Analysis of a lidar voxel-derived vertical profile at the plot and individual tree scales for the estimation of forest canopy layer characteristics

The goal of the current study was to develop methods of estimating the height of vertical components within plantation coniferous forest using airborne discrete multiple return lidar. In the summer of 2008, airborne lidar and field data were acquired for Loblolly pine forest locations in North Carolina and Virginia, USA, which comprised a variety of stand conditions (e.g. stand age, nutrient regime, and stem density). The methods here implement both field plot-scale analysis and an automated approach for the delineation of individual tree crown (ITC) locations and horizontal extents through a marker-based region growing process applied to a lidar derived canopy height model. The estimation of vertical features was accomplished through aggregating lidar return height measurements into vertical height bins, of a given horizontal extent (plot or ITC), creating a vertical ‘stack’ of bins describing the frequency of returns by height. Once height bins were created the resulting vertical distributions were smoothed with a regression curve-line function and canopy layers were identified through the detection of local maxima and minima. Estimates from Lorey’s mean canopy height was estimated from plot-level curve-fitting with an overall accuracy of 5.9% coefficient of variation (CV) and the coefficient of determination (R²) value of 0.93. Estimates of height to the living canopy produced an overall R² value of 0.91 (11.0% CV). The presence of vertical features within the sub-canopy component of the fitted vertical function also corresponded to areas of known understory presence and absence. Estimates from ITC data were averaged to the plot level. Estimates of field Lorey’s mean canopy top height from average ITC data produced an R² value of 0.96 (7.9% CV). Average ITC estimates of height to the living canopy produced the closest correspondence to the field data, producing an R² value of 0.97 (6.2% CV). These results were similar to estimates produced by a statistical regression method, where R² values were 0.99 (2.4% CV) and 0.98 (4.9% CV) for plot average top canopy height and height to the living canopy, respectively. These results indicate that the characteristics of the dominant canopy can be estimated accurately using airborne lidar without the development of regression models, in a variety of intensively managed coniferous stand conditions.     

The influence of partitioning on Domain Decomposition convergence rates

Computing and Visualization in Science - This paper discusses the effects that partitioning has on the convergence rate of Domain Decomposition. When Finite Elements are employed to solve a second...     

Adventures in adaptivity

Computing and Visualization in Science - In this work, we compare and contrast a few finite element h-adaptive and hp-adaptive algorithms. We test these schemes on three example PDE problems and we...     

Social Disadvantage, Tenure and Location: An Analysis of Sydney and Melbourne

This article focuses on the role that housing markets play in structuring patterns of social disadvantage in Australian cities, specifically Sydney and Melbourne. It explores the relationship between housing tenure and social disadvantage at the local scale (Census collector districts) for the two cities, following a discussion of the various stands of literature on housing tenure and socio-spatial polarisation in Australian cities. It analyses the relationship between areas of high social disadvantage and housing tenure. The analysis, which uses the ABS Index of Disadvantage, distinguishes locations where comparable levels of social disadvantage are associated with very different housing markets, one where public housing is prominent and others which are primarily areas of private sector housing. The social profiles of both types of area are described, drawing out differences between the two cities, as are changes in the extent of these areas over time. The policy implications for the areas of private sector housing are then discussed.     

Effect of Gapping on the Transient and Sustained Uplift Capacity of a Shallow Skirted Foundation in Clay

Shallow skirted foundations are an attractive solution for supporting offshore platforms that are subject to uplift due to overturning or buoyancy loading. In practice, gapping may occur along the skirt-soil interface leading to a detrimental effect on uplift capacity. This paper presents results from beam centrifuge tests that investigated the effect of gapping on the transient and sustained uplift capacity of shallow skirted foundations. The results indicate that the transient uplift capacity following the formation of a gap was around 60% of that for intact soil contact along the skirt-soil interface. Under sustained uplift, the time to accumulate a displacement of 1% of the foundation diameter was reduced by an order of magnitude due to the presence of a gap.     

Community renewal and large public housing estates

The extent of social disadvantage in local neighbourhoods has come to the fore in recent years, partly as a result of the problems that State Housing Authorities have faced in managing the concentrations of socially marginalised populations on larger public housing estates. However, a wider understanding of the processes at play in these neighbourhoods is needed to inform policy development. We consider the evolution of local renewal policy in New South Wales at the present time and suggest potential policy options for the future.     

Analysis of Factors Influencing Soil Classification Using Normalized Piezocone Tip Resistance and Pore Pressure Parameters

This paper discusses the development of a framework for classifying soil using normalized piezocone test (CPTU) data from the corrected tip resistance (qt) and penetration pore-water pressure at the shoulder (u2). Parametric studies for normalized cone tip resistance (Q = qcnet/σv0′) and normalized excess pressures (Δu2/σv0′) as a function of overconsolidation ratio (OCR = σvy′/σv0′) during undrained penetration are combined with piezocone data from clay sites, as well as results from relatively uniform thick deposits of sands, silts, and varietal clays from around the globe. The study focuses on separating the influence of yield stress ratio from that of partial consolidation on normalized CPTU parameters, which both tend to increase Q and decrease the pore pressure parameter (Bq = Δu2/qcnet). The resulting recommended classification chart is significantly different from existing charts, and implies that assessment of data in Q–Δu2/σv0′ space is superior to Q–Bq space when evaluating piezocone data for a range of soil types. Still, there are zones of overlap for silty soils and heavily overconsolidated clays, thus requiring that supplementary information to Q and Δu2/σv0′ be obtained in unfamiliar geologies, including variable rate penetration tests, dissipation tests, CPT friction ratio, or soil sampling.     

Regularization and frequency-domain stability of well-posed systems

We study linear control systems with unbounded control and observation operators using certain regularization techniques. This allows us to introduce a modification of the transfer function for the system even if the input and output operators are not admissible in the usual sense. The modified transfer function is utilized to show exponential stability of sufficiently smooth solutions for the internal system under appropriate admissibility conditions on the system operators and appropriately modified stabilizability and detectability assumptions. If the internal system satisfies additional, yet common, regularity properties, then its uniform exponential stability is obtained.     

On the convergence of adaptive feedback loops

Computing and Visualization in Science - We present a technique for proving convergence of h and hp adaptive finite element methods through comparison with certain reference refinement schemes...     

CRYSTALLIZATION OF SODIUM NITRATE FROM ALUMINUM AND CESIUM CONTAINING LIQUORS

Present inventory of Hanford single shell tank waste is about 180,000 tons. More than 70%by weight of the tank waste are non-radioactive sodium nitrate. The paper presents an entirely different approach to pretreatment of Hanford radioactive waste stored in underground tanks. Instead of removing radionuclides, ¹³⁷Cs in this case, from the bulk of the waste, this process selectively recovers the non-radioactive sodium salts from the waste by crystallization. It opens up a possible new way of looking at waste pretreatment. The feasibility teat has been done at the facility of Westinghouse Hanford Company. The result shows a potential of reclaim sodium nitrate with a total activity of less than 60 pCi/g

The objective of the research is to develop and demonstrate a scaleable crystallization process to recover sodium nitrate from aluminum and cesium containing mother liquor. Per-pass crystal yields and separation factors as well as the effects of crystal size, slurry density, growth rate and mother liquor concentrations on occlusion and entrainment are studied.