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.     

Analysis of the effects of main design parameters variation on the vibration characteristics of a vehicle sub-frame

In the design process of an automobile part, several analysis methods are usually used to evaluate the performance of the part. However, most automobile design engineers do not directly use CAE (computer aided engineering) tools since specific skills are required to obtain practical results. Moreover, CAE requires a huge amount of computation time and cost. To resolve these problems, a new design approach, termed first order analysis (FOA), has been proposed. In this paper, the FOA technique is employed to design a vehicle sub-frame. An equivalent model of the vehicle subframe which only consists of beam elements is proposed and the modal properties obtained with the model are compared to those obtained with a full scale finite element model. The effects of some parameter variations on the modal characteristics of the vehicle sub-frame are investigated by employing the FOA equivalent model. This paper was presented at the 4th Asian Conference on Multibody Dynamics(ACMD2008), Jeju, Korea, August 20–23, 2008. Hong Hee Yoo graduated from the Department of Mechanical Design and Production Engineering at Seoul National University in 1980 and received his Master’s degree from the same department in 1982. He received his Ph.D. degree in 1989 from the Department of Mechanical Engineering and Applied Mechanics at the University of Michigan at Ann Arbor, U.S.A. He is currently working as a professor in the School of Mechanical Engineering in Hanyang University, Seoul, Korea.     

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.     

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.     

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.     

ViPER: simulation software for high aspect ratio plasma etching of silicon

The process of pattern transfer of desired topological integrated circuits features into silicon or other semiconductor compounds plays a critical role for the production of microelectronic and photonic devices, and micro- and nanoelectromechanical systems. Any deviation from the desired shape of the pattern limits density, yield, and reliability of these devices. Gas reactivity, pressure, ion, electron, and reactant transport to the surface, and product transport away from the surface, have been identified as important issues that control the microscopic uniformity in high aspect ratio etching. A plasma etching simulation software, containing corresponding physical models, can be used to establish a link between etch process parameters such as pressure, rf power, etching gas chemistry, temperature, and the physical and chemical process parameters like energy and angular distribution of ions and neutrals, radical sticking, and surface charging. ViPER (Virtual Plasma Etch Reactor) is a full featured plasma processing simulation software developed at Ilmenau University of Technology, Department of Microelectronic and Nanoelectronic Systems (MNES) [http://www.tu-ilmenau.de/en/mne-mns/research/plasma-etching/viper-download]. The simulator allows a deep analysis of the most significant effects like reactive ion etching lag, charging, notching, bowing, faceting, microtrenching, profile shape dependence, and gives more insight into the physical phenomena occurring in the plasma reactor during plasma etching process, helping engineers to understand how plasma etching works.     

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.     

Salinity modelling by inverted Gaussian parameters of soil reflectance spectra

This paper presents an approach to estimate soil salinity through modelling of soil spectra using an inverted Gaussian (IG) function. The approach is tested on experimental datasets including measurements of soil physicochemical properties and their spectral reflectance which are obtained under controlled laboratory conditions. The near-infrared (NIR) and shortwave infrared (SWIR) region of the salt-affected soil spectra were fitted to an inverted Gaussian curve. Parameters of the fitted curve, such as functional depth, distance to the inflection point and area under curve, were then used as predictors in regression analysis to estimate soil salinity levels. The results suggest a successful estimation of salinity levels, especially, for soil samples treated with epsomite and bischofite solutions. Amongst the calculated IG parameters, the area under fitted curve resulted in the most accurate estimations. The results demonstrate the relative utility of high spectral resolution data for estimating soil salinity under laboratory controlled conditions.     

Robust extended Kalman filter of discrete-time Markovian jump nonlinear system under uncertain noise

This paper examines the problem of robust extended Kalman filter design for discrete-time Markovian jump nonlinear systems with noise uncertainty. Because of the existence of stochastic Markovian switching, the state and measurement equations of underlying system are subject to uncertain noise whose covariance matrices are time-varying or un-measurable instead of stationary. First, based on the expression of filtering performance deviation, admissible uncertainty of noise covariance matrix is given. Secondly, two forms of noise uncertainty are taken into account: Non-Structural and Structural. It is proved by applying game theory that this filter design is a robust mini-max filter. A numerical example shows the validity of the method.