Costabel S.,Federal Institute for Geosciences and Natural Resources |
Muller-Petke M.,Leibniz Institute for Applied Geophysics
Near Surface Geophysics | Year: 2014
In this paper three different despiking methods for surface-NMR data are investigated and compared. Two of these are applied in the time domain: a threshold is determined that identifies and marks a spiky event. Afterward, the marked time sequence is substituted with zeros or with the mean value of the signal amplitude of the measurement repetitions for the same passage on the time axis. The third despiking approach takes advantage of the wavelet-like nature of spiky events. It isolates and eliminates spiky signals in the wavelet domain, i.e., after transforming a single record with the help of the discrete wavelet transform. The latter is able to reconstruct the original signal content in the (spike-caused) distorted time sequence to some extent. If the spiky noise in surface-NMR measurements consists mainly of single spiky events, the three despiking methods show very similar results and are able to remove spiky noise from data very effectively, as we can show with two real data examples. However, a synthetic study shows that, if a series of spikes within a relatively short period of time occurs, the wavelet-based despiking approach shows significant shortcomings. Because the NMR signal content cannot be restored completely in a single record, the fitting of the signal after stacking leads to underestimation of the initial amplitude up to approximately 10%. Nevertheless, we can show that, in principle, the processing of surface-NMR data in the wavelet domain works and can lead to the same results as straight-forward applications. Moreover, waveletbased strategies have some interesting properties and thus have some potential for further development regarding surface-NMR processing, which is discussed in detail. © 2014 European Association of Geoscientists & Engineers.
Lisker F.,University of Bremen |
Laufer A.L.,Federal Institute for Geosciences and Natural Resources
Geology | Year: 2013
The Transantarctic Mountains (TAM) are the largest non-compressional mountain belt in the world. Their origin is traditionally related to crustal thickening during the Jurassic Ferrar magmatic event that was followed by episodic uplift in the Early and Late Cretaceous and since the Paleocene. This concept of a long-lived morphological high constitutes a base of virtually all Gondwana reconstructions and global climate models. Here we demonstrate that crossover age relationships between thermochronological (apatite fission track) data and stratigraphic information contradict this established interpretation. Instead these data, together with a wealth of independent thermal indicators and geological evidence require the existence of a vast intra-Gondwana basin between at least Late Triassic and Late Cretaceous times, including during the Ferrar magmatic event. Referred to here as the Mesozoic Victoria Basin (MVB), this basin formed during crustal extension across the paleo-Pacific margin of Antarctica and Australia. Uplift of the TAM with associated basin inversion commenced only with the development of the West Antarctic Rift System in Paleogene times. The recognition of the long-lived MVB has primary consequences for the general understanding of the landscape of Gondwana and the breakup between Antarctica and Australia, West Antarctic rifting and uplift of the TAM, and global long-term climate evolution and faunal radiation. © 2013 Geological Society of America.
News Article | February 16, 2017
Savannahs form one of the largest habitats in the world, covering around one-fifth of the Earth's land area. They are mainly to be found in sub-Saharan Africa. Savannahs are home not only to unique wildlife, including the 'Big Five' -- the African elephant, rhinoceros, Cape buffalo, leopard and lion -- but also to thousands of endemic plant species such as the baobab, or monkey bread tree. "What's more, the savannahs play a significant role in the global carbon cycle and therefore affect the planet's climate cycles," says Victor Odipo of Friedrich Schiller University, Jena (Germany). The ability of the savannahs to store the greenhouse gas carbon dioxide is ultimately determined by the amount of aboveground woody biomass, adds Odipo, a doctoral candidate at the Institute of Geography's Remote Sensing section. So far, though, it has been difficult to measure this important indicator, with current climate models relying on rough carbon estimates. However, a team of geographers from the universities of Jena and Oxford, and from Germany's Federal Institute for Geosciences and Natural Resources, has now succeeded in establishing a methodology that enables them to measure the aboveground biomass of the savannahs and record even minor changes in the ecosystem. They have presented their results in the specialist journal Forests (DOI: 10.3390/f7120294). The researchers from the University of Jena use both radar data recorded by satellites and laser scanning data collected from the ground. "Radar data can record the biomass over larger geographical areas, given its coverage, but it provides insufficient information about the structure of the vegetation at localised scales," explains Victor Odipo. Typical of the savannah is its patchwork-like structure: a mixture of grass and shrubs with trees of very different heights, either standing alone or in patches. In order to make a detailed record of this structure and be able to convert it into biomass, the satellite data is complemented by ground-based measurements. For this purpose, a terrestrial laser scanner (TLS) is used, which scans its surroundings with a laser beam within a radius of several hundred metres. "This provides us with a comprehensive three-dimensional digital model of the landscape, which enables a precise analysis of the vegetation structure," says Jussi Baade, associate professor of Physical Geography at the University of Jena. After exhaustive initial tests in the Stadtrodaer Forest and the slopes of the Saale valley near Jena, the researchers have now applied their methodology to the savannah of Kruger National Park in South Africa. In an area of some nine square kilometres for which radar satellite data is available, they collected laser scanning data from more than 40 plots, and integrated this data into a model for calculating the biomass. "The laser scanning data collected from selected points does give significantly more precise results than the satellite radar," notes Christian Berger, co-author of the study and head of the research project on which Victor Odipo's doctoral thesis is based. "But on its own, and due to smaller coverage compared with airborne data, this method is not suitable for investigating large areas." As this study shows, however, combining the two methods allows estimation of biomass with a range of 2.9 tonnes per hectare in areas of grass and shrubs to 101.6 tonnes per hectare in areas with trees. Monitoring changes in the ecosystem These results cannot be used to create new climate models. "We also need reliable data to monitor changes in the savannah ecosystem," says Victor Odipo. He points to a surprising incidental find: the researchers' measurements showed that the biomass of a substantial part of the study area in Kruger National Park is declining from year to year. "We didn't expect that," says Odipo, "given that this is a nature reserve." It turned out, however, that these changes - unlike those in most unprotected areas - were not primarily the result of human activity, but rather the work of elephants, which bring down a large number of trees. This study was supported by the German Academic Exchange Service (DAAD), the German Research Foundation (DFG), and the Federal Ministry of Education and Research (BMBF). The terrestrial laser scanner was acquired with the help of EFRD funds from the Free State of Thuringia. Odipo VO et al. Assessment of Aboveground Woody Biomass Dynamics Using Terrestrial Laser Scanner and L-Band ALOS PALSAR Data in South African Savanna, Forests; DOI:10.3390/f7120294
Gunnink J.L.,TNO |
Siemon B.,Federal Institute for Geosciences and Natural Resources
Near Surface Geophysics | Year: 2015
Airborne electromagnetic (AEM) measurements provide information regarding the electrical properties of the subsurface for large spatial coverage in a limited time. In mapping and modelling for geological and geohydrological purposes, electrical properties (e.g. resistivity) need to be converted to relevant parameters, like lithology. Helicopter-borne frequency-domain EM measurements from an area in the Netherlands were combined with borehole data to create a 3D model of two contrasting lithologies (sand and clay) that served as proxy for assessing the vulnerability of the aquifer to surface contamination. By comparing the lithology found in boreholes with the resistivity derived from AEM at that location, a probabilistic relationship between these two variables was determined. This relationship was used to convert the AEM resistivity models into a 3D model of clay probability. Using geostatistical Monte Carlo simulations, the boreholes (hard data) and the probability of clay from the AEM resistivity models (soft data) were combined. AEM improved the 3D model substantially, compared to using only borehole data. An independent validation dataset verified the improvement of the 3D model using AEM data. Areas with a high probability of clay occurrence could be distinguished and a clay thickness map with uncertainty (standard deviation) was calculated. Using a simple groundwater model, the capability of the clay to protect the underlying aquifer from contamination was quantified. This resulted in the delineation of distinct areas that are well protected due to the large travel time for infiltrating water from the surface to the aquifer. © 2015 European Association of Geoscientists & Engineers.
Spott O.,Helmholtz Center for Environmental Research |
Russow R.,Helmholtz Center for Environmental Research |
Stange C.F.,Federal Institute for Geosciences and Natural Resources
Soil Biology and Biochemistry | Year: 2011
At the end of the 19th century an experimental study had already reported N gas production during microbial nitrate reduction, which significantly exceeded the amount of nitrate N supplied to the microorganism. The observed excess gas production was suggested to be caused by a reaction of nitrous acid (produced during microbial nitrate reduction) with amino acids contained in the nutrient solution. Since the 1980's a number of 15N tracer experiments revealed that this biotic excess gas production was based on the formation of hybrid N2O and/or hybrid N2. It was shown that the N-N linkage forms due to a microbially mediated N-nitrosation reaction by which one N atom of nitrite or nitric oxide combines via a nitrosyl intermediate with one N atom of another N species (e.g., amino compound). Because of its cooccurrence with conventional denitrification this process was later on termed "codenitrification" Although the phenomenon of N2O and N2 formation by codenitrification was recognised over a century ago its impact on global N cycling is still unclear today. Nonetheless, the present literature review reveals codenitrification as a potentially important process of biospheric N cycling since (i) most codenitrifying species are already known as typical denitrifiers (e.g., Pseudomonas sp., Fusarium sp. etc.) and (ii) codenitrification was already reported to occur within the three domains archaea, bacteria, and eukarya (kingdom fungi). Furthermore, the present literature suggests that codenitrification acts not only as an additional source of N gas formation due to a mobilisation of organic N by N-nitrosation, but also acts as an N immobilising process due to a bonding of inorganic N (e.g., from NO3 - or NO2 -) onto organic compounds due to e.g., N- or even C-nitrosation reactions. From this it can be concluded that N gas formation by codenitrification represents a sub-phenomenon of a variety of possible biotic nitrosation reactions. Moreover, the review reveals that biotic nitrosation also occurs among nitrifying species, even under aerobic conditions. Furthermore, recent studies support the assumption that even anaerobic ammonium oxidation (anammox) appears to be based on biotically mediated N-nitrosation. Therefore, we propose to introduce the term BioNitrosation, which includes all biotically mediated nitrosation reactions resulting either in N gas release or in N immobilisation, independently from the acting microbial species or the environmental conditions. © 2011 Elsevier Ltd.
Hackley P.C.,U.S. Geological Survey |
Kus J.,Federal Institute for Geosciences and Natural Resources
Fuel | Year: 2015
We report here, for the first time, spectral properties of Tasmanites microfossils determined by confocal laser scanning fluorescence microscopy (CLSM, using Ar 458 nm excitation). The Tasmanites occur in a well-characterized natural maturation sequence (Ro 0.48-0.74%) of Devonian shale (n = 3 samples) from the Appalachian Basin. Spectral property λmax shows excellent agreement (r2 = 0.99) with extant spectra from interlaboratory studies which used conventional fluorescence microscopy techniques. This result suggests spectral measurements from CLSM can be used to infer thermal maturity of fluorescent organic materials in geologic samples. Spectra of regions with high fluorescence intensity at fold apices and flanks in individual Tasmanites are blue-shifted relative to less-deformed areas in the same body that have lower fluorescence intensity. This is interpreted to result from decreased quenching moiety concentration at these locations, and indicates caution is needed in the selection of measurement regions in conventional fluorescence microscopy, where it is common practice to select high intensity regions for improved signal intensity and better signal to noise ratios. This study also documents application of CLSM to microstructural characterization of Tasmanites microfossils. Finally, based on an extant empirical relation between conventional λmax values and bitumen reflectance, λmax values from CLSM of Tasmanites microfossils can be used to calculate a bitumen reflectance equivalent value. The results presented herein can be used as a basis to broaden the future application of CLSM in the geological sciences into hydrocarbon prospecting and basin analysis. © 2015, Elsevier Ltd. All rights reserved.
Stoeckl L.,Federal Institute for Geosciences and Natural Resources |
Houben G.,Federal Institute for Geosciences and Natural Resources
Journal of Hydrology | Year: 2012
The development and flow dynamics of freshwater lenses are investigated by physical experiments on a laboratory scale. Using an acrylic glass box and a combination of different tracers we were able to simulate a cross section of an infinite strip island and visualize its groundwater flow patterns. For validating our model, results of the generation and degeneration of the freshwater lens were compared to analytical and numerical models. Using recharge water of different colors we were able to visualize flow paths as well as the age stratification within a freshwater lens. Flow paths in the lens could be demonstrated to remain in contact to the outflow zone at all times during the experiments. Analytical solutions are in good accordance to our findings. Additional experiments show the differences between pumping from a horizontal and a vertical well on the interface. These experiments with identical boundary conditions confirm former presumptions: A horizontal well shows less up-coning of the interface and therefore allows a higher sustainable yield than a vertical well. © 2012 Elsevier B.V.
Torizin J.,Federal Institute for Geosciences and Natural Resources
Stochastic Environmental Research and Risk Assessment | Year: 2016
In applications of the weight of evidence (WofE) method, the informational redundancy in similar evidential patterns causes a significant increase in the posterior probability. Consequently, to estimate the posterior probability, combinations that pass the established conditional independence (CI) tests are considered rather than the combination of the ‘best’ information layers. This study introduces two methodological approaches to extend the WofE using a correction factor that eliminates the informational redundancy that is contained in different evidential layers. The proposed approaches allow the use of associated data in the same model without having to address issues with the constraints of the CI. The basic WofE approach that is used to estimate the weights is not changed, and only the interactions of the parameter layers and the transformation of the weights into probability values are considered. The method is applied to a real dataset that is used in a landslide susceptibility analysis on Lombok Island, Indonesia. © 2015, Springer-Verlag Berlin Heidelberg.
Kus J.,Federal Institute for Geosciences and Natural Resources
International Journal of Coal Geology | Year: 2015
Organic matter occurring in the form of macerals and natural solid bitumens in peats, coals, and siliciclastic sediments of various stratigraphic ages and locations was studied by means of conventional incident light microscopy and CLSM. Classical optical microscopic investigations are restricted by conventional 2-D imaging and are often hindered by the associated out-of-focus-blur effects. The qualitative application of CLSM overcomes these limitations, permitting to reveal precisely 3-D morphology and detailed microstructure of autofluorescent organic matter. The in depth examinations along Z-axis in XY, XZ, or YZ scanning modes at increments of 250. nm are capable to reconstruct 3-D internal configuration and arrangement occurring in autofluorescent macerals. The non-invasive and non-destructive laser-raster technique is applied to characterize in situ autofluorescent organic particles at micron to sub-micron scale resolution in polished whole rock pellets. In this study, we demonstrate that CLSM is suitable to (i) detect fine-scale microstructure of autofluorescent organic matter, (iii) reconstruct 3-D morphology at cellular and tissue level, (iii) analyze maceral composition in terms of its relicts and fragments beyond the classical optical assignment limits, (iv) detect and examine inorganic components enclosed in the embedding mineral-bituminous groundmass, and (v) differentiate mineral constituents from the remaining organic matter.CLSM as an optical microscopic technique was applied to generate high-resolution 2-D and 3-D images, projections as well as 3-D reconstructions of autofluorescent objects excited with aid of laser-induced light operating at variable visible wavelengths. CLSM is applicable to support microscopic studies of thermally immature and mature organic matter within the oil and early gas windows enclosed either within siliciclastic and carbonate sediments or in peat and low to medium rank coals.The application of this technique will be of great interest to a wide range of geology related disciplines such as petroleum geology, biostratigraphy, marine geology, peat petrography, and archeology. © 2014 Elsevier B.V.
Siemon B.,Federal Institute for Geosciences and Natural Resources
Geophysics | Year: 2012
Frequency-domain helicopter-borne electromagnetic (HEM) data are commonly interpreted using quasistatic approximations in forward and inverse solutions. At high-frequencies (f>some 10 kHz), the accuracy of this approach is often insufficient. Implementation of a full solution of the forward problem that includes displacement currents in both subsurface and air, however, may cause singularity problems during numerical evaluation of the secondary field integral using Hankel or Laplace transforms, particularly at high frequencies. These effects can be reduced by a wavenumber shift during numerical evaluation, a transformation of the integral by partial integration, or a combination of both. Based on these corrections, the resulting forward responses obtained with various fast Hankel transforms or numerical Laplace transforms are nearly identical. The inversion of HEM data also requires some modification. For a half-space inversion, the parameter sets, such as look-up tables, linear or polynomial approximations have to be modified for frequencies above some 10 kHz. The quasistatic formulas used in multi-layer inversion procedures have to be replaced by the accurate formulas. Fortunately, singularity problems are restricted to the forward calculation as the derivatives of the Jacobian matrix are not affected. Accurate high-frequency forward and inverse modeling enables a successful usage of helicopter-borne electromagnetics for near-surface investigations and expands the range of applications in environmental and geotechnical issues. © 2012 Society of Exploration Geophysicists.