.5 m resolution with the Multispectral Electro-optical Imaging Sensor (MEIS). It recorded imagery in six nadir looking spectral bands specifically designed to detect discolouration caused by budworm and a near-infrared band viewing forward at 35° was also used. A 2200 nm middle infrared image was acquired with a Daedalus scanner. Training and test areas of different levels of discolouration were created based on field observations and a maximum likelihood supervized classification was used to estimate four classes of discolouration (nil-trace, light, moderate and severe). Good discrimination was achieved with an overall accuracy of 84% for the four discolouration levels. The moderate discolouration class was the poorest at 73%, because of confusion with both the severe and light classes. Accuracy on a stand basis was also good, and regional and within stand discolouration patterns were portrayed well. Only three or four well-placed spectral bands were needed for a good classification. A narrow red band, a near-infrared and short wave infrared band were most useful. A forward looking band did not improve discolouration estimation, but further testing is needed to confirm this result.This method of detecting and classifying discolouration appears to provide a mapping capability useful for conducting jack pine budworm discolouration surveys and integrating this information into decision support systems, forest inventory, growth and yield predictions and the forest management decision-making process.  相似文献   

Compaction bands and induced permeability reduction in Tuffeau de Maastricht calcarenite     

Theocharis Baxevanis  Euripides Papamichos  Olav Flornes  Idar Larsen 《Acta Geotechnica》2006,1(2):123-135

The mechanical behavior and permeability of the Tuffeau de Maastricht calcarenite were studied. Compactions bands were found to form in the “transitional” regime between brittle faulting and cataclastic flow. In order to predict the formation of compaction bands, bifurcation analysis was applied on a model developed by Lade and Kim. The numerical results proved to be in good agreement with the experimental ones where the localization point was identified to be the onset of shear-enhanced compaction (a threshold in differential stress after which significant reduction of porosity is induced). Before the onset of shear-enhanced compaction, permeability was primarily controlled by the effective mean stress, independent of the deviatoric stresses. With the onset of shear-enhanced compaction, however, coupling of the deviatoric and hydrostatic stresses induced considerable permeability and porosity reduction.  相似文献   

大气辐射计算的吸收系数分布模式   总被引：20，自引：5，他引：15  

石广玉 《大气科学》1998,22(4):659-676

全面论述了大气辐射计算中的吸收系数分布（#FKk#FS分布）模式,包括均匀路径的#FKk#FS分布模式以及非均匀路径的相关#FKk#FS分布模式。重点是利用吸收系数重排计算大气吸收气体分布函数和相关#FKk#FS分布函数的方法。某些结果系作者第一次公开发表。  相似文献   

The 10-μm profile of molecular-cloud and diffuse ISM silicate dust     

J. E. Bowey  A. J. Adamson  & D. C. B. Whittet 《Monthly notices of the Royal Astronomical Society》1998,298(1):131-138

High signal-to-noise ratio spectra are presented of the 10-μm silicate absorption feature in lines of sight towards Elias 16 and 18 in the Taurus dark cloud, and towards the heavily reddened supergiant Cyg OB2 no. 12. The observations are fitted with laboratory and astronomical spectra to produce intrinsic absorption profiles. These features, which represent molecular-cloud and diffuse ISM dust respectively, are better fitted with emissivity spectra of the Trapezium and μ Cephei than they are with those of laboratory, terrestrial, or other observations of circumstellar silicates. The difference in width between the silicate band in the two environments can be almost entirely ascribed to a broad excess absorption in the long-wavelength wing of the profiles, which is much stronger in the molecular-cloud lines of sight, and possibly reflects grain growth in the denser environment. Limits are placed on the strength of fine spectral structure; if there is a crystalline silicate component in these spectra, it is most likely to be serpentine. Column-density upper limits for methanol and the photolysis product hexamethylenetetramine (HMT) are less than a few per cent of those of water ice and silicates.  相似文献   

ISO observations of molecular hydrogen in the DR 21 bipolar outflow     

Michael D. Smith    Jochen Eislöffel  & Christopher J. Davis 《Monthly notices of the Royal Astronomical Society》1998,297(3):687-691

We demonstrate that a wide range of molecular hydrogen excitation can be observed in protostellar outflows at wavelengths in excess of 5 μm. Cold H₂ in DR 21 is detected through the pure rotational transitions in the ground vibrational level (0–0). Hot H₂ is detected in pure rotational transitions within higher vibrational levels (1–1, 1–2, etc.). Although this emission is relatively weak, we have detected two 1–1 lines in the DR 21 outflow with the ISO SWS instrument. We thus investigate molecular excitation over energy levels corresponding to the temperature range 1015–15 722 K, without the uncertainty introduced by differential extinction when employing near-infrared data.
This gas is thermally excited. We uncover a rather low H₂ excitation in the DR 21 West Peak. The line emission cannot be produced from single C-shocks or J-shocks; a range of shock strengths is required. This suggests that bow shocks and/or bow-generated supersonic turbulence is responsible. We are able to distinguish this shock-excited gas from the fluoresced gas detected in the K band, providing support for the dual-excitation model of Fernandes, Brand & Burton.  相似文献   

A textbook case of bow shock entrainment in a YSO outflow     

Christopher J. Davis  Michael D. Smith  & Gerald H. Moriarty-Schieven 《Monthly notices of the Royal Astronomical Society》1998,299(3):825-833

Near-infrared images in H₂ line emission and submillimetre maps in CO J  = 3–2 emission illustrate the remarkable association between a molecular bow shock and the redshifted molecular outflow lobe in W75N. The flow lobe fits perfectly into the wake of the bow, as one would expect if the lobe represented swept-up gas. Indeed, these observations strongly support the 'bow shock' entrainment scenario for molecular outflows driven by young stars.   The characteristics of the bow shock and CO outflow lobe are compared with those of numerical simulations of jet-driven flows. These models successfully reproduce the bulge and limb-brightening in the CO outflow, although the model H₂ bow exhibits more structure extending back along the flow axis. We also find that the size of the flow, the high mass fraction in the flow at low outflow velocities (low γ values) and the high CO/H₂ luminosity ratio indicate that the system is evolved. We also predict a correlation, in evolved systems, between outflow age and the CO/H₂ luminosity ratio.  相似文献   

Migmatite structures in the Central Gneiss Complex, Boca de Quadra, Alaska   总被引：3，自引：0，他引：3  

E.L. McLELLAN 《Journal of Metamorphic Geology》1988,6(4):517-542

Abstract Migmatite structures in the Coast Plutonic-Metamorphic Complex are well exposed in the inlet of Boca de Quadra, southeast Alaska. Two types of anatectic migmatites are present. Patch migmatites formed by in situ melting and subsequent crystallization of melt. Diktyonitic migmatites comprise a discontinuous veined network of leucocratic material, in which leucosomes enclose boudins of host rock. The margins of these boudins show the development of both melanosomes and shear band fabrics.
Strain analysis of diktyonitic melanosomes indicates that these regions have undergone volume decreases of 20-27%. This volume decrease is attributed to melt extraction into the adjacent fracture-filling leucosomes. Thus, diktyonitic migmatites formed by shear-induced segregation of partial melt, whereas in patch migmatites the lack of shear stresses inhibited melt segregation. The variable structural style of anatectic migmatites in Boca de Quadra is not related to host-rock composition, but may be due to differences in the amount of differential stress during migmatization. These in turn may be controlled by host-rock strength and/or diachroneity of migmatization and deformation.
Determination of volume changes during migmatization using strain analysis is potentially capable of discriminating intrusive and anatectic migmatites and consequently of documenting melt segregation and subsequent migration across crustal levels.  相似文献   

Broad-band colours and overall photometric properties of template galaxy models from stellar population synthesis     

Alberto Buzzoni 《Monthly notices of the Royal Astronomical Society》2005,361(2):725-742

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Modeling infrared absorption bands with nonspherical particles     

T. V. Zinov’eva 《Astronomy Letters》2005,31(7):458-473

We investigated the two deepest absorption bands observed in the spectra of stars and protostars, the water-ice band with the center near 3.1 μm and the silicate band with the center near 9.7 μm, by using a core-mantle confocal spheroid model with various axial ratios and relative volumes of the core material. We considered the effect of grain size, shape, structure, chemical composition, and orientation on the central wavelengths of the two bands, their full widths at half maximum (FWHMs), the ratio of the optical depths at their centers, and the polarization. We found that the observed relationships between the FWHMs of the bands and the ratio of their optical depths at the band centers could be explained if we chose slightly oblate or prolate particles (a/b ? 2) of small sizes (r_v ? 0.35 μm) with a silicate core and a thin ice mantle (V_core/V_total ? 0.7).  相似文献   

An infrared proper motion study of the Orion bullets     

J.-K. Lee  M. G. Burton 《Monthly notices of the Royal Astronomical Society》2000,315(1):11-20

We report the first infrared proper motion measurements of the HerbigHaro objects in OMC-1 using a 4-yr time baseline. The [Fe  ii ]-emitting bullets are moving of the order of 0.08 arcsec per year, or at about 170 km s¹. The direction of motion is similar to that inferred from their morphology. The proper motions of H₂-emitting wakes behind the [Fe  ii ] bullets, and of newly found H₂ bullets, are also measured. H₂ bullets have smaller proper motion than [Fe  ii ] bullets, while H₂ wakes with leading [Fe  ii ] bullets appear to move at similar speeds to their associated bullets. A few instances of variability in the emission can be attributed to dense, stationary clumps in the ambient cloud being overrun, setting up a reverse-oriented bullet. Differential motion between [Fe  ii ] bullets and their trailing H₂ wakes is not observed, suggesting that these are not separating, and also that they have reached a steady-state configuration over at least 100 yr. The most distant bullets have, on average, larger proper motions, but are not consistent with free expansion. Nevertheless, an impulsive, or short-lived (<<1000 yr), duration for their origin seems likely.  相似文献