Creating high-resolution bare-earth digital elevation models (DEMs) from stereo imagery in an area of densely vegetated deciduous forest using combinations of procedures designed for lidar point cloud filtering

For areas of the world that do not have access to lidar, fine-scale digital elevation models (DEMs) can be photogrammetrically created using globally available high-spatial resolution stereo satellite imagery. The resultant DEM is best termed a digital surface model (DSM) because it includes heights of surface features. In densely vegetated conditions, this inclusion can limit its usefulness in applications requiring a bare-earth DEM. This study explores the use of techniques designed for filtering lidar point clouds to mitigate the elevation artifacts caused by above ground features, within the context of a case study of Prince William Forest Park, Virginia, USA. The influences of land cover and leaf-on vs. leaf-off conditions are investigated, and the accuracy of the raw photogrammetric DSM extracted from leaf-on imagery was between that of a lidar bare-earth DEM and the Shuttle Radar Topography Mission DEM. Although the filtered leaf-on photogrammetric DEM retains some artifacts of the vegetation canopy and may not be useful for some applications, filtering procedures significantly improved the accuracy of the modeled terrain. The accuracy of the DSM extracted in leaf-off conditions was comparable in most areas to the lidar bare-earth DEM and filtering procedures resulted in accuracy comparable of that to the lidar DEM.     

A statistical study of the relationship between the solar cycle length and tree-ring index values

We have determined the correlation coefficient between tree-ring index values and the sunspot cycle length for 69 tree-ring data sets from around the world of greater than 594 years duration. A matrix of correlation coefficients is formed with varying delay and smoothing parameters. Similar matrices, formed from the same data, but randomly scrambled, provide a control against which we can draw conclusions about the influence of the solar cycle length on climate with a reasonable degree of confidence. We find that the data confirm an association between the sunspot cycle length and climate with a negative maximum correlation coefficient for 80% of the data sets considered. This implies that wider tree-rings (i.e. more optimum growth conditions) are associated with shorter sunspot cycles. Secondly, we find that the climatic effect of the solar cycle length is smoothed by several decades and the degree of smoothing is dependent on the elevation and the geographical location of the trees employed. Thirdly, we find evidence for a cyclic variation of ∼200 years period in either solar cycle length or tree ring index. © 1999 Elsevier Science Ltd. All rights reserved.     

A backbarrier overwash record of intense storms from Brigantine, New Jersey

Analysis of aerial photographs and historic charts indicates that the barrier beach at Brigantine, NJ has migrated landward 300 to 400 m since 1869, primarily as a result of overwash during hurricanes and winter storms. A series of vibracores from the backbarrier salt marsh reveals a millennial-scale stratigraphic record of overwash deposition. Carbon-14 (C-14) and Cesium-137 (Cs-137) radioisotopic methods were used to date overwash deposits (washovers). The ages of recent washovers are consistent with deposition during intense storms in 1938, 1944, 1950, and 1962. An additional overwash deposit recovered in five of the sediment cores was likely deposited by an intense hurricane strike in 1821 or possibly in 1788. Two prehistoric overwash fans were likely deposited by intense storms striking the New Jersey Coast in the 7th to 14th centuries and 6th to 7th centuries A.D. The landward barrier migration indicates that the older overwash sediments were likely transported a considerably greater distance than the more recent overwash fans. The greater distance of transport may indicate that the prehistoric storms that deposited overwash fans across the study site were more intense than the most intense storm to strike this coast in the historic period, the hurricane of 1821. The spatially variable occurrence of overwash deposition at this site points to a need for multisite stratigraphic surveys of extensive stretches of the coast in order to develop reliable records of past intense storm frequency from backbarrier environments.     

Regional seismic observations of the Ontong Java plateau and East Mariana Basin

P-waves recorded on Ponape Island at the northern end of the Ontong Java plateau have been investigated. Different modes of propagation in the distance range 12° to 17° Δ between paths from Melanesian earthquakes across the Ontong Java plateau and paths from Mariana earthquakes across the eastern Mariana basin suggest that the mantle underlying the regions is not homogeneous. Travel-times of P-waves beneath the Ontong Java plateau are slower than for paths beneath the east Mariana basin. The frequency content of the first-arriving P-waves is lower for paths across the Ontong Java plateau than for the east Mariana basin. The disparate crustal thicknesses of the Ontong Java plateau and east Mariana basin may influence the relative amplitude of oceanic Pn, with smaller amplitudes corresponding to a thicker crust. Pn-P differential times for the Ontong Java plateau show a general decrease with the depth of earthquake focus but no comparable trend is seen in the Mariana data, possibly because of the scatter. The observation of high-frequency oceanic Pn propagation across the Ontong Java Plateau is suggestive that the plateau is not of continental origin.     

Alternative and Virtual Rurality: Agriculture and The Countryside as Embodied in American Imagination

Affection for agrarian livelihoods and rural and small‐town environments has long been held by residents in many of the world's “more developed” countries. Although the rural proportion of the U.S. population has shrunk to a minority over the last century, fondness for rurality continues to manifest itself in a number of ways. Attachment to the rural ideal or rural idyll can be considered as attachment to the idea of a type of place, rather than specific place attachment. Based on literature, field observation, computer searches, and data from the U.S. Census of Agriculture, connections to idea(l)s of rurality apparent in popular culture are identified and illustrated. These include rural and agricultural tourism, small‐scale farming and large‐lot rural subdivisions, urban agriculture, farmers’ markets and community‐supported agriculture, creation of housing developments around farm activities, and rural‐named housing and business developments. Idealized relationships with rurality call upon health and well‐being, connecting to nature, aesthetics, privacy, and respect and nostalgia for rural livelihoods.     

Global energy security under different climate policies,GDP growth rates and fossil resource availabilities

Energy security is one of the main drivers of energy policies. Understanding energy security implications of long-term scenarios is crucial for informed policy making, especially with respect to transformations of energy systems required to stabilize climate change. This paper evaluates energy security under several global energy scenarios, modeled in the REMIND and WITCH integrated assessment models. The paper examines the effects of long-term climate policies on energy security under different assumptions about GDP growth and fossil fuel availability. It uses a systematic energy security assessment framework and a set of global and regional indicators for risks associated with energy trade and resilience associated with diversity of energy options. The analysis shows that climate policies significantly reduce the risks and increase the resilience of energy systems in the first half of the century. Climate policies also make energy supply, energy mix, and energy trade less dependent upon assumptions of fossil resource availability and GDP growth, and thus more predictable than in the baseline scenarios.