Improved Receding Horizon Fourier Analysis for Quasi-periodic Signals

In this paper, an efficient short-time Fourier analysis method for the quasi-periodic signals is proposed via an optimal fixed-lag finite impulse response (FIR) smoother approach using a receding horizon scheme. In order to deal with time-varying Fourier coefficients (FCs) of quasi-periodic signals, a state space model including FCs as state variables is augmented with the variants of FCs. Through an optimal fixed-lag FIR smoother, FCs and their increments are estimated simultaneously and combined to produce final estimates. A lag size of the optimal fixed-lag FIR smoother is chosen to minimize the estimation error. Since the proposed estimation scheme carries out the correction process with the estimated variants of FCs, it is highly probable that the smaller estimation error is achieved compared with existing approaches not making use of such a process. It is shown through numerical simulation that the proposed scheme has better tracking ability for estimating time-varying FCs compared with existing ones.111Ysciescopuskc

Étude numérique de l'interaction des ondes de surface avec les cavités souterraines

L’effondrement des remblais routiers causé par le développement de cavités souterraines autour des ponceaux pose un risque majeur pour la sécurité des usagers et les installations à proximité. La détection de vides peu profonds est devenue l'une des missions récurrentes difficiles en génie civil à cause de la complexité de la réponse sismique d’un remblai routier en présence d’un ponceau et d’éventuelles cavités. Bien que les méthodes non intrusives basées sur les ondes de surface permettent d’estimer efficacement la vitesse des ondes de cisaillement des dépôts de sol, de nombreux défis sont rencontrés lorsqu'il s'agit de juger de la présence d'une inhomogénéité latérale locale en raison de la résolution limitée des approches géophysiques appliquées. Par conséquent, une étude numérique a été entreprise pour étudier la sensibilité des deux composantes des ondes de Rayleigh (la composante horizontale et la composante verticale désignées X et Z respectivement dans cette étude) et la seule composante des ondes de Love (désignée Y dans cette étude) à un contraste de rigidité (vide) dans différents contextes géologiques. Les accélérations des trois composants sont simulées au moyen du programme de modélisation numérique par éléments finis FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) pour différentes configurations de modèles en présence et en absence de cavité. Les données sismiques sont traitées avec la transformée de Stockwell généralisée (GST) dans le domaine temps-fréquence. Les résultats sont présentés sous forme des tomographies des courbes de dispersion des vitesses de groupe et de phase pour évaluer l'effet de la cavité et la localiser par rapport à la source. La signature de la cavité a également été étudiée à deux différentes profondeurs à partir du modèle parfaitement homogène. Les distributions de vitesse des trois composants ont révélé des changements négligeables après la création de la plus profonde cavité. Les observations numériques ont démontré que les vitesses de phase sont plus sensibles que la vitesse de groupe aux variations latérales de densité. De plus, on peut conclure que les trois composants ont révélé des distributions de vitesse de phase perceptibles et distinctes en présence d’un vide. La composante X s'est également avérée plus efficace pour localiser la cavité. Les résultats de cette étude numérique suggèrent l’acquisition des trois composantes lors des relevés sismiques sur terrain et d’intégrer simultanément ses trois composantes lors de l’analyse pour une plus grande fiabilité.Abstract : A road collapse caused by the development of near-surface cavities surrounding buried culverts poses a major hazard to road users’ safety and nearby facilities. The complexity of the road embankment seismic response has made it a challenging recurring mission in civil engineering to detect shallow voids. Although non-intrusive surface wave methods afford reliable shear wave velocity estimates of the subsurface materials, many challenges are encountered when judging the presence of a local lateral heterogeneity due to the limited resolution of the applied geophysical approaches. Therefore, a numerical study was conducted to investigate the sensitivity of the two Rayleigh waves components (the horizontal and vertical components, designed as X-component and Z-components, respectively in this study) and the only Love waves component (designed as Y-component in this study) to a contrast of rigidity (void) in different geological contexts. The accelerations of the three components are computed using a finite element commercial code FLAC3D (Fast Lagrangian Analysis of Continua in 3 Dimensions) for different model configurations both with and without a cavity. The seismic data are processed using the Generalized Stockwell transform (GST) in the time-frequency domain. To evaluate the effect of the cavity and locate it with respect to the source offset, the results are presented in the form of tomography maps and the group and phase velocity dispersion curve variations along the inspected array. The cavity signature was also studied at two depths relying on a perfectly homogeneous model. The velocity distribution change of the three components revealed minor changes after creating the deeper cavity. Moreover, the numerical observations demonstrated that the phase velocity is considerably more susceptible to lateral density variations than the group velocity. It was concluded that the three components revealed perceptible and distinct phase velocity changes in the presence of the void. The X-component was also found to be more effective in localizing the near and far boundaries of the cavity. The results of this numerical study suggest acquiring the three components during field seismic surveys and integrating the three components simultaneously during the analysis procedure for better efficiency

Radar Technology

In this book “Radar Technology”, the chapters are divided into four main topic areas: Topic area 1: “Radar Systems” consists of chapters which treat whole radar systems, environment and target functional chain. Topic area 2: “Radar Applications” shows various applications of radar systems, including meteorological radars, ground penetrating radars and glaciology. Topic area 3: “Radar Functional Chain and Signal Processing” describes several aspects of the radar signal processing. From parameter extraction, target detection over tracking and classification technologies. Topic area 4: “Radar Subsystems and Components” consists of design technology of radar subsystem components like antenna design or waveform design

Journal of Telecommunications and Information Technology, 2017, nr 3

kwartalni

Non-destructive evaluation of railway trackbed ballast

The “green agenda” combined with highway congestion has accelerated the demand for increased freight and passenger travel on the world’s railways. These increases have driven demand for more efficient and rapid investigation of trackbed ballast. Network Rail and other rail infrastructure operators spend significant financial sums on inspecting, tamping, adjusting, cleaning, and replacing trackbed ballast. Such maintenance is often to the detriment of normal network operation. Industry requires a method of ballast evaluation that is non-intrusive, cheap, can appraise long stretches of track in a short period of time, and give a fingerprinting result from which time-to-maintenance can be calculated and planned. Thus, the aim was to develop evaluation methods using non-destructive testing techniques. A 10-year old full-scale trackbed composed of variously fouled ballast was re-visited and used for experimentation. The condition of the ballast was calculated using the Ionescu Fouling Index. Earlier research at the University of Edinburgh enabled researchers worldwide to characterise ballast using ground penetrating radar (GPR). This research was repeated, validated and taken forward in a series of GPR experiments on the trackbed using a range of antennas from 500MHz to 2.6GHz. New "scatter" metrics were developed to determine ballast condition from the GPR waveforms. These metrics were then used to predict the Ionescu Fouling Index with a correlation coefficient greater than 0.9. One of the current approaches to evaluating the stiffness of railway ballast is to use a Falling Weight Deflectometer (FWD). The viability of using a Prima 100 mini-FWD on railways to measure stiffness was determined and deemed to be ineffective on ballast. The applicability of the impulse response technique on railways was determined. An instrumented hammer was used to excite the ballast, with a geophone measuring the response. The Frequency Response Function of this was successfully correlated with the Ionescu Fouling Index with a correlation coefficient also greater than 0.9. Finally, using GPR data and measured stiffness data collected by Banverket, Sweden, a numerical model to successfully relate radar responses to stiffness was developed

Real aperture synthetically organised radar

EThOS - Electronic Theses Online ServiceGBUnited Kingdo

Detection and quantification of permafrost change in alpine rock walls and implications for rock instability

The perennial presence of ice in permafrost rock walls alters thermal, hydraulic and mechanic properties of the rock mass. Temperature-related changes in both, rock mechanical properties (compressive and tensile strength of water-saturated rock) and ice mechanical properties (creep, fracture and cohesive properties) account for the internal mechanical destabilisation of permafrost rocks. Two hypothetical ice-/rock mechanical models were developed based on the principle of superposition. Failure along existing sliding planes is explained by the impact of temperature on shear stress uptake by creep deformation of ice, the propensity of failure along rock-ice fractures and reduced total friction along rough rock-rock contacts. This model may account for the rapid response of rockslides to warming (reaction time). In the long term, brittle fracture propagation is initialised. Warming reduces the shear stress uptake by total friction and decreases the critical fracture toughness along rock bridges. The latter model accounts for slow subcritical destabilisation of whole rock slopes over decades to millennia, subsequent to the warming impulse (relaxation time). To gain further understanding of thermal, hydraulic and mechanic properties of permafrost rocks, multidimensional and multi-temporal insights into the system are required. This Ph.D. adopted, modified and calibrated existing ERT (electrical resistivity tomography) techniques for the use in permafrost rocks. Laboratory analysis of electrical properties of eight rock samples from permafrost summits brought upon evidence that the general exponential temperature-resistivity relation, proposed by McGinnis (1973), is not applicable for frozen rocks, due to the effects of freezing in confined space. We found, that separate linear temperature-resistivity (T- ρ) approximation of unfrozen, supercooled and frozen behaviour offers a better explanation of the involved physics. Frozen T-ρ gradients approach 29.8 ±10.6 %/°C while unfrozen gradients were confirmed at 2.9 ±0.3 %/°C. Both increase with porosity. Path-dependent supercooling T-ρ behavior (3.3 ±2.3 %/°C) until the spontaneous freezing temperature -1.2 (±0.2) °C resembles unfrozen behavior. Spontaneous freezing subsequent to supercooling coincides with sudden self-induced temperature increases of 0.8 (±0.1) °C and resistivity increases of 2.9 (±1.4) kΩm. As temperature-resistivity gradients of frozen rocks are steep, temperature-referenced ERT with accuracies in the range of 1 °C is technically feasible in frozen rock. Technical design for field measurements in permafrost-affected bedrock was developed from 2005 to 2008 in consecutive measurements at a rock crest in the Swiss Alps (Steintaelli, 3150 m a.s.l., Matter Valley) and in a gallery along a north face in the German/ Austrian Alps (Zugspitze, 2800 m a.s.l.). 2D measurements in the Steintaelli along S-, NE-, NW- and Wfacing rock walls showed that ERT provides information on temporal and spatial patterns of thawing, refreezing, cleftwater flow and permafrost distribution in a decameter scale. Monthly, annual and multiannual data were compared using a time-lapse inversion technique and showed consistent results. Seasonal thaw at the Zugspitze was observed in February and monthly from May to October 2007 with high-resolution ERT (140 electrodes). An error model based on the measured offset of normal-reciprocal measurements was operated to empirically fit inherent error. A smoothness-constrained, error-controlled inversion routine (CRTomo) was applied to gain quantitatively reliable ERT data. Application of temperature-referenced laboratory data is consistent with temperature data observed in the adjacent borehole and with temperature logger data. Calculated temperature changes are in accordance with slow thermal conduction away from the rock surface and subsequent refreezing from the rock face in September/October. Smoothness-constrained, error-controlled inversion was transferred to pseudo-3D measurements collated from five 2D-transects with an offset of 4 m across a NE-SW facing ridge in the Steintaelli. In spite of the enormous topography, ERT transects were capable of resolving permafrost and thaw dynamics at the NE facing slope and along ice-filled crevices as well as disclosing unfrozen rock on the SW-facing rock slope. Consecutive measurements of 2006, 2007 and 2008 provide coherent results in line with temperature logger data. ERT measurements confirm that aspect is the most important control of permafrost distribution in rock walls, for a given altitude. At 3150 m a.sl., rock permafrost was found in NE-, NW- and E-facing rock walls in the Steintaelli but not in S-facing transects. Multiannual 3D data show that all NE-facing rock slopes still comprise decameter large permafrost bodies, but the 104.5 Ωm (31.6 kΩm) line which represents a definite transition to the –2 °C range is not reached in any of the transects apart from the surrounding of ice-filled clefts or at the surface. Semiconductive effects of centimetre to decimetre wide frozen fractures significantly cool ambient bedrock and have a dominant influence on the spatial distribution of permafrost under the crestline. Multiannual 2D data reveal that cleftwater inundation in two fracture systems can effectively prevent a decametre large rockwall from cooling below –1 °C (20 kΩm) during two years with permafrost aggradation (August 2005 to August 2007) in sheltered positions. An adjacent rockwall with similar surface characteristics but no hydraulic interconnectivity cooled significantly below –3 °C (> 60 kΩm) in the same time. Steep, highly dissected rock masses can create local permafrost occurrences of meter size even on SW-facing rock slopes. Seasonal thaw of rock permafrost occurs much faster than expected. Monthly measurements at the Zugspitze showed that maximum thaw depth in 2007 was already reached in July/August. In May, rapid warming of permafrost rocks with a resistivity increase equivalent to 1.5 °C warming and more was observed along a fracture zone with active cleftwater flows up to 30 m away from the rock face. Eighteen extensometer transects along the 3D-ERT array in the Steintaelli indicate that rock deformation on the permafrost-affected crest line and in the NE-facing slope is 3-4 times higher than in the non-perennially-frozen SW-facing slope. The velocity of rock displacements in late summer is 20 times higher than in all-season measurements. Velocities along a directly ERT-approved permafrost rock slope respond exponentially to mean air temperature during observation period with an R2; of 0.86. These findings support the hypothesised rapid sliding response to temperature change due to enhanced ice-creep and failure of ice in fractures

Science at the environmental research station Schneefernerhaus / Zugspitze

Das Buch enthält 22 Aufsätze, in denen die in der Forschungsstation Schneefernerhaus / Zugspitze aktiven Forscherinnen und Forscher ihre Arbeitsgebiete und bisherige Ergebnisse vorstellen. Die Aufsätze sind dabei so konzipiert, dass das Buch auch für die universitäre Lehre eingesetzt werden kann

Large scale dynamics of the atmosphere: Planetary waves

Planetary waves (PW) are global scale waves in the atmosphere, which are known to considerably impact weather patterns in the midlatitudes in the troposphere and the ozone distribution in the stratosphere. PW play an important role in coupling middle atmosphere dynamics. Due to the fact that climate change causes a decrease of the meridional temperature gradient, the strength of the zonal wind might decrease. This should, in turn, change the planetary wave activity (PWA). In order to quantify possible changes in the PWA we analyze ERA–Interim temperature data (10 m to 65 km height) on the Northern Hemisphere and calculate the so-called dynamical activity index (DAI) as measure for the PWA. We analyze the PWA to find indications for PWA changes and variability. We also use rotational temperature data from hydroxyl airglow measurements at UFS Schneefernerhaus (Germany) embedded in the international Network for the Detection of Mesospheric Change (NDMC) in the upper mesosphere/lower thermosphere (UMLT). We find an indication for a significant increase of the PWA in the stratosphere. The change of the PWA with higher zonal wavenumbers turns out to be strongest. This finding is in agreement with the expectation that a weakening of the meridional temperature gradient leads to improved vertical propagation conditions for planetary waves. With the empirical mode decomposition (EMD) we are able to extract non-stationary signals of the PWA time series. We further find that longer-term oscillations (QBO, ENSO and solar cycles) have a noticeable impact on the PW variability in all considered heights. Next to the 11-year cycle that is related to the sunspot-cycle in many studies, we also find a pronounced quasi-22-year signal. We tentatively interpret this signal as being due to the solar-magnetic-field (“Hale cycle”)