SRTM DEM enhancement using a single set of PolSAR data based on the polarimetry-clinometry model

ABSTRACT

The freely available global and near-global digital elevation models (DEMs) have shown great potential for various remote sensing applications. The Shuttle Radar Topography Mission (SRTM) data sets provide the near-global DEM of the Earth’s surface obtained using the interferometry synthetic aperture radar (InSAR). Although free accessibility and generality are the advantages of these data sets, many applications require more detailed and accurate DEMs. In this paper, we proposed a modified and advanced polarimetry-clinometry algorithm for improving SRTM topography model which requires only one set of polarimetric synthetic aperture radar (PolSAR) data. The azimuth and range slope components estimation based on polarization orientation angle (POA) shifts and the intensity-based Lambertian model formed the bases of the proposed method. This method initially compensated for the polarimetry topography effect corresponding to SRTM using the DEM-derived POA. In the second step, using a modified algorithm, POA was obtained from the compensated PolSAR data. The POA shifts by the azimuth and range slopes’ variations based on the polarimetric model. In addition to the polarimetric model, a clinometry model based on the Lambertian scattering model related to the terrain slope was employed. Next, two unknown parameters, i.e. azimuth and range slope values, were estimated in a system of equations by two models from the compensated PolSAR data. Azimuth and range slopes of SRTM were enhanced by PolSAR-derived slopes. Finally, a weighted least-square grid adjustment (WLSG) method was proposed to integrate the enhanced slopes’ map and estimate enhanced heights. The National Aeronautics and Space Administration Jet Propulsion Laboratory (NASA JPL) AIRSAR was utilized to illustrate the potential of the proposed method in SRTM enhancement. Also, the InSAR DEM was employed for evaluation experiments. Results showed that the accuracy of SRTM DEM is improved up to 2.91 m in comparison with InSAR DEM.     

Comparison and evaluation of dust detection algorithms using MODIS Aqua/Terra Level 1B data and MODIS/OMI dust products in the Middle East

Dust storms have a major impact on air quality, economic loss, and human health over large regions of the Middle East. Because of the broad extent of dust storms and also political–security issues in this region, satellite data are an important source of dust detection and mapping. The aim of this study was to compare and evaluate the performance of five main dust detection algorithms, including Ackerman, Miller, normalized difference dust index (NDDI), Roskovensky and Liou, and thermal-infrared dust index (TDI), using MODIS Level 1B and also MODIS Deep Blue AOD and OMI AI products in two dust events originating from Iraq and Saudi Arabia. Overall, results showed that the performance of the algorithms varied from event to event and it was not possible to use the published dust/no-dust thresholds for the algorithms tested in the study area. The MODIS AOD and OMI AI products were very effective for initial dust detection and the AOD and AI images correlated highly with the dust images at provincial scale (p-value <0.001), but the application of these products was limited at local scale due to their poor spatial resolution. Results also indicated that algorithms based on MODIS thermal infrared (TIR) bands or a combination of TIR and reflectance bands were better indicators of dust than reflectance-based ones. Among the TIR- based algorithms, TDI performed the best over water surfaces and dust sources, and accounted for approximately 93% and 90% of variations in the AOD and OMI AI data.     

Experiments with a Low-Cost Hot Isothermal Pressing Machine Developed for Superplastic Forming

Hot isothermal/isostatic pressing machines are technically good candidates for superplastic forming (SPF) of otherwise hard-to-shape materials such as superalloys. These machines are, however, very expensive so that small or medium-size enterprises can not afford them. This has impeded widespread use of SPF processing. In an attempt to alleviate the problem, the authors have developed a laboratory model of an affordable hot isothermal pressing machine with differential gas pressure as the forming medium. Careful selection of process parameters such as temperature, gas pressure, strain rate, and process time as well as monitoring of thickness changes in a workpiece has a pivotal role in successful operation of such machine. It has been illustrated in this article that SPF can be successfully performed with this machine on the basis of process parameters estimated with existing analytical relations. The performance of this machine has been verified by several experiments on SPF of titanium-based sheets, as reported in this article.     

Performance modeling of a manufacturing cell with a single material transporter: An approximation

We consider a flexible manufacturing system with a number of workstations, a single material transporter, and a common storage space of finite capacity. The material handling delay times are explicitly considered in the model and assumed to follow a two-stage Coxian distribution. The material processing times on a workstation also have a two-stage Coxian distribution. The routing of parts within the system follows a Markov chain. An approximate performance model is developed and the results are compared with the exact or simulation results. We also investigate how this performance model compares to a simulation with deterministic routing and processing times. Finally, we study the effect, on the performance measures, of ignoring the material transporter or of modeling the transporter as a central server with aggregation of routing information.     

EIS study of corrosion behavior of metallic materials in ethanol blended gasoline containing water as a contaminant

In the present paper, the effects of ethanol as a gasoline additive and water as a contaminant on the corrosion behavior of metallic components of a fuel delivery system were investigated. Electrochemical impedance spectroscopy (EIS) testing was performed in both water-free and water contaminated gasoline containing 0%, 5%, 10% and 15% ethanol without the addition of any supporting electrolyte. The surface of the specimens examined in 10% ethanol blended gasoline was observed by scanning electron microscope to understand what types of corrosion attack occurred. The results revealed that the addition of ethanol to gasoline fuel decreased the solution resistance and polarization resistance values of the specimens, resulting in an increase in the corrosion rates of these specimens in ethanol blended gasoline. Water contaminant caused a decrease in the polarization resistance of the ferrous specimens, whereas the observed behavior in others was reversed. Among the investigated metallic materials, the brazing alloy fared the best while Al 6061 alloy showed satisfactory corrosion resistance compared to the rest of the materials in both water-free and water-contaminated ethanol blended gasoline. Moreover, no localized attack was observed in corrosion products.     

Reuse of waste sludge from papermaking process in cement composites

Papermaking sludge (PS), a waste residue from the pulp and paper processing, has brought great pressure on the environment because of large quantities that are produced in paper mills. This work was carried out to explore the possibility of making PS/cement composite products using solid waste of PS. Boards measuring 350 × 270 × 12 mm³ were manufactured using PS contents of 40, 50, and 60 wt%, adhesive dosages of 0, 10, and 15 wt%, and 0 and 5 wt% of calcium chloride as an accelerator. At least three replications were fabricated for each treatment, and some mechanical and physical properties of the boards were evaluated. Test results showed that the bending and internal strengths of the specimens decreased with an increase in the PS content, and the maximum values were obtained at PS loading of 40 wt%. The negative influence of PS content on the mechanical properties can be explained by the reduced bonding ability because of weaker PS compared with cement. Screw withdrawal values were up to 22.7 kPa. Water absorption and thickness swelling of cement mortar considerably increased with increased content of PS, with a corresponding reduction of bulk density. In general, all properties of the boards were improved when the adhesive and calcium chloride contents were increased. The results showed that an increase in board density improved the mechanical and physical properties. Finally, results showed that PS has good potential for recycling and utilization in developing value‐added building components. POLYM. ENG. SCI., 2013. © 2012 Society of Plastics Engineers     

Benefits valuation of potable water quality improvement in Malaysia: the case of Kajang Municipality

This article estimates the benefits of potable water quality improvements in Kajang Municipality in the state of Selangor, Malaysia, using the avertive cost method. Households were willing to pay MYR 322 annually to improve potable water quality. This represents about 80% of their average annual water bill. The present value of aggregate benefits over a period of 30 years at various social discount rates ranged from MYR 301 million to MYR 768 million. These estimates can be used as a reference for public investment criteria. The findings suggest that there is merit in an upward revision of water tariffs if they provide improvements in water quality.     

Mechanical, rheological, and thermal behavior assessments in HDPE/PA-6/EVOH ternary blends with variable morphology

Visco-elastic and dielectric spectra of multiwalled carbon-nanotube reinforced silicon elastomer nanocomposites were used to study relaxation behavior. SEM photomicrographs shows well dispersion of MWCNT in elastomer matrix. In visco-elastic analysis primary relaxation was studied as a function of temperature (?100 to 100 °C) at frequency 1Hz and strain 1 %. The effect of MWCNT loadings on storage modulus, loss modulus, and loss tangent has been studied. The non-linearity in loss tangent, storage modulus and loss modulus was explained on the basis of MWCNT-elastomer interaction and the inter-aggregate attraction of MWCNT. The secondary β relaxation was studied using dielectric relaxation spectra in the frequency range of 0.1 Hz to 10⁶ Hz. The effect of MWCNT loadings on the complex and real parts of impedance was distinctly visible which has been explained on the basis of interfacial polarization of fillers in a heterogeneous medium and relaxation dynamics of polymer chains in the vicinity of fillers. The dielectric formalism has been utilized to further investigate the conductivity and relaxation phenomenon. The ‘percolation limit’ of the MWCNT in the silicon elastomer was found to be in the range of 4 phr loading.     

Combined Computational and Experimental Study on the Adsorption and Inhibition Effects of N2O2 Schiff Base on the Corrosion of API 5L Grade B Steel in 1 mol/L HCI

The electrochemical behavior of low carbon steel （API 5L grade B） in 1 mol/L HCI solution with different concentrations of N,Nr-bis（4-formylphenol）-trimethylenediamine Schiff base was studied by electrochemical techniques and density functional theory analysis. The inhibition efficiency was found to increase with increasing inhibitor concentration and decreased with increasing temperature. The high inhibition efficiency was attributed to the blocking of active sites by adsorption of inhibitor molecules on the steel surface. Thermodynamic parameters for the adsorption and activation processes were determined. Galvanostatic polarization data indicated that Schiff base act as a mixed-type inhibitor and the adsorption isotherm obeyed the Langmuir adsorption isotherm. Results obtained from quantum chemical studies show excellent correlations between the quantum chemical parameters and the experimental inhibition efficiencies using density functional theory at the B3LYP/6-31G（d,p） and B3LYP/3-21G basis set levels and ab initio calculations using HF/6-31G（d,p） and HF/3-21G methods.     

Study of Structural and Magnetic Properties of Superparamagnetic Fe3O4–ZnO Core–Shell Nanoparticles

In this work, Fe₃O₄–ZnO core–shell nanoparticles have been successfully synthesized using a simple two-step co-precipitation method. In this regard, Fe₃O₄ (magnetite) and ZnO (zincite) nanoparticles (NPs) were synthesized separately. Then, the surface of the Fe₃O₄ NPs was modified with trisodium citrate in order to improve the attachment of ZnO NPs to the surface of Fe₃O₄ NPs. Afterwards, the modified magnetite NPs were coated with ZnO NPs. Moreover, the influence of the core to shell molar ratio on the structural and magnetic properties of the core–shell NPs has been investigated. The prepared nanoparticles have been characterized utilizing transmission electron microscopy (TEM), X-ray diffraction (XRD), Fourier transform infrared (FTIR) spectroscopy and vibrating sample magnetometer (VSM). The results of XRD indicate that Fe₃O₄ NPs with inverse spinel phase were formed. The results of VSM imply that the Fe₃O₄–ZnO core–shell NPs are superparamagnetic. The saturation magnetization of prepared Fe₃O₄ NPs is 54.24 emu/g and it decreases intensively down to 29.88, 10.51 and 5.75 emu/g, after ZnO coating with various ratios of core to shell as 1:1, 1:10 and 1:20, respectively. This reduction is attributed to core–shell interface effects and shielding. TEM images and XRD results imply that ZnO-coated magnetite NPs are formed. According to the TEM images, the estimated average size for most of core–shell NPs is about 12 nm.