Using DORIS measurements for modeling the vertical total electron content of the Earth’s ionosphere     

Denise Dettmering  Marco Limberger  Michael Schmidt 《Journal of Geodesy》2014,88(12):1131-1143

The Doppler orbitography and radiopositioning integrated by satellite (DORIS) system was originally developed for precise orbit determination of low Earth orbiting (LEO) satellites. Beyond that, it is highly qualified for modeling the distribution of electrons within the Earth’s ionosphere. It measures with two frequencies in L-band with a relative frequency ratio close to 5. Since the terrestrial ground beacons are distributed quite homogeneously and several LEOs are equipped with modern receivers, a good applicability for global vertical total electron content (VTEC) modeling can be expected. This paper investigates the capability of DORIS dual-frequency phase observations for deriving VTEC and the contribution of these data to global VTEC modeling. The DORIS preprocessing is performed similar to commonly used global navigation satellite systems (GNSS) preprocessing. However, the absolute DORIS VTEC level is taken from global ionospheric maps (GIM) provided by the International GNSS Service (IGS) as the DORIS data contain no absolute information. DORIS-derived VTEC values show good consistency with IGS GIMs with a RMS between 2 and 3 total electron content units (TECU) depending on solar activity which can be reduced to less than 2 TECU when using only observations with elevation angles higher than \(50^\circ \) . The combination of DORIS VTEC with data from other space-geodetic measurement techniques improves the accuracy of global VTEC models significantly. If DORIS VTEC data is used to update IGS GIMs, an improvement of up to 12  % can be achieved. The accuracy directly beneath the DORIS satellites’ ground-tracks ranges between 1.5 and 3.5 TECU assuming a precision of 2.5 TECU for altimeter-derived VTEC values which have been used for validation purposes.  相似文献   

Mechanisms of failure on terraced slopes: the Valtellina case (northern Italy)   总被引：1，自引：1，他引：0  

Corrado A. S. Camera  Tiziana Apuani  Marco Masetti 《Landslides》2014,11(1):43-54

Slopes that are terraced by means of dry-stone retaining walls are very common in the alpine environment. In Valtellina, a typical Italian alpine valley, these slopes are widespread and quite often involved in superficial mass movements that can result in severe damage and casualties. For an in-depth understanding of the processes that can trigger these events, numerical modeling of groundwater movement and a related stability analysis were performed on a detailed scale, based on an intensive monitoring of rainfall events and groundwater movement. Field observations suggest that the formation of a perched groundwater table at the contact between the bedrock and the backfill soil of walls as well as the concomitant saturation of this backfill soil are the determining factors of potential slope failure. The numerical models support these observations. In addition, the models are able to explain the mechanisms of formation of perched water tables, highlighting the factors that can influence groundwater levels and slope instabilities.  相似文献   

Human alteration of groundwater–surface water interactions (Sagittario River,Central Italy): implication for flow regime,contaminant fate and invertebrate response     

Mariachiara Caschetto  Maurizio Barbieri  Diana M. P. Galassi  Lucia Mastrorillo  Sergio Rusi  Fabio Stoch  Alessia Di Cioccio  Marco Petitta 《Environmental Earth Sciences》2014,71(4):1791-1807

Many rivers worldwide are undergoing severe man-induced alterations which are reflected also in changes of the degree of connectivity between surface waters and groundwater. Pollution, irrigation withdrawal, alteration of freshwater flows, road construction, surface water diversion, soil erosion in agriculture, deforestation and dam building have led to some irreversible species losses and severe changes in community composition of freshwater ecosystems. Taking into account the impact of damming and flow diversion on natural river discharge, the present study is aimed at (i) evaluating the effects of anthropogenic changes on groundwater/surface water interactions; (ii) analyzing the fate of nitrogenous pollutants at the floodplain scale; and (iii) describing the overall response of invertebrate assemblages to such changes. Hydrogeological, geochemical and isotopic data revealed short- and long-term changes in hydrology, allowing the assessment of the hydrogeological setting and the evaluation of potential contamination by nitrogen compounds. Water isotopes allowed distinguishing a shallow aquifer locally fed by zenithal recharge and river losses, and a deeper aquifer/aquitard system fed by surrounding carbonate aquifers. This system was found to retain ammonium and, through the shallow aquifer, release it in surface running waters via the hyporheic zone of the riverbed. All these factors influence river ecosystem health. As many environmental drivers entered in action offering a multiple-component artificial environment, a clear relationship between river flow alteration and benthic and hyporheic invertebrate diversity was not found, being species response driven by the combination of three main stressors: ammonium pollution, man-induced changes in river morphology and altered discharge regime.  相似文献   

Monitoring large oil slick dynamics with moderate resolution multispectral satellite data     

Pieralberto Maianti  Marco Rusmini  Riccardo Tortini  Giorgio Dalla Via  Federico Frassy  Andrea Marchesi  Francesco Rota Nodari  Marco Gianinetto 《Natural Hazards》2014,73(2):473-492

Accidental release of crude oil into the sea due to human activity causes water pollution and heavy damages to natural ecosystems killing birds, fish, mammals and other organisms. A number of monitoring systems are used for tracking the spills and their effects on the marine environment, as well as for collecting data for feeding models. Among them, Earth observation technologies play a crucial role and moderate spatial resolution satellite systems are able to collect images with a very short revisit time or even daily. This paper describes the use of Moderate-Resolution Imaging Spectroradiometer data for monitoring large oil slicks with the fluorescence/emissivity index and object-based image analysis. Two case studies are presented: the Deepwater Horizon (2010) and the Campos Basin (2011) oil spill accidents. Results show that it is possible to track the dynamics of the slick both for massive and long-lasting accidents and for smaller and very quick accidents. The main advantages of the method proposed are a straightforward implementation, a fast and semi-automated data processing and the capability of integration of daytime and nighttime acquisitions, as well as its adaptability to different sensors.  相似文献   

LightSquared effects on estimated C/N 0, pseudoranges and positions     

Marco Rao  Cillian O’Driscoll  Daniele Borio  Joaquim Fortuny 《GPS Solutions》2014,18(1):1-13

We present experimental results showing the impact of the proposed LightSquared (LS) Long-term Evolution (LTE) signals on both GPS and Galileo civil modulations in the L1/E1 band. The experiments were conducted in radiated mode in a large anechoic chamber. Three Galileo enabled receivers were chosen for the tests, and a state of the art GNSS signal generator was used to simulate both GPS and Galileo signals. The LTE signals were generated by an Agilent Programmable Signal Generator with a license to generate the signals according to the 3GPP LTE FDD standard. The interference impact was measured in terms of a Carrier-to-Noise power spectral density ratio (C/N ₀) degradation, in accordance with the methodology which the LS/GPS Technical Working Group (TWG) established by mandate of the FCC. A model for determining the impact of the LS signal on the considered GNSS signals is provided and is validated against experimental data. It is shown that the Galileo E1 Open Service (OS) signal is marginally more susceptible to this form of interference than the GPS L1 C/A signal due to its greater proximity to the lower edge of the L1 band. The impact of LS interference was further analyzed in terms of pseudorange and position errors. Despite its relevance for most GNSS users, this aspect was not considered by the TWG. Measurement and position domain analysis along with the study of the LS impact on the Galileo OS signals are the major contributions. The analysis confirms the results obtained by the TWG and shows that the receiver front-end plays a major role in protecting GNSS signals against RF interference. While it appears that, for now, the LS network will not be deployed, the approach taken and the results obtained herein can be readily adapted for any future terrestrial mobile network that may take the place of LS.  相似文献   

A distributed thermodynamic model for energy and mass balance computation: FEST–EWB     

Chiara Corbari  Giovanni Ravazzani  Marco Mancini 《水文研究》2011,25(9):1443-1452

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Reef status in the Rasfari region (North Malé Atoll,Maldives) five years before the mass mortality event of 1998     

Carla Morri  Stefano Aliani  Carlo Nike Bianchi 《Estuarine, Coastal and Shelf Science》2010

The Maldives was severely hit by massive coral bleaching and subsequent mortality in 1998. The results of reef monitoring in the following years have supported contrasting views about their recovery potential, partly because of the scarcity of information on the situation before 1998. Quantitative data on coral assemblages collected in 1993 in the Rasfari region (North Malé Atoll) may provide a base-line for the evaluation of the present status of the Maldivian reefs. Five years before the 1998 mortality, most coral communities appeared to be similar, in terms of both coral cover and growth-form composition, to those described in 1958 and 1964, notwithstanding increased human pressure and local events such as minor bleaching episodes in 1987 and crown-of-thorns starfish (COTS) attacks in 1989. Three lessons can be learnt from these results to help to understand the present situation, some ten years after the 1998 mass mortality. First, Maldivian reefs proved in the past to be capable of maintaining flourishing coral life despite various disturbances. Second, four years had been sufficient for complete reef recovery after a (minor) bleaching event. Third, recovery after both COTS attack and bleaching follows a predictable path suggesting that the presence of a three-dimensional community structure, which should reduce post settlement mortality of coral recruits, is essential for rapid coral recovery. As coral recruitment remains high and large tabular Acropora colonies are now reappearing, it is expected that Maldivian reefs should return to their original condition within the next few years.  相似文献   

On the prediction of the Toce alpine basin floods with distributed hydrologic models     

Nicola Montaldo  Giovanni Ravazzani  Marco Mancini 《水文研究》2007,21(5):608-621

With the objective of improving flood predictions, in recent years sophisticated continuous hydrologic models that include complex land‐surface sub‐models have been developed. This has produced a significant increase in parameterization; consequently, applications of distributed models to ungauged basins lacking specific data from field campaigns may become redundant. The objective of this paper is to produce a parsimonious and robust distributed hydrologic model for flood predictions in Italian alpine basins. Application is made to the Toce basin (area 1534 km²). The Toce basin was a case study of the RAPHAEL European Union research project, during which a comprehensive set of hydrologic, meteorological and physiographic data were collected, including the hydrologic analysis of the 1996–1997 period. Two major floods occurred during this period. We compare the FEST04 event model (which computes rainfall abstraction and antecedent soil moisture conditions through the simple Soil Conservation Service curve number method) and two continuous hydrologic models, SDM and TDM (which differ in soil water balance scheme, and base flow and runoff generation computations). The simple FEST04 event model demonstrated good performance in the prediction of the 1997 flood, but shows limits in the prediction of the long and moderate 1996 flood. More robust predictions are obtained with the parsimonious SDM continuous hydrologic model, which uses a simple one‐layer soil water balance model and an infiltration excess mechanism for runoff generation, and demonstrates good performance in both long‐term runoff modelling and flood predictions. Instead, the use of a more sophisticated continuous hydrologic model, the TDM, that simulates soil moisture dynamics in two layers of soil, and computes runoff and base flow using some TOPMODEL concepts, does not seem to be advantageous for this alpine basin. Copyright © 2006 John Wiley & Sons, Ltd.  相似文献   

Two paleoecological histories spanning the period of human settlement in southeastern Brazil     

Marco F. Raczka  Paulo E. De Oliveira  Mark Bush  Crystal H. McMichael 《第四纪科学杂志》2013,28(2):144-151

The absence of human occupation sites in southeastern Brazil during the mid Holocene has been referred to as the 'Archaic Gap' (8970–1940 cal. a BP) and is predicted to have resulted from increased aridity. A ca. 14 000 cal. a pollen history from two well‐dated lake sediment cores located within the archeological district of Lagoa Santa, in the State of Minas Gerais, southeastern Brazil, was used to test this hypothesis. Our analyses indicated that the present cerrado and tropical semi‐deciduous forest mosaic persisted throughout the mid Holocene, until ca. 5500 cal. a BP, and the Lagoa Santa region did not experience especially dry conditions during the Holocene period. The early Holocene pollen spectra contained an assemblage of cold‐adapted taxa such as Podocarpus, Myrsine and Araucaria, co‐occurring with taxa from cerrado, e.g. Caryocar. A replacement of cold taxa by the modern cerrado–semi‐deciduous forest vegetation took place progressively, but appears to have been completed by the mid Holocene. No evidence of sustained drought was found in sedimentation or forest composition, nor any prolonged dry event in the study region. Holocene dryness as an explanation for the abandonment of Lagoa Santa region is not supported by the palynological analyses conducted in this study. Rather it is suggested that unpredictable climate may have underlain that abandonment. Copyright © 2012 John Wiley & Sons, Ltd.  相似文献   

The variability of ruthenium in chromite from chassignite and olivine‐phyric shergottite meteorites: New insights into the behavior of PGE and sulfur in Martian magmatic systems          下载免费PDF全文

Raphael J. Baumgartner  Marco L. Fiorentini  David Baratoux  Ludovic Ferrière  Marek Locmelis  Andrew Tomkins  Kerim A. Sener 《Meteoritics & planetary science》2017,52(2):333-350

The Martian meteorites comprise mantle‐derived mafic to ultramafic rocks that formed in shallow intrusions and/or lava flows. This study reports the first in situ platinum‐group element data on chromite and ulvöspinel from a series of dunitic chassignites and olivine‐phyric shergottites, determined using laser‐ablation ICP‐MS. As recent studies have shown that Ru has strongly contrasting affinities for coexisting sulfide and spinel phases, the precise in situ analysis of this element in spinel can provide important insights into the sulfide saturation history of Martian mantle‐derived melts. The new data reveal distinctive differences between the two meteorite groups. Chromite from the chassignites Northwest Africa 2737 (NWA 2737) and Chassigny contained detectable concentrations of Ru (up to ~160 ppb Ru) in solid solution, whereas chromite and ulvöspinel from the olivine‐phyric shergottites Yamato‐980459 (Y‐980459), Tissint, and Dhofar 019 displayed Ru concentrations consistently below detection limit (<42 ppb). The relatively elevated Ru signatures of chromite from the chassignites suggest a Ru‐rich (~1–4 ppb) parental melt for this meteorite group, which presumably did not experience segregation of immiscible sulfide liquids over the interval of mantle melting, melt ascent, and chromite crystallization. The relatively Ru‐depleted signature of chromite and ulvöspinel from the olivine‐phyric shergottites may be the consequence of relatively lower Ru contents (<1 ppb) in the parental melts, and/or the presence of sulfides during the crystallization of the spinel phases. The results of this study illustrate the significance of platinum‐group element in situ analysis on spinel phases to decipher the sulfide saturation history of magmatic systems.  相似文献