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Existing noise removal processes for airborne electromagnetic (AEM) data generally consist of several steps, with each using a specific method to remove a specific type of noise. To improve the efficiency of AEM denoising and reduce the impact of the subjective judgment of the operators on the processing results, we have adopted a deep learning method based on a denoising autoencoder (DAE), which enables in one single processing step the removal of multisource noise. The most common noise sources in AEM data, including motion-induced noise, nearby or moderately distant sferics noise, power-line noise, and background electromagnetic noise, will be combined with a large number of simulation responses to build a training set. The data in the training set will be used to train the deep learning DAE neural network so that the neural network could fully learn the respective characteristics of the signal and noise and further effectively distinguish the AEM response signal (useful signal) from the above noise. The field data were processed using this method, and the processing results were compared with those obtained using traditional methods. The comparison test revealed that this method is helpful to reduce the influence of subjective factors on the quality of data results and compress the entire AEM data processing time.

The water burst from the Ordovician limestone underlain by the Permo-Carboniferous coal seams have potential to trigger coalmine hazards in Northern China. Therefore, it is crucial to identify and accurately map the water enrichment zones and delineate coal seams using an integrated approach based on surface TEM and subsurface wireline log information to avoid water-inrush hazard and ensure safe production of coal. We inverted surface based TEM data using 1-D Occam inversion to identify the conductive anomaly and then further quantified the zone of interest by gamma and resistivity logs. 1-D Occam inversion results show conductive zone around 370 m while higher resistivity and lower gamma ray log signatures were observed against coal seams. Groundwater inrush zone falls within the mid-range gamma ray and resistivity interval as shown on the petrophysical logs. The distinct log signatures (low gamma-ray and high resistivity values) clearly indicated coal seams at depth of 410 and 470 m and subsequently the log trends were used to distinguish between coal units and more permeable sands. The magnitude and the variability of these parameters in the borehole are attributed to the subsurface stratigraphic heterogeneity. They can be key clues for interpretation of depositional facies of coal-bearing sequence and may also be used as a constraint in characterization of groundwater enrichment zone.

China is facing many challenges in the area of high-precision exploration for deep mineral resources, and also in environmental and engineering fields. It has become an urgent task to realize geophysical explorations with high precision and high efficiency in complex environments. It has been found that the traditional transient electromagnetic method (TEM) had a series of problems related to theory, method, and instrument, as well as data interpretation. Based on the reviews of present TEM achievements, three new improved measurements are introduced. The central-loop system was improved by a large fixed-loop system; the long-offset system was changed to the short-offset one; the resistivity profile was transformed into a virtual wave-field profile. Finally, this paper points out that the future research direction of the TEM method is in terms of equipment, data processing, and big data information.

The central and western regions of China have appropriate conditions for mining development, but there are many deserts, swamps and forest-covered areas in this vast land. As a result, the traditional on-ground methods are difficult to carry out efficiently in these areas. The airborne transient electromagnetic method can implement detection over large areas rapidly and efficiently, and play an important role in terms of resource and environment detection. In recent years, two Helicopter-borne Transient electromagnetic (HTEM) systems, CHTEM-I and CAS-HTEM, were developed in China. In this paper, the difficult issues in the development of HTEM hardware and software will be analyzed, firstly. By tracing the specific technical paths to solve these difficult issues, the latest research achievements in the development process of CHTEM-I and CAS-HTEM will be expounded. Finally, we would like to briefly discuss the research and development direction of HTEM technology in China to promote further development of the research and application of this technology.

Over the past decade, helicopter-borne transient electromagnetic (HTEM) systems have been rapidly developed. A new HTEM prototype (referred to as a CAS-HTEM) has been developed by the Chinese Academy of Sciences. In terms of hardware, the CAS-HTEM system uses an inflatable structure to carry the transmitting loop, which significantly reduces the weight of the system and makes it easier to transport. A dual gain receiver was innovated to extend the dynamic range of the system. In addition, an observation circuit for transmitting voltage waveform is introduced, so that the derivative waveform of transmitting current with higher SNR could be calculated. In terms of data processing, more reliable early time data could be obtained by band-limited effect removal; a weighted stacking algorithm is introduced to reduce the narrow band noise more effectively and increase the sensitivity of data to the anomaly location; a method based on τ-domain transform is used for late time signal processing. The results of the field test which was carried out in Inner Mongolia were found to be consistent with the drill data, which effectively verified the performance of this HTEM prototype.

Next generation wireless communication systems use massive Multi Input Multi Output (m-MIMO) antenna arrays for their enhanced beamforming capabilities. Providing accurate Channel State Information (CSI) is vital for optimizing m-MIMO communication systems. The complexity of channel reconstruction grows exponentially with the number of antennas, causing traditional methods to become increasingly complicated. Machine-learning techniques can be a useful alternative for channel reconstruction using partial CSI feedback. This paper presents the results of a simulation study built using the MATLAB 5G Toolbox and a neural network trained using the simulated data. The simulator emulates a 5G channel to generate its path delays and gains, and the realistic CSI feedback. This data was used to train and test a neural network to estimate the dominant path gains and delays. The models showed promising results while operating on limited CSI data.

During the past 20 years, due to the rapid development of China's economy, the amount of coal mining activities has rapidly increased, which has led to a large increase in the number of mined-out areas. Therefore, the role of geophysical exploration in coal fields has changed from the detection of coal resources to engineering geological environmental investigation. The safety, efficiency, and green production of coal mines require more advanced geophysical detection technologies. In particular, the accurate detections of the locations of water-rich mined-out areas, as well as concealed water diversion channels, have become the main focuses of coal electrical methods in recent years. Therefore, electromagnetic methods have become the main means of hydrogeological investigations and deep explorations in mine-out coal areas. In this study, a common DC method was briefly introduced, along with an induced polarization method. Then, three representative electromagnetic sounding methods, including a surface frequency-domain electromagnetic method, time-domain electromagnetic method, surface to air electromagnetic method, and mine electromagnetic method, were respectively introduced.

The surface transient electromagnetic method (TEM) is a geophysical technology normally used in detecting water-enriched zones. However, with an increase of mining depth, the accuracy and reliability of surface detection is gradually reduced, and surface TEM cannot meet the requirements of high-precision detection for coal mine production safety. In this study, surface-to-coal mine roadway TEM is proposed to detect water-enriched zones in coal mines. The resolution of this method in detecting targets, however, is still unknown. Based on a 1-D layered model, the surface-to-coal mine roadway TEM response is numerically simulated using the finite-difference time-domain method (FDTD). The results show that the surface-to-coal mine roadway TEM has higher resolution of the target above the underground receiving point and weaker resolution of the target below the receiving point. 3-D geo-electric models for typical water-enriched zones such as a water-filled mining goaf, a water-filled fault and a water-filled collapse column are established. The surface-to-coal mine roadway TEM responses are numerically simulated and compared with the surface TEM responses. The results show that for the goaf model, the surface-to-coal mine roadway TEM response is more sensitive than the surface TEM response. For fault and collapse column models, the surface-to-coal mine roadway response is more sensitive than surface response in the early delay stage but less sensitive in the late delay stage. The present study provides theoretical support for device selection and for data processing interpretation in actual work.

The grounded-wire transient electromagnetic (TEM) survey has been successfully applied in the mining industry to detect resources in the subsurface. Recently, research efforts have been devoted to developing both the theory and application of the short-offset TEM (SOTEM), which requires the layout of a line source for transmitting the electromagnetic signals. In practice, however, the terrain complexities of exploration areas, such as mountains and construction areas, often limit the layout of such linear geometry and moreover cause the source to be folded several times, which undesirably increases the computational differences especially when the line-source model is used for field data processing and interpretation. Therefore, to achieve high resolution TEM detection, it is now necessary to adapt the source layout to the local terrain. For describing the effect of source geometry on the SOTEM surveying, this study first presents a superposing-dipole approach for estimating the SOTEM field from arbitrarily-shaped sources and then qualifying the relative differences in the horizontal electric field due to varying source geometry. It is expected that such approach could be implemented for improving the TEM detection accuracy by taking into account all the turning points in a non-linear source layout, especially in the restricted areas. [Figure: see text]

Near-source electromagnetic technology has been developed and applied in the exploration of petroleum, metallic ore, coal, and engineering geology due to its high efficiency, high detection accuracy, and deep depth of investigation. In this paper, research and applications of the frequency-domain electromagnetic sounding method (FDEM), wide-field electromagnetic method (WFEM), modified central-loop transient electromagnetic method (TEM), and short-offset grounded-wire TEM (SOTEM) with obvious near-source characteristics, were reviewed and analyzed. From the 1960s to 1990s, the FDEM method and equipment were extensively developed in China. These methods have played important roles in the exploration of coal resources. Based on controlled source audio-frequency magnetotelluric (CSAMT) and FDEM methods, a new method has been developed by deriving a new expression to calculate apparent resistivity. This method, which is referred to as WFEM, has been studied, applied, and received great attention in China. To increase work efficiency and reduce the influence of local transverse anisotropy on the detection processes, a modified central-loop TEM detection technology based on the central loop transient electromagnetic method was developed in China. The advantages of SOTEM in near-source surveys with high resolution and increased depth detection stimulated academic research interest to further develop grounded-wire TEM techniques. [Figure: see text]

The water-rich zones in the coal fields of Northern China have seriously threatened the safe production of coal mines. It is necessary to accurately locate the deep seated and complex water bodies which are usually located in Ordovician limestone. Due to the relatively high cost of seismic exploration, the development effective electromagnetic detection methods and corresponding data processing techniques for the detection of these water-rich areas becomes a topic for the EM geophysicist. In this study, a method of rapidly estimating the burial depth and undulating morphology of coal bed foundations by employing frequency domain electromagnetic sounding data was proposed. The method uses the overshoot/undershoot phenomenon of the apparent resistivity for the frequency domain electromagnetic measurement to quantitatively determine the burial depth of the northern China coal structure bases. First, the featured frequency points were confirmed, where the overshoot and undershoot effects appeared in the electromagnetic sounding curves beside the borehole drilling sites. Then, the correlation coefficient between the confirmed frequency points and the burial depth of coal seam bed was obtained according to the drilling data. Finally, the burial depth of the coal seam beds in the entire survey area was evaluated based on the correlation coefficient and electromagnetic data. This method was applied in the northern areas of Taiyuan City in Shanxi Province, and achieved good results. [Figure: see text]

Combined cooling, heating and power (CCHP) systems have received wide attention for their potential of high efficiency and energy conservation. In this work, a novel CCHP system is designed coupling the solar thermal input (ST) system and the regenerative organic flash cycle (OFC) system. The OFC subsystem could recycle two kinds of heat sources to achieve cascade utilization of heat energy. The CCHP-ST-OFC system is evaluated by comparing with the conventional CCHP system and the CCHP-ST-ORC system (organic Rankine cycle). The effects of several operating parameters on the thermodynamic performance are discussed. Based on the negative feedback regulation, an operation strategy is proposed and applied to buildings to verify the thermodynamic economy. The results demonstrate that the electricity and heat provisions are 275.0 kW and 211.5 kW, which are 4.7 kW and 19.3 kW higher than the CCHP-ST-ORC system. The electricity of the OFC subsystem is 15.0 kW and 47% higher than the ORC system. Moreover, changing the smoke outlet temperature in the waste heat recovery equipment could effectively adjust the heat provision and power generation. The trend of the day and night power generation with the mass flow rate of the heat source is reversed. The energy provision and performance increased with the increasing partial load ratio of the internal combustion engine. The building case study reveals that the exergy efficiency of the CCHP-ST-OFC system is 38.7% and the primary energy ratio is 53.1%, respectively. Meanwhile, the natural gas consumption of the CCHP-ST-OFC system is 5.14×105 m3/year, with a 9% reduction than the CCHP-ST-ORC system.

Increases in the mining depth of coal pose a significant challenge to the conventional loop source time-domain electromagnetic (TEM) method that requires significant enlargement of the loop size and transmitting current to realize the deeper sounding results required. As an alternative, TEM devices based on a grounded wire source are generally used to solve detections deeper than several hundred meters. To map the water-enriched zones buried underneath approximately 1000 m at a coal mine in Shaanxi, China, loop TEM and short-offset transient electromagnetic (SOTEM) measurements were conducted. We carried out 1D forward modeling and inversion constrained by drilling informa-tion, and the results reveal that the resolution capability of loop TEM and SOTEM is almost the same in detecting a conductive layer in the absence of any noise. However, for a given noise level and decay time, the SOTEM method provides a deeper investigation than loop TEM without compromising sensitivity. The field examples validated the synthetic results. The loop TEM with dimensions of [Formula: see text] realized a maximum depth of 1000 m, whereas the reliable detection depth of 1500 m was achieved by using a 723 m long grounded wire source using the SOTEM method. Moreover, the labor required is significantly reduced, and the efficiency is dramatically raised using the SOTEM method. Our results predict that the SOTEM method should play a more important role in deep hydrogeophysical investigations.

The grounded-wire transient electromagnetic (TEM) surveying is often performed along the equatorial direction with its observation lines paralleling to the transmitting wire with a certain transmitter–receiver distance. However, such method takes into account only the equatorial component of the electromagnetic field, and a little effort has been made on incorporating the other major component along the transmitting wire, here denoted as axial field. To obtain a comprehensive understanding of its fundamental characteristics and guide the designing of the corresponding observation system for reliable anomaly detection, this study for the first time investigates the axial electric field from three crucial aspects, including its decay curve, plane distribution, and anomaly sensitivity, through both synthetic modeling and real application to one major coal field in China. The results demonstrate a higher sensitivity to both high- and low-resistivity anomalies by the electric field in axial direction and confirm its great potentials for robust anomaly detection in the subsurface.

The inline dipole–dipole time-domain electromagnetic method is a useful supplementary tool for the exploration of a resistive target such as a hydrocarbon resource. Currently, the interpretation of the data from this configuration is based on the fitting of the modeled response and the recorded response in a least square sense. In the paper, we propose an imaging method based on a mathematical transformation named the q-transform, which could make the subsequent imaging of TEM data using the interpretation technique in seismic method possible. The imaging strategy is based on analytical derivation and analysis of the transformed wave-field from which pseudo-velocity and resistivity can be extracted. A numerical test is employed to get the transformed wave-field from the time-domain electromagnetic response with the selected regularization method. The proposed imaging method is tested on the synthetic data obtained from a homogeneous and layered half space models. The results reveal that it is a useful method to recover the resistivity of an underground medium and can provide an additional tool for fast and qualitative imaging of the subsurface resistivity.

Traditional TEM study mainly focuses on the generation and application of the TE field using a loop or grounded-wire source; but in recent decades, lots of efforts have been made for implementation of the TM field and even the integration of the TE field with the TM one into anomaly detection in the subsurface. However, no applicable principles have been proposed for selecting the optimal electromagnetic field for various subsurface targets. The transient electromagnetic (TEM) fields generated from grounded-wire source consist of the TE-mode response (current-carrying wire), the TE–TM mode response (grounding ends) and the combined TEM-mode response (current-carrying wire and grounding ends). This study performs a comparison of TE/TE–TM/TEM fields by generating them from grounded-wire source and testing their distribution characteristics, detection depth, and sensitivity to anomalies, using both synthetic 1D model and two field surveys in China. The comparisons demonstrate that, the detection depth of the TE–TM field is smaller than those of both the TE and combined TEM fields. Meanwhile, for electric field, the TE–TM response provides a better detection than the TEM one, but with an uneven distribution. Therefore, the TE–TM electric field requires well-designed arrangements of receiving positions when applied to real projects. For the magnetic field, the TEM response has the best detection capability compared to the TE and TE–TM ones, but is least sensitive to layer thickness and resistivity, especially for an embedded layer with low resistivity.

The dipole hypothesis commonly used in the description of electromagnetic fields associated with TEM loop antennas or grounded wire source is not accurate enough in the near-source zones where the response is also of significant importance for clearly mapping subtle structures embedded in shallow settings with geologic complexities. In order to better understand these near-source errors, we investigate the scale of errors resulting from the direct-dipole and superposing-dipole approximation of the large loop or long grounded wire sources. The results demonstrate that both the direct-dipole approximation and the superposing-dipole approximation fail to give accurate results in the near-source zone. Not only the direct-dipole approximation but also superposing-dipole approximation will arouse some errors. Therefore, a ‘point-charge’ solution of the EM damped wave equation is proposed and derived to calculate the near source responses. Forward modeling and field data analysis demonstrate that the proposed method provides more accurate results in the near source areas and can be effectively used to calculate the TEM response in the near source region.

Water inrush from limestone coal beds is disastrous for coal mining. In general, it is very difficult to detect such water-enriched zones because of their relatively large burial depth. In this paper, we propose a novel transient electromagnetic method (TEM) configuration, short-offset transient electromagnetic method (SOTEM). Consistency of the results obtained from SOTEM measurements in the Shandong province, East China and drilling information indicate that the proposed TEM configuration not only improves the accuracy, but also enlarges the exploration depth for detecting water-enriched areas in coal mines ranging from 1,000 to 1,200 m depth. In this region, a majority of the deep coal beds are filled with water. The SOTEM technique was successfully employed in detecting the floor of a coal seam at a depth of about 1,500 m, as well as in identifying the location of the water-saturated area. These findings were later confirmed by subsequent drillings. Thus, our study indicates that SOTEM represents a convenient and effective technique for deep mineral and hydrogeological investigations due to its high sensitivity to conductive zones (water enriched areas) and vertical resolution.

Shanxi Province is a major coal base for the rapid development in China, but heavy production of coal resources has left abundant water-filled voids, creating significant geologic hazards around coal mines. It is necessary to quickly investigate the position and distribution of voids with effective geophysical methods. The feasibility of transient electromagnetic (TEM) method in detecting and monitoring water-filled voids is analyzed using 3D finite-element numerical simulation results as well as a case study in this paper. The case study was mainly to analyze and monitor the conditions around the site of a power transfer station under construction in the west of Shanxi province where many water-filled, mined-out voids existed. Central-loop TEM sounding was carried out three times from January 2010 to April 2011 around the building footprint. The low resistivity abnormal area had been repeatedly located and the survey results showed that the area of voids increased with time, which indicated that the ground at the site was in an unstable and dangerous state. The surveys provided more detailed geological information to the government for further safety arrangement and building re-design.

Transient Electromagnetic Method was first proposed by Soviet scientists in the 1930s that worked in far-field zone. The time-domain electromagnetic method with a dipole induced by a pulse current was proposed by Blau in 1933. Based on the similarity of electromagnetic wave at the formation interfaces of different conductivities with reflection signal of seismic wave, a lot of comparisons and experiments have been made. However, the frequency of transient EM signal induced by a pulse current was very low that made it difficult to achieve the resolution in identifying the reflection waves, resulting in TEM method be put aside. In 1950–1960s, Soviet scientists successfully completed one-dimensional (1D) forward modeling and inversion for TEM method and established the procedure for TEM field work and interpretations. TEM method began to enter the stage of practical use ever since. After the 1960s, people realized that time-domain electromagnetic sounding method can assume a much smaller transmitter–receiver offset than the expected exploration depth, TEM method underwent a rapid development. In Soviet Union, dozens of TEM teams were set up that made great achievements in oil and gas exploration. After that, the technologies like “short-offset,” “late time,” “near zone” were developed rapidly. In 1970–1980s, the short-offset method has been in the research and testing stage but not been widely used, while the long-offset TEM method has been used in the Western countries like the United States, particularly in geothermal exploration and investigation on crustal structure. During this time, people also conducted researches on 1D TEM forward modeling and inversion techniques. After 1980s, with the development of computer technology, European and American scholars published numerous papers on two-dimensional (2D) and three-dimensional (3D) forward modeling and inversion methods, using finite-difference, finite-element, integral equation algorithm, etc. The improvement on theory and understanding promotes the development and application of TEM method. The representative works of electromagnetic theory were written by Kaufman and Keller (1983) in their monograph “Frequency- and Time-domain Electromagnetic Sounding” and by Nabighian (1992) in his edited book “Electromagnetic Method in Applied Geophysics” “Electromagnetic Geophysical Survey Method.” Soviet scientist Бepдчeвcкий MH et al. (1985)

After putting forward the wave field transformation method, we have realized the transformation of the diffusive TEM field into a pseudo-seismic wave field. This creates the conditions for the realization of the synthetic aperture imaging of airborne transient EM method. The imaging method based on synthetic aperture technology for TEM takes advantage of the concept of synthetic aperture radar imaging, which uses the relative motion between the target and the real airborne aperture transmitting coil to synthetize via data processing a large equivalent aperture for the transmitting coil from the small-sized real antenna aperture, to improve the resolution and penetration capability. For airborne TEM method, the observation configuration is similar to airborne synthetic aperture radar (SAR), the imaging theory and technology of synthetic aperture radar can be used to realize the TEM synthetic aperture imaging based on the pseudo-seismic field transformation.

In some applications, especially for tunnel surveys and ancient tomb investigations, the scale of survey location is so small that it is impossible to lay a large enough transmitter loop for detection. A small-scale and high-power Transient Electromagnetic (TEM) transmitter configuration must be adapted to detect longer distance or greater depth. Redesigning the TEM surveying configuration may facilitate improving signal penetration and precision of TEM soundings. Based on physical simulation, a newly designed special-loop-source TEM survey configuration has been introduced, which employs four square apertures within a single large transmitter loop to excite stronger fields. The primary and secondary fields have been measured using both the new special-loop system and standard normal single loop TEM configuration for different receiver-transmitter separations and for different target depths. The response curves were compared, revealing that the primary field intensity and the secondary field response were improved by the special-loop transmitter system as compared to the standard system. The new special-loop configuration can be used for tunnel TEM prediction and other TEM investigations. A case study was conducted on tunnel forecasting in Hubei Province, China. This terra TEM survey showed that it is an effective and successful method for exploring and predicting challenging geological structures ahead of a tunnel wall during excavation.

The pseudo-seismic waves obtained by the transient electromagnetic method (TEM) can be used to explain geological conformations of underground objects. However, the directly transformed pseudo-wave always has a dispersive and broader waveform so that it cannot clearly indicate the geological–electrical boundary of the explored underground objects. This study shows that the reason for the waveform dispersion is because the variance of the kernel function with the Gauss distribution is the real time; the wave distribution range will increase with increasing time. Therefore, this study presents a technique for enhancing the resolving power of pseudo-seismic data processed by a de-convolution method, and detailed theory and algorithms are reported. The pseudo-seismic signals of two geological–electrical models are taken as the examples to verify the present algorithm. Results show that the pseudo-seismic waves after de-convolution processes have sharper waveforms and narrower distribution zones, and this can effectively control the waveform broadening phenomenon and is able to enhance the resolving power using the TEM pseudo-seismic waves to survey the boundary of underground objects.

Because of unreasonable coal mining in China, there are many unknown underground caves, and the inhabited environment of humans is threatened by many geologic hazards, such as cracking of the buildings, ground subsidence, etc. To make the coal companies aware of the harmfulness of these hazards, it is urgent to determine the reasons for the hazards. In this paper, transient electromagnetic method (TEM) is used to detect the ground resistance caves, instead of the time-consuming and expensive direct drilling survey. Numerical results of the 3-D synthetic model and real field survey data are given. The results showed that the TEM method can be used to detect a complicated air-filled underground 3-D cave and coincide with the results of direct drilling survey.

For the real-time, on-site, direct monitoring of coalfield fire area temperature, we developed a permanent WSN monitoring system with the functions of continuous collection, high temperature detection, remote control, etc. By designing the software and hardware of SPI interface between the JN5139 chip and the MAX31855 with K type thermocouple, we developed a new type of high temperature sensor node, which temperature range extended to  40°C ~ 1300°C from standard WSN node temperature range. This node can be placed directly on the underground burned area roadway for on-site monitoring. The solar power supply device with protective circuit and low power consumption peripheral circuit provide the data acquisition network with a sustainable energy for all-weather and real-time monitoring. In the uplink data transmission through mobile communication network and Internet to the monitoring center, the heartbeat packets mechanism without manual intervention was used to automatic reconnection, which keeps the link unobstructed to realize the remote control monitoring. The monitoring system that deployed in 12 fire areas of Xinjiang has worked for 45 mouths, and that means technical measures used can guarantee the long-term stability operation of the monitoring system without maintenance. Urumqi monitoring center has received more than 110 ten thousand field information that can be preserved permanently and queried freely after authorized. This information provides basic data for the management of large area of coal spontaneous combustion fire area in Xinjiang and for governance results defend. Keywords—WSN;real-time; high temperature; bidirectional communication; remote control; heartbeat package

Commonly, TEM data is plotted as apparent resistivity versus time. Later on, with improvement in computer technology, inversion programs have got attention of EM geophysical community. Recently, inversion routines are applied to 1-D problems. In this paper we propose a new approach to interpret SOTEM data by carrying out analysis in time, frequency and pseudo-seismic domain. At first, we processed synthetic data for H & K type models using 1-D Occam inversion. Then we transformed time-domain data into quasi-MT domain and conducted 1-D Bostick's algorithm. Finally, EM diffusion field is transformed into wave field reflecting seismic-like response with some reflection and refraction phenomena. Our proposed approach is validated by a case study of a coal field located in Henan province, China. Keywords—interpretation; SOTEM; transient electromagnetic method

Coal seam seismic survey collapse column is common in heterogeneous geologic bodies. Groud-3D seismic observation due to limitations of its accuracy, for uneven geological subsided column often small leakage test or position error is large, the impact of mining coal mine safety sometimes causing heavy casualties. Downhole observation of channel wave transmission is one of the most effective ways to detect the small anomalous bodies within mine working face. Transmission experiments carried on at the king coal mine working face, in SHANGXI province, with 56 excitation points at lane and 48 receiving points at next lane arranged , its interval distance is 150m along roadway. 1344 airy phrase travel time are picked through the dispersion analysis and tomographic inversion calculation of velocity and absorption coefficient is carried out. The distribution diagram of group velocity and absorption coefficient of the channel wave is built which obtain 10 anomalous bodies discovered and excluding the other collapse columns delineated by the three-dimensional seismic exploration in the test areas. There are number 1-9 collapse columns among the 10 anomalous bodies, Number 1-9 collapse columns are verified by the result of actual mining, and the location all deviation is less than 10m. Number 1, 6and 7 collapse columns are exposed by the roadways. Number 6 collapse column has a 40m’s extending length into the mining face. Number 7 collapse column has a 20m’s extending length into the mining face. Number 4 collapse column has 50m’s major axis and 30m’s minor axis. This is consistent with the location of the collapse column DX4 given by 3D seismic exploration. There is no abnormal of the collapse column DX5 and DX6 in the result of tomographic inversion, which is exposed by 3D seismic exploration. The existence of Number 2-5 collapse columns seriously influences the coal mining safety. Concerning the geological condition exposed by the roadways, the production scheme has been modified to ensure high production and high productivity and safety of mine. Keywords—collapse column, channel wave, dispersion analysis, tomographic imaging.

The denoising process is critical when processing transient electromagnetic (TEM) sounding data. For the full waveform PRBS response, an inadequate noise estimation may result in an erroneous interpretation. We consider the Hilbert- huang transform and its application to suppress the noise in the PRBS response. The focus is on the thresholding scheme to weed out the energy corresponding to the noise and the analysis of the signal based on its Hilbert time-frequency representation. The method firstly decomposes the signal into the intrinsic mode function, and then, inspired by the thresholding scheme in wavelet analysis, an adaptive and interval thresholding is conducted to set to zero all the components in intrinsic mode function which are lower than a threshold related to the noise level. The algorithm is based on the characteristic of the PRBS response. The HHT based denoising scheme is tested on the synthetic data and applied to the field data with different noise level. The result shows that the proposed method has a good capability in denoising and detail preservation.

The in-loop TEM field is a kind of vertex field propagating in a way of diffusion in the earth mainly. Plane-wave of electromagnetic has the features of reflection and refraction during the propagation in the earth. In order to draw on the experience of well processed method of electromagnetic plane-wave, we study equivalent transformation from TEM diffusion field sounding data to plane-wave electromagnetic sounding data. An equivalent transformation relationship between time and frequency domains can be constructed after theoretical model forward calculation, curve comparison, error analysis and the theoretical discussion about the propagation of diffusion field and plane-wave. Using this transformation, the diffusion field sounding data of TEM apparent resistivity can be quickly turned into the equivalent data of plane-wave sounding data. The result lays the foundation for the further study of TEM pseudo-seismic plane-wave interpretation.

In order to improve the distinguishing ability of TEM, a study of interpretation system of TEM tomography has been finished in this paper. The law of propagation of electromagnetic wave and seismic wave in medium and the response of TEM far-field have been fully discussed. According to the similarity between the propagation of magnetic dipole source TEM field and reflected-seismic wave, it is proposed to explain TEM data with the pseudo-seismic interpretation. The forward and inversion calculated result of theoretical model examples indicates that the theory is right; the processed results of the field data demonstrate that this method is useful and practical.

In order to improve the prospecting precision to the earth by the transient electromagnetic method (TEM), We propose an idea of TEM imaging technology and numerical calculation method. The transient electromagnetic response of the layered earth is discussed in the frequency domain, then a double integral in which the kernel is unknown is obtained. The solution of the electromagnetic field in the medium of the layered earth is separated into the form of upper and down traveling wave. Then a linear equation set in which reflection coefficients are unknown is derived. The numerical solution of wave-impedance and reflection coefficients is given as follows: Transforming the magnetic field data from time into the frequency domain, replacing the kernel of equation with the equivalent wave-impedance of homogeneous half-space, getting the equivalent wave-impedance in the frequency domain after digital filter, then returning the equivalent wave-impedance into the time domain, constructing equations with it getting reflection coefficients from the equation with the method of linear programming in the time domain. The imaging result section can be drawn. The imaging result from the theory model shows that the method put forward in this paper can improve greatly the ability to recognize underground electric interfaces.

This paper introduces a multistage interference cancellation (MIC) technique with diversity reception for quadrature phase shift keying (QPSK) asynchronous direct-sequence code division multiple access (DS/CDMA) systems over frequency-selective multipath Rayleigh fading channels. Unlike the previous MIC, which tries to remove the lump sum of the multiple-access interference (MAI) and self-interference (SI), this introduced MIC attempts to cancel only the MAI and part of the SI due to the intersymbol interference, while treating the remaining SI created by the current symbol as useful information for symbol decision. In this technique, the RAKE combining is used to collect signal replicas over multiple fading paths. Upper and lower bounds on the bit error probability are derived using a Gaussian approximation and the characteristic function method. Furthermore, effects of channel estimation error on the performance are studied. Analytical and simulation results show that the introduced MIC can provide a performance extremely close to that in an ideal single-user environment and outperforms the previous MIC even in the presence of channel estimation error.

A multistage interference cancellation (MIC) technique with RAKE diversity (MIC-RAKE) for QPSK asynchronous direct sequence code division multiple access (DS/CDMA) system over frequency selective multipath Rayleigh fading channels is presented. Unlike the conventional MIC, which tries to subtract the lump sum of the multiple access interference (MAI) and the self-interference (SI), the MIC-RAKE attempts to cancel the MAI and the partial SI, and to treat the residual SI as useful signal for symbol decision. The RAKE combining is employed to collect signal replicas over multiple fading paths. The upper and lower bounds on the bit error probability are derived by using a Gaussian approximation. Furthermore, the effect of the channel estimation error is studied. Analysis and simulation show that the MIC-RAKE can provide a performance close to the ideal performance of single-user system, and outperforms the conventional MIC even in the presence of channel estimation error.

The performance of a DS-CDMA system with M-ary orthogonal modulation is investigated; through computer experiments and mathematical analysis we find the variance of multiple access interference (MAI) in synchronous AWGN channels should be twice as much as adopted in previous references. The system performance of successive interference cancellation in multipath Rayleigh fading channels is also investigated by means of simulation. Our results show that successive interference cancellation is a simple yet effective way to mitigate MAI when the user density is low.

In this paper, a multilevel-quantized soft-limiting (SL-MQ) detector for frequency hopping spread spectrum multiple access (FH-SSMA) systems is proposed and analyzed. Numerical and simulation results in frequency selective Rayleigh fading channels show that compared to the hard-limiting (HL) detector, the new SL-MQ with M=4 can improve the system capacity by almost 10% at the bit error rate level of 10/sup -3/. Furthermore, the performance of the SL-MQ has low sensitivity to the optimum value of the amplitude threshold so that it can tolerate an inaccurate estimate of the optimum in practice.

To achieve a better tracking of time-varying channel parameters, a structure using blind adaptive minimum output energy (MOE) detection in conjunction with a RAKE combining diversity for direct-sequence code-division multiple-access (DS/CDMA) communications over the frequency selective multipath fading channels is introduced. In this MOE-RAKE structure, the signal replicas received from multiple fading paths are first independently produced by a bank of adaptive MOE detectors and then combined by a RAKE receiver for final symbol decision. A normalized, complex-valued stochastic gradient descent (SGD) algorithm is developed for blind adaptation used in the MOE-RAKE. Simulation results show that, in the time-varying channel, the MOE-RAKE provides a better performance than the other blind multiuser detection techniques. In practice, to further improve the detector performance, a hybrid scheme started with blind adaptation for initial updates and then switched to the decision-directed algorithm is desired.

Road traffic is the major noise source that impacts the largest numbers of city dwellers. Urban traffic noise control at the source typically involves providing quieter i.e. low noise pavement and regular maintenance. The aim of this paper is to propose a double-layer porous asphalt pavement for keeping the traffic noise at a low level with good durability. It contains the top layer of fine aggregates and bottom layer of course aggregates. The noise-absorption performance of this asphalt pavement is evaluated by adjusting the parameters of the pavement structure simulated in air–solid coupled numerical models. The reduction of noise by using the newly proposed asphalt pavement is compared with those of the traditional pavements such as the thin surfacing (TSF) with small aggregates and rubberized asphalt pavement (RAP). The results from the outdoor noise tests for the double-layer porous asphalt pavement verifies the virtual pavement models and noise reduction effects in practice. This asphalt pavement is designated to lower the noise level of urban road traffic and boost the living environments of the city dwellers.