Multifold borehole radar acquisition and processing     

Fabrice Hollender  Sylvie Tillard  & Laurent Corin 《Geophysical Prospecting》1999,47(6):1077-1090

The multifold acquisition principle was applied to a borehole radar survey, performed in a granitic site (Grimsel Test Site, Switzerland). Two multifold coverage acquisitions (40-fold and 20-fold) were carried out in a subhorizontal borehole. Instrumental drifts (transmission time and sampling frequency fluctuations) were corrected in order to remove shifts observed on CMP gathers and to optimize velocity analysis and trace stacking. Computation of velocity spectra was adapted in order to take into account the features of the medium investigated (homogeneous velocity, various reflector orientations). The NMO velocities were then interpreted as angles between reflectors and the survey line. The processing, based on the computation of several constant velocity stacked sections performed with different NMO velocities, leads to better results than the standard DMO + NMO processing. The signal-to-noise ratio of the stacked profile is improved in comparison with the single-fold section, which results from a standard acquisition. From a practical point of view, the implementation of a multifold radar survey within a borehole is difficult but a greater investigation range is obtained, more reflectors are detected and the mapping of geological discontinuities is improved.  相似文献   

Presence of Anthropogenic Markers in Water: A Case Study of the Guaporé River Watershed,Brazil          下载免费PDF全文

Marilia Camotti Bastos  Danilo Rheinheimer dos Santos  José A. Monteiro de Castro Lima  Thibaut le Guet  Maria A. Santanna dos Santos  Renato Zanella  Elodie Aubertheau  Leslie Mondamert  Laurent Caner  Jérôme Labanowski 《洁净——土壤、空气、水》2018,46(3)

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Use of terrestrial photosieving and airborne topographic LiDAR to assess bed grain size in large rivers: a study on the Rhine River     

Valentin Chardon  Laurent Schmitt  Hervé Piégay  Dimitri Lague 《地球表面变化过程与地形》2020,45(10):2314-2330

Most grain size monitoring is still being conducted by manual sampling in the field, which is time consuming and has low spatial representation. Due to new remote sensing methods, some limitations have been partly overcome, but methodological progress is still needed for large rivers as well as in underwater conditions. In this article, we tested the reliability of two methods along the Old Rhine River (France/Germany) to estimate the grain size distribution (GSD) in above-water conditions: (i) a low-cost terrestrial photosieving method based on an automatic procedure using Digital Grain Size (DGS) software and (ii) an airborne LiDAR topo-bathymetric survey. We also tested the ability of terrestrial photosieving to estimate the GSD in underwater conditions. Field pebble counts were performed to compare and calibrate both methods. The results showed that the automatic procedure of terrestrial photosieving is a reliable method to estimate the GSD of sediment patches in both above-water and underwater conditions with clean substrates. Sensitivity analyses showed that environmental conditions, including solar lighting conditions and petrographic variability, significantly influence the GSD from the automatic procedure in above-water conditions. The presence of biofilm in underwater conditions significantly altered the GSD estimation using the automatic procedure, but the proposed manual procedure overcame this problem. The airborne LiDAR topographic survey is an accurate method to estimate the GSD of above-water bedforms and is able to generate grain size maps. The combination of terrestrial photosieving and airborne topographic LiDAR methods is adapted to assess the GSD over several kilometers long reaches of large rivers. © 2020 John Wiley & Sons, Ltd.  相似文献   

Ontologies to interpret remote sensing images: why do we need them?     

Damien Arvor  Mariana Belgiu  Zoe Falomir  Isabelle Mougenot  Laurent Durieux 《地理信息系统科学与遥感》2019,56(6):911-939

The development of new sensors and easier access to remote sensing data are significantly transforming both the theory and practice of remote sensing. Although data-driven approaches based on innovative algorithms and enhanced computing capacities are gaining importance to process big Earth Observation data, the development of knowledge-driven approaches is still considered by the remote sensing community to be one of the most important directions of their research. In this context, the future of remote sensing science should be supported by knowledge representation techniques such as ontologies. However, ontology-based remote sensing applications still have difficulty capturing the attention of remote sensing experts. This is mainly because of the gap between remote sensing experts’ expectations of ontologies and their real possible contribution to remote sensing. This paper provides insights to help reduce this gap. To this end, the conceptual limitations of the knowledge-driven approaches currently used in remote sensing science are clarified first. Then, the different modes of definition of geographic concepts, their duality, vagueness and ambiguity, and the sensory and semantic gaps are discussed in order to explain why ontologies can help address these limitations. In particular, this paper focuses on the capacity of ontologies to represent both symbolic and numeric knowledge, to reason based on cognitive semantics and to share knowledge on the interpretation of remote sensing images. Finally, a few recommendations are provided for remote sensing experts to comprehend the advantages of ontologies in interpreting satellite images.  相似文献   

Cryptic metasomatic agent measured in situ in Variscan mantle rocks: Melt inclusions in garnet of eclogite,Granulitgebirge, Germany     

Alessia Borghini  Silvio Ferrero  Patrick J. O’Brien  Oscar Laurent  Christina Günter  Martin A. Ziemann 《Journal of Metamorphic Geology》2020,38(3):207-234

Garnet of eclogite (formerly termed garnet clinopyroxenite) hosted in lenses of orogenic garnet peridotite from the Granulitgebirge, NW Bohemian Massif, contains unique inclusions of granitic melt, now either glassy or crystallized. Analysed glasses and re-homogenized inclusions are hydrous, peraluminous, and enriched in highly incompatible elements characteristic of the continental crust such as Cs, Li, B, Pb, Rb, Th, and U. The original melt thus represents a pristine, chemically evolved metasomatic agent, which infiltrated the mantle via deep continental subduction during the Variscan orogeny. The bulk chemical composition of the studied eclogites is similar to that of Fe-rich basalt and the enrichment in LILE and U suggest a subduction-related component. All these geochemical features confirm metasomatism. In comparison with many other garnet+clinopyroxene-bearing lenses in peridotites of the Bohemian Massif, the studied samples from Rubinberg and Klatschmühle are more akin to eclogite than pyroxenites, as reflected in high jadeite content in clinopyroxene, relatively low Mg, Cr, and Ni but relatively high Ti. However, trace elements of both bulk rock and individual mineral phases show also important differences making these samples rather unique. Metasomatism involving a melt requiring a trace element pattern very similar to the composition reported here has been suggested for the source region of rocks of the so-called durbachite suite, that is, ultrapotassic melanosyenites, which are found throughout the high-grade Variscan basement. Moreover, the Th, U, Pb, Nb, Ta, and Ti patterns of these newly studied melt inclusions (MI) strongly resemble those observed for peridotite and its enclosed pyroxenite from the T-7 borehole (Staré, České Středhoři Mountains) in N Bohemia. This suggests that a similar kind of crustal-derived melt also occurred here. This study of granitic MI in eclogites from peridotites has provided the first direct characterization of a preserved metasomatic melt, possibly responsible for the metasomatism of several parts of the mantle in the Variscides.  相似文献   

Analysis of calibrated seafloor backscatter for habitat classification methodology and case study of 158 spots in the Bay of Biscay and Celtic Sea     

Ridha Fezzani  Laurent Berger 《Marine Geophysical Researches》2018,39(1-2):169-181

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The new fisheries multibeam echosounder ME70: description and expected contribution to fisheries research   总被引：1，自引：0，他引：1  

Trenkel  Verena M.; Mazauric  Valerie; Berger  Laurent 《ICES Journal of Marine Science》2008,65(4):645-655

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Influence of food supply on the δ13C signature of mollusc shells: implications for palaeoenvironmental reconstitutions     

Franck Lartaud  Laurent Emmanuel  Marc de Rafelis  Stephane Pouvreau  Maurice Renard 《Geo-Marine Letters》2010,30(1):23-34

Compared to oxygen isotopes, the carbon isotope composition of biogenic carbonates is less commonly used as proxy for palaeoenvironmental reconstructions because shell δ¹³C is derived from both dissolved inorganic (seawater) and organic carbon sources (food), and interactions between these two pools make it difficult to unambiguously identify any independent effect of either. The main purpose of this study was to demonstrate any direct impact of variable food supply on bivalve shell δ¹³C signatures, using low/high rations of a ¹³C-light mixed algal diet fed to 14-month-old (adult) cultured Japanese Crassostrea gigas under otherwise essentially identical in vitro conditions during 3 summer months (May, June and July 2003, seawater temperature means at 16, 18 and 20 °C respectively) in experimental tanks at the Argenton laboratory along the Brittany Atlantic coast of France. At a daily ration of 12% (versus 4%) oyster dry weight, the newly grown part of the shells (hinge region) showed significantly lower δ¹³C values, by 3.5‰ (high ration: mean of −5.8  ± 1.1‰, n = 10; low ration: mean of −2.3  ± 0.7‰, n = 6; ANOVA Scheffe’s test, p < 0.0001). This can be explained by an enhanced metabolic activity at higher food supply, raising ¹³C-depleted respiratory CO₂ in the extrapallial cavity. Based on these δ¹³C values and data extracted from the literature, and assuming no carbon isotope fractionation between food and shell, the proportion of shell metabolic carbon would be 26  ± 7 and 5  ± 5% for the high- and low-ration C. gigas shells respectively; with carbon isotope fractionation (arguably more realistic), the corresponding values would be 69  ± 14 and 24  ± 9%. Both groups of cultured shells exhibited lower δ¹³C values than did wild oysters from Marennes-Ol éron Bay in the study region, which is not inconsistent with an independent influence of diet type. Although there was no significant difference between the two food regimes in terms of δ¹⁸O shell values (means of 0.1  ± 0.3 and 0.4  ± 0.2‰ at high and low rations respectively, non-significant Scheffe’s test), a positive δ¹³C vs. δ¹⁸O relationship recorded at high rations supports the interpretation of a progressive temperature-mediated rise in metabolic activity fuelled by higher food supply (in this case reflecting increased energy investment in reproduction), in terms not only of δ¹³C (metabolic signal) but also of δ¹⁸O (seawater temperature signal). Overall, whole-shell δ¹⁸O trends faithfully recorded summer/winter variations in seawater temperature experienced by the 17-month-old cultured oysters.  相似文献   

The effects of altered freshwater inflows on catch rates of non-estuarine-dependent fish in a multispecies nearshore linefishery     

Stephen J. Lamberth  Laurent Drapeau  George M. Branch 《Estuarine, Coastal and Shelf Science》2009,84(4):527-538

In KwaZulu-Natal on the east coast of South Africa, the commercial and recreational boat-based linefishery is the largest fishery accounting for 1235 t (40%) of the total landed mass there. In particular, the Thukela Banks are where most fishing takes place. Numerous developments ranging from dams to inter-basin transfer schemes either exist or have been proposed for the Thukela River, which is the largest of 17 catchments entering the sea in the region and provides over 40% of the mean annual runoff. Exploratory analyses of the relationships between monthly flows and catch-per-unit-effort were performed using spectral analysis and general linear models on a data set comprising 17 years of monthly commercial catch-and-effort data for 140 species and monthly flow data from 17 catchments. Catchments having a significant influence on catches were those providing the bulk of the runoff volume (75%) reaching the sea. Significant relationships existed between flow and the catches of 14 species, which provided over 90% of the total linefish catch on the Thukela Banks. Time lags between flow events (wet and drought periods) and changes in catch-per-unit-effort corresponded in many cases to age at 50% maturity and/or age-at-first-capture of the species concerned. Under a future maximum-development scenario, corresponding to a 44% reduction in flow from the Thukela River, catches of slinger Chrysoblephus puniceus and squaretail kob Argyrosomus thorpei are forecast to decline by 36% and 28% respectively. These two species currently provide over 50% of the landed mass on the Thukela Banks. Some species should respond positively to a reduction in flow, but any increases in their catches will be negligible, falling within natural variability, and will be insufficient to offset losses of other species because their abundance is naturally low or has been fished down to low levels. National legislation requires that sufficient freshwater flows be set aside to protect ecosystems, so these findings have important management implications, as marine needs for freshwater flows have not previously been addressed.  相似文献   

Recruitment patterns of young-of-the-year mugilid fishes in a West African estuary impacted by climate change     

Sébastien Trape  Jean-Dominique Durand  François Guilhaumon  Laurent Vigliola  Jacques Panfili 《Estuarine, Coastal and Shelf Science》2009

With the persistence of the sub-Saharan drought since the 1970s, the Sine Saloum estuary (Senegal) – the second largest coastal Biosphere Reserve of West-Africa – has become an “inverse estuary” and hypersaline (salinity > 60) in its upstream part. A one-year survey was conducted from April 2007 to March 2008 at eight sites distributed along the salinity gradient, to investigate the recruitment patterns of young-of-the-year mugilids in such an impacted ecosystem. Fishes were sampled monthly with a conical net and a beach seine in salinities ranging from 31 to 104. Samples were identified to the species level. For the smallest individuals (<20 mm SL) a PCR–RFLP technique, developed on the mitochondrial 16S ribosomal RNA region, was used for identification. A total of 8438 juveniles belonging to six of the eight species of mugilids known for the tropical Eastern Atlantic were collected: Mugil bananensis, Mugil cephalus, Mugil curema, Liza dumerili, Liza falcipinnis and Liza grandisquamis. One species, L. dumerili, represented 89% of the total catch. Length–frequency distributions revealed that M. cephalus and L. dumerili preferentially recruited during the dry season whereas the recruitment of M. curema, M. bananensis and L. falcipinnis generally occurred during the wet season. Minimal size at recruitment ranged from 9 to 19 mm SL depending on the species, the smallest size being that of L. dumerili. Despite the general salinity increase in the estuary, most parts of the Sine Saloum were suitable for the juveniles. Only the hypersaline area in the uppermost part of the estuary presented very low fish abundance for all species. According to the species, small recruits (12–20 mm SL) were collected at salinities up to 47–78, suggesting that osmoregulatory capacities had been gained early during ontogenesis, possibly resulting from an adaptation of these populations to changing environmental conditions.  相似文献