The Use of LiDAR in Digital Surface Modelling: Issues and Errors

Modelling and extracting 3D geographical data presents numerous challenges that require continual research to attempt to evolve an efficient, reliable and accurate solution. LiDAR data capture and analysis has become a preferred acquisition choice for elevation data because the resulting quality and level of detail far exceeds traditional methods for large survey areas. As with any data collection system, LiDAR is prone to errors. Analysing these errors, ascertaining causes and producing error correction strategies is vital if accurate and confident results are to be obtained. Eight years of LiDAR datasets (from 1998 to 2005) have been closely analysed for a large coastal area of South Wales. This article provides a detailed and accurate summary of the identified LiDAR data issues and subsequent errors which affect the accuracy of end products such as Digital Surface Models (DSMs).     

Use of SPOT 5 and IKONOS imagery for mapping biocenoses in a Tunisian Coastal Lagoon (Mediterranean Sea)

Mapping marine biocenoses is an efficient method for providing useful data for the management and conservation of Mediterranean lagoons. Fused images from two satellites, SPOT 5 and IKONOS, were tested as management tools for identifying specific ecosystems in the El Bibane lagoon, situated in southern Tunisia near the Libyan border. The objectives of this study were to provide a precise map of the entire El Bibane lagoon using fused images from SPOT 5 and to compare fused images from SPOT 5 and IKONOS over a test-area. After applying a supervised classification, pixels are automatically classified in four classes: low seagrass cover, high seagrass cover, superficial mobile sediments and deep mobile sediments. The maps of the lagoon revealed and confirmed an extremely wide distribution of seagrass meadows within the lagoon (essentially Cymodocea nodosa; 19 546 ha) and a large area of mobile sediments more or less parallel to the shore (3 697 ha). A direct comparison of overall accuracy between SPOT 5 over the entire area, SPOT 5 over the test-area and IKONOS over the test-area revealed that these tools provided accurate mapping of the lagoon environment (83.25%, 85.91% and 73.41% accuracy, respectively). The SPOT 5 images provided greater overall accuracy than the IKONOS image, but did not take into account the heterogeneous spatial structure of the seagrasses and sediments present in the lagoon environment. Although IKONOS imagery provided lower overall accuracy than SPOT 5, it proved a very useful tool for the mapping of heterogeneous structures as it enabled the patchiness of formations to be better taken into account. The use of SPOT 5 and IKONOS fused images appears to be very promising for completing the mapping of lagoons in other regions and countries of the Mediterranean Sea.     

Phase transitions in perturbed stiff-fluid Friedmann-Robertson-Walker cosmological models

We consider one-soliton perturbations of a flat Friedmann-Robertson-Walker (FRW) cosmological model, with an ideal fluid with pressure equal to the energy density (stiff fluid), in the case where the “pole trajectory” parameter is negative, introducing thereby singularities along certain null hypersurfaces. Starting with a metric that approaches asymptotically the FR W background, we show that it is possible to construct an extension through these hypersurfaces such that the energy momentum tensor T_ab is finite and satisfies the energy conditions. The extension is only C₁, providing a sort of “shock front” with continuity in T_ab, that has an associated phase transition from null dust to stiff fluid, the transition being of the form described by CHANDRASEKHAR and XANTHOPOULOS.     

Syntectonic growth of garnets: Discussion of a new model proposed by M. J. de Wit

Textural and compositional zoning observed in paracrystalline rotated garnets, as well as the euhedral shape of some of these crystals, show that each of them has originated from a single nucleus and acted as a rigid body during subsequent growth and rotation. The alternative multiple nucleus model of de Wit (1976) is thus considered inapplicable as a general model. It is argued that even for the specific cases described by de Wit the classic single nucleus model could be applied.     

Tokaido — megalopolis of Japan

The Tokaido east coast road has been the main road of Japan since Mediaeval times, and the journey from Tokyo at one end to Kyoto or Osaka at the other, which used to take a fortnight, can now be completed in about three hours by bullet train, and an even faster linear-motor car is likely to be in operation in the near future.Already during the 18. cent., Edo (Tokyo) was the largest city in the world, with a population over a million, and the rapid urbanization of Japan's population since Meiji times, and particularly during the post-WW II period, has been quite unprecendented. In 1950, the median size of place was 13,000 and by 1975 it was 140,000. About 60 million lived in the Tokaido zone.The Kanto, Nobi and Osaka plains, adjacent to the good harbours of Tokyo, Ise and Osaka bays, enjoying the relatively mild climate of the Pacific coast, and being within 600 km of each other, have been the focii of urban and industrial development in Japan. The emergence of Tokaido megalopolis was boosted by capital investment in this zone, and was contingent upon the industriousness and high level of education of the people.The concept of megalopolis in Japan is popularly associated with rapid urbanization, poly-nuclear and linear form, and concentration of population, capital and information, all of which elements are typified by the Tokaido zone. The linear megalopolis pattern has been postulated as a more efficient growth form for high-dense society than the radial metropolitan pattern. It has even been suggested that megalopolis is a concept perceived by the intellect, its physical structure determined by information networks, metropolis being perceived by the eye and its physical structure being determined by transport and energy networks.Quite irrespective of the concept of megalopolis, there can be no denying that Japan's society is a high-dense society. In 1975, 57% of the population lived in Densely Inhabited Districts (DIDs) at minimum densities of 40 persons per hectare, and these DIDs covered only 2.2% of the land area of Japan. The current trend is for more and more people to live in DIDs, but for overall DID densities to decrease. During the past 25 years, there has been a huge influx of population into the Tokaido zone, and while until 1960 the greatest increases were in the three main metropolitan centres, as these became saturated, rapid urbanization spread into the neighbouring prefectures. Since the mid-sixties, the central metropolitan wards have begun to lose residents, but the daytime population has continued to increase, giving rise to increasingly complex commuting patterns. To give an example, the commuting field of Yokohama includes almost all the prefectures of Tokaido megalopolis.Like the image of megalopolis itself, life in Tokaido megalopolis has its good and bad aspects. Although per capita space in dwellings is increasing somewhat, housing is extremely expensive and people commute long distances. Incomes are high but environmental problems persist. There is a U-turn phenomenon, but metropolitan suburbs remain a popular choice of residence.Central management functions and knowledge and information oriented occupations are predominantly concentrated in Tokyo and Osaka, the two main nodes of Tokaido megalopolis. In the intermediate cities, new employment opportunities are stimulated by the expansion of second-level managerial functions. The transport and communications networks of Tokaido are becoming congested as mobility and information flow increase.Planning in the eighties will be affected by the switch from industries dependent on raw materials to knowledge intensive industries; from investment in production to investment in public facilities and pollution control. Within Tokaido megalopolis, there is room for local governments to expand efforts to improve the existing situation, and at its fringes to avert some of the less desirable consequences of rapid urbanization.     

Petrogenesis of voluminous mid-Tertiary ignimbrites of the Sierra Madre Occidental,Chihuahua, Mexico

The mid-Tertiary ignimbrites of the Sierra Madre Occidental of western Mexico constitute the largest continuous rhyolitic province in the world. The rhyolites appear to represent part of a continental magmatic arc that was emplaced when an eastward-dipping subduction zone was located beneath western Mexico.In the Batopilas region of the northern Sierra Madre Occidental the mid-Tertiary Upper Volcanic sequence is composed predominantly of rhyolitic ignimbrites, but volumetrically minor lava flows as mafic as basaltic andesite are also present. The basaltic andesite to rhyolite series is calc-alkalic and contains 1% K₂O at 60% SiO₂. Trace element abundances of a typical ignimbrite with 73% SiO₂ are Sr 225 ppm, Rb 130 ppm, Y 32 ppm, Th 12 ppm, Zr 200 ppm, and Nb 15 ppm. The entire series plots as coherent and continuous trends on variation diagrams involving major and trace elements, and the trends are distinct from those of geographicallyassociated rocks of other suites. We interpret these and other geochemical variations to indicate that the rocks are comagmatic. Mineral chemistry, Sr isotopic data, and REE modelling support this interpretation.Least squares calculations show that the major element variations are consistent with formation of the basaltic andesite to rhyolite series by crystal fractionation of observed phenocryst phases in approximate modal proportions. In addition, calculations modelling the behavior of Sr with the incompatible trace element Th favor a fractional crystallization origin over a crustal anatexis origin for the rock series. The fractionating minerals included plagioclase (> 50%), and lesser amounts of Fe-Ti oxides, pyroxenes, and/or hornblende. The voluminous ignimbrites represent no more than 20% of the original mass of a mantle-derived mafic parental magma.