The high-density electrical method is a primary method
used in shallow geophysical prospecting. Due to the rapid industrial
development that has taken place in recent years, the function and performance of high-density
electrical instruments have been considerably improved in several aspects.
However, most of the electrical instruments currently available on the
market still exhibit some shortcomings, such as being bulky, heavy, limited
in their data acquisition accuracy, and difficult to connect to the Internet
for remote monitoring. To address these problems, this study developed a new
multifunctional four-dimensional (4D) high-density electrical instrument based
on remote wireless communication technology. The system is small and
lightweight, includes an integrated transceiver, has high data acquisition
accuracy, and is capable of remote wireless real-time control. In this
study, the hardware circuit was designed. The Arm all-in-one (AIO)
LJD-eWinV5-ST7 with a 154.4 cm
Energy serves as the foundation for social and economic development, and
geological work serves all aspects of the social economy. With the rapid
development of science and technology and the fast growth of national
economies, there is an increasing demand for energy in all countries. It is
pointed out in the
There are several challenges that arise in the process of resource extraction. It is necessary to assess the geological conditions of the location targeted for extraction. Different rocks and minerals possess different physical properties. In geophysical prospecting, these differences are observed and studied, allowing mineral resources to be assessed indirectly through an exploration of the stratum lithology and geological structure. Relative to other prospecting methods such as drilling, this method offers the advantages of high efficiency, high resolution, strong imaging effectiveness, low cost, and low destructiveness, among others. Electrical prospecting is an important branch of geophysical prospecting methods. It observes and analyzes the spatial and temporal distributions and the propagation of the Earth's electric field based on the different electrical properties of the underground rocks and minerals, thereby identifying the geological structures in the stratum and solving the corresponding geological problems. This type of geophysical prospecting explores and searches for distributions of underground mineral deposits with extraction value (Zhang et al., 2013). Among its advantages are high resolution, accurate results, and ease of use. However, as conventional electrical prospecting can obtain only one set of data from each power supply measurement, the amount of information acquired is small, and the speed of measurement is slow. As a result, the geological information that it provides on the structural characteristics of the geoelectric section is sparse and, therefore, not readily processed statistically. Thus, the concept of a high-density electrical method has been proposed. The high-density electrical prospecting technique arranges hundreds of electrodes at a time and uses an electrode multiplexer to switch between them to direct the power and control the measurements. In addition to indicating the lithological changes in the prospected geological body horizontally at a given depth, this method can represent differences that run vertically. The high-density electrical instrument can obtain highly accurate and rich geological information and, therefore, play an important role in prospecting for minerals, water, specific hydrogeological conditions, underground buildings, caves, and geofractures (Yang and Tian, 2014; Wang et al., 2013; Gu et al., 2010; Yang, 2011). With improvements in the depth of detection, observation accuracy, and the diversity of observation forms, the range of applications of high-density electrical methods has also been expanding (Zhou et al., 2018; Song et al., 2020), offering broad promise for further development. Development of these methods will continue to trend toward multiple channels, multiple parameters, multiple dimensions, multiple functions, high power, and wide ranges (Yan et al., 2012).
Owing to the complexity of conditions on the surface and underground, electrical instruments used in prospecting complex terrain continuously face new requirements and challenges and must be constantly improved. At present, most electrical instruments available on the market are bulky and heavy, limited in their data acquisition accuracy, and difficult to connect to the Internet for remote monitoring. Therefore, it is important to continuously seek ways to improve upon the conventional high-density electrical instruments.
Suppose that power is supplied to the underground via two power supply
electrodes,
Principle of the basic electrical method.
Principle of the high-density electrical method.
Development of the system used in this study included designing hardware circuits, software programs, and mechanical structures. The system's stability and accuracy in actual use are particularly important (Mendecki et al., 2010).
A block diagram of the IoT-based 4D high-density electrical instrument is
shown in Fig. 3. The instrument consists mainly of a high-voltage board, an
acquisition board (AB), and an Arm all-in-one (AIO) PC, which form a
complete system with the electrodes and electrode multiplexers. The AIO is
the Arm LJD-eWinV5-ST7 with a 154.4 cm
High-level architecture of the 4D high-density electrical instrument based on IoT.
The system design is described in detail in the following subsections.
The AB serves as the front-end circuit, which is responsible for processing the analog signals acquired by the electrodes and converting them into digital signals to be processed. The analog-to-digital converter (ADC) chip is a high-precision 24 bit serial A/D converter CS5532. The chip's gain can be controlled, and it contains a very-low-noise, chopper-stabilized instrumentation amplifier, and a fourth-order delta–sigma modulator followed by a digital filter.
The front ends of the ADC chip's two channels (ch1 and ch2) are
connected to the precision resistors of the MN and AB electrodes' front
ends, respectively. The voltage and current values can be read simultaneously using dual
channels. Figure 4 shows a block diagram of the acquisition device. The
processing of the two analog channels is similar, with the difference being that
the MN voltage channel has self-potential compensation. Figure 5 shows a
schematic of the MN channel of the acquisition device. The signals first
undergo impedance matching and then pass through the low-pass filter to
filter out high-frequency clutter. Because the input to the ADC is a
differential signal, the single-ended signal must be converted into a
differential signal to enter the ADC chip, which then outputs the digital
signal. The ADC chip of this circuit performs sampling at 20 ms (50 Hz
corresponds to a 20 ms period), thereby effectively suppressing the
interference from the 50 Hz grid power and multiple waves. In addition, the
channel connecting AD and MN has an INA128 as a subtractor, which subtracts
the natural self-potential (
Block diagram of the AB.
Schematic of the MN channel on the AB.
Comparison of instrument performance indicators.
The transmitting circuit can be divided into alternating current (AC) transmission and direct current (DC) transmission, and different devices are applied in different environments and for different measurements (Li et al., 2020; Zeng et al., 2018).
This system uses a DC power supply. Compared with an AC power supply, DC
provides a greater prospecting depth and exhibits advantages in reducing
electromagnetic coupling interference. The transmitting circuit consists
mainly of a protection circuit, an isolation circuit, the intelligent power
module (IPM) (10 A/1200 V) (Xing, 2001), a power conversion circuit, the
output electrodes, and a high-voltage source. The external DC high-voltage
power supply is connected to the IPM via the protection circuit. The main
control unit sends control commands through the multiple optocoupler to
control the IPM. The optocoupler used here is the HCPL-4504 from Agilent,
which is an optocoupler dedicated to the IPM interface. This product's
emitting light source and receiving light source are insulated by a
transparent insulator, and there is no actual electrical connection. It has
high speed, a high common-mode ratio, and an extremely short parasitic
delay. Its instantaneous common-mode ratio is greater than 10 kV
This system is an integrated transceiver with no separate transmitter; it exhibits the advantages of being lightweight, small, and portable.
The Arm AIO LJD-eWinV5-ST7 has abundant hardware resources and a complete
set of software functions. It contains, for example, an I/O (input/output) port, SD card,
dual-channel ADC, multiple RS232 ports, and multiple RS485 ports. The
built-in ADC sampling rate is fixed at 2
The slave computer program is the STC15 microcontroller program based on the Keil4 platform and is used to perform current and voltage acquisition, self-potential compensation, data transmission, communication, and other functions. It also sends the acquired current and voltage values to the Arm AIO for calculation and processing.
C# is an object-oriented programming language derived from C and C
Flowchart of the instrument's program.
The use of sophisticated narrowband IoT (NB-IoT) technologies enables long-distance wireless communication between a control center and a high-density electrical instrument (Li et al., 2011; Dong and Nie, 2017; Li et al., 2019). This study used the USR-G780 module, which is an machine to machine (M2M) product launched in 2016. It supports 4G high-speed access for China Mobile, China Unicom, and China Telecom as well as 3G and 2G access for China Mobile and China Unicom. The software includes a complete set of functions, covering the majority of conventional application scenarios. Users can perform transparent two-way data transmission from the serial port to the network by using simple settings. It also supports the custom registration package, heartbeat package function, four-way socket connection, and transparent cloud access. The USR-G780 was developed using an embedded Linux system and has high stability. Under the 4G network, it exhibits high speed and low latency and is, therefore, suitable in scenarios involving the transmission of large quantities of data and frequent interactions (Chen et al., 2015; Wang, 2017; Wang et al., 2017; Jia et al., 2016; He et al., 2018). Thus, it was an appropriate choice for the needs of this study. The connection topology is shown in Fig. 7.
Connection topology.
The 4D high-density electrical method adds a time dimension to the
three-dimensional (3D) method; that is,
After the instrument was developed, its practical application capabilities
needed to be tested. To test the instrument's accuracy in the laboratory, an
experiment was conducted using the resistor string method. A resistor string
network was soldered as shown in Fig. 8 to form the equivalent of a dummy
load. There were forty-eight 510
Schematic of resistor string connections for laboratory experiment.
Data results from laboratory experiment.
Further testing was conducted on the China University of Geosciences (Beijing) campus, as shown in the photo in Fig. 10. A large lawn in front of the main building was selected as the ground to be tested; there is a tube well on the lawn. The electrodes were arranged in a space of approximately 60 m. A real-time profile view of the test site as displayed on the instrument is shown in Fig. 11; it can be seen that the lawn and the tube well have different colors on the profile view. To validate the remote solution, in addition to adjusting the 4G module in the laboratory, transparent cloud transmission was used to monitor the data remotely on the PC in the laboratory. The profile view displayed on the notebook PC (Fig. 12) was the same as that displayed on the electrical instrument. Thus, the feasibility of using the program remotely was confirmed.
Photo of the scene of the campus test.
Real-time profile view of the test site as displayed on the electrical instrument.
Real-time profile view of the test site as displayed on the remote PC.
To further verify the stability and feasibility of the instrument, it was
used to conduct high-density electrical prospecting in Lantian village, Anxi
County, in the province of Fujian, China. In correspondence with the actual
terrain and topography of the farmland on the east side of Huazhang natural
village, Lantian village, Lantian township, three high-density electrical
survey lines were arranged (Fig. 13 shows their schematic layout), with
electrodes spaced at 10 m on each survey line. Survey line L1 had 96
electrodes, whose starting and ending coordinates were (25.132667
Schematic layout of the survey lines. (The 75th measurement point on the L1 survey line intersects with the 59th measurement point on the L2 survey line, and the 72nd measurement point on the L3 survey line intersects with the 57th measurement point on the L2 survey line.) (© Gaode Map, 2021.)
Photo of the field testing.
Survey line L1 had 96 electrodes, a trace spacing of 10 m, and a profile
length of 960 m. The latitude, longitude, and elevation of the first
electrode were 25.132667
Profile view of survey line L1 obtained using the high-density electrical method.
Survey line L2 had 64 electrodes, a trace spacing of 10 m, and a profile
length of 640 m. The hill is more than 40 m higher than the flat ground. The
first electrode measurement point was located on the hill platform, and its
latitude, longitude, and elevation were 25.124000
According to the profile view obtained using the high-density electrical method (Fig. 16), the highest part of the hill is relatively flat, where the underground medium is relatively uniform and dense. At the foot of the hill is a low-resistance zone containing a larger amount of underground water; the western tail of the survey line passes through the water-bearing region.
Profile view of survey line L2 obtained using the high-density electrical method.
Survey line L3 was east of L1 and closer to the hill. It had 80 electrodes,
a trace spacing of 10 m, and a profile length of 800 m. The latitude,
longitude, and elevation of the first electrode were 25.132250
Profile view of survey line L3 obtained using the high-density electrical method.
From the profile of L2 obtained using the high-density electrical method, it can be seen that the terrain on the hill is relatively flat, where the underground medium is relatively uniform and dense, and that there are no faults, karst caves, or abnormal bodies in the surrounding area, making it a suitable site for construction of a geoelectric observatory station. From the low-resistance zone in the electrical method profile of the three survey lines, it can be inferred that this area is likely to have been an ancient river course, which was filled in as a result of geological changes and erosion.
This paper has described the development of an IoT-based 4D high-density electrical instrument system; the hardware and software design of the electrical instrument and the system's performance indicators are also briefly introduced. By combining the system with cables, electrodes, and electrode converters, tests were carried out in the laboratory, on campus, and in the field. The acquired data were processed and analyzed, and the results show that the system can be applied to perform actual field measurements.
The current trend in the development of electrical instruments is toward the increased use of multiple channels, multiple parameters, multiple dimensions, multiple functions, high power, and wide ranges (Yan et al., 2012). From this point of view, although our instrument successfully addresses a number of shortcomings of high-density electrical instruments currently available on the market for use in geophysical prospecting, including bulkiness, weight, limitations in data acquisition accuracy, and difficulty of connecting to the Internet for remote monitoring, there are still some aspects that need to be improved. For instance, it only has one channel and it does not have a GPS module. Therefore, our research group plans to continue improving the instrument, for example by upgrading the channel board to a multichannel version, increasing the power of the transmitting board, and adding a GPS module.
Our research is supported by national projects; thus, the data are not publicly accessible due to a confidentiality agreement.
This research was designed, tested, and implemented by the authors of the paper. The full text was designed and implemented by KZ. KZ and YL worked on the hardware design. ZW, ZL, and BZ worked on the software design. The other three authors (QZ, XJ, and PL) carried out revision and correction during the completion of the article, and they also performed the tests.
The authors declare that they have no conflict of interest.
Publisher’s note: Copernicus Publications remains neutral with regard to jurisdictional claims in published maps and institutional affiliations.
This work was supported by the National Natural Science Foundation of China (grant nos. 42074155 and 41574131), the PetroChina Innovation Foundation (grant no. 2019D-5007-0302) and the Fundamental Research Funds for the Central Universities of China.
This work was supported by the National Natural Science Foundation of China (grant nos. 42074155 and 41574131), the PetroChina Innovation Foundation (grant no. 2019D-5007-0302), and the Fundamental Research Funds for the Central Universities of China.
This paper was edited by Alessandro Fedeli and reviewed by two anonymous referees.