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Journal articles on the topic 'Polarisation horizontale'
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1
Aubert, M. "La méthode de polarisation spontanée en hydrogéologie des terrains volcaniques." Revue des sciences de l'eau 16, no. 2 (April 12, 2005): 219–35. http://dx.doi.org/10.7202/705505ar.
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En terrain volcanique, les eaux de pluie s'infiltrent jusqu'à leur rencontre avec un niveau imperméable qui correspond le plus souvent au socle cristallin. Ce sont les talwegs et les lignes de crête des paléo- reliefs de ce socle dont la profondeur peut dépasser la centaine de mètres qu'il convient de détecter, parfois avec une précision décamétrique. La méthode géophysique la plus utilisée en hydrogéologie des terrains volcaniques est la prospection électrique qui fournit des coupes verticales des résistivités électriques. La morphologie du substratum imperméable ou saturé peut aussi être obtenue en mesurant en surface les potentiels électriques de polarisation spontanée (en abrégé PS) qui se forment par la percolation de l'eau infiltrée dans le terrain poreux. La base de la zone non saturée, appelée surface SPS, est calculée par une relation faisant intervenir les données PS, les altitudes et deux coefficients définis à partir des données géologiques. Cette surface indique directement les axes de circulation et les lignes de partage des eaux. Deux exemples pris sur des sites bien documentés montrent la validité de la méthode pour localiser les axes de circulation de l'eau souterraine et les limites entre bassins versants. Un troisième exemple montre les résultats PS comparés à ceux des méthodes électromagnétiques VLF et AMT. La méthode PS est légère et offre une bonne précision horizontale, mais elle demande au moins un forage d'étalonnage pour préciser la profondeur des interfaces.
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Gahé, Emile, Michel Allard, and Maurice K.-Seguin. "Géophysique et dynamique holocène de plateaux palsiques à Kangiqsualujjuaq, Québec nordique." Géographie physique et Quaternaire 41, no. 1 (December 18, 2007): 33–46. http://dx.doi.org/10.7202/032663ar.
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RÉSUMÉ Les plateaux palsiques étudiés sont localisés dans une vallée près de Kangiqsualujjuaq, le long de l'estuaire du George, à quelque 15 km du littoral de la baie d'Ungava. Le tond de la vallée a émergé des eaux de la mer D'Iberville et a été occupé par un lac avant 5400 BP. Une tourbière a commencé à se développer et à progresser au détriment du lac il y a environ 4500-4300 BP. L'aggradation du pergélisol près du lac actuel, au centre de la vallée, a eu lieu vers 1800-1600 BP; le soulèvement gélival a été plus tardif en bordure du plateau palsique, soit vers 800 BP. Selon les méthodes géophysiques employées en surface et dans les trous de forage (résistivité électrique, polarisation provoquée, polarisation spontanée et électromagnétisme), l'épaisseur du mollisol varie de 30 à 80 cm et celle du pergéiisol, de 3,5 m à plus de 15 m. On note également la présence de taliks sous les dépressions topographiques qui percent le plateau. La méthode de calométrie in situ et les mesures de la teneur en eau avec une sonde à neutron ont permis de déterminer la composition du mollisol et du pergéiisol. L'utilisation de toutes ces méthodes sur le même site donne une connaissance précise des propriétés physiques du milieu et une bonne perception de l'extension verticale et horizontale du pergéiisol. Le concept de morcellement des plateaux palsiques en palses isolées le long de « lignes de fusion » dans le pergéiisol est appuyé par les résultats des méthodes d'investigation électriques.
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Eriksson, P., B. Rydberg, and S. A. Buehler. "On cloud ice induced absorption and polarisation effects in microwave limb sounding." Atmospheric Measurement Techniques 4, no. 6 (June 30, 2011): 1305–18. http://dx.doi.org/10.5194/amt-4-1305-2011.
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Abstract. Microwave limb sounding in the presence of ice clouds was studied by detailed simulations, where clouds and other atmospheric variables varied in three dimensions and the full polarisation state was considered. Scattering particles were assumed to be horizontally aligned oblate spheroids with a size distribution parameterized in terms of temperature and ice water content. A general finding was that particle absorption is significant for limb sounding, which is in contrast to the down-looking case, where it is usually insignificant. Another general finding was that single scattering can be assumed for cloud optical paths below about 0.1, which is thus an important threshold with respect to the complexity and accuracy of retrieval algorithms. The representation of particle sizes during the retrieval is also discussed. Concerning polarisation, specific findings were as follows: Firstly, no significant degree of circular polarisation was found for the considered particle type. Secondly, for the ±45° polarisation components, differences of up to 4 K in brightness temperature were found, but differences were much smaller when single scattering conditions applied. Thirdly, the vertically polarised component has the smallest cloud extinction. An important goal of the study was to derive recommendations for future limb sounding instruments, particularly concerning their polarisation setup. If ice water content is among the retrieval targets (and not just trace gas mixing ratios), then the simulations show that it should be best to observe any of the ±45° and circularly polarised components. These pairs of orthogonal components also make it easier to combine information measured from different positions and with different polarisations.
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Hallgren, K., P. Hartogh, and C. Jarchow. "A new microwave spectrometer for ground-based observations of water vapour." Atmospheric Measurement Techniques Discussions 6, no. 3 (May 27, 2013): 4677–703. http://dx.doi.org/10.5194/amtd-6-4677-2013.
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Abstract. We have developed a new, high time-resolution, microwave heterodyne spectrometer for observations of water vapour in the middle atmosphere. It measures the rotational transition of water vapour at 22.235 GHz in the vertical and horizontal polarisation. The two polarisations are averaged in order to optimise the signal-to-noise ratio. The different polarisations have separate, but identical, signal chains consisting of a 22 GHz cooled HEMT amplifier, a second, warm, 22 GHz HEMT booster amplifier, an IF stage and a Chirp Transform Spectrometer (CTS) backend. Continuous calibration with two internal loads kept at temperatures close to the observed atmosphere, a wobbling optical table to reduce standing waves in the optical path and the low receiver temperature ensures a time resolution of an order of magnitude better than what has been achieved by earlier instruments. The error sources in the retrieved spectrum are discussed and the data is compared and validated against EOS-MLS on the NASA Aura satellite. The profiles are found to be in good agreement with each other.
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Eriksson, P., and B. Rydberg. "On cloud ice induced absorption and polarisation effects in microwave limb sounding." Atmospheric Measurement Techniques Discussions 4, no. 2 (March 2, 2011): 1493–531. http://dx.doi.org/10.5194/amtd-4-1493-2011.
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Abstract. Detailed simulations of microwave limb sounding in the presence of ice clouds have been performed. It is clarified that, while particle absorption normally gives no significant change of the measured radiance for down-looking measurements, this is not the case for limb sounding. The particles were treated as horizontally aligned oblate spheroids and for this assumption on particle shape, and comparable situations, no significant degree of circular polarisation is generated. Differences between the brightness temperature of the ±45° polarisation components up to 4 K were found, but this difference appears to be small as long as single scattering conditions apply. The cloud extinction is the smallest for the vertically polarised component, but it should be more beneficial to observe any of the ±45° and circularly polarised components if ice water content is also a target of the retrievals. These latter pairs of orthogonal components also make it easier to combine information measured from different positions and with different polarisations. The results indicate that single scattering can be assumed for cloud optical thicknesses below about 0.1, which is thus an important threshold with respect to the complexity and accuracy of retrievals. The representation of particle sizes during the retrieval is discussed.
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Scharien, R. K., K. Hochheim, J. Landy, and D. G. Barber. "First-year sea ice melt pond fraction estimation from dual-polarisation C-band SAR – Part 2: Scaling in situ to Radarsat-2." Cryosphere 8, no. 6 (November 25, 2014): 2163–76. http://dx.doi.org/10.5194/tc-8-2163-2014.
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Abstract. Sea ice melt pond fraction (fp), linked with lower sea ice surface albedo and increased light transmittance to the ocean, is inadequately parameterised in sea ice models due to a lack of observations. In this paper, results from a multi-scale remote-sensing program dedicated to the retrieval of level first-year sea ice (FYI) fp from dual co- and cross-polarisation C-band synthetic aperture radar (SAR) backscatter are detailed. Models which utilise the dominant effect of free-water melt ponds on the VV / HH (vertical transmit and vertical receive / horizontal transmit and horizontal receive) polarisation ratio at high incidence angles are tested for their ability to provide estimates of the subscale fp. Retrieved fp from noise-corrected Radarsat-2 quad-polarisation scenes are in good agreement with observations from coincident aerial survey data, with root mean square errors (RMSEs) of 0.05–0.07 obtained during intermediate and late stages of ponding. Weak model performance is attributed to the presence of wet snow and slush during initial ponding, and a synoptically driven freezing event causing ice lids to form on ponds. The HV / HH (horizontal transmit and vertical receive / horizontal transmit and horizontal receive) ratio explains a greater portion of variability in fp, compared to VV / HH, when ice lids are present. Generally low HV channel intensity suggests limited applications using dual cross-polarisation data, except with systems that have exceptionally low noise floors. Results demonstrate the overall potential of dual-polarisation SAR for standalone or complementary observations of fp for process-scale studies and improvements to model parameterisations.
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Scharien, R. K., J. Landy, and D. G. Barber. "First-year sea ice melt pond fraction estimation from dual-polarisation C-band SAR – Part 1: In situ observations." Cryosphere 8, no. 6 (November 25, 2014): 2147–62. http://dx.doi.org/10.5194/tc-8-2147-2014.
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Abstract. Understanding the evolution of melt ponds on Arctic sea ice is important for climate model parameterisations, weather forecast models and process studies involving mass, energy and biogeochemical exchanges across the ocean–sea ice–atmosphere interface. A field campaign was conducted in a region of level first-year sea ice (FYI) in the central Canadian Arctic Archipelago (CAA), during the summer of 2012, to examine the potential for estimating melt pond fraction (fp) from satellite synthetic aperture radar (SAR). In this study, 5.5 GHz (C-band) dual co- (HH + VV – horizontal transmit and horizontal receive + vertical transmit and vertical receive) and cross-polarisation (HV + HH – horizontal transmit and vertical receive + horizontal transmit and horizontal receive) radar scatterometer measurements of melt-pond-covered FYI are combined with ice and pond properties to analyse the effects of in situ physical and morphological changes on backscatter parameters. Surface roughness statistics of ice and ponds are characterised and compared to the validity domains of the Bragg and integral equation model (IEM) scattering models. Experimental and model results are used to outline the potential and limitations of the co-polarisation ratio (VV / HH) for retrieving melt pond information, including fp, at large incidence angles (≥35°). Despite high variability in cross-polarisation ratio (HV / HH) magnitudes, increases at small incidence angles (<30°) are attributed to the formation of ice lids on ponds. Implications of the results for pond information retrievals from satellite C-, L- and P-band SARs are discussed.
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Parkyn, D. C., and C. W. Hawryshyn. "Spectral and ultraviolet-polarisation sensitivity in juvenile salmonids: a comparative analysis using electrophysiology." Journal of Experimental Biology 203, no. 7 (April 1, 2000): 1173–91. http://dx.doi.org/10.1242/jeb.203.7.1173.
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Spectral and polarisation sensitivity were compared among juvenile (parr) rainbow trout (Oncorhynchus mykiss), steelhead (O. mykiss), cutthroat trout (O. clarki clarki), kokanee (O. nerka) and brook char (Salvelinus fontinalis) using multi-unit recording from the optic nerve. Although reared under the same conditions, differences in photopic spectral sensitivity were evident. Specifically, ON-responses were co-dominated by L- and M-cone mechanisms in all fish except O. nerka, consistent with an M-cone mechanism sensitivity. The sensitivity of OFF-responses was dominated by the M-cone mechanism for all fish, but O. mykiss appeared to show an additional contribution from the L-cone mechanism. Using chromatic adaptation, an independent ultraviolet-sensitive mechanism is described for the first time for the salmonid genus Salvelinus. In addition, this ultraviolet-cone mechanism was present in the members of the genus Oncorhynchus that were examined. Thus, ultraviolet sensitivity appears to be common to the major extant clades of the subfamily Salmoninae. All species showed differential sensitivity to both vertical and horizontal linearly polarised light. This sensitivity differed between ON- and OFF-responses. The ON-responses were maximally sensitive to both vertically and horizontally polarised light, whereas the OFF-responses displayed maximal sensitivity to horizontally polarised light in all species, with reduced sensitivity to vertically polarised light compared with ON-responses. Because of the similarity in the physiological characteristics of polarisation sensitivity among the salmonid species examined, no relationship between the degree of migratory tendency and the ability to detect polarised light could be identified.
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Kelber, Almut, Christel Thunell, and Kentaro Arikawa. "Polarisation-dependent colour vision inPapiliobutterflies." Journal of Experimental Biology 204, no. 14 (July 15, 2001): 2469–80. http://dx.doi.org/10.1242/jeb.204.14.2469.
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SUMMARYButterflies of the genus Papilio have polarisation-sensitive photoreceptors in all regions of the eye, and different spectral types of receptor are sensitive to different e-vector orientations. We have studied the consequences of this eye design for colour vision in behavioural tests and find that Papilio spp. see false colours due to the polarisation of light. They discriminate between vertically and horizontally polarised light of the same colour in the contexts of oviposition and feeding. The discrimination depends on the spectral composition of the stimuli. In the blue and probably in the green range, discrimination does not depend on intensity. However, colour discrimination is influenced by polarisation. Thus, colour and polarisation processing are not separated in the visual system of Papilio spp. From these results, we propose hypotheses about which photoreceptors contribute to colour vision in Papilio spp. and what adaptational value such a system might have for the butterflies. Finally, we give examples for other eyes that have a similar structure.
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Maaß, N., L. Kaleschke, X. Tian-Kunze, and M. Drusch. "Snow thickness retrieval over thick Arctic sea ice using SMOS satellite data." Cryosphere 7, no. 6 (December 20, 2013): 1971–89. http://dx.doi.org/10.5194/tc-7-1971-2013.
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Abstract. The microwave interferometric radiometer of the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission measures at a frequency of 1.4 GHz in the L-band. In contrast to other microwave satellites, low frequency measurements in L-band have a large penetration depth in sea ice and thus contain information on the ice thickness. Previous ice thickness retrievals have neglected a snow layer on top of the ice. Here, we implement a snow layer in our emission model and investigate how snow influences L-band brightness temperatures and whether it is possible to retrieve snow thickness over thick Arctic sea ice from SMOS data. We find that the brightness temperatures above snow-covered sea ice are higher than above bare sea ice and that horizontal polarisation is more affected by the snow layer than vertical polarisation. In accordance with our theoretical investigations, the root mean square deviation between simulated and observed horizontally polarised brightness temperatures decreases from 20.9 K to 4.7 K, when we include the snow layer in the simulations. Although dry snow is almost transparent in L-band, we find brightness temperatures to increase with increasing snow thickness under cold Arctic conditions. The brightness temperatures' dependence on snow thickness can be explained by the thermal insulation of snow and its dependence on the snow layer thickness. This temperature effect allows us to retrieve snow thickness over thick sea ice. For the best simulation scenario and snow thicknesses up to 35 cm, the average snow thickness retrieved from horizontally polarised SMOS brightness temperatures agrees within 0.1 cm with the average snow thickness measured during the IceBridge flight campaign in the Arctic in spring 2012. The corresponding root mean square deviation is 5.5 cm, and the coefficient of determination is r2 = 0.58.
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Maaß, N., L. Kaleschke, X. Tian-Kunze, and M. Drusch. "Snow thickness retrieval over thick Arctic sea ice using SMOS satellite data." Cryosphere Discussions 7, no. 4 (July 23, 2013): 3627–74. http://dx.doi.org/10.5194/tcd-7-3627-2013.
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Abstract. The microwave interferometric radiometer of the European Space Agency's Soil Moisture and Ocean Salinity (SMOS) mission measures at a frequency of 1.4 GHz in the L-band. In contrast to other microwave satellites, low frequency measurements in L-band have a large penetration depth in sea ice and thus contain information on the ice thickness. Previous ice thickness retrievals have neglected a snow layer on top of the ice. Here, we implement a snow layer in our emission model and investigate how snow influences L-band brightness temperatures and whether it is possible to retrieve snow thickness over thick Arctic sea ice from SMOS data. We find that the brightness temperatures above snow-covered sea ice are higher than above bare sea ice and that horizontal polarisation is more affected by the snow layer than vertical polarisation. In accordance with our theoretical investigations, the root mean square deviation between simulated and observed horizontally polarised brightness temperatures decreases from 20.0 K to 4.4 K, when we include the snow layer in the simulations. Under cold Arctic conditions we find brightness temperatures to increase with increasing snow thickness. Because dry snow is almost transparent in L-band, this brightness temperature's dependence on snow thickness origins from the thermal insulation of snow and its dependence on the snow layer thickness. This temperature effect allows us to retrieve snow thickness over thick sea ice. For the best simulation scenario and snow thicknesses up to 35 cm, the average snow thickness retrieved from horizontally polarised SMOS brightness temperatures agrees within 0.7 cm with the average snow thickness measured during the IceBridge flight campaign in the Arctic in spring 2012. The corresponding root mean square deviation is 6.3 cm, and the correlation coefficient is r2 = 0.55.
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Ram Krishna, R. V. S., and R. Kumar. "Slotted ground microstrip antenna with FSS reflector for high‐gain horizontal polarisation." Electronics Letters 51, no. 8 (April 2015): 599–600. http://dx.doi.org/10.1049/el.2015.0339.
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Otto, T., and M. Chandra. "On the statistics of differential phases in C-band weather radar." Advances in Radio Science 5 (June 13, 2007): 447–50. http://dx.doi.org/10.5194/ars-5-447-2007.
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Abstract. Differential phases open a new parameter in polarimetric weather radar data analysis. In polarimetric S-matrices measured at the linear polarisation bases (vertical and horizontal) there exist basically three differential phases namely the differential propagation phase and two co-to-crosspolar phases. In this paper we shall investigate the statistics of differential propagation phase and co-to-crosspolar phases in weather radar data recorded with the C-band weather radar of DLR, Wessling.
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Kochukhov, O., M. Shultz, and C. Neiner. "Magnetic field topologies of the bright, weak-field Ap stars θ Aurigae andεUrsae Majoris." Astronomy & Astrophysics 621 (January 2019): A47. http://dx.doi.org/10.1051/0004-6361/201834279.
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Context.The brightest magnetic chemically peculiar stars θ Aur andεUMa were targeted by numerous studies of their photometric and spectroscopic variability. Detailed maps of chemical abundance spots were repeatedly derived for both stars. However, owing to the weakness of their surface magnetic fields, very little information on the magnetic field geometries of these stars is available.Aims.In this study we aim to determine detailed magnetic field topologies of θ Aur andεUMa based on modern, high-resolution spectropolarimetric observations.Methods.Both targets were observed in all four Stokes parameters using the Narval and ESPaDOnS spectropolarimeters. A multi-line technique of least-squares deconvolution was employed to detect polarisation signatures in spectral lines. These signatures were modelled with a Zeeman-Doppler imaging code.Results.We succeed in detecting variable circular and linear polarisation signatures for θ Aur. Only circular polarisation was detected forεUMa. We obtain new sets of high-precision longitudinal magnetic field measurements using mean circular polarisation metal line profiles as well as hydrogen line cores, which are consistent with historical data. Magnetic inversions revealed distorted dipolar geometries in both stars. The Fe and Cr abundance distributions, reconstructed simultaneously with magnetic mapping, do not show a clear correlation with the local magnetic field properties, with the exception of a relative element underabundance in the horizontal field regions along the magnetic equators.Conclusions.Our study provides the first ever detailed surface magnetic field maps for broad-line, weak-field chemically peculiar stars, showing that their field topologies are qualitatively similar to those found in stronger field stars. The Fe and Cr chemical abundance maps reconstructed for θ Aur andεUMa are at odds with the predictions of current theoretical atomic diffusion calculations.
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Granet, Michel, Sebastien Judenherc, and Annie Souriau. "Des images du systeme lithosphere-asthenosphere sous la France et leurs implications geodynamiques; l'apport de la tomographie telesismique et de l'anisotropie sismique." Bulletin de la Société Géologique de France 171, no. 2 (March 1, 2000): 149–67. http://dx.doi.org/10.2113/171.2.149.
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Abstract From seismic tomography and seismic anisotropy, images of the lithosphere-asthenosphere system beneath France for some remarkable tectonic areas have been computed : a continental rift system (the Upper Rhinegraben), an Hercynian structure reactivated by Neogene volcanism (Massif central), a region of a recent continental collision (Pyrenees) and finally a region of an ancient orogeny (Armorican Massif). These images have a horizontal spatial resolution of the order of 10 km and show not only the geometry of the deep geological structures but will also illustrate the link between surface observations and structures detected at depth. The images demonstrate the passive character of the Rhinegraben mainly because no low-velocity was found below the Moho, show the presence of a thermal anomaly beneath the Massif central interpreted as caused by a mantle plume in the decaying phase of its evolution and prove the lithospheric scale of the North Pyrenean fault and of the South-Armorican shear zone. The anisotropic measurements suggest a lithospheric deformation related to the most recent tectonic event. In the Pyrenees, the Armorican Massif or the Rhinegraben areas, the directions of the fast-polarisation azimuth (the polarisation direction of the fast shear wave) are parallel to the tectonic texture of the last events, but suggest also a reactivation of inherited Hercynian discontinuities. In the Massif central, the splitting parameters distinguish between two lithospheric units regions marked by a distinct fast-polarisation azimuth on each side of the Sillon Houiller fault zone.
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Hendrick, N., and S. Hearn. "VECTOR WAVEFIELD-SEPARATION TECHNIQUES FOR IMPROVED MULTI-COMPONENT SEISMIC EXPLORATION." APPEA Journal 42, no. 1 (2002): 613. http://dx.doi.org/10.1071/aj01037.
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Analysis of multi-component seismic data commonly involves scalar processing of the vertical component to provide a conventional P-wave image, and scalar processing of the horizontal component(s) to yield an Swave image. A number of convincing examples now exist where such S-wave imagery has significantly enhanced hydrocarbon exploration.There is potential to achieve cleaner P- and S-wave images by more fully exploiting the true vector nature of multi-component reflection data. The simplest form of vector analysis, termed polarisation analysis, allows identification of different wave types. It does not, however, generally lead to effective wavefield separation, due to significant interference between the different waves in a typical exploration-seismic recording.More effective vector separation is possible if the particle-motion information from polarisation analysis is coupled with the more familiar tools of frequency and velocity filtering. Three related separation algorithms, termed MUSIC, IWSA and PIM are considered here. These techniques all utilise a parametric approach whereby wavefield slowness and polarisation are modelled simultaneously in the frequency domain.Synthetic and ocean-bottom cable examples are used to demonstrate practical issues relating to the use of these tools. The PIM algorithm is considered to be the most generally useful of the three multi-component wavefield separation algorithms. Implementation of these tools in a highly automated production environment is considered non-trivial. Hence, it is envisaged that such vector separation schemes will have most application for specialised data processing over identified target zones. Vector wavefield separation has the potential to amplify the considerable success already achieved with integrated P- and S-wave exploration.
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Champollion, N., G. Picard, L. Arnaud, E. Lefebvre, and M. Fily. "Hoar crystal development and disappearance at Dome C, Antarctica: observation by near-infrared photography and passive microwave satellite." Cryosphere 7, no. 4 (August 8, 2013): 1247–62. http://dx.doi.org/10.5194/tc-7-1247-2013.
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Abstract. Hoar crystals episodically cover the snow surface in Antarctica and affect the roughness and reflective properties of the air–snow interface. However, little is known about their evolution and the processes responsible for their development and disappearance despite a probable influence on the surface mass balance and energy budget. To investigate hoar evolution, we use continuous observations of the surface by in situ near-infrared photography and by passive microwave remote sensing at Dome C in Antarctica. From the photography data, we retrieved a daily indicator of the presence/absence of hoar crystals using a texture analysis algorithm. The analysis of this 2 yr long time series shows that Dome C surface is covered almost half of the time by hoar. The development of hoar crystals takes a few days and seems to occur whatever the meteorological conditions. In contrast, the disappearance of hoar is rapid (a few hours) and coincident with either strong winds or with moderate winds associated with a change in wind direction from southwest (the prevailing direction) to southeast. From the microwave satellite data, we computed the polarisation ratio (i.e. horizontal over vertical polarised brightness temperatures), an indicator known to be sensitive to hoar in Greenland. Photography data and microwave polarisation ratio are correlated, i.e. high values of polarisation ratio which theoretically correspond to low snow density values near the surface are associated with the presence of hoar crystals in the photography data. Satellite data over nearly ten years (2002–2011) confirm that a strong decrease of the polarisation ratio (i.e. signature of hoar disappearance) is associated with an increase of wind speed or a change in wind direction from the prevailing direction. The photography data provides, in addition, evidence of interactions between hoar and snowfall. Further adding the combined influence of wind speed and wind direction results in a complex picture of the snow–atmosphere interactions in Antarctica which deserves further quantification and modelling.
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Champollion, N., G. Picard, L. Arnaud, E. Lefebvre, and M. Fily. "Hoar crystal development and disappearance at Dome C, Antarctica: observation by near-infrared photography and passive microwave satellite." Cryosphere Discussions 7, no. 1 (January 10, 2013): 175–217. http://dx.doi.org/10.5194/tcd-7-175-2013.
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Abstract. Hoar crystals episodically cover the snow surface in Antarctica and affect the roughness and reflective properties of the air-snow interface. However, little is known about their evolution and the processes responsible for their development and disappearance despite a probable influence on the surface mass balance and energy budget. To investigate hoar evolution, we use continuous observations of the surface by in-situ near-infrared photography and by passive microwave remote sensing at Dome C in Antarctica. From the photography data, we retrieved a daily indicator of the presence/absence of hoar crystals using a texture analysis algorithm. The analysis of this 2-yr long time series shows that Dome C surface is covered almost half of the time by hoar. The development of hoar crystals takes a few days and seems to occur whatever the meteorological conditions. In contrast, the disappearance of hoar is rapid (a few hours) and coincident with either strong winds or with moderate winds associated with a change in wind direction from Southwest (the prevailing direction) to Southeast. From the microwave satellite data, we computed the polarisation ratio (i.e. horizontal over vertical polarised brightness temperatures), an indicator known to be sensitive to hoar in Greenland. Photography data and microwave polarisation ratio are correlated, i.e. high values of polarisation ratio which theoretically correspond to low snow density values near the surface are associated with the presence of hoar crystals in the photography data. Satellite data over nearly ten years (2002–2011) confirm that a strong decrease of the polarisation ratio (i.e. signature of hoar disappearance) is associated with an increase of wind speed or a change in wind direction from the prevailing direction. The photography data provides, in addition, evidence of interactions between hoar and snowfall. Further adding the combined influence of wind speed and wind direction results in a complex picture of the snow-atmosphere interactions in Antarctica which deserves further quantification and modelling.
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Steinert, J., and M. Chandra. "Cloud physical properties and empirical polarimetric measurements of rain signatures at C-Band." Advances in Radio Science 6 (May 27, 2008): 315–18. http://dx.doi.org/10.5194/ars-6-315-2008.
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Abstract. Raindrops are one type of precipitation in stratiform and convective clouds. To get relationships for describing the raindrops two different methods were used. In the first way, the microphysical properties of the liquid hydrometeors were examined. For this the use of the Rayleigh approximation for small particles (raindrops at C-Band) and the drop size distribution by Ulbrich (Γ-DSD) lead to the calculation of the reflectivity at horizontal polarisation ZHH, the reflectivity at vertical polarisation ZVV and the differential reflectivity ZDR. In the second way, rain signatures were separated from polarimetric measurements. The database of these measurements consists of datasets measured by the dual polarimetric C-Band weather radar POLDIRAD (DLR, Oberpfaffenhofen). The aim of this study was then to combine and to compare the results from the real radar measurements against the theoretical calculations in the ZHH-ZDR plane. Based on these observations and calculations, scientific results for future practical use will be presented in form of empirical equations including ZHH-ZDR. Finally in form of scientific discussion, the ZHH-ZDR plane will be critically assessed for outstanding problems or issues.
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Del Gaudio, V., J. Wasowski, and S. Muscillo. "New developments in ambient noise analysis to characterise the seismic response of landslide prone slopes." Natural Hazards and Earth System Sciences Discussions 1, no. 2 (April 17, 2013): 1319–53. http://dx.doi.org/10.5194/nhessd-1-1319-2013.
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Abstract. We report on new developments in the application of ambient noise analysis applied to investigate the dynamic response of landslide prone slopes to seismic shaking with special attention to the directional resonance phenomena recognised in previous studies. Investigations relying on the calculation of horizontal-to-vertical noise spectral ratio (HVNR) were carried out in the area of Caramanico Terme (central Italy) where an ongoing accelerometer monitoring on slopes with different characteristics offers the possibility of validation of HVNR analysis. The noise measurements, carried out in different times to test the result repeatability, revealed that sites affected by response directivity persistently show major peaks with a common orientation consistent with the resonance direction inferred from accelerometer data. At sites where directivity is absent, the HVNR peaks do not generally show a preferential orientation, with rare exceptions that could be linked to the presence of temporarily active sources of polarised noise. The observed spectral ratio amplitude variations can be related to temporal changes in site conditions, which can hinder the recognition of main resonance frequencies. Therefore, it is recommended to conduct simultaneous measurements at nearby sites within the same study area and to repeat measurements at different times in order to distinguish significant systematic polarisation caused by site specific response directivity from polarisation controlled by properties of noise sources. Furthermore, an analysis of persistence in noise recordings of signals with systematic directivity showed that only a~portion of recordings contains wave trains having a clear polarisation representative of site directional resonance. Thus a careful selection of signals for HVNR analysis is needed for a correct characterisation of site directional properties.
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Steinert, J., and M. Chandra. "Classification of ice crystals at C-band." Advances in Radio Science 7 (May 19, 2009): 273–77. http://dx.doi.org/10.5194/ars-7-273-2009.
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Abstract. Clouds consist of water particles (hydrometeors) in different aggregate states. Above the melting layer these hydrometeors are formed mainly as ice crystals and other completely or partly frozen particles. With measurements from the C-band dual polarimetric radar POLDIRAD (Oberpfaffenhofen, Germany) the backscattered signals of the ice particles in the horizontal/vertical polarisation base were analysed. The focus is lying on the co-polar reflectivities and therefore the differential reflectivity. In the next step a simulation of the backscattered signals deliver the physical ansatz for the creation of an ice crystal class. Finally the comparison of this class with a raindrop classification is shown.
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Del Gaudio, V., J. Wasowski, and S. Muscillo. "New developments in ambient noise analysis to characterise the seismic response of landslide-prone slopes." Natural Hazards and Earth System Sciences 13, no. 8 (August 20, 2013): 2075–87. http://dx.doi.org/10.5194/nhess-13-2075-2013.
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Abstract. We report on new developments in the application of ambient noise analysis applied to investigate the dynamic response of landslide-prone slopes to seismic shaking, with special attention to the directional resonance phenomena recognised in previous studies. These phenomena can be relevant for seismic slope susceptibility, especially when maximum resonance orientation is close to potential sliding directions. Therefore, the implementation of an effective technique for site response directivity detection is of general interest. In this regard methods based on the calculation of horizontal-to-vertical noise spectral ratio (HVNR) are promising. The applicability of such methods is investigated in the area of Caramanico Terme (central Italy), where ongoing accelerometer monitoring of slopes with different characteristics offers the possibility of validation of HVNR analysis. The noise measurements, carried out in different times to test the result repeatability, revealed that sites affected by response directivity persistently show major peaks with a common orientation, consistent with the resonance direction inferred from accelerometer data. In some cases such a directivity turned out parallel to maximum slope direction, but this cannot be considered a systematic feature of slope dynamic response. At sites where directivity is absent, the HVNR peaks do not generally show a preferential orientation, with rare exceptions that could be linked to the presence of temporarily active sources of polarised noise. The observed variations of spectral ratio amplitude can be related to temporal changes in site conditions (e.g. groundwater level/soil water content variations affecting P wave velocity and Poisson's ratio of surficial layer), which can hinder the recognition of main resonance frequencies. Therefore, we recommend conducting simultaneous measurements at nearby sites within the same study area and repeating measurements at different times in order to distinguish significant systematic polarisation caused by site-specific response directivity from polarisation controlled by properties of noise sources. Furthermore, an analysis of persistence in noise recordings of signals with systematic directivity showed that only a portion of recordings contains wave trains having a clear polarisation representative of site directional resonance. Thus a careful selection of signals for HVNR analysis is needed for a correct characterisation of site directional properties.
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Hassan, Bilal, Stephen D. Butt, and Charles A. Hurich. "Geotechnical Site Investigation Using S-waves with Implications for Ground Motion Analysis." Materials and Geoenvironment 64, no. 4 (December 1, 2017): 205–19. http://dx.doi.org/10.1515/rmzmag-2017-0018.
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AbstractEvaluation results of shear wave attenuation-based ground motion restricted by fracture orientation and rheology, from among those of an extended experimental study, are presented herein. The issues of competence of fractured bedrock dynamically disturbed multilaterally are assessed. Disturbance is primarily modelled by Sh and Sv stimulation, given fracture orientation, while subjected to direct fracture stress regime conditions varying in time. Hence, directionalities of polarisation and stress are taken into consideration simultaneously following simple site-specific non-erodetic approach. Comparison of spectral curves and spectral ratio curves of attenuation with respect to variations of direction and stress emphasise the amplification of the ‘seismic response’ in one direction compared to the other, i.e. vertical vs. horizontal, in terms of weighing possibilities of or predicting structural integrity against failure. The composite analyses of multiple spectral curves not only enable determination of the orientation of the fracture set/s in space but also allow inferring the nature of more amplified response perpendicular to the crack surface compared to that of a response parallel to the crack surface.
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Chai, Shui‐Rong, Li‐Xin Guo, and Rui Wang. "PO–PO method for electromagnetic backscattering from a 2D arbitrary dielectric‐coated conducting target located above a 1D randomly rough surface: horizontal polarisation." IET Microwaves, Antennas & Propagation 8, no. 15 (December 2014): 1340–47. http://dx.doi.org/10.1049/iet-map.2014.0139.
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Murabito, Mariarita, Juie Shetye, Marco Stangalini, Erwin Verwichte, Tony Arber, Ilaria Ermolli, Fabrizio Giorgi, and Tom Goffrey. "Unveiling the magnetic nature of chromospheric vortices." Astronomy & Astrophysics 639 (July 2020): A59. http://dx.doi.org/10.1051/0004-6361/202038360.
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Context. Vortex structures in the Sun’s chromosphere are believed to channel energy between different layers of the solar atmosphere. Aims. We investigate the nature and dynamics of two small-scale quiet-Sun rotating structures in the chromosphere. Methods. We analysed two chromospheric structures that show clear rotational patterns in spectropolarimetric observations taken with the Interferometric Bidimensional Spectrometer at the Ca II 8542 Å line. Results. We present the detection of spectropolarimetric signals that manifest the magnetic nature of rotating structures in the chromosphere. Our observations show two long-lived structures of plasma that each rotate clockwise inside a 10 arcsec2 quiet-Sun region. Their circular polarisation signals are five to ten times above the noise level. Line-of-sight Doppler velocity and horizontal velocity maps from the observations reveal clear plasma flows at and around the two structures. A magnetohydrodynamics simulation shows these two structures are plausibly magnetically connected. Wave analysis suggests that the observed rotational vortex pattern could be due to a combination of slow actual rotation and a faster azimuthal phase speed pattern of a magnetoacoustic mode. Conclusions. Our results imply that the vortex structures observed in the Sun’s chromosphere are magnetic in nature and that they can be connected locally through the chromosphere
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Fischer, C. E., J. M. Borrero, N. Bello González, and A. J. Kaithakkal. "Observations of solar small-scale magnetic flux-sheet emergence." Astronomy & Astrophysics 622 (February 2019): L12. http://dx.doi.org/10.1051/0004-6361/201834628.
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Aims. Two types of flux emergence were recently discovered in numerical simulations: magnetic loops and magnetic sheet emergence. While magnetic loop emergence has been documented well in recent years using high-resolution full Stokes data from ground-based telescopes as well as satellites, magnetic sheet emergence is still an understudied process. We report here on the first clear observational evidence of a magnetic sheet emergence and characterise its development. Methods. Full Stokes spectra from the Hinode spectropolarimeter were inverted with the Stokes Inversion based on Response functions (SIR) code to obtain solar atmospheric parameters such as temperature, line-of-sight velocities, and full magnetic field vector information. Results. We analyse a magnetic flux emergence event observed in the quiet-Sun internetwork. After a large-scale appearance of linear polarisation, a magnetic sheet with horizontal magnetic flux density of up to 194 Mx cm−2 hovers in the low photosphere spanning a region of 2–3 arcsec. The magnetic field azimuth obtained through Stokes inversions clearly shows an organised structure of transversal magnetic flux density emerging. The granule below the magnetic flux sheet tears the structure apart leaving the emerged flux to form several magnetic loops at the edges of the granule. Conclusions. A large amount of flux with strong horizontal magnetic fields surfaces through the interplay of buried magnetic flux and convective motions. The magnetic flux emerges within 10 minutes and we find a longitudinal magnetic flux at the foot points of the order of ∼1018 Mx. This is one to two orders of magnitude larger than what has been reported for small-scale magnetic loops. The convective flows feed the newly emerged flux into the pre-existing magnetic population on a granular scale.
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Kalewicz, T., and V. Bommier. "Magnetic field vector ambiguity resolution in a quiescent prominence observed on two consecutive days." Astronomy & Astrophysics 629 (September 2019): A138. http://dx.doi.org/10.1051/0004-6361/201935488.
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Context. Magnetic field vector measurements are always ambiguous, that is, two or more field vectors are solutions of the observed polarisation. Aims. The aim of the present paper is to solve the ambiguity by comparing the ambiguous field vectors obtained in the same prominence observed on two consecutive days. The effect of the solar rotation is to modify the scattering angle of the prominence radiation, which modifies the symmetry of the ambiguous solutions. This method, which is a kind of tomography, was successfully applied in the past to the average magnetic field vector of 20 prominences observed at the Pic du Midi. The aim of the present paper is to apply this method to a prominence observed with spatial resolution at the THÉMIS telescope (European site at Izaña, Tenerife Island). Methods. The magnetic field vector is measured by interpretation of the Hanle effect observed in the He I D3 5875.6 Å line, within the horizontal field vector hypothesis for simplicity. The ambiguity is first solved by comparing the two pairs of solutions obtained for a “big pixel” determined by averaging the observed Stokes parameters in a large region at the prominence centre. Each pixel is then disambiguated by selecting the closest solution in a propagation from the prominence centre to the prominence boundary. Results. The results previously obtained on averaged prominences are all recovered. The polarity is found to be inverse with a small angle of about −21° between the magnetic field vector and the long axis of the filament. The magnetic field strength of about 6 G is found to slightly increase with height, as previously observed. The new result is the observed decrease with height, of the absolute value of the angle between the magnetic field vector and the long axis of the filament. Conclusions. This result is in excellent agreement with prominence magnetohydrodynamical models.
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Agapiou, Athos. "Multi-Temporal Change Detection Analysis of Vertical Sprawl over Limassol City Centre and Amathus Archaeological Site in Cyprus during 2015–2020 Using the Sentinel-1 Sensor and the Google Earth Engine Platform." Sensors 21, no. 5 (March 8, 2021): 1884. http://dx.doi.org/10.3390/s21051884.
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Urban sprawl can negatively impact the archaeological record of an area. In order to study the urbanisation process and its patterns, satellite images were used in the past to identify land-use changes and detect individual buildings and constructions. However, this approach involves the acquisition of high-resolution satellite images, the cost of which is increases according to the size of the area under study, as well as the time interval of the analysis. In this paper, we implemented a quick, automatic and low-cost exploration of large areas, for addressing this purpose, aiming to provide at a medium resolution of an overview of the landscape changes. This study focuses on using radar Sentinel-1 images to monitor and detect multi-temporal changes during the period 2015–2020 in Limassol, Cyprus. In addition, the big data cloud platform, Google Earth Engine, was used to process the data. Three different change detection methods were implemented in this platform as follow: (a) vertical transmit, vertical receive (VV) and vertical transmit, horizontal receive (VH) polarisations pseudo-colour composites; (b) the Rapid and Easy Change Detection in Radar Time-Series by Variation Coefficient (REACTIV) Google Earth Engine algorithm; and (c) a multi-temporal Wishart-based change detection algorithm. The overall findings are presented for the wider area of the Limassol city, with special focus on the archaeological site of “Amathus” and the city centre of Limassol. For validation purposes, satellite images from the multi-temporal archive from the Google Earth platform were used. The methods mentioned above were able to capture the urbanization process of the city that has been initiated during this period due to recent large construction projects.
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Rusomarov, N., O. Kochukhov, and A. Lundin. "Magnetic field topology and chemical spot distributions of the Ap star HD 119419." Astronomy & Astrophysics 609 (January 2018): A88. http://dx.doi.org/10.1051/0004-6361/201731914.
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Context. Analysis of high-resolution spectropolarimetric time-series observations of early-type magnetic stars is currently the most advanced method of obtaining detailed information on their surface magnetic field topologies and horizontal spot distributions. Aims. In this study we analyse a new set of high-quality full Stokes vector observations of the magnetic Ap star HD 119419 – a member of the 14 Myr old Lower Cen-Cru association – for the purpose of studying the surface field topology and mapping the chemical abundance spots. Methods. We made use of the circular and linear polarisation data collected for HD 119419 with the HARPSpol instrument at the ESO 3.6-m telescope. These observations were analysed with a multi-line magnetic diagnostic technique and modelled in detail with a Magnetic Doppler imaging (MDI) code. Results. We present a new set of high-precision mean longitudinal magnetic field measurements and derive a revised stellar rotational period by comparing our measurements with the literature data. We also redetermine the basic stellar atmospheric parameters. Our four Stokes parameter magnetic inversions reveal a moderately complex surface field topology with a mean field strength of 18 kG and a maximum local strength of 24 kG. A poloidal dipolar component dominates the magnetic energy spectrum of the surface field in HD 119419. However, significant contributions of the higher-order spherical harmonic components are also present. We show that the dipole plus quadrupole part of the reconstructed field geometry is incapable of reproducing the observed amplitudes and shapes of the Stokes Q and U profiles. The chemical abundance distributions of Fe, Cr, Ti, and Nd, derived self-consistently with the magnetic field geometry, are characterised by large abundance gradients and a lack of clear correlation with the magnetic field structure. Conclusions. This full Stokes vector analysis of HD 119419 extends the modern hot-star magnetic mapping investigations to an open cluster Ap star with a well-determined age. Further, MDI studies of cluster members will allow us to study the field topologies and chemical abundance spots as a function of stellar age.
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Schlenz, F., J. T. dall'Amico, W. Mauser, and A. Loew. "Analysis of SMOS brightness temperature and vegetation optical depth data with coupled land surface and radiative transfer models in Southern Germany." Hydrology and Earth System Sciences 16, no. 10 (October 5, 2012): 3517–33. http://dx.doi.org/10.5194/hess-16-3517-2012.
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Abstract. Soil Moisture and Ocean Salinity (SMOS) L1c brightness temperature and L2 optical depth data are analysed with a coupled land surface (PROMET) and radiative transfer model (L-MEB). The coupled models are validated with ground and airborne measurements under contrasting soil moisture, vegetation and land surface temperature conditions during the SMOS Validation Campaign in May and June 2010 in the SMOS test site Upper Danube Catchment in southern Germany. The brightness temperature root-mean-squared errors are between 6 K and 9 K. The L-MEB parameterisation is considered appropriate under local conditions even though it might possibly be further optimised. SMOS L1c brightness temperature data are processed and analysed in the Upper Danube Catchment using the coupled models in 2011 and during the SMOS Validation Campaign 2010 together with airborne L-band brightness temperature data. Only low to fair correlations are found for this comparison (R between 0.1–0.41). SMOS L1c brightness temperature data do not show the expected seasonal behaviour and are positively biased. It is concluded that RFI is responsible for a considerable part of the observed problems in the SMOS data products in the Upper Danube Catchment. This is consistent with the observed dry bias in the SMOS L2 soil moisture products which can also be related to RFI. It is confirmed that the brightness temperature data from the lower SMOS look angles and the horizontal polarisation are less reliable. This information could be used to improve the brightness temperature data filtering before the soil moisture retrieval. SMOS L2 optical depth values have been compared to modelled data and are not considered a reliable source of information about vegetation due to missing seasonal behaviour and a very high mean value. A fairly strong correlation between SMOS L2 soil moisture and optical depth was found (R = 0.65) even though the two variables are considered independent in the study area. The value of coupled models as a tool for the analysis of passive microwave remote-sensing data is demonstrated by extending this SMOS data analysis from a few days during a field campaign to a longer term comparison.
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Picard, G., A. Royer, L. Arnaud, and M. Fily. "Influence of meter-scale wind-formed features on the variability of the microwave brightness temperature around Dome C in Antarctica." Cryosphere Discussions 7, no. 4 (July 23, 2013): 3675–716. http://dx.doi.org/10.5194/tcd-7-3675-2013.
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Abstract. Space-borne passive microwave radiometers are widely used to retrieve information in snowy regions by exploiting the high sensitivity of microwave emission to snow properties. For the Antarctic Plateau, many studies presenting retrieval algorithms or numerical simulations have assumed, explicitly or not, that the subpixel-scale heterogeneity is negligible and that the retrieved properties were representative of whole pixels. In this paper, we investigate the spatial variations of brightness temperature over a range of a few kilometers in the Dome C area. Using ground-based radiometers towed by a vehicle allowing measurements with meter resolution, we collected brightness temperature transects at 11, 19 and 37 GHz at horizontal and vertical polarizations. The most remarkable observation was a series of regular undulations of the signal with a significant amplitude of up to 10 K at 37 GHz and a quasi-period of 30–50 m. In contrast, the variability at longer length scales seemed to be weak in the investigated area and the mean brightness temperature was close to AMSR-E and WindSat satellite observations for all the frequencies and polarisations. To establish a link between the snow characteristics and undulation-scale variations of microwave emission, we collected detailed snow grain size and density profiles to run the DMRT-ML microwave emission model at two points where opposite extrema of brightness temperature were observed. The numerical simulations revealed that the difference in density of the upper first meter of the snowpack explained most of the brightness temperature variations. In addition, we found in the field that these variations of density were linked to the hardness of the snowpack. Areas of hard snow – probably formed by the wind – were clearly visible and covered as much as 39% of the investigated area. Their brightness temperature was higher than in normal areas. This result implied that the microwave emission measured by satellites over Dome C is more complex than expected and very likely depends on the areal proportion of the two different types of areas having distinct snow properties.
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Singh, Abhilash, Kumar Gaurav, Atul Kumar Rai, and Zafar Beg. "Machine Learning to Estimate Surface Roughness from Satellite Images." Remote Sensing 13, no. 19 (September 22, 2021): 3794. http://dx.doi.org/10.3390/rs13193794.
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We apply the Support Vector Regression (SVR) machine learning model to estimate surface roughness on a large alluvial fan of the Kosi River in the Himalayan Foreland from satellite images. To train the model, we used input features such as radar backscatter values in Vertical–Vertical (VV) and Vertical–Horizontal (VH) polarisation, incidence angle from Sentinel-1, Normalised Difference Vegetation Index (NDVI) from Sentinel-2, and surface elevation from Shuttle Radar Topographic Mission (SRTM). We generated additional features (VH/VV and VH–VV) through a linear data fusion of the existing features. For the training and validation of our model, we conducted a field campaign during 11–20 December 2019. We measured surface roughness at 78 different locations over the entire fan surface using an in-house-developed mechanical pin-profiler. We used the regression tree ensemble approach to assess the relative importance of individual input feature to predict the surface soil roughness from SVR model. We eliminated the irrelevant input features using an iterative backward elimination approach. We then performed feature sensitivity to evaluate the riskiness of the selected features. Finally, we applied the dimension reduction and scaling to minimise the data redundancy and bring them to a similar level. Based on these, we proposed five SVR methods (PCA-NS-SVR, PCA-CM-SVR, PCA-ZM-SVR, PCA-MM-SVR, and PCA-S-SVR). We trained and evaluated the performance of all variants of SVR with a 60:40 ratio using the input features and the in-situ surface roughness. We compared the performance of SVR models with six different benchmark machine learning models (i.e., Gaussian Process Regression (GPR), Generalised Regression Neural Network (GRNN), Binary Decision Tree (BDT), Bragging Ensemble Learning, Boosting Ensemble Learning, and Automated Machine Learning (AutoML)). We observed that the PCA-MM-SVR perform better with a coefficient of correlation (R = 0.74), Root Mean Square Error (RMSE = 0.16 cm), and Mean Square Error (MSE = 0.025 cm2). To ensure a fair selection of the machine learning model, we evaluated the Akaike’s Information Criterion (AIC), corrected AIC (AICc), and Bayesian Information Criterion (BIC). We observed that SVR exhibits the lowest values of AIC, corrected AIC, and BIC of all the other methods; this indicates the best goodness-of-fit. Eventually, we also compared the result of PCA-MM-SVR with the surface roughness estimated from different empirical and semi-empirical radar backscatter models. The accuracy of the PCA-MM-SVR model is better than the backscatter models. This study provides a robust approach to measure surface roughness at high spatial and temporal resolutions solely from the satellite data.
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Hioki, Souichiro, Jérôme Riedi, and Mohamed S. Djellali. "A study of polarimetric error induced by satellite motion: application to the 3MI and similar sensors." Atmospheric Measurement Techniques 14, no. 3 (March 4, 2021): 1801–16. http://dx.doi.org/10.5194/amt-14-1801-2021.
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Abstract. This study investigates the magnitude of the error introduced by the co-registration and interpolation in computing Stokes vector elements from observations by the Multi-viewing, Multi-channel, Multi-polarisation Imager (3MI). The Stokes parameter derivation from the 3MI measurements requires the syntheses of three wide-field-of-view images taken by the instrument at 0.25 s interval with polarizers at different angles. Even though the synthesis of spatially or temporally inhomogeneous data is inevitable for a number of polarimetric instruments, it is particularly challenging for 3MI because of the instrument design, which prioritizes the stability during a long life cycle and enables the wide-field-of-view and multiwavelength capabilities. This study therefore focuses on 3MI's motion-induced error brought in by the co-registration and interpolation that are necessary for the synthesis of three images. The 2-D polarimetric measurements from the Second-generation Global Imager (SGLI) are weighted and averaged to produce two proxy datasets of the 3MI measurements, with and without considering the effect of the satellite motion along the orbit. The comparison of these two datasets shows that the motion-induced error is not symmetric about zero and not negligible when the intensity variability of the observed scene is large. The results are analyzed in five categories of pixels: (1) cloud over water, (2) clear sky over water, (3) coastlines, (4) cloud over land, and (5) clear sky over land. The most spread distribution of normalized polarized radiance (Lp) difference is in the cloud-over-water class, and the most spread distribution of degree of linear polarization (DOLP) difference is in the clear-sky-over-water class. The 5th to 95th percentile ranges of Lp difference for each class are (1) [-0.0051,0.012], (2) [-0.0040,0.0088], (3) [-0.0033,0.012], (4) [-0.0033,0.0062], and (5) [-0.0023,0.0032]. The same percentile range of DOLP difference for each class are (1) [-0.023,0.060], (2) [-0.043,0.093], (3) [-0.019,0.082], (4) [-0.0075,0.014], and (5) [-0.011,0.016]. The medians of the Lp difference are (1) 0.00035, (2) 0.000049, (3) 0.00031, (4), 0.000089, and (5) 0.000037, whereas the medians of the DOLP difference are (1) 0.0014, (2) 0.0015, (3) 0.0025, (4) 0.00027, and (5) 0.00014. A model using Monte Carlo simulation confirms that the magnitude of these errors over clouds are closely related to the spatial correlation in the horizontal cloud structure. For the cloud-over-water category, it is shown that the error model developed in this study can statistically simulate the magnitude and trends of the 3MI's motion-induced error estimated from SGLI data. The obtained statistics and the simulation technique can be utilized to provide pixel-level quality information for 3MI Level 1B products. In addition, the simulation method can be applied to the past, current, and future spaceborne instruments with a similar design.
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"Single Patch Antenna with Multiple Feed." International Journal of Innovative Technology and Exploring Engineering 8, no. 9 (July 10, 2019): 1743–47. http://dx.doi.org/10.35940/ijitee.i8618.078919.
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In this article single patch antenna with multiple feed lines is presented. The antenna is tested with four ports each separated at 90 degrees. The ports separated at 180 degrees have the same effects and same polarisation. The S-parameter of port 1 and port 2 are same due to horizontal polarisation then port 2 and port 4 are same due to vertical polarisation. The Port 1 and Port 3 resonates at frequency of 2.092GHz and 4.563GHz. It covers applications of UMTS (1.885GHz - 2.2 GHz) and C band (4 GHz – 8GHz). The Port 2 and Port 4 resonates at frequency of 1.66GHz and 5.155GHz. It covers applications of GPS (1.565GHz – 1.665GHz) and WLAN (5 GHz – 6 GHz). The return loss of the frequencies is less than10dB. The isolation among the ports are less than 15 dB.
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S. Lepidi, U. Villante, M. Vellante, P. Palangio, and A. Meloni. "High resolution geomagnetic field observations at Terra Nova bay, Antarctica." Annals of Geophysics 39, no. 3 (May 18, 1996). http://dx.doi.org/10.4401/ag-3987.
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he preliminary results obtained from the analysis in the micropulsation frequency range of high time resolution magnetic field data recorded at the Antarctic Italian geomagnetic observatory at Terra Nova Bay for 11 consecutive days in February 1994 are reported. The spectral index over the whole Pcl-Pc5 frequency range is of the order of 3.5 and its value significantly increases beyond about 50 mHz. Spectral peaks in the Pc3 frequency range are common, especially during the daytime hours, and are probably due to the direct penetration of upstream waves in the cusp region. From the local time distribution of the micro pulsation power, a signifi - cant activity enhancement around the local magnetic noon emerges, in agreement with previous observations. The analysis of the signal polarisation characteristics in the horizontal plane shows a predominant CW polarisation in the Pcl-Pc3 frequency ranges with the major axis of the polarisation ellipse in the first quadrant.