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161.
Angela Aragon-Angel Manuel Hernandez-Pajares J. Miguel Juan Zornoza Jaume Sanz Subirana 《GPS Solutions》2010,14(1):23-33
The FORMOSAT-3/COSMIC satellite constellation has become an important tool toward providing global remote sensing data for
sounding of the atmosphere of the earth and the ionosphere in particular. In this study, the electron density profiles are
derived using the Abel transform inversion. Some drawbacks of this transform in LEO GPS sounding can be overcome by considering
the separability concept: horizontal gradients of vertical total electron content (VTEC) information are incorporated by the
inversion method, providing more accurate electron density determinations. The novelty presented in this paper with respect
to previous works is the use of the phase change between the GPS transmitter and the LEO receiver as the main observable instead
of the ionospheric combination of carrier phase observables for the implementation of separability in the inversion process.
Some of the characteristics of the method when applied to the excess phase are discussed. The results obtained show the equivalence
of both approaches but the method exposed in this work has the potentiality to be applied to the neutral atmosphere. Recent
FORMOSAT-3/COSMIC data have been processed with both the classical Abel inversion and the separability approach and evaluated
versus colocated ionosonde data. 相似文献
162.
Araceli Zamora-Camacho Juan Manuel Espíndola Gabriel Reyes-Dávila 《Pure and Applied Geophysics》2007,164(1):39-52
Volcán de Colima, the most active volcano in Mexico, had a climactic episode on 20 November, 1998. On this date, a dome formed
on the small summit crater during the previous few days, collapsed generating block-and-ash flows. The event was preceded
by almost twelve months of seismic activity, which continued afterwards for several more months. We analyzed the main seismic
activity, which occurred from 20 March, 1998 to 31 March, 1999. The seismicity was dominated by volcano-tectonic earthquakes
before the climax, and subsequently by hybrid and long-period earthquakes. We determined the frequency of events for the entire
period, and located most of the volcano-tectonic events. To assess the possibility that these earthquakes were generated by
the same source, they were tested for their similitude through cross correlation in the time domain. Six groups of similar
events, or earthquake families, were generated. The members of these families appeared before the 20 November event, apparently
ceasing afterwards. We examined the location of the families' events with respect to an existing gravity model in which an
anomalous body of negative density contrast suggests the presence of the magma chamber. Most of the family events occur on
top of the anomalous body, which suggests they were associated with the passage of magma through the feeding conduits of the
volcano. 相似文献
163.
Communicating human health risks associated with disinfection by-products in drinking water supplies: a fuzzy-based approach 总被引:1,自引:2,他引:1
Rehan Sadiq Manuel J. Rodriguez Syed A. Imran Homayoun Najjaran 《Stochastic Environmental Research and Risk Assessment (SERRA)》2007,21(4):341-353
Chlorine used for the disinfection of water supplies can react with naturally occurring organic compounds and form potentially
harmful disinfection by-products (DBPs). A risk index for two regulated groups of chlorinated DBPs—trihalomethanes (THMs)
and haloacetic acids (HAAs), using fuzzy C-means (FCM) clustering algorithm and fuzzy rule-based modeling is proposed for risk communication. The proposed index evaluates
the cancer and non-cancer risks individually for THMs and HAAs using the FCM algorithm. Subsequently, two different fuzzy
rule-bases were used to evaluate the overall risk-index based on cancer and non-cancer risks. The overall risk-index will
provide drinking water utilities with an effective communication tool for communicating aggregated water quality compliance.
Simulated DBP occurrence data obtained from the City of Quebec, Canada, is used to demonstrate the application of this methodology. 相似文献
164.
The main objective of the present paper is to show a methodology for undertaking rainfall regionalization of a region taking into account the convective features of the precipitation, and useful for establishing homogeneous zones for improving the alert system. This methodology has been applied to a hydrographic region located in northeast Spain, with an area of 16000 km2 and characterized by a highly contrasted topography. Information provided by meteorological radar and 5-min precipitation data for 126 automatic raingauges has been used for the period 1996–2002. The previous analysis done on the basis of the 1927–1981 rainfall rate series for the Jardí raingauge, located in Barcelona, has also been considered. To that end, the first step was to draw up a proposal for classification of the pluviometric episodes. Recourse was had for this purpose to definition of the β parameter, related with the greater or lesser convective character of the event and calculated on the basis of the rainfall intensity at the surface (Llasat, 2001) and, when data are available, on the basis of radar reflectivity. Results show that the threshold of 35 mm/h to characterize convective episodes from raingauge data can be corroborated from the radar point of view when convective precipitation is identified using 2-D algorithms with a reflectivity threshold of 43 dBZ. Once the soundness of the β parameter had been corroborated, it was applied to more than 2900 precipitation episodes recorded in the region, in order to discriminate the features of the different subregions and their time and space distribution throughout the entire series of the samples. Using this definition, 92% of the precipitation events recorded in this region, with accumulated rainfall above 35 mm, are classified as convective ones, representing 95% of the precipitation amount. Application of the β parameter combined with monthly rainfall data allows differentiation of 8 regions with different convective precipitation features. 相似文献
165.
There are two types of planetary noble gases: One, containing isotopically “anomalous” argon, krypton and xenon but isotopically “normal” helium and neon, was derived from outer stellar regions. The other, consisting almost entirely of isotopically “normal” argon, krypton and xenon, with little or no helium or neon, was derived from inner stellar regions. Mixing of nucleosynthesis products from different regions of a supernova is responsible for the observed correlations between elemental and isotopic ratios of planetary noble gases in different classes of meteorites. The solar system condensed directly from the chemically and isotopically heterogeneous debris of a single supernova. There is no convincing evidence, however, of separate nucleogenetic components in neon. Fractionation and spallation can account for all previously identified components of trapped meteoritic neon, Ne-A, Ne-B, Ne-C, Ne-D, Ne-E, Ne-Al, Ne-A2, Ne-E(L), Ne-E(H) and Ne-O, and this same mechanism also explains differences between the isotopic compositions of meteoritic, atmospheric, and solar wind neon. Variations in the abundance pattern of planetary noble gases are primarily the result of stellar fusion reactions and physical adsorption, rather than gas solubility. 相似文献
166.
167.
Elizabeth?J.?PetrieEmail author Manuel?Hernández-Pajares Paolo?Spalla Philip?Moore Matt?A.?King 《Surveys in Geophysics》2011,32(3):197-253
Higher order ionospheric effects are increasingly relevant as precision requirements on GPS data and products increase. The
refractive index of the ionosphere is affected by its electron content and the magnetic field of the Earth, so the carrier
phase of the GPS L1 and L2 signals is advanced and the modulated code delayed. Due to system design the polarisation is unaffected.
Most of the effect is removed by expanding the refractive index as a series and eliminating the first term with a linear combination
of the two signals. However, the higher order terms remain. Furthermore, transiting gradients in refractive index at a non-perpendicular
angle causes signal bending. In addition to the initial geometric bending term, another term allows for the difference that
the curvature makes in electron content along each signal. Varying approximations have been made for practical implementation,
mainly to avoid the need for a vertical profile of electron density. The magnetic field may be modelled as a tilted co-centric
dipole, or using more realistic models such as the International Geomagnetic Reference Field. The largest effect is from the
second term in the expansion of the refractive index. Up to several cm on L2, it particularly affects z-translation, and satellite orbits and clocks in a global network of GPS stations. The third term is at the level of the errors
in modelling the second order term, while the bending terms appear to be absorbed by tropospheric parameters. Modelling improvements
are possible, and three frequency transmissions will allow new possibilities. 相似文献
168.
Sin Chan Chou Andr de Arruda Lyra Jorge Lus Gomes Daniel Andrs Rodriguez Minella Alves Martins Nicole Costa Resende Priscila da Silva Tavares Claudine Pereira Dereczynski Isabel Lopes Pilotto Alessandro Marques Martins Lus Felipe Alves de Carvalho Jos Luiz Lima Onofre Idalcio Major Manuel Penhor Adrito Santana 《Climate Dynamics》2020,54(9):4021-4042
Sao Tome and Principe is a small insular African country extremely vulnerable to rising sea levels and impacts such as inundation, shore line change, and salt water intrusion into underground aquifers. Projections of climate change have considered coarse model resolutions. The objective of this work is to dynamically downscale the global model projections to 4-km resolution and to assess the climate change in the Sao Tome and Principe islands. The global climate projections are provided by the Canadian Earth System Model under two Representative Concentration Pathways greenhouse gas scenarios, RCP4.5 and RCP8.5. The downscaling is produced by the Eta regional climate model. The baseline period is taken between 1971 and 2000, and the future climate period is taken between 2041 and 2070. The 2-m temperature simulations show good agreement with station data. The model simulates temperature more accurately than precipitation. The precipitation simulations systematically show underestimation and delay of the rainy and the dry seasons by about 1 month, a feature inherited from the global climate model. In the middle of the 21st century, projections show the strongest warming in the elevated parts of the Sao Tome Island, especially in February under RCP8.5. Warmer nights and warmer days become more frequent in the islands when compared with those in the present. While under RCP4.5, precipitation increases in the islands; under RCP8.5, it decreases everywhere in both islands. Heavy precipitation rates should increase, especially in the south-southwestern parts of the Sao Tome islands. Detailed spatial variability of the temperature and precipitation changes in the islands can only be revealed at very high spatial model resolution. Implications for the potential energy production from two major river basins are assessed in this work. 相似文献
169.
Antonio T. Mozas-Calvache Manuel Antonio Ureña-Cámara José Luis Pérez-García 《International journal of geographical information science》2013,27(12):2362-2374
This article describes a new methodology for the planimetric control of contour lines. The method is based on the generation of buffers around the contour lines which define a 3D buffer around the maximum slope line. After that we analyze the quantity of points from a more accurate source which is inside this buffer. As a result, we obtain a distribution function of the control points included when we apply several widths to the buffers. We have also determined the angularity and height differences of these points. The method has been applied to several sets of contour line intervals derived from a digital elevation model (DEM) and to the contour lines of one published topographic map using the DEM as the control source. We have also analyzed the representative behaviour of the contour lines, taking into account the contour line interval and the detection of an uncertainty model based on the slope variation. This study demonstrates the viability of the proposed method for obtaining the uncertainty of the contour lines depending on a given level of confidence and the variability of this uncertainty in the map. Finally, we propose a range of contour line intervals based on the scale and slopes. 相似文献
170.
Ricardo Conceição Hugo Gonçalves Silva Alec Bennett Rui Salgado Daniele Bortoli Maria João Costa Manuel Collares Pereira 《Boundary-Layer Meteorology》2018,166(1):69-81
The spectral response of atmospheric electric potential gradient gives important information about phenomena affecting this gradient at characteristic time scales ranging from years (e.g., solar modulation) to fractions of a second (e.g., turbulence). While long-term time scales have been exhaustively explored, short-term scales have received less attention. At such frequencies, space-charge transport inside the planetary boundary layer becomes a sizeable contribution to the potential gradient variability. For the first time, co-located (Évora, Portugal) measurements of boundary-layer backscatter profiles and the 100-Hz potential gradient are reported. Five campaign days are analyzed, providing evidence for a relation between high-frequency response of the potential gradient and strong dry convection. 相似文献