Feature reduction using a singular value decomposition for the iterative guided spectral class rejection hybrid classifier

Feature reduction in a remote sensing dataset is often desirable to decrease the processing time required to perform a classification and improve overall classification accuracy. This paper introduces a feature reduction method based on the singular value decomposition (SVD). This SVD-based feature reduction method reduces the storage and processing requirements of the SVD by utilizing a training dataset. This feature reduction technique was applied to training data from two multitemporal datasets of Landsat TM/ETM+ imagery acquired over a forested area in Virginia, USA and Rondônia, Brazil. Subsequent parallel iterative guided spectral class rejection (pIGSCR) forest/non-forest classifications were performed to determine the quality of the feature reduction. The classifications of the Virginia data were five times faster using SVD-based feature reduction without affecting the classification accuracy. Feature reduction using the SVD was also compared to feature reduction using principal components analysis (PCA). The highest average accuracies for the Virginia dataset (88.34%) and for the Rondônia dataset (93.31%) were achieved using the SVD. The results presented here indicate that SVD-based feature reduction can produce statistically significantly better classifications than PCA.     

Triangle based interpolation

Triangle based interpolation is introduced by an outline of two classical planar interpolation methods, viz. linear triangular facets and proximal polygons. These are shown to have opposite local bias. By applying cross products of triangles to obtain local gradients, a method designated “slant-top proximal polygon interpolation” is introduced that is intermediate between linear facets and polygonal interpolation in its local bias. This surface is not continuous, but, by extending and weighting the gradient planes, a C¹ surface can be obtained. The gradients also allow a roughness index to be calculated for each data point in the set. This index is used to control the shape of a blending function that provides a weighted combination of the gradient planes and linear interpolation. This results in a curvilinear, C¹,interpolation of the data set that is bounded by the linear interpolation and the weighted gradient planes and is tangent to the slant-top interpolation at the data points. These procedures may be applied to data with two, three, or four independent variables.     

The remnant of Nova Cassiopeiae 1993 (V705 Cassiopeiae)

We have detected radio emission from the remnant of V705 Cas, beginning 221 d after visual maximum. We follow the remnant from first detection while still optically thick through the turn-over to optically thin emission, and finally confirming the absence of emission due to expansion and fading by the end of 1998. While the emission is consistent with thermal bremsstrahlung, as seen in most previous novae, the small-scale structure shows two ridge-like features, which develop significantly from day 585 until our last detection on day 1544. While the development is fairly rapid, it is also much smoother than that seen in V1974 Cyg, in that we can follow individual features as they change over almost 1000 d. Our optical spectra unequivocally indicate some form of axial symmetry, as derived from the velocity structure. This is difficult to reconcile with the observed development in the radio images. We suggest a number of possible explanations.     

美国荒野风景河流的空间分布特征及其对中国的启示

美国荒野风景河流体系是全球最早建立的河流保护地类型。经过50年发展,其完善的体系呈现出一定空间分布特征。将线状国家荒野风景河流（NWSR）抽象为点状单元,对208个NWSR单元进行空间计算,并与自然生态和社会经济等因素进行叠加分析。结果表明,美国已有40个州分布NWSR,其中以俄勒冈等3个州的数量分布最多,且集中分布于特定的区域：西部的太平洋海岸、落基山脉和山间高地3个自然地理区;极地、温湿润、干旱3个Ⅰ级生态区;太平洋西北部、加利福尼亚、阿拉斯加及五大湖4个流域。NWSR线密度与州域的人口密度、经济水平相关性不强,但与大坝建设密切相关。荒野思想影响了法案制定,法案指导了遴选标准,遴选标准又进一步影响了NWSR的空间分布。研究对中国的借鉴意义在于：应当明确保护地指导思想、关注价值突出区域、确定合适遴选标准、重视保护地系统规划等。     

Mercury in the Southern Ocean

We present here the first mercury speciation study in the water column of the Southern Ocean, using a high-resolution south-to-north section (27 stations from 65.50°S to 44.00°S) with up to 15 depths (0-4440 m) between Antarctica and Tasmania (Australia) along the 140°E meridian. In addition, in order to explore the role of sea ice in Hg cycling, a study of mercury speciation in the “snow-sea ice-seawater” continuum was conducted at a coastal site, near the Australian Casey station (66.40°S; 101.14°E). In the open ocean waters, total Hg (Hg_T) concentrations varied from 0.63 to 2.76 pmol L⁻¹ with “transient-type” vertical profiles and a latitudinal distribution suggesting an atmospheric mercury source south of the Southern Polar Front (SPF) and a surface removal north of the Subantartic Front (SAF). Slightly higher mean Hg_T concentrations (1.35 ± 0.39 pmol L⁻¹) were measured in Antarctic Bottom Water (AABW) compared to Antarctic Intermediate water (AAIW) (1.15 ± 0.22 pmol L⁻¹). Labile Hg (Hg_R) concentrations varied from 0.01 to 2.28 pmol L⁻¹, with a distribution showing that the Hg_T enrichment south of the SPF consisted mainly of Hg_R (67 ± 23%), whereas, in contrast, the percentage was half that in surface waters north of PFZ (33 ± 23%). Methylated mercury species (MeHg_T) concentrations ranged from 0.02 to 0.86 pmol L⁻¹. All vertical MeHg_T profiles exhibited roughly the same pattern, with low concentrations observed in the surface layer and increasing concentrations with depth up to an intermediate depth maximum. As for Hg_T, low mean MeHg_T concentrations were associated with AAIW, and higher ones with AABW. The maximum of MeHg_T concentration at each station was systematically observed within the oxygen minimum zone, with a statistically significant MeHg_Tvs Apparent Oxygen Utilization (AOU) relationship (p < 0.001). The proportion of Hg_T as methylated species was lower than 5% in the surface waters, around 50% in deep waters below 1000 m, reaching a maximum of 78% south of the SPF. At Casey coastal station Hg_T and Hg_R concentrations found in the “snow-sea ice-seawater” continuum were one order of magnitude higher than those measured in open ocean waters. The distribution of Hg_T there suggests an atmospheric Hg deposition with snow and a fractionation process during sea ice formation, which excludes Hg from the ice with a parallel Hg enrichment of brine, probably concurring with the Hg enrichment of AABW observed in the open ocean waters. Contrastingly, MeHg_T concentrations in the sea ice environment were in the same range as in the open ocean waters, remaining below 0.45 pmol L⁻¹. The MeHg_T vertical profile through the continuum suggests different sources, including atmosphere, seawater and methylation in basal ice. Whereas Hg_T concentrations in the water samples collected between the Antarctic continent and Tasmania are comparable to recent measurements made in the other parts of the World Ocean (e.g., Soerensen et al., 2010), the Hg species distribution suggests distinct features in the Southern Ocean Hg cycle: (i) a net atmospheric Hg deposition on surface water near the ice edge, (ii) the Hg enrichment in brine during sea ice formation, and (iii) a net methylation of Hg south of the SPF.     

Assessment of the UV camera sulfur dioxide retrieval for point source plumes

Digital cameras, sensitive to specific regions of the ultra-violet (UV) spectrum, have been employed for quantifying sulfur dioxide (SO₂) emissions in recent years. The instruments make use of the selective absorption of UV light by SO₂ molecules to determine pathlength concentration. Many monitoring advantages are gained by using this technique, but the accuracy and limitations have not been thoroughly investigated. The effect of some user-controlled parameters, including image exposure duration, the diameter of the lens aperture, the frequency of calibration cell imaging, and the use of the single or paired bandpass filters, have not yet been addressed. In order to clarify methodological consequences and quantify accuracy, laboratory and field experiments were conducted. Images were collected of calibration cells under varying observational conditions, and our conclusions provide guidance for enhanced image collection. Results indicate that the calibration cell response is reliably linear below 1500 ppm m, but that the response is significantly affected by changing light conditions. Exposure durations that produced maximum image digital numbers above 32 500 counts can reduce noise in plume images. Sulfur dioxide retrieval results from a coal-fired power plant plume were compared to direct sampling measurements and the results indicate that the accuracy of the UV camera retrieval method is within the range of current spectrometric methods.     

Distribution of partial melt in a felsic system: the importance of surface energy

The texture, distribution, and infiltration tendency of a quartz-albite melt in equilibrium with a synthetic, texturally-equilibrated quartzite was examined in a series of distribution and infiltration experiments at 1,250° C and 8 kbar hydrostatic pressure. Wetting angle measurements from melt distribution experiments show a dihedral angle () of 60 degrees, implying a quartz/quartz interfacial energy approximately 1.7 times the quartz/melt value. Because of this specific relationship between interfacial energies, the system can achieve its lowest surface free energy state with the melt either in pools or along grain edge intersections, possibly forming some interconnected channels. Stability of melt in pockets and along grain edge intersections was observed in a fourteen-day, dispersed-melt experiment, yet melt pools failed to disperse into the quartzite during infiltration experiments. Comparison of the observed dihedral angle with previously measured surface energy values for the melt and quartz shows excellent agreement, and also demonstrates that an aggregate of randomly orientated anisotropic grains acts approximately isotropically.While these experiments are not strictly applicable to real crustal systems, they do indicate that, at least in some felsic systems, the melt has no preference for uniform grainedge wetting relative to collection at grain corners or in large pools. This ambivalent behavior is attributable to the 60-degree wetting angle, which has been shown to separate systems in which melt tends to disperse in interconnected channels (<60°) from those in which melt tends to become isolated at grain corners (> 60°).     

Nutrient enrichment and precipitation changes do not enhance resiliency of salt marshes to sea level rise in the Northeastern U.S.

In the Northeastern U.S., salt marsh area is in decline. Habitat change analysis has revealed fragmentation, displacement of high marsh by low marsh species, and marsh drowning, while development of adjacent uplands limits upslope migration. Measures of marsh vegetation loss for eight sites in Rhode Island and New York between ca.1970 and 2011 indicate that substantial loss has occurred over past decades, with higher loss rates found for lower elevation salt marshes. Using inundation experiments, field surveys, and LiDAR datasets, we developed an elevation-productivity relationship for Spartina alterniflora specific to the U.S. Northeast, and located current salt marsh orthometric heights on this curve. We estimate that 87 % of Northeastern salt marshes are located at elevations where growth is limited by inundation. By manipulating water column nutrients, precipitation, and elevation, we further found that altered precipitation regime was associated with significant reductions in biomass, and that nutrient enrichment adversely impacts organic matter accumulation and peat formation. These results provide evidence that Northeastern U.S. marshes are vulnerable to the effects of accelerated sea level rise, and that neither precipitation changes, nor cultural eutrophication, will contribute positively to long-term salt marsh survival.