A Continuity Flow Based Tomographic Reconstruction Algorithm for 4D Multi-Beam High Temporal—Low Angular Sampling

A mathematical framework and accompanying numerical algorithm exploiting the continuity equation for 4D reconstruction of spatiotemporal attenuation fields from multi-angle full-field transmission measurements is presented. The algorithm is geared towards rotation-free dynamic multi-beam X-ray tomography measurements, for which angular information is sparse but the temporal information is rich. 3D attenuation maps are recovered by propagating an initial discretized density volume in time according to the advection equations using the Finite Volumes method with a total variation diminishing monotonic upstream-centered scheme (TVDMUSCL). The benefits and limitations of the algorithm are explored using dynamic granular system phantoms modelled via discrete elements and projected by an analytical ray model independent from the numerical ray model used in the reconstruction scheme. Three phantom scenarios of increasing complexity are presented and it is found that projections from only a few (unknowns:equations > 10) angles can be sufficient for characterisation of the 3D attenuation field evolution in time. It is shown that the artificial velocity field produced by the algorithm sub-iteration, which is used to propagate the attenuation field, can to some extent approximate the true kinematics of the system. Furthermore, it is found that the selection of a temporal interpolation scheme for projection data can have a significant impact on error build up in the reconstructed attenuation field.

Exploring the Laplace Prior in Radio Tomographic Imaging with Sparse Bayesian Learning towards the Robustness to Multipath Fading

Radio tomographic imaging (RTI) is a technology for target localization by using radiofrequency (RF) sensors in a wireless network. The change of the attenuation field caused by thetarget is represented by a shadowing image, which is then used to estimate the target’s position.The shadowing image can be reconstructed from the variation of the received signal strength (RSS)in the wireless network. However, due to the interference from multi-path fading, not all the RSSvariations are reliable. If the unreliable RSS variations are used for image reconstruction, someartifacts will appear in the shadowing image, which may cause the target’s position being wronglyestimated. Due to the sparse property of the shadowing image, sparse Bayesian learning (SBL) canbe employed for signal reconstruction. Aiming at enhancing the robustness to multipath fading,this paper explores the Laplace prior to characterize the shadowing image under the frameworkof SBL. Bayesian modeling, Bayesian inference and the fast algorithm are presented to achieve themaximum-a-posterior (MAP) solution. Finally, imaging, localization and tracking experiments fromthree different scenarios are conducted to validate the robustness to multipath fading. Meanwhile,the improved computational efficiency of using Laplace prior is validated in the localization-timeexperiment as well.

Features of the 1976 and 2011 Van earthquakes, swarm seismicity and S-wave attenuation field

В работе рассмотрено положение очагов землетрясений 1976 и 2011 гг. и роев землетрясений в районе озера Ван на фоне неоднородностей поля поглощения поперечных волн. Поле поглощения получено методом короткопериодной коды, когда по набору огибающих коды для многих землетрясений строится распределение поля поглощения в верхней мантии. В районе озера Ван прослеживаются такие же, как и в других сейсмоактивных зонах, особенности структуры поля поглощения поперечных волн в мантии. Выделяются блоки слабого поглощения изометричной формы, в которых поглощение уменьшается в направлении от границ к центральным областям блоков, где добротность достигает 300 и даже 700. Среди зон сильного поглощения наиболее заметна широкая зона севернее 39с.ш., где QS80110. Кроме того, выделены небольшой протяженности линейные зоны сильного поглощения, ориентированные в направлениях ЮЗСВ и ЮВСЗ. Эпицентры сильнейших землетрясений района, в том числе и землетрясений 1976 и 2011 гг., как правило, приурочены к границам добротных блоков и ослабленных зон. Сейсмическая ситуация, предшествовавшая землетрясению 1976г., отличалась от таковой перед землетрясением 2011 г. В первом случае, за год до землетрясения на северовостоке от очага будущего толчка сформировалась сейсмическая брешь. Во втором случае слабые землетрясения в области очага будущего землетрясения не прекращались в течение предшествовавшего главному событию года. За несколько месяцев до главного толчка на северозападе от области очага имела место роевая серия землетрясений, которая ассоциируется с ослабленной низкодобротной зоной. Гипоцентры землетрясений, составляющих роевую серию, образуют одномерный объем изометричный в плане и вытянутый по вертикали (глубины очагов 3 30 км). Предполагается, что рои землетрясений, приуроченные к одномерным объемам, связаны с каналами миграции глубинных флюидов повышенной проводимости. Такие объекты можно интерпретировать как локальные сейсмогенные источники. The earthquake sources position (1976 and 2011) and swarm seismicity near Van Lake in the background inhomogeneities of Swave attenuation field is considered in the work. The attenuation field was obtained by the method of shortperiod coda waves, when the attenuation field distribution in the upper mantle is built using of coda waves envelopes of many earthquakes. In the Van Lake area, the same features of the structure of the Swaves attenuation field in the mantle, as in other seismically active zones, are revealed. The blocks of weak attenuation which is isometric in plan, where the attenuation decreases in the direction from the boundaries to the center and Qfactor reaches 300 and even 700 detected. The wide zone located to the north of 39 N (QS 80110) is most noticeable among the zones of strong attenuation. Short linear zones of strong attenuation, oriented in the SWNE and SWNW directions, were also identified. Usually sources of the strongest earthquakes, including the earthquakes of 1976 and 2011, localized in the zones of maximum attenuation contrast, on the block and weakened zone boundaries. The seismic situation preceding the earthquake of 1976 differed from that before the earthquake of 2011.In the first case, one year before the main shock to northeast from the source, a seismic gap formed.In the second case, weak earthquakes were not stopping in the source zone during the previous year.A few months before the main shock a swarm series of earthquakes occurred to the northwest of the source area. It is assumed that swarms associated with the migration channels of deep fluids of increased conductivity. Such objects can be interpreted as local seismogenic sources.