Performance of the L2C civil GPS signal under various ionospheric scintillation effects     

H. A. S. Marques  J. F. G. Monico  H. A. Marques 《GPS Solutions》2016,20(2):139-149

As GPS is modernizing, there are currently fourteen satellites transmitting L2C civil code and seven satellites transmitting L5 signal. While the GPS observables are subject to several sources of errors, the ionosphere is one of the largest error sources affecting GPS signals. Small irregularities in the electrons density along the GPS radio signal propagation path cause ionospheric scintillation that is characterized by rapid fluctuations in the signal amplitude and phase. The ionospheric scintillation effects are stronger in equatorial and high-latitude geomagnetic latitude regions and occur mainly due to equatorial anomaly and solar storms. Several researchers have analyzed the L2C signal quality since becoming available in December, 2005. We analyze the performance of L2C using GPS data from stations in the equatorial region of Brazil, which is subject of weak, moderate and strong ionospheric scintillation conditions. The GPS data were collected by Septentrio PolaRxS–PRO receivers as part of the CIGALA/CALIBRA network. The analysis was performed as a function of scintillations indexes S4 and Phi60, lock time (time interval in seconds that the carrier phase is tracked continuously without cycle slips), multipath RMS and position variation of precise point positioning solutions. The analysis shows that L2C code solutions are less affected by multipath effects than that of P2 when data are collected under weak ionospheric scintillation effects. In terms of analysis of positions, the kinematic PPP results using L2C instead P2 codes show accuracy improvements up to 33 % in periods of weak or strong ionospheric scintillation. When combining phase and code collected under weak scintillation effects, the results by applying L2C against P2 provide improvement in accuracy up to 59 %. However, for data under strong scintillation effects, the use of L2C for PPP with code and phase does not provide improvements in the positioning accuracy.  相似文献   

Seasonal variations of water quality in a highly populated drainage basin,SE Brazil: water chemistry assessment and geochemical modeling approaches     

Eduardo Duarte Marques  Emmanoel V. Silva-Filho  Giovana V. C. Souza  Olga Venimar O. Gomes 《Environmental Earth Sciences》2016,75(24):1498

The São João Drainage Basin is a very important and strategic waterbody located in the Lagos Region, Rio de Janeiro State, one of the most popular tourist regions of Brazil. However, the fast economic and subsequent population growth in that region has created untreated wastes from several anthropogenic activities, which include the trace metals disposal into the surface waterbody. This study aims to relate the major ions and trace metals behavior during a 1-year sampling campaign and to provide information about the sources of chemical constituents and the factors that control their concentrations in the three main fluvial compartments of the drainage basin, including the Juturnaíba Reservoir which has a crucial role for water supply in the Lagos Region. The chemical data reveal that rainfall is the main factor responsible for the physicochemical parameters and the water dissolved constituent’s variations. The geological and anthropogenic factors which are the main sources of water constituents were assessed by the Inorganic Chemical Index. Those data corroborate the great influence of rainfall and reveal the importance of anthropogenic sources of chemical constituents in some parts of the Juturnaíba Reservoir. The geochemical modeling suggests that hydrolysis reactions are primarily responsible for the trace metals availability in the three fluvial compartments in both dry and wet seasons, followed by carbonate and sulfate complexation.  相似文献   

Fluvial carbon export and CO2 efflux in representative nested headwater catchments of the eastern La Plata River Basin          下载免费PDF全文

Mino Viana Sorribas  David da Motta Marques  Nilza Maria dos Reis Castro  Fernando Mainardi Fan 《水文研究》2017,31(5):995-1006

This study involved a baseline evaluation of fluvial carbon export and degas rates in three nested rural catchments (1 to 80 km²) in Taboão, a representative experimental catchment of the Upper Uruguay River Basin. Analyses of the carbon content in stream waters and the catchment carbon yield were based on 4‐year monthly in situ data and statistical modeling using the United States Geological Survey load estimator model. We also estimated p CO₂ and degas fluxes using carbonate equilibrium and gas‐exchange formulas. Our results indicated that the water was consistently p CO₂ saturated (~90% of the cases) and that the steep terrain favors high gas evasion rates. The mean calculated fluvial export was 5.4 tC·km^?2·year^?1 with inorganic carbon dominating (dissolved inorganic carbon:dissolved organic carbon ratio >4), and degas rates (~40 tC km^?2·year^?1) were nearly sevenfold higher than the downstream export. The homogeneous land use in this nested catchment system results in similar water‐quality characteristics, and therefore, export rates are expected to be closely related to the rainfall–runoff relationships at each scale. Although the sampling campaigns did not fully reproduce storm‐event conditions and related effects such as flushing or dilution of in‐stream carbon, our results indicated a potential link between dissolved inorganic carbon and slower hydrological pathways related to subsurface water storage and movement.  相似文献   

Input of Sr/Sr ratios and Sr geochemical signatures to update knowledge on thermal and mineral waters flow paths in fractured rocks (N-Portugal)     

J.M. Marques  P.M. Carreira  F. Goff  H.G.M. Eggenkamp  M. Antunes da Silva 《Applied Geochemistry》2012

Strontium isotopes and other geochemical signatures are used to determine the relationships between CO₂-rich thermal (Chaves: 76 °C) and mineral (Vilarelho da Raia, Vidago and Pedras Salgadas: 17 °C) waters discharging along one of the major NNE–SSW trending faults in the northern part of mainland Portugal. The regional geology consists of Hercynian granites (syn-tectonic-310 Ma and post-tectonic-290 Ma) intruding Silurian metasediments (quartzites, phyllites and carbonaceous slates). Thermal and mineral waters have ⁸⁷Sr/⁸⁶Sr isotopic ratios between 0.716713 and 0.728035. ⁸⁷Sr/⁸⁶Sr vs. 1/Sr define three end-members (Vilarelho da Raia/Chaves, Vidago and Pedras Salgadas thermal and mineral waters) trending from rainfall composition towards that of the CO₂-rich thermal and mineral waters, indicating different underground flow paths. Local granitic rocks have ⁸⁷Sr/⁸⁶Sr ratios of 0.735697–0.789683. There is no indication that equilibrium was reached between the CO₂-rich thermal and mineral waters and the granitic rocks. The mean ⁸⁷Sr/⁸⁶Sr ratio of the thermal and mineral waters (0.722419) is similar to the Sr isotopic ratios of the plagioclases of the granitic rocks (0.71261–0.72087). The spatial distribution of Sr isotope and geochemical signatures of waters and the host rocks suggests that the thermal and mineral waters circulate in similar but not the same hydrogeological system. Results from this study could be used to evaluate the applicability of this isotope approach in other hydrogeologic investigations.  相似文献   

Are taxonomic distinctness measures compliant to other ecological indicators in assessing ecological status?   总被引：1，自引：0，他引：1  

Salas F  Patrício J  Marcos C  Pardal MA  Pérez-Ruzafa A  Marques JC 《Marine pollution bulletin》2006,52(2):162-174

Assessing the ecological status, a concept implemented in the European Water Framework Directive [Directive of the European Parliament and of the Council 2000/60/EC establishing a framework for community action in the field of water policy PE-CONS 3639/1/00, 72 p.], requires the application of methods capable of distinguishing different levels of ecological quality. Somerfield and Clarke [Marine Environmental Research 43 (2003) 145-156] proposed Average Taxonomic Distinctness to be used as tool in this context. We tested the robustness of Taxonomic Distinctness measures applying it in different scenarios (estuarine eutrophication, organic pollution, and re-colonisation after physical disturbance), analysing simultaneously its compliance to other types of ecological indicators. Results show that, in most of the case studies, only Total Taxonomic Distinctness was relatively satisfactory in discriminating between disturbed situations. Other Taxonomic Distinctness measures have not proved to be more sensitive than other ecological indicators (Shannon-Wiener, Margalef, and Eco-Exergy indices). Therefore, this approach does not seem to be particularly helpful in assessing systems' ecological status with regard to the WFD implementation.  相似文献   

Opportunistic macroalgae metrics for transitional waters. Testing tools to assess ecological quality status in Portugal     

Patrício J  Neto JM  Teixeira H  Marques JC 《Marine pollution bulletin》2007,54(12):1887-1896

Macroalgae communities constitute one of the ecological quality elements for the evaluation of the ecological quality status (EQS) of coastal and transitional waters, required to implement the WFD. While these algae are natural components of estuarine systems and play important roles in several estuarine processes, macroalgal blooms are of ecological concern because they can reduce the habitat quality. Several works are being carried out to set standard methods for monitoring macroalgae blooms, in order to develop tools to derive EQS based upon this biological quality element. The aim of this paper is to apply the methodology described by Scanlan et al. [Scanlan, C.M., Foden, J., Wells, E., Best, M.A., 2007. The monitoring of opportunistic macroalgal blooms for the water framework directive. Marine Pollution Bulletin 55, 162–171] to a series of data assembled in the south arm of the Mondego estuary (Atlantic coast of Portugal) considering two different ecological situations. Additionally, an alternative assessment method intended to be used when no biomass data are available was also tested. In general, both options captured the inter-annual variations in accordance with the system evolution. Option 2, less expensive and time-consuming, allowed an EQS evaluation with accurate results when biomass data were not available. The results suggest that sampling should be carried out from April to June.  相似文献   

Palaeoenvironmental Evolution During the Holocene in Itapeva Lake, RS, Brazil:Palynological and Geochemical Records     

Meyer K.E.B  Reichnart K  Marques T.M  Ashraf A.R  Mosbrugger V 《世界地质(英文版)》2002,5(2)

Based on palynological and geochemical data (Organic Carbon-Corg and Sulphur-S) of sedimentary samples from a vibrocore, considerations about the palaeoenvironmental evolution of Itapeva Lake region during the Holocene are made. The analysed core (BOXVI) consists in its lowermost part of a fine to medium sand packet, rich in glauconitic minerals, whose upper limit is considered to be the Holocene-Pleistocene contact. Using Cluster analysis on palynomorphs combined with Corg and S data, it was possible to distinguish four zones related to the Holocene transgression-regression cycle. Variations in Corg and S data permitted the recognition of changes in palaeosalinity. Zone 1 represents the beginning of the Holocene sedimentation; palynomorphs composition reveals a marsh environment under predominating freshwater conditions. In Zone 2, the occurrence of dinoflagellate cysts and high S values, indicating brackish water, reflects Holocene sea level highstand around 5100yrs. B.P. High concentration of Cyperaceae associated with a significant increase in Corg in Zone 3 indicates a typical marsh environment influenced at least sometimes by higher saline water, reflecting a regression phase. Salvinia natans (L)All. and Cyperaceae grains are considered to be the most significant palynomorpha in Zone 4, characterising a freshwater marsh. Based on the occurrence of dinoflagellates sample 2, Operculodinium sp., related to marine to estuarine environments, a question arises regarding about the time at which Barrier Ⅳ became completely closed.  相似文献   

Interplanetary medium condition effects in the South Atlantic Magnetic Anomaly: A case study     

Aracy Mendes da Costa  Margarete Oliveira Domingues  Odim Mendes  Christiano Garnett Marques Brum 《Journal of Atmospheric and Solar》2011,73(11-12):1478-1491

One way to investigate the magnetosphere–ionosphere coupling is through the simultaneous observation of different parameters measured at different locations of the geospace environment and try to determine some relationships among them. The main objective of this work is to examine how the solar energetic particles and the interplanetary medium conditions may affect the space and time configuration of the ring current at low-latitudes and also to get a better understanding on how these particles interfere with the lower ionosphere in the South Atlantic Magnetic Anomaly region (SAMA). To accomplish this, the cosmic noise absorption (CNA) and the horizontal component of the Earth's magnetic field data measured from sites located in the SAMA region were compared with the proton and electron fluxes, interplanetary medium conditions (solar wind and the north–south component of the interplanetary magnetic field measured on board satellites), the SYM-H index and magnetometer data from Kakioka (KAK-Japan), located significantly outside the SAMA region. The time series analyzed correspond to the geomagnetic disturbance that occurred on August 25–30, 1998. The analysis was performed by implementing wavelet techniques, with particular attention to singularities detection, which highlights the presence of transient signals. The results are discussed in terms of the first three wavelet decomposition levels of the parameters. The magnitude of wavelet coefficients of the solar wind and proton flux at the two energy ranges analyzed is timely well correlated, indicating that these two signals are energetically linked. The larger wavelet coefficient amplitude of KAK and VSS magnetograms shows time delays that are compatible with an asymmetric configuration of the ring current, considering that at the storm time, VSS was at the dawn sector of the magnetosphere and KAK at the dusk side. The wavelet analysis of CNA signals reveals that the signal may be sensitive to the ionization produced by energetic electrons and protons as well. The time delays observed in wavelet coefficients may give an indication of the different accelerating process to which the particles are submitted when traveling along the magnetic field lines, from higher to lower latitudes, and the likely contribution of these particles to the ionization measured as an absorption of the cosmic noise in the lower ionosphere.  相似文献   

Macrobenthic associations in a South Atlantic Brazilian enclosed bay: the historical influence of shrimp trawling     

de Almeida TC  Vivan JM 《Marine pollution bulletin》2011,62(10):2190-2198

This study characterized the macrobenthos of Tijucas Bay and related the distribution and dominance patterns with historical trawling activities. Fifteen sampling sites were established in the bay and were sampled in summer and winter for the characterization of the macrobenthos. To evaluate the trawling effects, three passages were established at each site with control and impacted areas analyzed before and after trawl-net action in impacted area. Seasonal differences occurred in macrobenthos, possibly influenced by rainfall where the relative water level of the Tijucas River was directly associated with the discharge of freshwater and particulate matter. The associations identified in the bay were distinct in comparison with the Zimbros Embayment. The trawling assessment showed no significant variation in the macrobenthos after the trawl, possibly due to decades of shrimp exploitation in the bay. Trawling and instable environmental conditions inside the bay make the establishment of a stable macrobenthic community difficult.  相似文献   

Artificial Intelligence Applications in Transportation Geotechnics   总被引：1，自引：1，他引：0  

A. Gomes Correia  P. Cortez  J. Tinoco  R. Marques 《Geotechnical and Geological Engineering》2013,31(3):861-879

This paper presents a brief overview of artificial intelligence applications in transportation geotechnics, highlighting new approaches and current research directions, including issues related to data mining interpretability and prediction capacities. Several practical applications to earthworks, including the compaction management and quality control aspects of embankments, as well as pavement evaluation, design and management, and the mechanical behaviour of jet grouting material, are presented to illustrate the advantages of using data mining, including artificial neural networks, support vector machines, and evolutionary computation techniques in this domain. This study also propose a novel simplified compaction table for reusing geomaterials and compaction management in embankments and applied one- and two-dimensional advanced sensitivity analyses to better interpret the proposed data-driven models for the prediction of the deformability modulus of jet grouting field samples. These applications show the capabilities of data mining models to address complex problems in transportation geotechnics involving highly nonlinear relationships of data and optimisation needs.  相似文献