Model-based interpretation of ERS-1 SAR images of Arctic sea ice

Interpretation of Synthetic Aperture Radar (SAR) images of sea ice is complex because of the natural variability of sea ice and sensor-induced effects, such as speckle. Most of the research on SAR image interpretation has focused on the winter months and algorithms were developed to classify sea ice successfully under cold conditions. However, interpretation of SAR images during the seasonal transitions has proved difficult due to rapidly changing weather conditions. In this paper we address the application of SAR during the transition from summer to the fall freeze-up. This period is important because it signals the start of significant new ice growth, which affects the air-ocean heat exchange and injects brine into the upper layers of the ocean. We have interpreted SAR images of the sea ice in terms of the basic ice characteristics by using shipborne radar measurements of sea ice during the freeze-up and models derived from these measurements. We have shown that the model-based approach is effective in interpreting SAR images during this seasonal transition. This work also provides the physical mechanisms responsible for the large increase in backscatter observed at the end of the summer melt season.     

Environmental quality and its changes,an analysis using NDVI

Normalized difference vegetation index (NDVI) derived from SPOT HRV multispectral data was used to study the changing environmental quality of Hong Kong from 1987, 1991 and 1993 to 1995. Conventional change detection techniques such as image differencing or principal components analysis helped to highlight salient changes. These techniques, however, were less effective in identifying subtle changes, in particular the amount and quality of green space. Integrating the mean NDVI values at the Tertiary Planning Unit (TPU) level with census and land-cover data showed that the NDVI values were related to woodland, tall scrubland and high-density urban areas. It was also related to the level of crowding as depicted from a factor analysis of census data. Tracing the changing pattern of mean NDVI values revealed that areas with continuous increases in NDVI values are scattered around old urban districts experiencing improved landscaping. Areas of continuous decrease in NDVI values covered a large part of rural New Territories and western Hong Kong Island revealing the urban expansion process. This provided valuable information for the assessment of environmental quality for planning and management of the environment.     

MODIS‐derived visible atmospherically resistant index for monitoring chaparral moisture content

Time series of normalized difference indices (NDIs) derived from MODIS surface reflectance data provide potentially useful information for monitoring fuel moisture content (FMC) for fire risk assessment. The visible atmospherically resistant index (VARI) and normalized difference water index (NDWI) were compared for monitoring live FMC of chaparral shrublands. Regression coefficients are encouraging given disparate spatial resolutions of ground‐based FMC measurements and MODIS‐derived NDIs. VARI exhibited greater temporal co‐variability (0.79>r ²<0.94) and spatial robustness with FMC than NDWI, even though the former is based solely on visible waveband reflectance data.     

Particulate Carbon Speciation by MnO2 Oxidation

A selective thermal oxidation method was developed for the speciation of carbonaceous aerosols collected on filters into organic carbon (OC) and elemental carbon (EC). The technique is based on studying the thermal oxidation of microcrystalline graphite by MnO₂as well as various organic compounds. The procedure uses a modified Dohrmann DC-52 carbon analyzer with a flame ionization detector to detect the CO₂resulting from the oxidation as methane after catalytic conversion. The results led to the selection of 525 °C as the optimal temperature for the oxidation of OC while leaving EC intact. After the organic oxidation, the sample is heated at 850° C, at which EC is oxidized rapidly and completely by MnO₂. Carbonates that may be present in either the particles or the filter medium are removed by acidification and heating to ～ 120°C prior to performing the organic and EC measurements. Analysis of split ambient particulate samples in which the OC levels had been reduced by solvent extraction produced EC results statistically the same as the original untreated samples. These results suggest that the speciation is not sensitive to the level of organics in the sample. During the Carbonaceous Species Methods Comparison Study (CSMCS) in which the participants analyzed 20 blind samples, with four being triplicates, this technique yielded results in good agreement with the average results of the participants, with coefficients of variation (CV) derived from the triplicate analysis being 2.1%, 2.6%, and 8.1%, respectively, for total, organic, and elemental carbon.     

Experiments on paper insulation in a corona environment

Insertion of an insulating paper between point-plane electrodes normally increases the total breakdown potential threshold, except when its position is next to the plane. A series of DC [both (+) and (-)] experiments was designed and conducted to examine this latter distinction. It was found that visual ionic spots on the paper surface are a dominant prebreakdown phenomenon. Local failure at one of such discrete spots ultimately brings about a streamer sparkover in air at a sufficiently high potential. This paper describes the variability and other characteristics of the pattern in a two-dimensional spot distribution. Related experiments reveal that, with double paper layers already in the barrier, the pattern of spots becomes less dense visually but the breakdown potential would increase for the case of (+) point but would decrease further for the case of (-) point if a third sheet is introduced. A sharply defined “dark” band on the double-layer side in which glow spots are absent was always observed to clearly bridge the separate domains of, respectively, single-layer and double-layer spot distributions. Also related were the mechanical agitations of the paper accompanying all phases of the different discharge activities     

EC-EGI: enriched complex EGI for 3D shape registration

Extended Gaussian image (EGI) and complex EGI (CEGI) have been widely used as the representation of 3D shapes for shape recognition and pose estimation. In this work, we extend the representations and present a new representation named enriched complex extended Gaussian image (EC-EGI). The representation follows the same framework of EGI and CEGI, which is to represent each surface patch of the target 3D shape as a weight at the associated spot on the surface of the Gaussian sphere. However, while the original CEGI uses a single complex number as the weight, the new representation uses three complex numbers, which are related to the centroid position of the surface patch in 3D. With the inclusion of more information in the new representation, not only could object pose be determined more accurately, but also some key ambiguities of shape representation that CEGI and EGI have also removed. The translation parameters in the pose estimation application could also be determined in a simpler and more accurate way. In addition, the Gaussian sphere partition problem of CEGI is no longer present. Experimental results on synthetic and real image data are shown to illustrate the performance of the proposed representation in pose estimation.     

Geometry of the minimum zone flatness functional: planar and spatial case

The zone straightness and flatness functional is constructed from the definition of the measure. The geometry of the straightness functional is illustrated in the plane, and in three dimensions, a novel means to visually represent flatness is described using the zone separation body. The zone separation body is a new construction that is uniquely associated with every measurement dataset and can be used to represent the flatness functional visually.     

Mining-induced stress change and consequences of stress path on excavation stability — a case study

For stability assessments as well as for support design, it is important to understand the factors leading to detrimental stress changes. Stress changes not only influence the demand on the rock support, they also change the support capacity of frictional support components such as plain cablebolts. Stress and stress changes are commonly predicted by numerical models but it is rarely possible to verify these predictions. This study presents a practical example illustrating the usefulness of stress change measurements in providing an accurate picture of the mining-induced stress changes and their value for numerical model calibration. Stress changes, associated with mining of the 565#6 stope at Winston Lake Mine, were measured by four CSIRO HI stress cells, two in the hangingwall and two in the back of a sill drift. In order to obtain the full stress history of the hangingwall, stresses at the installation time were calculated by use of a three-dimensional boundary element program — MAP3D. Two types of rockmass failure were observed at this mine: hangingwall delamination and collapse leading to ore dilution, and wedge-like failures in the backs of sill drifts. All stress cells were located such that they were affected by these failure mechanisms. Using measured and predicted stress paths, this study explains the nature of these two failure modes, as experienced at Winston Lake Mine. Excellent correspondence between measured and predicted stresses is achieved for both the hangingwall and the back of the sill drifts. Modelled stress rotations in the hangingwall follow closely the stress rotations determined in the field, except at the end of the monitoring campaign when the stress cells were affected by inelastic straining of the host rock. These measurements assist in understanding the failure processes and in defining the limitations of the adopted numerical models.