Ultrawideband (UWB) radar technology has emerged as one of the preferred choices for through-wall detection due to its high range resolution and good penetration. The resolution is a result of high ...bandwidth of UWB radar and helpful for better separation of multiple targets in complex environment. Detection of human targets through a wall is interesting in many applications. One significant characteristic of human is the periodic motion, such as breathing and limb movement. In this letter, we apply the UWB radar system in through-wall human detection and present the methods based on fast Fourier transform and S transform to detect and identify the human's life characteristic. In particular, we can extract the center frequencies of life signals and locate the position of human targets from experimental data with high accuracy. Compared with other research studies in through-wall detection, this letter is concentrated in the processing and identifying of the life signal under strong clutter. It has a high signal-to-noise ratio and simpler to implement in complex environment detection. We can use the method to search and locate the survivor trapped under the building debris during earthquake, explosion, or fire.
The Chang'E‐4 (CE‐4) achieved the first successful soft landing on the floor of the Von Kármán crater located in the northeast of the South Pole‐Aitken (SPA) basin on the Moon. Here, through analysis ...and processing of the dual‐channel lunar penetrating radar (LPR) data, the shallow regolith structure and deep geological strata below the landing site are exposed. The high‐frequency data (CH‐2, 500 MHz) show that the Von Kármán crater underwent remodeling because of ejecta from multiple craters within a thickness of 40 m. Under the surface fine‐grained regolith, superpositions among these crater materials and mare basalt units establish shallow regolith stratigraphic sequences. The low‐frequency data (CH‐1, 60 MHz) show a deep stratigraphic structure to the depth of 360 m that indicates the previous geological evolution history of the Von Kármán crater. The LPR results provide an important scientific basis for understanding the geological history of the far side of the Moon.
Plain Language Summary
The Chang'E‐4 (CE‐4) landed in the Von Kármán crater, which is located on the far side of the Moon. The lunar penetrating radar (LPR) loaded on the Yutu‐2 rover can be used to determine the shallow lunar regolith structure and deep geological strata of the Von Kármán crater. In this article, first, different processing procedures focused on the two channels of LPR data (CH‐1 and CH‐2) are designed, and clear radar images that can be used to explain the underground structure of the Von Kármán crater are obtained. The radar images are then combined with previous geological information to reveal the subsurface geological structure of the Von Kármán crater. The Von Kármán crater underwent various geological processes, including basaltic magmatism, ejecta coverage, and the interaction of volcanic eruptive clastics and lava. The regolith layer on the surface has a thickness of more than 10 m, and below the regolith layer is a multilayer formed by the ejecta material of surrounding impacts, which is as thick as more than 30 m. Underneath are three basalt magma covers.
Key Points
The CH‐2 LPR data reveal that the landing site underwent remodeling because of ejecta from multiple craters within a thickness of 40 m
The CH‐1 LPR data provide the deep stratigraphic structure within 360 m, including more than three basalt magma activities
The LPR data demonstrate that the Von Kármán crater was landscaped by various geological processes
In this letter, we apply a time and frequency analysis method based on the complete ensemble empirical mode decomposition (CEEMD) method in ground-penetrating radar (GPR) signal processing. It ...decomposes the GPR signal into a sum of oscillatory components, with guaranteed positive and smoothly varying instantaneous frequencies. The key idea of this method relies on averaging the modes obtained by empirical mode decomposition (EMD) applied to several realizations of Gaussian white noise added to the original signal. It can solve the mode-mixing problem in the EMD method and improve the resolution of ensemble EMD (EEMD) when the signal has a low signal-to-noise ratio. First, we analyze the difference between the basic theory of EMD, EEMD, and CEEMD. Then, we compare the time and frequency analysis with Hilbert-Huang transform to test the results of different methods. The synthetic and real GPR data demonstrate that CEEMD promises higher spectral-spatial resolution than the other two EMD methods in GPR signal denoising and target extraction. Its decomposition is complete, with a numerically negligible error.
Magnetic resonance sounding (MRS) technology is the only geophysical means to directly and quantitatively detect groundwater and has achieved good results in hydrogeological prospecting applications. ...In recent years, researchers have conducted considerable research on the efficiency of a single instrument, yielding certain results. However, the overall work efficiency of this method has not been effectively determined in its application to a large-scale survey. Hence, we propose both a joint detection method for MRS that determines the minimum working distance when multiple systems operate simultaneously and a collaborative measurement method of dual systems operating simultaneously in a fixed range of work areas. The cooperative working mode of the instruments is tested in the detection area, and the working mode proposed in this paper is shown to effectively avoid measurement interference between systems. Compared with the working mode of a single set of instruments, the measurement efficiency is more than doubled. Through this research, the feasibility of multiple MRS instruments working together in the same work area is verified, which provides effective technical support for the rapid and high-efficiency utilization of MRS over a wide range of measurement areas.
•CE-4 LPR data of the first 450 m drive reveal a ∼40 m deep subsurface structure.•Four ejecta layers underlying the surface regolith are discontinuous.•The energy map of suggests the cause of ...inconsistencies to be a buried crater.•The rock distribution indicates a brief weathering period of each ejecta layer.•The local evolutionary history is constructed based on the revealed stratigraphy.
The Yutu-2 rover, part of the Chang'e-4 (CE-4) mission to the lunar farside, has been exploring the Von Kármán crater (VK) within the South Pole-Aitken (SPA) gathering data on its geology. The Lunar Penetrating Radar's (LPR) 500 MHz antenna reveals the subsurface structure up to 40 m in depth, which helps to construct models on the evolution of the shallow stratum. This work presents the analysis and interpretation of the data collected during the first twenty lunar days, from January 2019 to July 2020. Below an 11±4-meter surface regolith layer, the radar image reveals well-defined reflectors that are interpreted as discrete depositional layers. These marked density boundaries could indicate a geologically brief time interval between each arrival, which prevented the materials to undergo a deeper homogenization through space weathering. To investigate further, we generated a subsurface rock distribution map using the correlation of dual-channel antennas data from the same channel. Clusters of rocks located at the bottom of each ejecta stratum are revealed, probably sorted by size due to the statistically less frequent occurrence of larger impact events admixing the deeper-seated materials. The bowl-shaped outline discovered in both rock and LPR energy distribution maps is interpreted to represent a 150±30 m wide and 10±5 m deep paleo-crater that was excavated within three thin ejecta layers. The CE-4 LPR reveals a complex geological history within the Von Kármán crater with no fewer than four impact events delivering meters thick ejecta at the CE-4 landing area following the end of the infilling phase.
Structural analysis of lunar regolith not only provides important information about lunar geology but also provides a reference for future lunar sample return missions. The Lunar Penetrating Radar ...(LPR) onboard China’s Chang’E-3 (CE-3) provides a unique opportunity for mapping the subsurface structure and the near-surface stratigraphic structure of the regolith. The problem of rock positioning and regolith-basement interface highlighting is meaningful. In this paper, we propose an adaptive rock extraction method based on local similarity constraints to achieve the rock location and quantitative analysis for regolith. Firstly, a processing pipeline is designed to image the LPR CH-2 A and B data. Secondly, we adopt an f-x EMD (empirical mode decomposition)-based dip filter to extract low-wavenumber components in the two data. Then, we calculate the local similarity spectrum between the filtered CH-2 A and B. After a soft threshold function, we pick the local maximums in the spectrum as the location of each rock. Finally, according to the extracted result, on the one hand, the depth of regolith is obtained, and on the other hand, the distribution information of the rocks in regolith, which changes with the path and the depth, is also revealed.
The spatial distribution of rock fractures during water injection in hot dry rock (HDR) geothermal is essential information for evaluating geothermal well fracturing. The rock fractures produce ...anisotropic electrical characteristics, which may facilitate geophysical methods for monitoring fracture distribution. This paper studies the anisotropic magnetotelluric (MT) response in water injection fracturing based on the finite difference method (FEM). It uses the residual phase tensor (PT) method to calculate the characteristics of fracture strike and dip angle. The feasibility analysis of the technique under a different angle and resistivity conditions in geothermal reservoir investigation is discussed in detail. The results demonstrate that the MT can explain the characteristics of anisotropic resistivity structure changes from the water injection fracturing of HDR at the 5 km depth. The time-lapse MT monitoring method can provide a reliable scientific basis for fracture distribution direction and spreading characteristics.
SUMMARY
Full-waveform inversion (FWI) of ground-penetrating radar (GPR) data is a promising technique for the parameter imaging of near subsurface. In this paper, we present an innovative model-based ...layer stripping FWI (MLS FWI) approach for reconstructing dielectric permittivity that is specifically applicable to the propagation of radar waves. From top to bottom in the model domain, relative permittivity is updated layer by layer. Differing from the traditional layer stripping FWI, which uses an offset and/or temporal window to extract partially observed data for calculating a partial gradient, a spatial Hanning window in the model domain is applied to the overall gradient calculated from the entire gathers for getting the gradient of a layer. We designate the traditional layer stripping as data-based and the proposed layer stripping as model-based. Most importantly, when combined with the source encoding, this MLS FWI fundamentally solves the problem that forward simulation of all source positions is required when adding the window in a data-based layer stripping FWI, and thus greatly improves the calculation efficiency and saves the memory. Furthermore, in such a scheme, we also propose a new stepped inversion sequence to improve the inversion at depth. Here, we illustrate our approach with two synthetic examples based on on-ground multioffset data. Compared to the results of the frequency multiscale FWI and that of the data-based layer stripping FWI, the MLS FWI with the stepped inversion sequence yields substantially higher resolution images and accurately reconstructs a relative permittivity model, effectively avoiding severe local minimum problems. This GPR FWI process can help retrieve near-surface model parameters in heterogeneous media.
The 3D inversion is a challenging task in the research of the frequency-domain airborne electromagnetic (AEM) method due to the massive amounts of data and limited computational efficiency. In this ...paper, we introduce the 3D FAEM inversion based on the vector finite element method (FEM). Compare with the traditional nodal FEM, the vector FEM can improve the computational efficiency by reducing the number of variables and the scale of linear equations. To tackle the computational demands, in the calculation process we apply the PARDISO solver with shared-memory distributed-memory multi-processors to solve the multi-source forward linear equations and calculate the gradient of the objective function by adjoint equations. Then typical resistivity model with the anomalous body is carried out to verify the validity of the proposed method. Meanwhile, in allusion to the multi-solution problem caused by the inversion problem, we study the influence of typical initial models on inversion results. Finally, we applied our algorithm to invert field data. The inversion results demonstrate that the proposed method can obtain reliable AEM resistivity inverted results.
•Proposed the 3D FAEM inversion based on the Vector FEM modeling and the NLCG method.•The PARDISO solver is applied to improve computing efficiency.•The proposed method performs well fitness both on the model and field data.
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