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21.
Anette Eltner László Bertalan Jens Grundmann Matthew Thomas Perks Eliisa Lotsari 《地球表面变化过程与地形》2021,46(14):2773-2787
Unoccupied aerial systems (UASs) are frequently used in the field of fluvial geomorphology due to their capabilities for observing the continuum rather than single sample points. We introduce a (semi-)automatic workflow to measure river bathymetry and surface flow velocities of entire river reaches at high resolution, based on UAS videos and imagery. Video frame filtering improved the visibility of the riverbed using frame co-registration and averaging with a median filter. Subsequently, these video frames were incorporated with still images acquired by UASs into a structure from motion (SfM) photogrammetry approach to reconstruct the camera poses (i.e. positions and orientations) and the 3D point cloud of the river reach. The heights of submerged points were further processed using small-angle and multi-view refraction correction approaches to account for the refraction impact. The flow velocity pattern of the river surface was measured using the estimated camera pose from SfM, the reconstructed bathymetric point cloud and the co-registered video frames in combination with image velocimetry analysis. Finally, discharge was estimated at selected cross-sections, considering the average surface velocity and the bathymetry. Three case studies were considered to assess the performance of the workflow under different environmental conditions. The studied river reaches spanned a length between 0.15 and 1 km. The bathymetry was reconstructed with average deviations to RTK-GNSS point measurements as low as 1 cm with a standard deviation of 6 cm. If frames were processed with the median filter, the number of underwater points increased by up to 21%. The image-based surface velocities revealed an average deviation to reference measurements between 0.05 and 0.08 m s−1. The image-based discharge was estimated with deviations to ADCP references of up to 5%, however this was sensitive to errors in water-level retrieval. The output of our workflow can provide a valuable input to hydro-morphological models. 相似文献
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Anette Reenberg Peter Oksen Jannick Svendsen 《Geografisk tidskrift / udgivet af Bestyrelsen for Det Kongelige danske geografiske selskab》2013,113(2):57-69
The paper deals with land use changes in semi arid Burkina Faso, specifically the issue of field encroachment on extensively used land. Some theoretical perspectives of field expansions in agricultural production systems characterised by crop-livestock interaction are discussed with reference to Boserup's theories on intensification. The empirical part provides documentation for the land use patterns and practices, based on aerial photos from 1978 and 1994 and village surveys. Answers are sought to some of the key questions presented by the ‘land use land cover change community’, i.e.: how has ‘land cover been changed by human land use?’—how do immediate human and biophysical dynamics affect the sustainability of specific types of land uses?—and how do land uses and land covers affect the vulnerability of land users in the face of change? Based on the findings, the paper proposes the notion of the expansion dilemma which questions the theory that agricultural expansion should always be perceived as a forerunner of intensification. 相似文献
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We present boron isotope and concentration data from magmatic (komatiitic to rhyolitic) and sedimentary geological silicate and artificial glass reference materials that cover a wide spectrum of boron isotope compositions and boron concentrations. Boron isotope compositions were determined by TIMS (Cs2 BO2 + -graphite and BO2 - method) and boron concentrations by ICP-AES. Boron concentrations ranged from 7 to 159μ g-1 and agree within 14% with published values. Based on replicate analyses of individually prepared sample aliquots an overall external reproducibility of better than 10% was determined. The obtained δ11 B values ranged from -12.6 to +13.6% and were reproducible within 1.1 % (2 RSD; excluding NTIMS) on the basis of individually prepared sample aliquots. The δ11 B values of JA-1 (+5.3%), JB-3 (+5.9%) and JR-2 (+2.9%) overlap the published data within analytical uncertainty. For the first time δ11 B values for the TB (-12.6%) and the MPI-DING glasses GOR-128-G (+13.6%), GOR-132-G (+7.1 %) and StHs6/80-G (-4.5%) are reported. The δ11 B values obtained by the Cs2 BO2 + -graphite and the BO2 - method as well as the majority of δ11 B values obtained using different sample preparation methods agree within analytical uncertainty. Therefore, we conclude that none of these analytical methods introduce any systematic error on the obtained δ11 B values. 相似文献
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Simone A. Kasemann Anette Meixner Jrg Erzinger Jos G. Viramonte Ricardo N. Alonso Gerhard Franz 《Journal of South American Earth Sciences》2004,16(8):2562
We have measured the boron concentration and isotope composition of regionally expansive borate deposits and geothermal fluids from the Cenozoic geothermal system of the Argentine Puna Plateau in the central Andes. The borate minerals borax, colemanite, hydroboracite, inderite, inyoite, kernite, teruggite, tincalconite, and ulexite span a wide range of δ11B values from −29.5 to −0.3‰, whereas fluids cover a range from −18.3 to 0.7‰. The data from recent coexisting borate minerals and fluids allow for the calculation of the isotope composition of the ancient mineralizing fluids and thus for the constraint of the isotope composition of the source rocks sampled by the fluids. The boron isotope composition of ancient mineralizing fluids appears uniform throughout the section of precipitates at a given locality and similar to values obtained from recent thermal fluids. These findings support models that suggest uniform and stable climatic, magmatic, and tectonic conditions during the past 8 million years in this part of the central Andes. Boron in fluids is derived from different sources, depending on the drainage system and local country rocks. One significant boron source is the Paleozoic basement, which has a whole-rock isotopic composition of δ11B=−8.9±2.2‰ (1 SD); another important boron contribution comes from Neogene-Pleistocene ignimbrites (δ11B=−3.8±2.8‰, 1 SD). Cenozoic andesites and Mesozoic limestones (δ11B≤+8‰) provide a potential third boron source. 相似文献
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Lipids and trophic linkages in harp seal (Phoca groenlandica) from the eastern Barents Sea 总被引：2，自引：0，他引：2
Stig Falk-Petersen Tore Haug Kjell T. Nilssen Anette Wold Trine M. Dahl 《Polar research》2004,23(1):43-50
Fatty acid profiles and lipid biomarkers from 20 harp seals were used to investigate the foraging ecology of harp seals and the transfer of energy through the Franz Josef Land-Novaya Zemlya food chain. High levels of the Calanus fatty acid trophic markers (FATMs) 20:1(n-9) (mean 14.6%) and 22:1(n-11) (mean 6.5%), together with the typical dinoflagellate FATMs 22:6(n-3) (mean 6.5%) and C18PUFA (mean 5.5%), were found in blubber samples. Based on the analyses of the fatty acid profiles separated by principal component analysis, we confirmed the importance of polar cod ( Boreogadus saida ) and the pelagic amphipod Themisto libellula in the diet of harp seal. The high levels of 22:6(n-3), C18PUFA and C20 and C22 FATMs show that the harp seal lipids mainly originate from dinoflagellates consumed by Calanus copepods. 相似文献
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We conducted laboratory experiments to study the behavioural responses of Calanus finmarchicus females and nauplii exposed to artificial ultraviolet radiation (UVR) and photosynthetically active radiation (PAR). Both nauplii and females migrated downwards when exposed to UVR. Nauplii reacted mainly to UV-B radiation, while females responded also to UV-A. Nauplii were also collected in the field to check if vertical distributions supported the experimental findings. Light measurements in Vestfjorden showed that plankton were exposed to quite low doses of UVR most of the time. However, on days with a thin ozone layer, clear sky and low turbidity UV-B doses in the surface waters might be harmful. Strong turbulence in the surface layer prevents nauplii from adjusting their position, exposing them to fluctuating levels of UVR due to vertical mixing. Under calm conditions, however, copepods could migrate sufficiently to avoid harmful UVR doses. 相似文献
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Afforestation of European landscapes: How do different farmer types respond to EU agri-environmental schemes? 总被引：1，自引：0，他引：1
This paper investigates how different types of farmers manage the landscape with primary emphasis on farmland afforestation, planned landscape changes, and the extent to which EU agri-environmental schemes take farm type specific characteristics into account in information strategies. The empirical data concern landscape practices of more than 2,000 landowners in 16 European areas in eight countries who were surveyed using quantitative questionnaires. Supplementary in-depth interviews were conducted for two case areas in Denmark to further investigate the role of the policy information environment. The analysis is based on a categorization of the farmers into hobby, part-time, full-time and retired farmers. This study shows that hobby farmers constitute a high proportion of landowners and manage a large part of the rural landscape. At the same time, hobby farmers are relatively more interested in landscape changes and differ from other landowners by considering farmland afforestation more often than full-time landowners, for example. Yet, 40% of the hobby farmers who are considering farmland afforestation are not familiar with the agri-environmental scheme for farmland afforestation. One reason may be their low membership rate in traditional information networks such as farmers’ or foresters’ associations, as revealed by the in-depth analysis of the cases in Denmark. Thus, it is proposed that policy impact may be improved if farmer type specific differences are explicitly taken into account in the scheme logistics for EU agri-environmental schemes. 相似文献