An optimization approach to estimate and calibrate column water vapour for hyperspectral airborne data

The article describes a novel approach to estimate and calibrate column water vapour (CWV), a key parameter for atmospheric correction of remote-sensing data. CWV is spatially and temporally variable, and image-based methods are used for its inference. This inference, however, is affected by methodological and numeric limitations, which likely propagate to reflectance estimates. In this article, a method is proposed to estimate CWV iteratively from target surface reflectances. The method is free from assumptions for at sensor radiance-based CWV estimation methods. We consider two cases: (a) CWV is incorrectly estimated in a processing chain and (b) CWV is not estimated in a processing chain. To solve (a) we use the incorrect estimations as initial values to the proposed method during calibration. In (b), CWV is estimated without initial information. Next, we combined the two scenarios, resulting in a generic method to calibrate and estimate CWV. We utilized the hyperspectral mapper (HyMap) and airborne prism experiment (APEX) instruments for the synthetic and real data experiments, respectively. Noise levels were added to the synthetic data to simulate real imaging conditions. The real data used in this research are cloud-free scenes acquired from the airborne campaigns. For performance assessment, we compared the proposed method with two state-of-the-art methods. Our method performed better as it minimizes the absolute error close to zero, only within 8–10 iterations. It thus suits existing operational chains where the number of iterations is considerable. Finally, the method is simple to implement and can be extended to address other atmospheric trace gases.     

Oxidation of ferritic steels dispersion strengthened with TiO2 and Y2O3 oxides in lead melt

We study the structure and composition of scales formed during the contact of Fe–13Cr–2Motype ferritic steels hardened with oxides TiO₂ and Y₂O₃ with oxygen-containing (10⁻³ mass% O) lead melt at 550°C for 1000 h. It is established that a Fe₃ O₄ – Fe (Fe_{1 − x} , Cr _x )₂ O₄ two-layer scale forms. Its upper layer (Fe₃ O₄) grows in the direction of the melt, and the internal layer (Fe (Fe_{1 – x} , Cr _x )₂ O₄) grows in the direction to the matrix. Oxide particles favor an increase in the porosity of the internal sublayer of the scale. Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 44, No. 5, pp. 38 – 44, September–October, 2008.     

Wavelength selective nanophotonic components utilizing channel plasmon polaritons

We fabricate and investigate wavelength selective components utilizing channel plasmon polaritons (CPPs) and operate at telecom wavelengths: a waveguide-ring resonator-based add-drop multiplexer (WRR-ADM) and a compact (3.75-microm-long) Bragg grating filter (BGF). The CPP waveguides represent 0.5-microm-wide and 1.3-microm-deep V-grooves in gold, which are combined with a 5-microm-radius ring resonator (in the WRR-ADM) or 0.5-microm-long wells milled with the period of 0.75 microm across a groove (in the BGF). The CPP-based components are characterized in the wavelength range of 1425-1600 nm by use of near-field optical microscopy, exhibiting the wavelength selectivity of approximately 40 nm.     

Elastic Gallium Phosphide Nanowire Optical Waveguides—Versatile Subwavelength Platform for Integrated Photonics

Emerging technologies for integrated optical circuits demand novel approaches and materials. This includes a search for nanoscale waveguides that should satisfy criteria of high optical density, small cross-section, technological feasibility and structural perfection. All these criteria are met with self-assembled gallium phosphide (GaP) epitaxial nanowires. In this work, the effects of the nanowire geometry on their waveguiding properties are studied both experimentally and numerically. Cut-off wavelength dependence on the nanowire diameter is analyzed to demonstrate the pathways for fabrication of low-loss and subwavelength cross-section waveguides for visible and near-infrared (IR) ranges. Probing the waveguides with a supercontinuum laser unveils the filtering properties of the nanowires due to their resonant action. The nanowires exhibit perfect elasticity allowing fabrication of curved waveguides. It is demonstrated that for the nanowire diameters exceeding the cut-off value, the bending does not sufficiently reduce the field confinement promoting applicability of the approach for the development of nanoscale waveguides with a preassigned geometry. Optical X-coupler made of two GaP nanowires allowing for spectral separation of the signal is fabricated. The results of this work open new ways for the utilization of GaP nanowires as elements of advanced photonic logic circuits and nanoscale interferometers.     

Topography characterization of a deep grating using near-field imaging

Using near-field optical microscopy at the wavelength of 633 nm, we image light intensity distributions at several distances above an approximately 2-microm-deep and a 1-microm-period glass grating illuminated from below under the condition of total internal reflection. The intensity distributions are numerically modeled, and an inversion procedure based on a least-squares-fit optimization is employed to extract the grating geometry from the optical images.     

Assessment of subcritical crack growth in hydrogen-containing environment by the parameters of acoustic emission signals

Estimation models (differential equations, initial and final conditions) for determining the crack propagation kinetics in hydrogen-containing environments using the acoustic emission (AE) signal parameters are proposed. The formulation of these models is based on the main ideals of the AE method, dependence between the crack increment area and a sum of AE-signals amplitude, main criteria of fracture mechanics and laws of thermodynamics.     

Segmentation of Rumex obtusifolius using Gaussian Markov random fields

Rumex obtusifolius is a common weed that is difficult to control. The most common way to control weeds—using herbicides—is being reconsidered because of its adverse environmental impact. Robotic systems are regarded as a viable non-chemical alternative for treating R. obtusifolius and also other weeds. Among the existing systems for weed control, only a few are applicable in real-time and operate in a controlled environment. In this study, we develop a new algorithm for segmentation of R. obtusifolius using texture features based on Markov random fields that works in real-time under natural lighting conditions. We show its performance by comparing it with an existing real-time algorithm that uses spectral power as texture feature. We show that the new algorithm is not only accurate with detection rate of 97.8 % and average error of 56 mm in estimating the location of the tap-root of the plant, but is also fast taking just 0.18 s to process an image of size $576 \times 432$ pixels making it feasible for real-time applications.     

Interaction of Solid Metals with Melts Containing Nonmetallic Impurities

We present a systematic survey of the mechanisms of interaction of solid metals (Me) with melts (L) taking into account the activity of nonmetallic impurities (I) and suggest a general scheme of interaction of components in Me–L–I systems. The physicochemical aspects of formation of different layers on the Me–L phase boundary are analyzed. Special attention is given to the conditions of formation of protective layers with various functional properties. It is shown that this problem can be solved theoretically within the framework of the problem of reaction-controlled diffusion by taking into account the behavior of the concentrations of the components on the phase boundaries.     

Effect of temperature on the interaction of ÉP823 steel with lead melts saturated with oxygen

We study the corrosion behavior of ferritic-martensitic éP823 steel in a static lead melt, saturated with oxygen, at 550 and 650°C. At these temperatures, a complex magnetite-base scale is formed on the surface of steel, but the mechanisms of its growth are different. At 550°C, corrosion has a cyclic character. On the surface of steel, a Fe_1+x Pb_2−x O₄−Fe_1+x Cr_2−x O₄ two-layer scale is formed periodically. Reaching the critical thickness (18 μm), it exfoliates along the interface with the matrix, to which oxygen-containing lead penetrates, whereupon this process is repeated. The corrosion rate is ∼0.08 mm/year. At 650°C, the intensification of reactions of formation of chromium spinel and plumboferrite induces the growth of a porous scale, where lead is accumulated. This scale has good adherence to the matrix and is formed as a compact conglomerate owing to the efficient mass transfer at all interfaces, which leads to a catastrophic rate of thinning of the specimen (3.82 mm/yr) in a lead melt. On the basis of experimental data, we propose schemes of the oxidation of chromium steels in a lead melt with a high oxygen activity at different temperatures. __________ Translated from Fizyko-Khimichna Mekhanika Materialiv, Vol. 43, No. 2, pp. 77–84, March–April, 2007.