Using snakes for the registration of topographic road database objects to ALS features

For historical reasons many national mapping agencies store their topographic data in a dual system consisting of a Digital Landscape Model (DLM) and a Digital Terrain Model (DTM). The DLM contains 2D vector data representing objects on the Earth’s surface, such as roads and rivers, whereas the DTM is a 2.5D representation of the related height information, often acquired by Airborne Laser Scanning (ALS). Today, many applications require reliable 3D topographic data. Therefore, it is advantageous to convert the dual system into a 3D DLM. However, as a result of different methods of acquisition, processing, and modelling, the registration of the two data sets often presents difficulties. Thus, a straightforward integration of the DTM and DLM might lead to inaccurate and semantically incorrect 3D objects.In this paper we propose a new method for the fusion of the two data sets that exploits parametric active contours (also called snakes), focusing on road networks. For that purpose, the roads from a DLM initialise the snakes, defining their topology and their internal energy, whereas ALS features exert external forces to the snake via the image energy. After the optimisation process the shape and position of the snakes should coincide with the ALS features. With respect to the robustness of the method several known modifications of snakes are combined in a consistent framework for DLM road network adaptation. One important modification redefines the standard internal energy and thus the geometrical model of the snake in order to prevent changes in shape or position not caused by significant features in the image energy. For this purpose, the initial shape is utilized creating template-like snakes with the ability of local adaptation. This is one crucial point towards the applicability of the entire method considering the strongly varying significance of the ALS features. Other concepts related to snakes are integrated which enable our method to model network and ribbon-like characteristics simultaneously. Additionally, besides ALS road features information about context objects, such as bridges and buildings, is introduced as part of the image energy to support the optimisation process. Meaningful examples are presented that emphasize and evaluate the applicability of the proposed method.     

Mycological evidence of coprophagy from the feces of an Alaskan Late Glacial mammoth

Dung from a mammoth was preserved under frozen conditions in Alaska. The mammoth lived during the early part of the Late Glacial interstadial (ca 12,300 BP). Microfossils, macroremains and ancient DNA from the dung were studied and the chemical composition was determined to reconstruct both the paleoenvironment and paleobiology of this mammoth. Pollen spectra are dominated by Poaceae, Artemisia and other light-demanding taxa, indicating an open, treeless landscape (‘mammoth steppe’). Fruits and seeds support this conclusion. The dung consists mainly of cyperaceous stems and leaves, with a minor component of vegetative remains of Poaceae. Analyses of fragments of the plastid rbcL gene and trnL intron and nrITS1 region, amplified from DNA extracted from the dung, supplemented the microscopic identifications. Many fruit bodies with ascospores of the coprophilous fungus Podospora conica were found inside the dung ball, indicating that the mammoth had eaten dung. The absence of bile acids points to mammoth dung. This is the second time that evidence for coprophagy of mammoths has been derived from the presence of fruit bodies of coprophilous fungi in frozen dung. Coprophagy might well have been a common habit of mammoths. Therefore, we strongly recommend that particular attention should be given to fungal remains in future fossil dung studies.     

The Sirente crater field,Italy

Abstract— We propose the Sirente crater field to be the first discovered impact craters in Italy. They are located in the Sirente plain within the mountains of the Abruzzo region, central Italy. The craters are distributed in a field 450 m long and 400 m wide. This field consists of ?17 smaller craters close to a larger main crater. The main crater is located in the southern end of the crater field and is 140 m long and 115 m wide, measured rim‐to‐rim. It has a well‐developed, saddle‐shaped rim that rises at a maximum 2.2 m above the surrounding plain. Radiocarbon dating of the target surface preserved below the rim gave a calibrated age of formation at about a.d. 412 (1650 ± 40 radiocarbon years b.p.). This young age is consistent with the apparent little modification of the rim. The morphology of the main crater and its relation to a crater field strongly points to its origin by impact from a projectile that broke up during its passage through the atmosphere. Quartz is very rare in the target and no planar deformation features have been found so far. The rim material and the upper 4 m of the main crater infill are impregnated with ferric oxides, which gives a more reddish colour compared to the other sediments of the plain. Rusty crusts with high Fe and Mn content occur in the rim material, but have not been found in the plain's sediments. Some of these crusts can be separated by magnet, and have sporadic micron‐sized Ni‐rich granules. The main crater is in the size range of the craters with explosive dispersion of the projectile and has many features comparable to both large experimental and meteoritic impact craters formed in loose sediments. We suggest that this crater represents a rare example of well‐preserved, small impact crater formed in unconsolidated target materials.     

Holocene environmental reconstruction from deltaic deposits in northeast Greenland

Terraces of different age in the Zackenberg delta, located at 74°N in northeast Greenland, have provided the opportunity for an interdisciplinary approach to the investigation of Holocene glacial, periglacial, pedological, biological and archaeological conditions that existed during and after delta deposition. The raised Zackenberg delta accumulated mainly during the Holocene Climatic Optimum, starting slightly prior to 9500 cal. yr BP (30 m a.s.l.) and continued until at least 6300 cal. yr BP (0.5 m a.s.l.). Evidence of sea‐level change is based on conventional ¹⁴C dates of shells from the marine delta bottomsets, ¹⁴C AMS dating of macroscopic plant material from the foresets and of fluvial deposits. Arthropod and plant remains from 7960 cal. yr BP in the delta foresets include the oldest evidence of the arctic hare in Greenland and evidence of a rich herb flora slightly different from the modern flora. Empetrum nigrum and Salix herbacea remains indicate a summer temperature at least as high as today during delta deposition. Post‐depositional nivation activity, dated by luminescence, lichenometry and Schmidt Hammer measurements indicate mainly late Holocene activity, at least since 2900 yr BP, including Little Ice Age (LIA) avalanche activity. Pedological analyses of fossil podsols in the Zackenberg delta, including ¹⁴C AMS dating of selected organic rich B‐horizons, show continued podsol development during the Holocene Climatic Optimum and into the subsequent colder period of the late Holocene, until 3000–2400 yr BP. A Neo‐Eskimo house ruin found on the lower part of the delta, presently being eroded by the sea, is dated to AD 1800. It presumably was abandoned prior to AD 1869, and suggests that some of the last Eskimos that lived in northeast Greenland might have occupied the Zackenberg delta. Copyright © 2002 John Wiley & Sons, Ltd.     

GPS radio holography as a tool for remote sensing of the atmosphere, mesosphere, and terrestrial surface from space

GPS radio occultation (RO) signals are highly coherent and precise, and thus sufficient for holographic investigation of the atmosphere, ionosphere, and the Earth's surface from space. In principle, three-dimensional radio-holographic remote sensing is possible by using new radio holographic equations to retrieve the radio field within the atmosphere from a radio field known at some interface outside the atmosphere. A simplified two-dimensional form of the radio-holographic equations which are developed under an assumption of local spherical symmetry can be used to obtain two-dimensional radio images of the atmosphere and terrestrial surface. To achieve this, radio holograms recorded by a GPS receiver onboard a low earth orbit (LEO) satellite at two GPS frequencies can be used and focused synthetic aperture principle applied. Analysis of GPS/MET RO data is presented to show the effectiveness of a radio-holographic approach. It is shown that the amplitude of GPS radio signals (in addition to phase data) can be used to obtain detailed altitude profiles of the vertical gradient of refractivity in the atmosphere and electron density in the mesosphere. The results demonstrate the applicability of GPS radio holography for a detailed global study of the natural processes in the atmosphere and mesosphere. Electronic Publication     

Hydrogeological and Gasgeochemical Earthquake Precursors – A Review for Application

Even if earthquake precursory signals can be identified, how can they be useful? This paper investigates relationships among the attributes of 229 proposed earthquake related gasgeochemical and hydrogeological precursory signals, and applies these results to improve future earthquake prediction strategies. Sub-groups of these reported signals and relationships between sub-groups are established using parameters, including earthquake magnitude, signal duration, precursory time, and epicentral distance to the monitoring site (original studies are used wherever possible to improve data quality). A strong correlation (r=0.86) between signal duration and precursory time was identified. This suggests a relationship between the investigated precursory signals and tectonic processes related to the referenced earthquakes. Moreover, these signals are categorized into four groups, reflecting differences in monitoring station densities, measurement methods and physical processes related to signal occurrence: (a) radon exhalation from the earth’s crust, (b) exhalation of other gases (helium, argon and others), (c) temporal variation in water level or discharge of springs and (d) temporal variation in temperature and dissolved ions in the water of the monitoring sites. In addition, boundary functions are used to separate signal group subsets. Finally, it is shown how these boundary functions can be used in the context of an earthquake prediction strategy by identifying potential minimum magnitudes and maximum epicentral distances from the monitoring site.     

Lander radioscience for obtaining the rotation and orientation of Mars

The paper presents the concept, the objectives, the approach used, and the expected performances and accuracies of a radioscience experiment based on a radio link between the Earth and the surface of Mars. This experiment involves radioscience equipment installed on a lander at the surface of Mars. The experiment with the generic name lander radioscience (LaRa) consists of an X-band transponder that has been designed to obtain, over at least one Martian year, two-way Doppler measurements from the radio link between the ExoMars lander and the Earth (ExoMars is an ESA mission to Mars due to launch in 2013). These Doppler measurements will be used to obtain Mars’ orientation in space and rotation (precession and nutations, and length-of-day variations). More specifically, the relative position of the lander on the surface of Mars with respect to the Earth ground stations allows reconstructing Mars’ time varying orientation and rotation in space.Precession will be determined with an accuracy better by a factor of 4 (better than the 0.1% level) with respect to the present-day accuracy after only a few months at the Martian surface. This precession determination will, in turn, improve the determination of the moment of inertia of the whole planet (mantle plus core) and the radius of the core: for a specific interior composition or even for a range of possible compositions, the core radius is expected to be determined with a precision decreasing to a few tens of kilometers.A fairly precise measurement of variations in the orientation of Mars’ spin axis will enable, in addition to the determination of the moment of inertia of the core, an even better determination of the size of the core via the core resonance in the nutation amplitudes. When the core is liquid, the free core nutation (FCN) resonance induces a change in the nutation amplitudes, with respect to their values for a solid planet, at the percent level in the large semi-annual prograde nutation amplitude and even more (a few percent, a few tens of percent or more, depending on the FCN period) for the retrograde ter-annual nutation amplitude. The resonance amplification depends on the size, moment of inertia, and flattening of the core. For a large core, the amplification can be very large, ensuring the detection of the FCN, and determination of the core moment of inertia.The measurement of variations in Mars’ rotation also determines variations of the angular momentum due to seasonal mass transfer between the atmosphere and ice caps. Observations even for a short period of 180 days at the surface of Mars will decrease the uncertainty by a factor of two with respect to the present knowledge of these quantities (at the 10% level).The ultimate objectives of the proposed experiment are to obtain information on Mars’ interior and on the sublimation/condensation of CO₂ in Mars’ atmosphere. Improved knowledge of the interior will help us to better understand the formation and evolution of Mars. Improved knowledge of the CO₂ sublimation/condensation cycle will enable better understanding of the circulation and dynamics of Mars’ atmosphere.     

Melting and Sublimation of Planetary Ices Under Low Pressure Conditions: Laboratory Experiments with a Melting Probe Prototype

One possibility to explore the subsurface layers of icy bodies is to use a probe with a “hot tip", which is able to penetrate ice layers by melting. Such probes have been built and used in the past for the exploration of terrestrial polar ice sheets and may also become useful tools to explore other icy layers in the Solar System. Examples for such layers are the polar areas of Mars or the icy crust of Jupiter’s moon Europa. However, while on Earth a heated probe launched into an ice sheet always causes melting with subsequent refreezing, the behaviour of such a probe in a low pressure environment is quite different. We report on the results of some experiments with a simple “melting probe" prototype with two different kinds of hot tips in a vacuum environment. For one of the tips the probe moved into two types of ice samples: (i) compact water ice and (ii) porous water ice with a snow (firn) like texture. It was also found that the penetration behaviour was basically different for the two sample types even when the same kind of tip was used. While in the porous sample the ice was only subliming, the phase changes occurring during the interaction of the tip with the compact ice are much more complex. Here alternating phases of melting and sublimation occur. The absence of the liquid phase has severe consequences on the performance of a “melting probe" under vacuum conditions: In this environment we find a high thermal resistance between the probe surface and the underlying ice. Therefore, only a low percentage of the heat that is generated in the tip is used to melt or sublime the ice, the bulk of the power is transferred towards the rear end of the probe. This is particularly a problem in the initial phases of an ice penetration experiment, when the probe has not yet penetrated the ice over its whole length. In the compact ice sample, phases could be observed, where a high enough gas pressure had built up locally underneath the probe, so that melting becomes possible. Only during these melting periods the thermal contact between the probe and the ice is good and in consequence the melting probe works effectively.     

‘Box‐Profile’ Ion Implants as Geochemical Reference Materials for Electron Probe Microanalysis and Secondary Ion Mass Spectrometry

Although electron probe microanalysis and secondary ion mass spectrometry are widely used analytical techniques for geochemical and mineralogical applications, metrologically rigorous quantification remains a major challenge for these methods. Secondary ion mass spectrometry (SIMS) in particular is a matrix‐sensitive method, and the use of matrix‐matched reference materials (RMs) is essential to avoid significant analytical bias. A major problem is that the number of available RMs for SIMS is extremely small compared with the needs of analysts. One approach for the production of matrix‐specific RMs is the use of high‐energy ion implantation that introduces a known amount of a selected isotope into a material. We chose the more elaborate way of implanting a so‐called ‘box‐profile’ to generate a quasi‐homogeneous concentration of the implanted isotope in three dimensions, which allows RMs not only to be used for ion beam analysis but also makes them suitable for EPMA. For proof of concept, we used the thoroughly studied mineralogically and chemically ‘simple’ SiO₂ system. We implanted either ⁴⁷Ti or ⁴⁸Ti into synthetic, ultra‐high‐purity silica glass. Several ‘box‐profiles’ with mass fractions between 10 and 1000 μg g^?1 Ti and maximum depths of homogeneous Ti distribution between 200 nm and 3 μm were produced at the Institute of Ion Beam Physics and Materials Research of Helmholtz‐Zentrum Dresden‐Rossendorf. Multiple implantation steps using varying ion energies and ion doses were simulated with Stopping and Range of Ions in Matter (SRIM) software, optimising for the target concentrations, implantation depths and technical limits of the implanter. We characterised several implant test samples having different concentrations and maximum implantation depths by means of SIMS and other analytical techniques. The results show that the implant samples are suitable for use as reference materials for SIMS measurements. The multi‐energy ion implantation technique also appears to be a promising procedure for the production of EPMA‐suitable reference materials.