-Scintillation is one of the most challenging problems in Global Navigation Satellite Systems (GNSS) navigation. This phenomenon appears when the radio signal passes through ionospheric irregularities. These irregularities represent rapid changes on the refraction index and, depending on their size, they can produce also diffractive effects affecting the signal amplitude and, eventually producing cycle slips. In this work, we show that the scintillation effects on the GNSS signal are quite different in low and high latitudes. For low latitude receivers, the main effects, from the point of view of precise navigation, are the increase of the carrier phase noise (measured by s f ) and the fade on the signal intensity (measured by S4) that can produce cycle slips in the GNSS signal. With several examples, we show that the detection of these cycle slips is the most challenging problem for precise navigation, in such a way that, if these cycle slips are detected, precise navigation can be achieved in these regions under scintillation conditions. For high-latitude receivers the situation differs. In this region the size of the irregularities is typically larger than the Fresnel length, so the main effects are related with the fast change on the refractive index associated to the fast movement of the irregularities (which can reach velocities up to several km/s). Consequently, the main effect on the GNSS signals is a fast fluctuation of the carrier phase (large s f ), but with a moderate fade in the amplitude (moderate S4). Therefore, as shown through several examples, fluctuations at high-latitude usually do not produce cycle slips, being the effect quite limited on the ionosphere-free combination and, in general, precise navigation can be achieved also during strong scintillation conditions.

This manuscript presents a method to identify the occurrence of Equatorial Plasma Bubbles (EPBs) with data gathered from receivers of Global Navigation Satellite System (GNSS). This method adapts a previously existing technique to detect Medium Scale Travelling Ionospheric Disturbances (MSTIDs), which focus on the 2nd time derivatives of total electron content estimated from GNSS signals (2DTEC). Results from this tool made possible to develop a comprehensive analysis of the characteristics of EPBs. Analyses of the probability of occurrence, effective time duration, depth of the depletion and total disturbance of the EPBs show their dependence on local time and season of the year at global scale within the latitude belt from 35°N to 35°S for the descending phase of solar cycle 23 and ascending phase of solar cycle 24, 2002–2014. These results made possible to build an EPBs model, bounded with the Solar Flux index, that simulates the probability of the number of EPBs and their characteristics expected for a representative day at given season and local time (LT). The model results provided insight into different important aspects: the maximum occurrence of bubbles take place near the equatorial anomaly crests, asymmetry between hemispheres and preferred longitudes with enhanced EPBs activity. Model output comparisons with independent observations confirmed its soundness.

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RESUMOO presente estudo mostra uma relação entre o comportamento das espécies ativas do plasma com as propriedades superficiais do titânio. Para tanto, espécies ativas como N 2 + (391,4 nm) e O (844,6 nm) foram analisadas por espectroscopia de emissão óptica (OES) em plasma produzido por uma mistura de gases ABSTRACTThe present study correlates plasma active species with titanium surface properties. This was achieved by performing optical emission spectroscopy (OES) analysis of N 2 + (391.4 nm) and O (844.6 nm) within a N 2 -A r -O 2 plasma. The fluxes of gases were established to be 1 and 4 sccm (standard cubic centimeter) for nitrogen and argon, while that of oxygen was varied between 2 and 4 sccm. A non-linearity of the intensity of N 2 + (391.4 nm) species with the increase on O 2 flux was observed with an intensity peak at 3 sccm. It was also concluded that the active species influence the modification of properties after the plasma treatment. The N 2 + (391.4 nm) species were more effective to form nitrides and the surface roughness was bigger when those species presented higher intensity. Surface hardness and surface stress were also higher whenever using higher intensity fluxes of N 2 + (391.4 nm). Furthermore, while the N 2 + (391.4 nm) specie influenced the dispersive component, the O (844.6 nm) specie influenced the polar component.

RESUMOSuperfícies de TiCxNy foram produzidas por tratamento termoquímico auxiliado por mistura de plasma N2 -Ar -CH4. A influência da concentração do metano, bem como a inserção de átomos C e N na rede cristalina do Ti foram investigadas através da caracterização das propriedades tribomecânicas desse material. Para tanto, amostras de titânio comercialmente puro (grau II) foram carbonitretadas em plasma com mistura de x N2 -y Ar -z CH4 (onde x e y = 4 sccm e z variando de 2,3 e 4 sccm) a 500°C, durante 1 h. Os perfis de concentração de C e N após o tratamento foram analisados por reação nuclear (NRA). As fases na superfície foram identificadas por difração de raios-X com incidência rasante (GIXRD). Foi utilizado ensaio de pino sobre disco para determinação do coeficiente de atrito, cujas áreas desgastadas foram avaliadas por perfilometria e microscopia eletrônica de varredura (MEV). Foi observado que tanto o coeficiente de atrito quanto o mecanismo de desgaste do titânio foram fortemente dependentes da concentração de C e N na superfície. Porém, o perfil de concentração desses elementos intersticiais não foi diretamente proporcional ao fluxo de metano.Palavras chaves: plasma, titânio, carbonitretação, tribologia. Tribological properties modification of titanium by plasma carbonitriding ABSTRACTTiCxNy surfaces were produced by thermochemical treatment achieved by N 2 -Ar -CH 4 plasma mixture. The influence of methane concentration and C and N atoms inserted into the crystalline lattice of Ti were investigated through the characterization of its tribomechanical properties. Therefore, commercially pure Ti (grade II) samples were carbonitrided in the x N 2 -y Ar -z CH 4 plasma mixture (where x and y = 4 SCCM and z = 2, 3 and 4 SCCM) at 500 °C, during 1 h. C and N concentration profile after treatments were determinate by NRA. The superficial phases were identified by GIXRD. Pin-on-disk assays were utilized to determine the friction coefficient, whose damaged areas were studied by perfilometry and scanning electron microscopy (SEM) techniques. It was observed that the friction coefficient and the damage mechanism of Ti are intensively dependent of C and N concentration on the surface. However, the concentration profile of those interstitial elements is not directly proportional to the methane gas flow.Keywords: plasma, titanium, carbonitriding, tribology. INTRODUÇÃOO titânio e suas ligas possuem várias propriedades que as habilitam para serem usadas em muitas aplicações industriais. Algumas de suas vantagens são: excelente resistência à corrosão e erosão, baixa densidade e alta razão de E/m (módulo de elasticidade/massa), permitindo estruturas mais leves e mais resistentes; capacidade de trabalho em altas temperaturas e, em alguns casos, propriedades criogênicas. Entretanto, elas apresentam algumas limitações que reduzem o seu espectro de aplicações, especialmente

The ionosphere impacts radio-wave propagation, notably up to a few GHz. The main applications impacted by the ionosphere are GNSS positioning and timing, Earth Observations (especially low frequency SAR missions e.g. BIOMASS, and GNSS-R), and Space Weather. While most effects can be compensated by using dual-frequency receivers and circular polarization antennas, ionospheric scintillation (rapid intensity and phase fluctuations) cannot. Climatological models for the mean stable part of the electron density in the ionospheric layers (e.g. IRI or NeQuick) or for the magnetic field (e.g. WMM) have significantly improved in the past years. However, models of the inhomogeneous part, responsible for scintillation, can be improved, since they are based on relatively old data (e.g. WBMOD), or climatological inputs are limited to properly characterize all latitudes and solar conditions (e.g. GISM or WAM). This study first assesses the goodness of GISM, the model adopted by the ITU-R, by comparing GISM predictions and measured scintillation data. Then, the impact of measured intensity and phase scintillation on TDS-1 GNSS-R data is illustrated.

Existing climatological ionosphere models, e.g. GISM, SCIONAV, WBMOD and STIPEE, have known limitations that prevent their wide use. In the framework of ESA study “Radio Climatolo-gy Models of the Ionosphere: Status and Way Forward” their performance was assessed using experimental observations of ionospheric scintillation collected over the past years to evaluate their ability to properly support future missions, and eventually indicate their weaknesses for fu-ture improvements. Model limitations are more important in terms of the intensity scintillation parameter (S4). To improve them, the COSMIC model has been fit (scaling factor and offset) to the measured data, and it became the one better predicting the intensity scintillation in a statistical sense.