The microtremor survey method (MSM) has the potential to be an important geophysical method for identifying the strata velocity structure and detecting the buried fault structures. However, the existing microtremor exploration equipment has been unable to satisfy the requirements of the MSM, which suffers from low data accuracy, long measurement time, and blind acquisition. In this study, we combined a 2 Hz moving coil geophone with advanced acquisition systems to develop a new integrated energy-efficient wireless sensor node for microtremor exploration. A high-precision AD chip and noise matching technology are used to develop a low-noise design for the sensor node. Dynamic frequency selection technology (DFS) and dynamic power management technology (DPM) are used to design an energy-efficient mode. The data quality monitoring system solves the closed technical flaws between the acquisition systems and the control center via 4G wireless monitoring technologies. According to the results of a series of in situ tests and field measurements, the noise level of the system was 0.7 μV@500 Hz with 0 dB attenuation and 220 mW power consumption of the system in the autonomous data acquisition mode. Therefore, it provides substantial support for the effective data acquisition over long measurement durations in microtremor exploration processes. The applicability of the system is evaluated using field data, according to which the integrated energy-efficient wireless sensor node is convenient and effective for MSM.

High-density seismic array survey has attracted high R&D interest in geophysical methods in recent years, and it is an advanced seismic observation technology which is of great significance in oil and gas resource detection and underground space exploration. However, designing a portable sensor node that prolongs the lifetime and equips wireless monitoring system to improve construction efficiency has been still a challenge. In this paper, a portable energy-efficient wireless sensor node and a wireless communication system that content them with complex terrain, large-scale and reliable transmission is proposed to tackle the restrictions of high-density seismic array survey. This paper proposes a directed diffusion routing method which performs the energy-efficient design by maintaining the link gradient and the ability of automatic power adjustment. In addition, when the sink node initiates an instruction, it quickly covers all nodes and receives the response from the nodes. Then, a series of simulations and experiments are carried out for verification. The experiments show that the equivalent noise of the sensor node is 0.8μV@500Hz, which suggest good performance among the existing sensor nodes. Simulation results and performance analysis validate that the effectiveness of the proposed routing method can maintain the network with only 20mW at autonomous working mode. The field measurement results indicate that the wireless multi-hop energy-efficient system based on the directed diffusion routing method is suitable for the high-density seismic survey.

Large numbers of seismic channels and high-density energy-efficient acquisition systems are the development trend of seismic instruments and have attracted high R&D interests in recent years. The combination of remote sensing and wireless sensor network technology provides superior observation capabilities for high-density seismic exploration. However, large-scale and multi-node acquisition methods place higher requirements on time synchronization performance. Seismic data with poor time synchronization will cause considerable errors in the interpretation of seismic data and even have no practical significance. Thus, the strict time synchronization performance is the prerequisite and basis for the application of cable-less storage seismograph in high-density seismic array applications. The existing time synchronization methods have high power consumption and poor time synchronization accuracy, which is not suitable for the long-time task. In addition, these methods are affected by the number of nodes and the distance. This paper presents an energy-efficient time-sharing indexed interpolation intercept method for the seismic data synchronization. The time synchronization method uses the high-precision TCXO as the main clock and records GPS time in the SD card at intervals to achieve the high-precision time-stamp for the seismic data. Then the seismic data is intercepted intermittently based on precise time stamps, which achieves the strict seismic data synchronization. Performance analysis shows that the time synchronization accuracy of the proposed method is 0.6 μs and saves 73% energy of the time-sync periods compared to the common GPS timing method. The field measurement results indicate that the time synchronization accuracy is not associated with the working time and the distance between nodes so that the proposed synchronization method is suitable for the high-density seismic survey.

The performance of seismic exploration instruments directly affects the quality of acquired seismic data as well as the efficiency of seismic survey operation. Consequently, they play a pivotal role in oil/gas and mineral resource exploration. Compared with traditional cabled seismic acquisition systems, nodal seismic acquisition systems have the advantages of light weight, small size, low capital and operational cost, reduced health safety and environment risk and strong adaptability to complex terrain environment. Therefore, they have been widely used in seismic exploration and have shown a trend of accelerated development. The major manufacturers have carried out research and development of nodal instruments, and various types of nodal seismographs have appeared. Based on the investigation of influential nodal seismographs, we summarize the research status of nodal seismographs. Based on different wireless monitoring capabilities and data harvesting modes, we classify the nodal seismographs into a shoot-blind system, semi-blind system, real-time system and enhanced real-time system. We discuss structural principles and key technologies of the four types of nodal seismographs, analyze their characteristics and predict their future development directions. Focusing on node data quality monitoring, we discuss the application of communication technologies, such as Bluetooth, Wi-Fi, ZigBee, Long Term Evolution, and satellites in nodal seismographs in detail. Furthermore, we analyze and evaluate three main networking architectures including planar multi-hop networks, hierarchical cluster networks and hybrid networks, and sum up the research progress of wireless routing algorithms and large-scale seismic data real-time harvesting methods. Finally, the latest applications of nodal seismographs in energy and mineral resource exploration, geological environment monitoring, urban subsurface space survey and novel seismic technologies are covered. As research on the application of micro-electro-mechanical systems technology, cloud computing, 5G, Internet of Things, edge computing, machine learning and robotics in nodal systems deepens, the performance of nodal seismographs will be greatly promoted.

Seismic communication might promise to revolutionize the theory of seismic waves. However, one of the greatest challenges to its widespread adoption is the difficulty of signal extraction because the seismic waves in the vibration environments, such as seas, streets, city centers and subways, are very complex. Here, we employ segmented correlation technology with Morse code (SCTMC), which extracts the target signal by cutting the collected data into a series of segments and makes these segments cross-correlate with the decoded signal to process the collected data. To test the effectiveness of the technology, a seismic communication system composed of vibroseis sources and geophones was built in an environment full of other vibration signals. Most notably, it improves the signal-to-noise ratio (SNR), extending the relay distance and suppressing other vibration signals by using technology to deal with seismic data generated by the system.

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High-density seismic array method has attracted enormous interest in geophysical methods, and it is an advanced seismic observation technology which is of great significance in oil and gas resource detection and underground space exploration. However, designing a portable sensor node that prolongs the lifetime and equips wireless monitoring system to improve construction efficiency has been still a challenge for the high-density seismic array method. In this paper, a portable energy-efficient wireless sensor node and a hybrid communication system that content themselves with complex terrain, large-scale and reliable transmission are proposed to tackle the restrictions of high-density seismic survey. A Wi-Fi communication system based on the star network structure at the core network layer and a ZigBee communication system based on wireless multi-hop structure in the extended network layer form the hybrid communication system. In order to balance the energy of nodes in the extended network and prolong the network lifetime, this paper proposes a multi-hop variable weight routing method (MVWRM). The method selects the cluster-head node and the multi-hop route by changing the weight of the residual energy of the node and the weight of the distance at different periods. Then, a series of simulations and experiments are carried out for verification. The experiments show that the proposed sensor node suggest good performance in equivalent noise level (0.8µV@500Hz, PGA = 1), total harmonic distortion (124dB). Simulation results and performance analysis validate that the effectiveness of the proposed MVWRM can extend about 10% of the node lifetime. INDEX TERMS Energy-efficient, wireless sensor networks, multi-hop, high-density seismic array.