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Nicolas Coppo Pierre-André Schnegg Pierik Falco Roberto Costa Martin Burkhard 《Swiss Journal of Geoscience》2008,101(2):409-413
The local and regional structural pattern of volcanic edifices strongly controls the space distribution of electrical resistivity. Here we report on the structural context of the western part of the Las Cañadas caldera of Tenerife (LCC) thought to have initiated the formation of the caldera. Using a new dataset of 11 audiomagnetotelluric tensors we emphasize the resistivity distribution of Ucanca caldera and propose a major revision of its extension. We find that Ucanca caldera has a limited westwards extent and that El Cedro sector is a depression margin of the caldera. According to the extent of hydrothermalized rocks at the base of the LCC wall and the distribution of Pico Teide – Pico Viejo vents, we constrain the location and size of Ucanca caldera. The interpretation of these results also constrains the extension of the Icod Valley and proposes a headwall located below the Pico Teide – Pico Viejo Complex. 相似文献
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Dennis Lemke Pierre-André Schnegg Marc Schwientek Karsten Osenbrück Olaf A. Cirpka 《Environmental Earth Sciences》2013,69(2):349-358
Performing tracer tests using artificial tracer compounds is a common practice to characterize natural streams regarding their (reactive) transport properties. Recently, the fluorescent compound resazurin was introduced as a reactive stream tracer to quantify hyporheic exchange and metabolic activity of streams. This tracer, together with its reaction product resorufin and a conservative tracer (in our case fluorescein), provides additional information about transport properties of the stream and its hyporheic zone and can therefore overcome restrictions that are commonly affiliated with the use of conservative tracers alone. However, all previously published studies using this tracer system were based on manual sampling of the water. This usually limits the number of measurements and thus the achievable temporal resolution, and potentially endangers data quality due to inadequate handling of samples. In this paper, a modified version of the GGUN-FL30 on-line fluorometer is presented in which the optics have been modified to allow measuring the concentrations of all three tracers simultaneously at intervals of 10 s. Experiments under controlled and natural conditions showed that the performance of the on-line fluorometer regarding tracer separation efficiency and practical detection limits is comparable to a high-performance laboratory spectrofluorometer. Furthermore, suggestions are given on how to correct tracer signal fluctuations caused by temporal changes in temperature and pH that might occur during a field tracer test. 相似文献
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Youssef Tawk Cyril Botteron Aleksandar Jovanovic Pierre-André Farine 《GPS Solutions》2012,16(2):243-258
The world of global navigation satellite systems has been enhanced with several new or improved signals in space aiming to
optimize accuracy, reliability, navigation solution, and interoperability between different constellations. However, such
developments bring various challenges to the receivers’ designers. For example, acquisition and tracking stages turn into
more complex processes while handling the increasing bandwidth requires additional processing power. In this context, we study
the code tracking of Galileo E5ab in a full band or of only one of its components, i.e., either E5a or E5b. More specifically,
an architecture for tracking the E5 pilot channel as an AltBOC(15,10) or BPSK(10) modulation is introduced, and the performance
of well-known discriminator types is analyzed using analytical derivations and simulations of linearity and stability regions,
thermal noise tracking errors, multipath error envelopes and tracking thresholds. Different parameters, such as the front-end
filter bandwidth, the early/late chip spacing, un-normalized and normalized discriminators, are taken into consideration.
The results obtained are used to illustrate the main advantages and drawbacks of tracking the E5 signal as well as to help
defining the main tracking loop parameters for an enhanced performance. 相似文献
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Myriam Foucras Jérôme Leclère Cyril Botteron Olivier Julien Christophe Macabiau Pierre-André Farine Bertrand Ekambi 《GPS Solutions》2017,21(2):293-306
In global navigation satellite system (GNSS) receivers, the first signal processing stage is the acquisition, which consists of detecting the received GNSS signals and determining the associated code delay and Doppler frequency by means of correlations with a code and carrier replicas. These codes, as part of the GNSS signal, were chosen to have very good correlation properties without considering the effect of a potential received Doppler frequency. In the literature, it is often admitted that the maximum GPS L1 C/A code cross-correlation is about ?24 dB. We show that this maximum can be as high as ?19.2 dB when considering a Doppler frequency in a typical range of [?5, 5] kHz. We also show the positive impact of the coherent integration time on the cross-correlation and that even a satellite with Doppler outside the frequency search space of a receiver impacts the cross-correlation. In addition, the expression of the correlation is often provided in the continuous time domain, while its implementation is typically made in the discrete domain. It is then legitimate to ask the validity of this approximation. Therefore, the purpose of this research is twofold: First, we discuss typical approximations and evaluate their regions of validity, and second, we provide characteristic values such as maximums and quantiles of the auto- and cross-correlation of the GPS L1 C/A and Galileo E1 OS codes in the presence of Doppler, for frequency ranges up to 50 kHz and for different integration times. 相似文献
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In eutrophic Lake Biel, Switzerland, the qualitative and quantitative food composition of roach (Rutilus rutilus L.) was examined monthly from August 1978 to August 1979. The fish caught in the littoral zone fed on phytoplankton, periphyton, makrophytes, zooplankton and molluscs. The food composition was different from month to month as well as between the different size classes of the fishes. The fish caught in the pelagic zone fed almost exclusively on crustaceans. 相似文献
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